JP2003328078A - High hardness and high toughness steel and track parts, earth and sand wear parts, fastening bolts, high toughness gears, high toughness and high surface pressure resistance gears and wear-resistant steel plates using the steel materials - Google Patents

Abstract

(57) [Summary] [Problem] Si, Al, Cr, Mo, V, W, Ni, C
o with a hardness of HRC 50 or more and a Charpy impact value of 5 k
To provide a high hardness and toughness steel having a g-m / cm ² or more. SOLUTION: In a steel containing at least 0.15 to 1.2% by weight of C and 0.05 to 1.8% by weight of Si, a part of Si is 0.15 to 1.6% by weight of Al. And 0.3 to 2.5% by weight of Ni is added, and Cr is 0.1 to 3.5% by weight, and Mo is 0.1% by weight.
In the range of 1 to 1.7% by weight and the formula Mo (% by weight) =
1.7−0.5 × (Si (% by weight) + Al (% by weight))
And V: 0.05
0.40% by weight, W: 0.1-1.0% by weight, or both.
one or more alloying elements of u, Ti, B, Nb and P, S,
This is a tempered martensitic steel containing unavoidable impurity elements such as N and O, with the balance being substantially Fe.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydraulic excavator, a bulldozer, a wheel loader, a motor grader, an underground pipe burying machine, a soil improvement machine, a crusher for concrete, wood, etc.,
The present invention relates to high hardness and toughness wear-resistant steel and gear steel used for a cutting edge of a construction / civil engineering machine such as a tunnel excavator, a crawler track of a tracked vehicle, and a speed reducer, and members thereof.

[0002]

2. Description of the Related Art Conventional wear-resistant steels widely used in construction and civil engineering machines include SMnB, SCr and SCr.
There are B, SCM and SNCM medium carbon added steels that have been subjected to heat treatment such as quenching and tempering. For example, the track bushes, track shoes, track links, roller links, sprockets, etc. that make up the track of a tracked vehicle are subject to wear during running and the load of the vehicle shockingly impacts the toughness of the carbon content. The wear resistance has been optimized with consideration given to securing it. In addition, the cutting edge (ripper point, bucket tooth, cutting edge, etc.) used to break or excavate rock is required to have high performance and prevents cracking or breakage due to a more shocking load. The toughness and wear resistance are improved by increasing the hardness. In particular, in the excavating cutting edge, since the vicinity of the cutting edge is heated to about 600 ° C. due to severe frictional heat with the rock mass, high hardness and high toughness steel with improved temper softening resistance is often used. .

Further, the construction / civil engineering machine often rides over obstacles such as rocks and structures or excavates the obstacles while turning, and the gear reducer for running and turning is often used. Since the gears of No. 1 have a problem of being damaged by an impact load, gears made by carburizing and tempering low-carbon case-hardening steel are used.

[0004]

The crawler belt parts, excavating blade edges, etc. of the construction / civil engineering machinery described above have a high toughness and earth and sand that do not crack or break due to an impact load.
It is desired to achieve both high hardness and excellent wear resistance against rocks, etc., but in general, since high toughness and high hardness are contradictory properties, first, the carbon addition amount is kept low to secure toughness, Since a steel material (wear-resistant steel) to which an alloying element that enhances hardenability is appropriately added is used after quenching and tempering, there is a problem that the wear resistance is insufficient.

The wear-resistant member constituting the crawler belt has, for example, a crawler track shoe of 0.25 to 5, from the viewpoint of placing emphasis on toughness.
0.3% by weight, roller roller: 0.3 to 0.35% by weight,
Track links: 0.35-0.4% by weight, sprockets:
The carbon content is set to a low value such as 0.35% by weight, and the quenching and tempering hardness is adjusted to about HRC45 to 52 before use, so in many cases it is not sufficient in terms of wear resistance, There is a problem that the track repair costs for construction and civil engineering machinery will increase.

Further, since the wear resistance of the crawler belt of the crawler belt is important because of its structure, it is used, for example, by subjecting SCM420 having high toughness to carburizing, quenching and tempering, but it is deep carburizing with high hardness. Since the carburizing treatment for forming the hardened layer takes a very long time, the cost becomes high, and the toughness is significantly impaired by the carburizing treatment.

Further, in a member such as a disk cutter for tunnel excavation or a shank which emphasizes toughness, as disclosed in, for example, Japanese Patent No. 3227730, the carbon addition amount is kept low and Ni content is reduced. Steel materials added in large amounts (for example, SNCM625, SNCM630
(Equivalent) is hardened and tempered, and is used under the condition of HRC45 or more and Charpy impact value of 5 kgf · m / cm ² or more, but its durability is not sufficient in terms of both hardness and toughness.
There is a problem that it is expensive in terms of cost.

Further, in order to emphasize the toughness more importantly in the tooth plate of the jaw crusher for crushing rock or concrete, since the hadfield steel is often used,
There is a problem that the wear resistance is not sufficient.

Further, even in a cutter (soil cutter, pin) of an agitator for agitating and refining earth and sand like a soil conditioner or a cultivator, the carbon content is suppressed to 0.25 to 0.3% by weight, and the hardness is Since it is used after being quenched and tempered to the HRC48 level, there is a problem that the abrasion resistance is not sufficient.

Further, as described above, a cutting edge (a ripper point, a bucket tooth, a cutting edge, an end bit) for breaking or excavating rock using construction / civil engineering machines such as a bulldozer, a wheel loader, a hydraulic excavator, and a motor grader. Etc.) and in a disk cutter for tunnel excavation, the cutting edge is 30 due to severe frictional heat with the rock.
Since it is heated to 0 to 600 ° C., there is a problem that the initial hardness is remarkably softened and the wear resistance becomes insufficient, and the steel material to be used is not only the above-mentioned high toughness and high hardness, but also
It is desirable to retain sufficient temper softening resistance even when heated to about 600 ° C. However, since the proper addition method of alloying elements (selection of alloying elements and the addition amount, etc.) to improve the temper softening resistance is unclear, deterioration of toughness due to excessive addition of this alloying element, etc. There is a problem that it cannot be prevented, or it is likely to be economically expensive.

In addition, in the wear resistant steel containing various alloy elements, it is extremely difficult to avoid the "tempering embrittlement" that appears in the tempering at 350 to 550 ° C. after quenching, so that a sufficiently high toughness is obtained. There is a problem that it cannot be done.

Further, since carbon steel which hardly shows "tempering embrittlement" which appears in tempering at 350 to 550 ° C cannot secure sufficient hardenability, it has a low P and a low S in a high alloy wear-resistant steel. The "tempering brittleness" has been reduced by improving the cleanliness of the steel.
To achieve this high cleanliness steel, it becomes more expensive and there is a problem in market availability.

As a conventional technique relating to this type of wear-resistant steel, for example, in Japanese Patent Publication No. 55-12177,
C: 0.25 to 0.40%, Si: 1.5 to 2.5%,
Mn: 1.6% or less, Cr: 3.0 to 5.0%, Mo:
Wear-resistant steel containing 0.5 to 1.2% has been proposed,
In this wear-resistant steel, the tempering hardness at 550 ° C. or more is rapidly decreased by the addition of excessive Si, Cr, and Mo, and the wear resistance is not sufficient, and it is not economical. There is a problem.

Further, in JP-A-54-124816, C: 0.4 to 0.6%, Si: 0.8 to 1.
7%, Mn: 0.4 to 0.8%, Cr: 0.6 to 2.0
%, Mo: 0.1 to 0.8%, Al: 0.2 to 1.0%
Wear-resistant steels containing Al have been proposed and are disclosed in JP-A-54-143715
In the publication, C: 0.4-0.6%, Si: 0.
8 to 1.7%, Mn: 0.4 to 0.8%, Cr: 0.6
~ 2.0%, W: 0.1-0.5%, Al: 0.2-
Wear resistant steels containing 1.0% have been proposed, but none of them have sufficient temper softening resistance and toughness.

Further, in JP-A-59-107066, C: 0.4-0.6%, Si: 1.6-
2.2%, Mn: 0.5% or less, Cr: 1.0 to 1.5
%, Mo: 0.8 to 1.2%, V: 0.2 to 0.5%,
A wear resistant steel containing Ni: 1.0 to 2.0% has been proposed, but in this wear resistant steel, its toughness is not sufficient due to the addition of excessive Mo and V in addition to temper softening resistance. There is a problem.

Further, in JP-A-60-215743, C: 0.35-0.45%, Si: 0.6-
1.5%, Mn: 1.8% or less, Cr: 2.5 to 4.5
%, Mo: 0.2 to 1.0% and / or V: 0.0
1 to 0.5%, Nb: 0.01 to 0.10%, W: 0.
01-0.5% of one or more, and Ti: 0.01-
A wear-resistant steel containing 0.10% and B: 0.0005 to 0.0030% has been proposed. However, in this wear-resistant steel, by adding too much Cr, the resistance to temper softening due to the addition of Si is improved. There is a problem that the toughness is unavoidable as well as the decrease.

Furthermore, in JP-A-5-78781, C: 0.35-0.55%, Si: 0.5
% Or less, Mn: 0.5% or less, P: 0.015% or less,
S: 0.010% or less, Cr: 1.00 to 2.5%, M
o: 1.00 to 2.00%, V: 0.05 to 0.30
%, B: 0.0003 to 0.0050%, Al: 0.0
A wear resistant steel containing 0. 05 to 0.10% and Nb: 0.01 to 0.20% has been proposed, and the decrease in temper softening resistance due to the reduction of Si is compensated by increasing Mo and adding V. , Tempering softening resistance is not sufficient. In order to secure toughness, grain boundaries are strengthened by lowering P, lowering S and lowering Mn, but they are generally expensive, have problems in market availability, and have insufficient toughness. There is a problem.

In order to prevent the gears of the gear reducer for running and turning of the construction / civil engineering machine from being damaged by an impact load, a high toughness low carbon case-hardening steel (0.1 to 0.25) is used.
Gears that have been carburized and quenched and tempered at (% by weight C) are used, but the toughness deteriorates rapidly as the carburized and hardened layer deepens on the surface. Especially, surface pressure strength and root bending fatigue There is a problem that the toughness is not improved in the above-mentioned gear that requires the formation of a carburized hardened layer of 0.5 mm or more from the viewpoint of strength. Also in low carbon case-hardened steel,
Although grain boundaries are strengthened by lowering the P content and the S content, there are problems in that they are generally expensive, have problems in market availability, and have insufficient toughness.

The present invention has been made in order to solve the above problems, and is made of Si, Al, Cr, Mo, V,
It is intended to provide a high hardness and high toughness steel in which W, Ni and Co are added more appropriately and a Charpy impact value is 5 kgf · m / cm ² or more at hardness HRC50 or more by high temperature tempering at 600 ° C. or more. To do.

A further object of the present invention is to provide a steel capable of achieving a high toughness even in a quenched and tempered martensitic steel having a high carbon and a high hardness by adding Al and Ni in combination.

Still another object of the present invention is to provide various wear resistant members, gear members and bolt members having high hardness and toughness by subjecting these steels to appropriate heat treatment.

[0022]

According to the present invention, first, the excavating cutting edge is subjected to frictional heat to
Focusing on the commonality of being heated to 600 ° C and avoiding temper embrittlement of hardened steel by tempering treatment at 550 ° C or higher, and recovering toughness, 550 ° C or higher after quenching,
HRC45 is also preferable by tempering at 600 ° C.
Selection of carbon content and various alloying elements (C, Si, Al, etc.) to obtain sufficient hardness above (preferably HRC 50 or above)
Cr, Mo, V, W) and its addition amount are optimized, and optimization is performed in consideration of the interaction between alloying elements as described later to prevent brittleness deterioration due to addition of more alloying elements than necessary.
At the same time, we aimed to ensure economic efficiency.

Further, it has been found that Al significantly enhances the resistance to temper softening, and that by adding Al and Ni in combination, the toughness can be remarkably enhanced by the low temperature tempering treatment without exhibiting the temper embrittlement. , Charpy impact value is 5 in the range of carbon addition amount up to 1.2% by weight
The wear resistance of the above various wear resistant members using a tempered martensitic steel having high toughness of kgf · m / cm ² or more and high hardness and high toughness was improved.

Furthermore, in order to avoid high temperature tempering brittleness and obtain high toughness, by adding an appropriate amount of Co which raises the magnetic transformation temperature of the quenched and tempered martensite, the softening resistance due to the high temperature tempering is improved without impairing the toughness. Improved.

In the present invention, the reason for limiting the content (% by weight) of each alloying component in steel is as follows. This is obtained based on the result of analyzing the hardness data obtained by tempering various wear-resistant steels at 200 to 700 ° C., as shown in Examples described later.

C: 0.10 to 1.2% by weight As a result of investigating the hardness of the hardened steel containing various amounts of carbon after low-temperature tempering at 200 ° C., the lower limit of the amount of carbon ensuring HRC45 or higher was found. The upper limit of the carbon content is 0.15% by weight and the Charpy impact value of 5 kgf · m / cm ² or more is almost 0.60% by weight. Since the upper limit carbon content in the invention steel is 1.20% by weight, and the lower limit carbon content is 0.1% by weight in the case where the invention steel is used for the carburized gear, etc., The carbon content of the invention is 0.1 to 1.2% by weight.

Regarding the high hardness and high toughness steel used for the member in which the temper softening resistance is important as described above,
In steel containing 25 to 0.55% by weight of carbon, but containing almost no alloying elements, the hardness in the tempered state at 400 to 600 ° C. is not so much influenced by the amount of carbon (when it is 0.55% by weight or more of carbon, ΔHRC = + at 500 ℃
2.5 and 600 ° C. ΔHRC = + 1.0), and the difference between the hardness of 400 to 600 ° C. tempering treatment by the addition of alloying elements and the standard hardness of carbon steel is the temper softening resistance amount by the addition of alloying elements ( The hardness increase amount) was analyzed. Further, in order to obtain hardness of HRC 45 or more by tempering at 600 ° C., the carbon content is preferably 0.25% by weight or more.

In order to enhance resistance to temper softening,
In the high hardness and high toughness steel to which alloy elements such as Mo and V described below are positively added, when the amount of carbon increases to 0.60% by weight or more, the temper softening resistance in the austenite phase region during quenching heating is increased. It is not economical because the amount of the alloying element that contributes is reduced and the role of the alloying element that contributes to temper softening resistance is diminished.Furthermore, the toughness deteriorates due to an increase in the amount of carbides and coarsening in tempered martensite. It is not preferable because

Further, carbon is an element which remarkably stabilizes austenite, and in the steel of the present invention containing a large amount of Si, Al and Mo which stabilizes ferrite as described later, the quenching temperature is 950 ° C. or lower. To hold down
It is preferable to add at least 0.10% by weight or more of carbon, and from the viewpoint of suppressing the addition amount of Mn, Ni and Cr which are austenite stabilizing elements capable of lowering the quenching temperature, the carbon content is It is more preferably 0.10% by weight or more.

Si: 0.05 to 2.5 wt% Si is unavoidably contained in steel making, and is usually contained in 0.05 to 0.3 wt%, but in the present invention, It suppresses the precipitation of cementite, contributes to the improvement of toughness by tempering at about 400 ° C. or less, and allows the addition of less than 2.5% by weight as an element for further increasing the temper softening resistance. It is known that if the amount of Si added is less than 0.3% by weight, the effect is not remarkable, and that up to about 4% by weight, the temper softening resistance is enhanced, but Si stabilizes the αFe phase and A3 Since the addition amount should be determined within the range that the transformation temperature is raised and the quenching temperature is not raised too much, it is used after being subjected to carburizing quenching and tempering treatment in the range of 0.1 to 0.35% by weight of carbon. When applied to a gear member, it is preferably suppressed to 2.5% by weight or less, and more preferably Si for Mo and V described later.
It is 1.8% by weight in consideration of the effect of addition.

For the addition of Si, the maximum addition amount (YMo weight%), which will be described later, in which Mo effectively acts, is YMo = 1.7.
It was found that it is preferable to reduce it by the relational expression of −0.5 × Si weight% (at 950 ° C.) so that the Mo addition becomes equal to or less than the effective addition amount according to the Si addition amount.

In the relationship between Si and V, the same interaction as that of Mo is recognized, and the effective maximum addition amount (YV) of V above 1.8 wt% Si is 0.15 wt% at 925 ° C.
Below that, it was 0.3% by weight, and at 950 ° C., it was 0.2% by weight and 0.4% by weight, respectively. In the present invention, Al that stabilizes the ferrite phase of steel, like Si, is used.
Since Al is also contained, Al + Si ≦ 1.8% by weight is set to avoid unnecessarily increasing the quenching treatment temperature.

Further, the resistance to temper softening at 400 ° C. or higher due to the addition of Si is significantly reduced when Cr is present in an amount of 3.5 wt% or more (about 600 ° C.).
It was found that the combined addition of Cr and Si of 3.5 wt% or more is not effective. This is because the effect of suppressing the cementite precipitation of Si is reduced by increasing the amount of Cr.

When Cr is present in an amount of 3.5% by weight or more, the upper limit amount of Mo added, which effectively acts to enhance temper softening resistance, is reduced to about 1/2. It is clear that the addition of Al reduces the toughness.

Al: 0.15 to 1.6% by weight Al is known to have a very strong deoxidizing effect, and to form nitrogen and AlN in the steel to act on the refinement of crystal grains. , 0.005 for normal killed case hardened steel
Is added in the range of .about.0.05% by weight. Al, which is a solid solution in steel, has a strong tendency to segregate to the grain boundaries, and strongly excludes the impurity elements P and S that deteriorate the grain boundary strength from the grain boundaries, and strongly attracts Ni that improves the grain boundary toughness. In the present invention, since it acts, Al and Ni are positively added simultaneously to contain a higher concentration of carbon, and the toughness of the tempered martensitic steel having a high hardness of HRC 45 or higher is significantly improved. . Further, by positively adding Al and Ni at the same time, temper brittleness, which is conventionally caused by tempering at 350 ° C. or higher, can be prevented. Furthermore, the revolutionary improvement of the toughness of the high hardness tempered martensitic steel can lead not only to withstand impact loads but also to prevent grain boundary fracture. It is well known that, by utilizing this characteristic, for example, high tension bolts such as track shoe bolts, which will be described later, and track bushes and track links of track link assemblies used by press-fitting track bushes and track pins. The delayed fracture resistance can be dramatically improved.

Further, while Mo and V, which will be described later, enhance the tempering softening resistance on the high temperature side at 400 ° C. or higher, Al, like Si, has the tempering softening resistance on the low temperature side at 400 ° C. or lower and It was found that it is effective in increasing both the tempering softening resistance on the high temperature side, and the above Al + Si ≦
Although it is possible to add it at any time while maintaining 1.8% by weight, the effect is not sufficient if the addition amount range of Al is 0.15% by weight or less, and if it is 1.6% by weight or more, from the viewpoint of improving toughness. Since the A3 temperature is unnecessarily increased and its toughness improving effect is saturated, the content is set to 0.15 to 1.6% by weight.
When applied to a gear member in which the carbon content is suppressed to a low level in the same manner as described above, at the quenching temperature of 950 ° C., αFe
It is preferably 1.2% by weight or less so that the phases do not coexist.

When Al coexists with Ni, the expression of age hardening acts to further enhance the resistance to temper softening, as will be described later (1Al-1Ni: ΔHR
C = + 4, at 600 ° C.), which is preferable from the viewpoint of wear resistance.

Ni: 0.3 to 2.5% by weight Ni is an element that enhances the hardenability and improves the toughness of the low temperature tempered martensitic steel, for example, SNC.
In case of M case hardened steel and AISI 4340 high-strength steel, it is added in a range of 3.5% by weight or less. In addition, as a shank steel material for tunnel excavation (Patent No. 3227730)
No.), a quenching and tempering material containing 2.5 to 4.0% by weight of Ni is used.

In the present invention, the composite addition of 0.3 to 2.0% by weight of Al and Ni is indispensable to contribute more effectively to the improvement of toughness, so the lower limit of the addition of Ni is 0.3% by weight. %. Further, the upper limit of this Ni increases the temper softening resistance due to precipitation of NiAl intermetallic compound by the composite addition of Ni and Al, and improves the wear resistance, but excessive addition deteriorates the toughness and damages economically. Since it is disadvantageous, 2.5 wt% is preferable as the upper limit addition amount.

Further, since Al and Si are strong ferrite stabilizing elements, if they are added in a high concentration, Ac and
3 There is a problem that the temperature shifts to a higher temperature side and the quenching temperature rises. For example, as shown in FIG. 1, from the influence of various alloying elements on the A3 temperature line of the Fe-3 wt% Si-C alloy, the alloy steel on the lower carbon side (0.10 wt% ~),
It can be seen that it is preferable to add Mn, Ni, and Cr to suppress the quenching temperature to a low level in terms of heat treatment cost, and it is preferable to add Mn or Ni in an amount of about 1 wt% even in the vicinity of 0.4 wt% C.

Mn: 0.3 to 3.0% by weight Mn not only has a remarkable desulfurizing effect, but is an effective element for improving the hardenability of steel, and also has a strong austenitic phase of steel like Ni. Is an element that is effective in lowering the quenching temperature by stabilizing the A3 transformation temperature by lowering the A3 transformation temperature. In addition, Al which is the ferrite stabilizing element,
Since it is an effective element that suppresses an increase in the A3 transformation temperature due to the addition of Si, in the present invention, Mn with respect to the eutectoid temperature,
Approximate (Si + 2 × A) due to the influence of Ni, Si and Al
l) ≈ (Ni + Mn), 3.0 wt%
The following is set so that the quenching temperature does not exceed 950 ° C and the former austenite grains are
It is preferable in terms of heat treatment cost to prevent coarsening beyond the grain size number 8.

Cr: 0.1 to 3.5 wt% Cr is an element that improves the hardenability of steel and the resistance to temper softening, but its degree of hardening is less than that of Mo, V and W. . In addition, the coexisting carbon amount of about 7.
If it exceeds 5 times, the tempering softening resistance on the high temperature side per the amount of Cr added (% by weight) decreases, and Si, A
Since it has the effect of reducing the temper softening resistance on the high temperature side of 1 l, the maximum amount of Cr addition is 7. It was 5 times or less. More specifically, 0.55% by weight
3.5 wt% Cr for C, 2.9 wt% Cr for 0.45 wt% C, 2.3 for 0.35 wt% C
1.6% by weight C with respect to% by weight Cr, 0.25% by weight C
Let r. When adding more Cr than this,
The alloy design should be made in consideration of reducing the effective addition amount of Mo described later to about 1/2.

Further, the temper softening resistance of Cr is reduced to about 1/2 at 5.5% by weight or more. Therefore, the following two methods can be considered as means for alloy design. Keeping the amount of Cr added to 3.5% by weight or less, Si, A
Method of adjusting l, Mo, V, W After setting the Cr addition amount in the range of 3.5 to 5.5% by weight, the addition amount of Si is 0.5% by weight or less, the effective addition amount range of Mo (To 1.0% by weight) to adjust Al, V, and W (addition of 1.0% by weight or more of Mo does not effectively contribute to increasing temper softening resistance).

In the above-mentioned method, it is more desirable to keep the maximum addition amount of Cr to less than 3.5% by weight in terms of cost, and since the temper softening resistance of Cr is not so large, the content of Cr is not so large. The lower limit addition amount is preferably 0.1% by weight or more in consideration of enhancing the hardenability of steel. However, Cr is more preferable from the viewpoint of toughness, in order to significantly promote the precipitation of cementite and to significantly enhance the temper embrittlement that appears in tempering at about 350 ° C. or higher, from the viewpoint of toughness.

Further, in the above-mentioned method, in the steel containing 3.5% by weight or more of Cr, Si is added in a small amount, and Mo is added in the range of the effective addition amount or less. It is preferable to increase the temper softening resistance by adding V and W that significantly increase For example, hot work tool steel SKD6 (C: 0.32 to 0.42%, Si:
0.8-1.2%, Mn: 0.5% or less, Cr: 4.5
-5.5%, Mo: 1.0-1.5%, V: 0.3-
0.5%) as a component for achieving 600 ° C. temper hardening, Si: 0.5 wt% or less, Cr: 3.5 to 5.5.
% By weight, Mo: 0.3 to 1.0% by weight, V: 0.2 to
0.4% by weight, W: 0.1-0.8% by weight and / or Al: 0.15-0.6% by weight, Ni: 0.3-
It is preferable to use the one to which 1.5% by weight is added.

Mo: 0.1 to 1.9% by Weight Mo is an element that improves the hardenability and enhances the toughness of the low temperature tempered martensitic steel, and as described above, enhances the temper softening resistance. . Therefore, 0.1% by weight at which effective tempering softening resistance appears is the lower limit value, and the upper limit value is the maximum addition amount (YMo% by weight) at which Mo at the quenching temperature acts on the quenching softening resistance. Based on the relationship with the solid solubility limit of Mo carbide, Si, Al
When not containing YMo = 1.6 (900 ° C.), when Si and Al coexist, YMo = 1.6 wt% -0.5 × (Si wt% + Al wt%). However, the constant of 1.6% by weight changes with the quenching temperature, and is 1.6 at 900 ° C and 1.9 and 10 at 950 ° C.
2.3 is suitable at 00 ° C. The quenching temperature is preferably set to 950 ° C. or lower, more preferably 900 ° C. or lower, in consideration of the quenching equipment, its productivity, and the coarsening of crystal grains due to the growth of crystal grains during heating.

Further, the contribution to temper softening resistance at 600 ° C. is that HRC per 1% by weight of Si and Al.
= + 5.8, whereas Mo has HRC = + 11. Therefore, from the relational expression of YMo, it has been found that by effectively utilizing Si and Al to the maximum extent, the addition amount of Mo can be reduced without significantly reducing the temper softening resistance, so that the present invention is economical. From this viewpoint, it is preferable to set the maximum addition amount of Mo to less than 1% by weight.

Further, as described above, 3.5% by weight or more of Cr
When coexisting, the effective maximum addition amount (YMo
(Wt%) is further reduced to about 1/2, so 3.5
Mo for steels containing ~ 5.5 wt% Cr 1 Mo
It is preferably not more than wt%.

V: 0.05 to 0.4 wt% V is an element effective for significantly increasing the temper softening resistance and the wear resistance even in the tempering temperature range of 600 ° C. or higher, unlike Cr and Mo. Therefore, in the present invention,
It is essential to contain any one of V and W described below that exhibits the same action as V, but the solid solubility of V carbide is small, and V carbide precipitates in the austenite phase during heating at the quenching temperature. In order to deteriorate the toughness, it is preferable that the upper limit addition amount be 0.3% by weight. Incidentally, it is appropriate that the upper limit of the addition amount is 0.4% by weight when the quenching temperature is 950 ° C. and 0.5% by weight when the quenching temperature is 1000 ° C., as described above.

When coexisting with Si and Al, (Si
+ Al) is 1.8 wt% or more, the upper limit addition amount is 1 / each of the upper limit addition amount according to the quenching temperature.
0.15 wt%, 0.2 wt%, 0.25 corresponding to 2
It was set to% by weight. The quenching temperature is preferably set to 950 ° C. or lower in consideration of quenching equipment, productivity thereof, and coarsening of crystal grains due to crystal grain growth during heating. It was 4% by weight. Since the quenching temperature is more preferably 900 ° C. or lower, the upper limit of the addition amount is more preferably 0.3% by weight. Furthermore, by adding 1.0 wt% or more, Si
In the case of coexistence with Si, the maximum addition amount is preferably 0.4% by weight or less because the resistance to temper softening of Si is reduced.

W: 0.1 to 1.0 wt% W does not have tempering softening resistance as much as Mo and V described above, but 6
It is essential to contain either W or V because it exhibits the maximum tempering softening resistance at 00 to 700 ° C. and has a large upper limit (YW) of the added amount that works effectively. When the amount of W added is 0.1% by weight or more, the effect becomes effective, and like V and Mo, the effective upper limit is 9
0.8% by weight at 00 ° C, 1.7% by weight at 950 ° C, 10
It becomes 2.5% by weight at 00 ° C. When W is added in an amount of 1% by weight or more, the temper softening resistance of Mo is significantly reduced, and since W is an expensive material compared to Mo, its maximum addition amount is 1.0% by weight or less. Is preferred.

Co: 1 to 20% by Weight It is well known that Co itself is not an element that exhibits temper softening resistance. In the present invention, the addition of Co rapidly increases the magnetic transformation point of martensite and suppresses the diffusivity of other alloying elements, such as Si, Al,
Exhibits the effect of raising various carbide reactions that give rise to resistance to temper softening of Cr, Mo, V, and W to the high temperature side.
Coexistence with i and Al exerts age hardenability, and coexistence with Al enhances the magnetic transformation point of Co more efficiently. As an appropriate amount of Co added, the effect of increasing the magnetic transformation point at 18 ° C per 1% by weight is recognized up to about 10% by weight, and up to 20% by weight, the increase of 10 ° C per 1% by weight is observed. Admitted. However, if it is more than that, there is a problem that the effect is saturated and the cost becomes too high. In addition, more efficiently, it is preferable to use 10% by weight or less.

B: 0.0005 to 0.0030% by Weight B is an element for significantly improving the hardenability, and in many cases, the amount of alloying elements such as Mn, Cr and Mo which improve the hardenability is reduced. Not only is the expected economic effect expected, but the addition amount of Cr, which easily causes high temperature temper embrittlement, can be reduced. Therefore, positive use is preferable in the present invention. The amount of B added is 0.0005% by weight
The effect is not obtained below, and 0.0030% by weight
It is known that the toughness is deteriorated due to the precipitation of BN when the amount exceeds 0.005%.
It was set to 0.0030% by weight.

B is P at the austenite grain boundary,
It is preferable to positively utilize it because it is more likely to segregate more strongly than S, to easily segregate S strongly, and particularly to eject S strongly from the grain boundaries and improve the grain boundary strength.

Zr, Nb, Ti: 0.005 to 0.20
Weight% Zr, Nb, and Ti are well known as elements for refining crystal grains, and are added within the usual range. However, if over 0.2% by weight, precipitation of carbides and nitrides occurs. It is known that the amount becomes large and the toughness is not good.

P, S: 0.03% by weight or less P and S are contained as unavoidable impurity elements,
It is an important element involved in temper embrittlement at 0 to 550 ° C, and high cleanliness steel reduces these elements as much as possible. In the present invention, since high temperature tempering at 600 ° C. or higher is applied and / or temper brittleness is avoided by adding Al + Ni, the maximum content of P and S exceeds 0.03% by weight. However, it is preferably 0.03% by weight or less in consideration of stabilization of high toughness, and 0.015% by weight or less which is not a cost problem in the current steelmaking technology. More preferable.

On the basis of the above-mentioned examination results, the high hardness and high toughness steel according to the first aspect of the present invention is suitable for Mo, V and W which exhibit strong temper softening resistance while efficiently utilizing temper softening resistance by Si. Economical toughness wear-resistant steel added in an amount of at least C: 0.15 to 0.60 wt%, Si: 0.05 to 1.8 wt%, Cr: 0.1
In steel containing 3.5% by weight, Mo is 0.1 to 0.1%.
In the range of 1.7% by weight and with the formula Mo (% by weight) = 1.7
-0.5xSi (weight%) is added as an upper limit, and V: 0.10 to 0.40 weight% and W: 0.
Either one or both of 1 to 1.0% by weight is added, and Mn, Ni, Co, Cu, Al, Ti, B,
One or more alloying elements of Nb, Zr, Ta, Hf, Ca and inevitable impurity elements such as P, S, N, O are contained.
It is characterized by being a tempered martensitic steel with the balance being substantially Fe.

A second aspect of the present invention is the same as the first aspect of the present invention, in which the amount of Cr added is suppressed to less than 1% by weight in order to improve the toughness of steel of higher hardness tempered at 150 ° C. or higher. : 0.8 to 1.6% by weight, Cr: 0.1
It is limited to 1.0% by weight and 0.5 to 1.3% by weight of Mo, and 0.0005 to 0.005% by weight of B is added.

In the third invention, the addition amount of each alloy element in the composition range of the first invention or the second invention is expressed by the formula 2
6.2 ≦ 5.8 × (Si (wt%) + Al (wt%))
+2.8 x Cr (wt%) +11 x Mo (wt%) +2
5.7 × V (wt%) + 7.5 × W (wt%) ≦ 36.
It is a high hardness and high toughness steel that is adjusted to have a relationship of 2 and is tempered at a temperature of 950 ° C. or lower and then tempered at 600 ° C. so as to be adjusted to a hardness of HRC 50 to 60. is there.

Further, in the fourth invention, at least 0.1 to 1.20% by weight of carbon and 0.05 to 1.8 of Si are contained.
In the steel containing wt%, a part of Si is 0.15-
Replaced by 1.6 wt% Al and 0.3-
2.5% by weight of Ni was added, and Mn, Cr,
Mo, V, W, Co, Cu, Ti, B, Nb, Zr, T
a, Hf, Ca, one or more alloy elements, P, S, N,
The high hardness and high toughness steel is characterized by containing an unavoidable impurity element such as O and having a quenched and tempered martensite structure in which the balance is substantially Fe.

A fifth invention is characterized in that, in the fourth invention, Cr is contained within a range of 0.1 to 3.5% by weight.

A sixth aspect of the present invention is the same as the fourth and fifth aspects, wherein Mo is in the range of less than 1.7% by weight and S
The formula Mo (% by weight) = 1.7 with respect to the amounts of i and Al added.
A toughness wear-resistant steel having improved toughness is provided by being configured so that the upper limit is the relationship of −0.5 × (Si (wt%) + Al (wt%)).

Further, in the seventh invention, in the fourth to sixth inventions, 0.05 to 0.40 wt% V, 0.1
One or both of W-1.0 wt% W are added to further enhance the temper softening resistance.

Further, in the eighth invention, in the fourth to seventh inventions, Al is made 0.15 to 0.75% by weight in order to optimize the increase of the A3 transformation temperature due to excessive addition of Al, Ni is limited to 0.3 to 2.0% by weight and B is 0.0 to improve hardenability at a low cost.
One or both of 005 to 0.005% by weight is carried out.

Further, in the ninth invention, the addition amount of each alloying element is set so that HRC45 to 65 can be secured by tempering at 600 ° C. or higher in the toughness wear-resistant steel in the component range in which Al and Ni coexist. , Expression 21.2 ≦ 5.8 ×
(Si (weight%) + Al (weight%)) + 2.8 × Cr
(Wt%) + 11 × Mo (wt%) + 25.7 × V (wt%) + 7.5 × W (wt%) ≦ 41.2.

Next, the high hardness and high toughness steel according to the tenth aspect of the invention comprises at least C: 0.25 to 0.55% by weight and Si:
In steel containing less than 0.8 wt% and Cr: 3.5 to 5.5 wt%, Mo is added in the range of 0.3 to 1.0 wt% and V: 0.10 to 0. 40% by weight,
W: One or both of 0.1 to 1.0 wt% is added, and Mn, Ni, Co, Cu, Al,
A tempered martensitic steel containing one or more alloying elements of B, Ti, Nb, Zr, Ta, Hf, Ca, and unavoidable impurity elements such as P, S, N, O, and the balance being essentially Fe. It is characterized by being.

Further, the eleventh invention is the steel according to the tenth invention, wherein the Cr content is 3.5 to 5.5% by weight, and 0.15 to 1.0% by weight of Al and 0.3 to 2. 5% by weight of Ni is added, and Mo is added in a range of 0.3 to 1.0% by weight.

Furthermore, the twelfth invention is the same as the eleventh invention, wherein the formula 21.2 ≦ 3 × (Si (wt%) + Al (wt%)) + 2.8 × Cr (wt%) + 11 × Mo (wt%) ) + 25.7 x V (wt%) + 7.5 x W (wt%)
The alloy element addition amount is adjusted to satisfy the relation of ≦ 41.2.
It is characterized in that a hardness of HRC 45 or higher is secured by tempering at ℃.

The thirteenth invention is based on the first invention to the first invention.
2 In the invention, the magnetic transformation temperature of tempered martensite is adjusted to 20 by adding 1 to 20% by weight of Co.
By increasing the temperature by about 0 ° C., the diffusion of the alloy in the tempering process is remarkably delayed, whereby the softening resistance can be remarkably exhibited even by tempering at 600 ° C. or higher.

In the fourteenth invention, in each of the above inventions, one or more of Nb, Ti, Zr, Ta, and Hf are added in a total amount of 0. 0 in order to refine the crystal grains when heated at a high temperature for quenching. 005 to 0.2 wt% is added.

Further, in the fifteenth invention, in each of the above inventions, a hardness HRC of 50 or more and a Charpy impact value of 5 kgf · m / cm ² or more are obtained by performing high temperature tempering at a temperature of 600 ° C. or more after the quenching treatment. It is to provide high hardness and high toughness steel.

According to a sixteenth invention, in each of the above inventions, the hardness is adjusted to HRC45 or more by performing a tempering treatment at 150 ° C. or more after the quenching treatment.
In the hardness range of 45 to 55, the Charpy impact value is expressed by the expression log (Charpy impact value (kgf · m / cm ² )) ≧
-The relationship of 0.0263 × HRC + 2.225 is satisfied,
Further, it is characterized by having a Charpy impact value of 6 kgf · m / cm ² or more at a hardness of HRC 55 or more.

The seventeenth invention is the first invention to the first invention.
6 is a high hardness and high toughness steel of the invention, the hardness after quenching and tempering is HRC52 or more, and the Charpy impact value is 6
A track bush, a track link, a vertical roller wheel for a track, and a track shoe, characterized in that the wear resistance of the wear-resistant part is improved by 1.2 times or more as compared with the conventional one by setting it to be kgf · m / cm ² or more. It is a tracked component characterized by being present. In addition, these applied parts are tempered at 150 ° C to 400 ° C after quenching with an appropriate cooling medium such as water, a water-soluble quenching liquid, quenching oil, etc. It is obvious that the method may be induction heating and tempering of the part.

Incidentally, the through-hardened crawler belt bush and crawler belt link also contain, for example, 0.6 wt% carbon, 1 wt% Al, and 1 wt% Ni as described later (see FIG. 11). Maintains a high hardness of HRC55 or higher even at tempering temperatures of 400 ° C or lower, and exhibits an extremely high Charpy impact value, improving delayed fracture resistance of track links and track bushes when the track bush is press-fitted into the track links. Is clearly done,
It is manufactured at a much lower cost than the heat treatment of the track bushes conventionally manufactured by the carburizing and quenching tempering method and the inner and outer diameter induction hardening method. In addition, even for a crawler belt link in which the tread surface with the lower roller is deeply induction hardened after the material is tempered, not only can inexpensive heat treatment be performed, but both ends of the crawler link that impact with the lower roller can be impacted. It is also clear that chipping at the edge can be prevented.

The eighteenth invention is based on the first invention to the first invention.
6 is a high hardness and high toughness steel of the invention, the hardness after quenching and tempering is HRC50 or more, and the Charpy impact value is 8
A shank for tunnel excavation, characterized in that it has a kgf · m / cm ² or more and is improved by 1.2 times or more on average as compared with the conventional one.
It is a sand and sand wear resistant component such as a disk cutter for tunnel excavation, a chisel tool, and a stirring blade for soil improvement. Note that these applied parts are tempered at 150 ° C to 350 ° C after quenching with an appropriate cooling medium such as water, a water-soluble quenching liquid, and quenching oil after overall heating. It is obvious that the method may be induction heating and tempering of the part. Further, in terms of cost, it is preferable that the added amount of Ni is 1% by weight.

The nineteenth invention is the first invention to the first invention.
6 is a high hardness and high toughness steel of the invention, the carbon content is 0.30 wt% or more, the hardness after quenching and tempering is HRC 40 or more, and the Charpy impact value is the expression log (Charpy impact value kgf · m. / Cm ² ) ≧ −0.0263 × HRC +
A fastening bolt used for construction machines, such as a track shoe bolt, a gear reducer, and a swing circle fixing bolt, which satisfies the relationship of 2.225.
Note that these applied parts are tempered at a temperature of 150 ° C to 500 ° C after quenching with an appropriate cooling medium such as water, water-soluble quenching liquid, quenching oil, etc. It is obvious that the method of quenching and tempering may be used.

The twentieth invention is the first invention to the first invention.
After the high hardness and high toughness steel of the invention is processed into a gear shape, the surface carbon concentration is 0.6 to 6 by carburizing and tempering.
1.0% by weight, the surface carburizing depth is 0.4 mm or more, the hardness thereof is adjusted to HRC55 to 64, and the impact value of the Charpy test piece having an equivalent depth is 5 kgf · m / cm ² , preferably High toughness gears such as gears, crawler belt bushes and crawler belt shoe bolts, which are characterized by being 8 kgf · m / cm ² or more.

The twenty-first invention is the first invention to the first invention.
6 After machining the high hardness and high toughness steel of the invention into a gear shape, carburizing so that the amount of surface carbon becomes 0.8 to 1.3% by weight, then once cooling to below the A1 transformation temperature, and then reheating After quenching and tempering, the surface carburized layer depth is 0.4
Cementite having an average particle diameter of 1 μm or less is dispersed in the hardened layer and the hardness thereof is adjusted to HRC59 to 65, and the impact value of the Charpy test piece having the equivalent depth is 4 kgf · m / cm. It is a high toughness and high surface pressure resistant gear characterized by having ² or more.

The twenty-second invention is the first invention to the first invention.
After processing the high hardness and high toughness steel of 6 invention into a gear shape,
Induction hardening and tempering are applied, and the surface hardness is HRC52-64.
Of the Charpy test piece adjusted to
Impact value is 5 kgf · m / cm ^TwoIt is characterized by the above
It is a high toughness gear. In addition, this gear after the whole heating
Use an appropriate cooling medium such as water, water-soluble quenching liquid, quenching oil, etc.
After using and tempering, it is tempered at 150 ℃ -350 ℃
However, it is a method of induction hardening and tempering the tooth mold part
It is clear that is also good, the Charpy impact value at that time
5 kgf ・ m / cm^TwoThe above is characterized.

The twenty-third invention is based on the first invention to the first invention.
By quenching and tempering the high hardness and high toughness steel of 6 invention,
High tension of 50 kgf / mm ² or more and / or HRC
A wear-resistant steel plate that is adjusted to a hardness of 50 or more and is welded to a bucket, a bulldozer blade, etc., and is used for cold cracking during welding to a bucket, blade, etc. of construction / civil engineering machinery. A wear-resistant steel plate with improved cracking susceptibility due to reheating.

The 24th invention is applied to the cutting edges for excavation in which the resistance to temper softening by frictional heat is important in each of the above inventions, and contains less than 3.5% by weight of Cr, HRC5 by tempering at 600 ℃
The formula 26.2 ≦ 5.8 × (Si (wt%) + Al (wt%)) + 2.8 × Cr (wt%) + 1 so that 0 or more.
1 x Mo (wt%) + 25.7 x V (wt%) + 7.5
15. A ripper point, an end bit, characterized by using the high hardness and high toughness steel according to any one of claims 1 to 14, wherein an alloy addition amount is adjusted in a relationship of × W (% by weight) ≤ 41.2. It is a wear and sand wear resistant component used for earth and sand excavation such as bucket teeth, edges and disk cutters for tunnel excavation.

[0082]

EXAMPLES Next, specific examples of the high hardness and high toughness steel according to the present invention will be described with reference to the drawings.

(Example 1; Preliminary Investigation and Preliminary Experiment) In this Example 1, various kinds of heat treatment described in "The Heat Treatment of Steel", 5th edition, edited by Japan Iron and Steel Institute (1985, published by Maruzen Co., Ltd.) The relationship between the tempering temperature of the tough steel (martensitic steel) and the Rockwell hardness was arranged, and the improvement target value of the wear resistant steel in the present invention was examined.

As a result of this examination, as shown in FIG. 2, SCr and SC containing 0.6% by weight or less of carbon were obtained.
60 for M, SNCM and high Si tough steels
Nothing exceeds HRC45 by tempering at 0 ℃,
It was found that the target can be achieved in SKD6 (0.4C5Cr1.3Mo0.3V).

FIG. 3 and FIG. 4 show the relationship between the tempering hardness at 150 to 700 ° C. and the Charpy impact value of steels including SUJ2 and SKH9. From this graph, it can be seen that the upper limit hardness for the Charpy impact value of 5 kgf · m / cm ² or more is about HRC56. Further, the preliminary test results of investigating the relationship between the Charpy impact value and the carbon content of the steel having the composition shown in Table 1 after quenching at 200 ° C. for 2 hours after quenching are shown in FIG. Charpy impact value of 5k at 0.55 wt% or more
It can be seen that there is almost no possibility that gf · m / cm ² or more will occur.

[0086]

[Table 1]

Example 2 Preparation of Abrasion Resistance Test Steel Table 2 shows the composition of the steel material used in the present invention. The range of addition of various elements is C: 0.14 to 0.73% by weight, S
i: ~ 2.5 wt%, Mn: ~ 1.3 wt%, Cr:
0.3 to 8% by weight, Mo: to 4% by weight, V: to 1% by weight, W: to 2% by weight, Al: to 2% by weight, Ni: to 2% by weight, and other Nb, B, Ti Add trace amount, etc., P, S
Was selected for use in investigating the effect (and Charpy impact value) of tempering softening resistance of each alloy element. About 25 kg of each steel was melted in a high-frequency melting furnace, hot-forged into a round bar shape with a diameter of 32 mm, and then machined into a round bar with a diameter of 25 mm.
A piece cut into an appropriate length was subjected to a predetermined heat treatment and subjected to the following experiment.

[0088]

[Table 2]

Example 3 Confirmation Test of Tempering Softening Resistance (Effect of Alloying Elements on Tempered Hardness) In this example, a test piece having a composition shown in Table 2 and having a diameter of 25 mm was N ₂
After heating in a gas atmosphere at 870 to 980 ° C for 1 hr, water quenching, tempering at 200 to 700 ° C for 2 hr, and quenching in water, the hardness is measured, and the effect of each alloying element on temper softening resistance is investigated and analyzed. Together with 600
The purpose is to establish an alloy design method in which tempering hardness is HRC 45 or more even by tempering at ℃.

As a result of this confirmation test, it was found that the effect of alloying elements on the hardness of martensitic steel by tempering at 600 ° C. after quenching at 900 ° C. is calculated by the following equation. ΔHRC = 5.7 × (Si weight% + Al weight%) + 2.
8 × Cr wt% + 11 × Mo wt% + 25.7 × V wt% + 7.5 × W wt% However, as described above, the maximum addition amounts YMo, YV, and YW exist for Mo, V, and W, respectively. The hardness of the alloy steel added above the maximum addition amount is calculated by substituting the maximum addition amount in the calculation formula.

6 to 10 show the results of measuring the tempering hardness of each of the sample steels shown in Table 2 (denoted as "actual measurement").
And the results (expressed as “calculation”) calculated based on the calculation method by analyzing and quantifying the influence of each alloying element on the tempering hardness. As is clear from these graphs, it was found that the calculated values of the tempering hardness of the alloy steels and the measured values match each other very well, and the effects of the various alloy elements described above can be quantified substantially reasonably.

In FIG. 6, No. 1-No. The measured value (tempering temperature 870 ° C.) of the tempering hardness of No. 9 and the calculated value are shown in comparison. In this figure, No. 1-No. Three
Is a low Cr-high Si system in which the effects of addition of Mo and V are investigated, No. 4 to No. No. 6 is the result of examining the effects of V, Ni, and W, No. 7-No. 9 is the result of examining the effect of the combined addition of Al and Ni. As is clear from this figure, even in low Cr, Si, Mo, V, W, and Al have remarkable temper softening resistance, and in particular, they are extremely well calculated with the same degree of influence as temper softening resistance Si of Al, It was found that the mechanism of development of temper softening resistance is almost equal to that of Si.

Further, from the comparison between the calculation result based on the analysis and the measured value, when Al and Ni coexist, N
Hardening due to the aging effect of the iAl intermetallic compound was confirmed (ΔHRC = + 4 for 1Al + 1Ni). However,
When the quenching temperature was 870 ° C., No. 2 is M
o, No. In No. 4, Mo and V are No. 5, V, No.
6, V and W slightly exceeded the above-mentioned effective addition amount, and for example, the case of tempering after quenching from 950 ° C. (for example, effective Mo amount; YMo = 1.3-0.5 × (S
It has been found that i + Al)) exhibits more effective temper softening resistance.

In FIG. 7, No. 10-No. The measured value (tempering temperature 870 ° C.) of the tempering hardness of No. 22 and the calculated value are shown in comparison. In this figure, No. No. 16 was tempered by raising the quenching temperature to 980 ° C. The solidification of 0.5 wt% V contained in the alloy and the tempering treatment effectively contributed to the temper softening resistance. I found out that

In FIG. 23-No. The measured value (tempering temperature 900 ° C.) of the tempered hardness of No. 29 and the calculated value are shown in comparison. This was an investigation of the relationship between high Cr and Mo content and V addition, and it was confirmed that the above relationship between Mo and V was established even when about 3 wt% Cr coexisted. In addition, No. No. 28 has Mo added at a high concentration, but its effective Mo amount considers coexisting Si amount and high carbon (precipitation of Mo carbide in austenite (ΔYMo
= 0.15)), it is about 1.0% by weight, and for example, it is extremely hardened with HRC55 which is equal to or higher than the tempering hardness of hot work tool steel SKD6 at 600 ° C. all right. Furthermore, SKD6 is 1000-
Compared with quenching from 1050 ° C., tempering treatment at 550 to 600 ° C. and adjusting to HRC 53 or less for practical use, No. 1 of the present example. 23-No. 29
Shows that Cr is less than 3% by weight and Mo is less than 1% by weight, and is also effective as a more economical hot work tool steel having a quenching temperature of 900 ° C. The carbon content of these steels is controlled to 0.55% by weight or less, more preferably S
It can be seen that it is more preferable to set it to 0.45% by weight or less in consideration of the component range of KD6.

In FIG. 9, No. 30-No. The measured value (tempering temperature 950 ° C.) of the tempering hardness of No. 33 and the calculated value are shown in comparison. This figure has a higher Cr than that of FIG.
This is the result of investigating the influence of the conversion. For example, No. 31 and N
o. As is clear from the comparison with 33, a high Cr content of about 3.5% by weight or more prevents the Cr softening resistance from increasing.
It was found from the results of this analysis that the effect of 1) is drastically reduced, and that the temper softening resistance of Si is drastically reduced in the steel having Cr in excess of 3.5% by weight. Therefore, in order to effectively exhibit the tempering softening resistance of Cr, it is preferable to use Cr in an amount of 3.5% by weight or less.

No. 29-No. In the case where high Cr is added as in No. 33, the mechanism of manifesting resistance to temper softening of Cr becomes more prominent as the amount of carbon becomes smaller than the amount of addition of Cr, and as a result of analysis, about 7. It can be seen that when the amount of Cr added exceeds 5 times, the resistance per amount of added Cr decreases as described above.

In FIG. 10, No. 34-No. The measured value of the tempering hardness of 38 (hardening temperature 900 ° C.) and the calculated value are shown in comparison. This figure shows M in the higher Cr region
The influence of o, W, and Si was investigated. From these results, it was found that the maximum effective addition amount of W was about 1.0 wt% at 900 ° C., and the addition of 1 wt% or more of W drastically reduced the maximum effective addition amount of Mo. It can be seen that it is desirable that the amount does not exceed 1% by weight. Also, Cr
It was also found that the Cr temper softening resistance further sharply decreases when the content of Cr is 6% by weight or more (No. 38).

From the above, in developing a high toughness hard wear-resistant steel, addition of alloying elements exceeding the above-mentioned maximum addition amount is uneconomical, as well as
It is clear that toughness is impaired with little contribution to wear resistance. Also, regarding alloying elements such as Si, Al, and Cr, the effect on tempering softening resistance differs depending on the addition amount range, so it is preferable to add more effectively in consideration of economic efficiency. .

Further, in order that the hardness of the martensitic steel by tempering at 600 ° C. is HRC 45 or more, it is necessary to combine alloy elements satisfying the following formula. 21.1 ≦ 5.7 × (Si (wt%) + Al (wt%)) + 2.8 × Cr (wt%) + 11 × Mo (wt%) + 25.7 × V (wt%) + 7.5 × W (weight%)

In order to have high toughness wear-resistant steel,
The upper limit hardness obtained by tempering at 600 ° C. is preferably regulated. For example, when SKD6 or the like is used as a reference, it is preferable to set it to HRC55 or less, but the upper limit is set by the combined addition of Al and Ni. Since the hardness can be increased to HRC65, the alloy element addition range is more preferably the following formula. 21.2 ≤ 5.8 x (Si (wt%) + Al (wt%)) + 2.8 x Cr (wt%) + 11 x Mo (wt%) + 25.7 x V (wt%) + 7.5 x W (weight%)
≤41.2

Example 4 Impact Test Results Table 2 shows
The results of the 2U Charpy impact test of the material subjected to the tempering treatment at 200 ° C. and 600 ° C. for 2 hours are also shown together, and Table 3 also shows the results of the additional material of the present invention and the comparative material. As a result, in both materials of tempering treatment at 200 ° C. and 600 ° C. for 2 hours, Cr was suppressed to about 1 wt% or less, Mo was positively added, W was added 0.81 wt% or less, Al and Ni. The composite addition of etc. shows toughness, and the Charpy impact value is 5 kgf ・ m / c
It can be seen that the upper limit carbon content of the tempered martensitic steel showing a toughness of m ² or more becomes approximately 1.2% by weight by the combined addition of Al and Ni.

[0103]

[Table 3]

In FIG. 11, No. Quench 47, 48, 49 from the temperatures in the table, and 3 hours at each temperature of 200 to 500 ° C.
The relationship between the tempered hardness and the Charpy impact value is shown. From the low temperature tempered state of HRC60 to 50 of HRC47
No decrease in impact value due to temper embrittlement was observed before tempering at 0 ° C, and rapid recovery of toughness was observed at a tempering temperature of 200 ° C.

Further, in FIG. No. 47 in Table 2 and No. 47 in Table 2. 10, No. No. 12 shows the relationship between each tempering temperature and the Charpy impact value. 12 is 20
In contrast to the rapid embrittlement caused by tempering above 0 ° C,
No. It can be seen that the high Si material of No. 10 maintains the toughness at 350 ° C. or less, becomes significantly brittle at 500 ° C., and recovers the toughness at 600 ° C. In addition, N containing Al and Ni added together
o. No. 47 tempering embrittlement phenomenon was not observed, and it can be seen that extremely high toughness is exhibited.

Low carbon AlNi steel (No. 40)
It can be seen that in the above example, extremely excellent toughness is exhibited even in the state of low temperature tempering at 200 ° C. In addition, the steel materials in Table 3 (No. 39, No. 41, No. 45, No. 46)
Comparing these results, it can be seen that the AlNi steel has extremely high toughness in a wide carbon-containing region and a wide hardness range, and an appropriate carbon content is 0.15 wt% to 1.20 wt%. . Therefore, wear resistance is
It can be seen that an alloy design that can secure HRC of 45 or more by tempering at 600 ° C. is preferable while considering that of 5 or more.

(Example 5: Impact test result of carburized and tempered steel) The test piece used in this example is N in Table 3.
o. The steel materials of 39, 40, and 41 were subjected to normalizing treatment at 980 ° C. and then processed into Charpy impact test piece shapes. In addition, the carburizing, quenching and tempering process is shown in Fig. 1.
As shown in 3, the carbon potential is 0.85 at 930 ° C.
Carburization depth of 0.8-
The carburizing diffusion time was set to 5 hours so as to be 1.2 mm. The tempering treatment was performed at 180 ° C. for 3 hours.

FIG. 14 shows the hardness distribution of the test piece after carburizing and tempering. The hardness of the surface carburized layer is Vickers hardness Hv750 to 800 (equivalent to HRC62 to 64).
The Charpy impact value of the test piece is No. 39:
1.74 kgf · m / cm ² , No. 40: 11.9k
gf · m / cm ² , No. 41: 1.24 kgf · m /
It was cm ² . In addition, as a result of the tissue observation No. 39, N
o. In No. 40, since the αFe phase remained, a Charpy impact test was conducted on a test piece whose quenching temperature after carburization was increased from 850 ° C to 910 ° C. 39:
2.52 kgf · m / cm ² , No. 40: 22.6k
An epoch-making improvement of gf · m / cm ² was observed. In particular, No. The impact value of 40 is close to the impact value of the low carbon concentration base material shown in Table 3.

It can be seen that this result is extremely preferable to be applied to a gear reducer of a construction machine / civil engineering machine or a gear of a turning device which is likely to receive an impact load. Furthermore, it can be seen that it is also preferable for the track bushes and the like that are used after carburizing, quenching and tempering.

15 (a) and 15 (b) show No. 40 so that the amount of surface carbon is 1.1% by weight and 1.3% by weight.
Carburizing at 00 ° C., once cooling to A1 temperature or lower, reheating and quenching to 870 ° C., and then tempering at 200 ° C. for 3 hours.
It is a photograph showing a structure having a depth of 2 mm. Cementite particles having an average particle diameter of 1 μm or less are dispersed almost uniformly, and the hardness of the surface carburized hardened layer is HRC62. Gear members having a surface hardened layer structure in which such cementite particles are finely dispersed are excellent in surface pressure resistance, and are expected as more compact gears for gear reducers.
There was a problem of extremely poor toughness, but the results of the Charpy impact test (No. 40; 4 to 6 kgf · m /
cm ² , No. 41; 0.7 to 1.0 kgf · m / cm
^{From 2} ), it was found that the use of the steel of the present invention in which Al and Ni are added together improves the toughness and can be applied to a gear for high surface pressure resistance in which the cementite particles are dispersed.

(Embodiment 6; Form 1 of application example of high hardness and high toughness steel) In this embodiment, wear resistance of wear resistant parts in construction and civil engineering machines expected to apply the above high hardness and high toughness steel. The sex was organized, and the action and effect of the present invention were clarified. Table 4 shows the carbon concentration of each representative part, the quenching and tempering hardness, and the tempering parameters calculated from the typical alloy components. First, many of these parts have both high toughness and high hardness. In consideration of the above, as a whole, the contained carbon amount is set in the range of 0.25 to 0.40% by weight, and H
Since it is rarely used with a hardness of RC52 or higher,
It can be seen that its wear resistance is not sufficient. Further, in the bucket tooth, the ripper point, the end bit, and the cutting edge that require frequent tempering softening resistance, such as rock excavation work, the tempering parameters described above are component-adjusted in the range of 10 to 22, Since the hardness after tempering at 600 ° C. is as low as HRC33 to 46,
It can be seen that sufficient wear resistance cannot be obtained.

In these steel materials, Al and N
There is no case of high hardness and high toughness due to the combined addition of i, and from the results of the Charpy impact value in the above-mentioned examples, the problems of cracking, chipping and breakage due to insufficient toughness have not been sufficiently solved.

In our company, Vickers hardness H
Wear resistance (W; wear amount) of v500 tempered and tempered steel
There is data investigating the relationship between the hardness of various steel materials and the gouging wear resistance under conditions where the hardness softening due to friction heat generation is not remarkable when 1 is set to 1, and the wear resistance is approximately expressed by the formula W ×
It is expressed by the relationship of (Hv) ² = 250,000 (see FIG. 16). According to this result, for example, the average hardness HRC50 (Hv513) is changed to HRC55 without changing the toughness of the component.
It has been found that when it becomes possible to increase (Hv600), the wear resistance is greatly improved by about 20% or more. For example, by using the high hardness and high toughness steel to which Al and Ni are added in combination, appropriate heat treatment is performed. The track links, crawler shoes, crawler bushes, and bucket teeth that have improved the Charpy impact value to 5 kgf · m / cm ² or more at HRC 55 or above.
It is possible to significantly improve the wear resistance of cutting edges, end bits, segment teeth, lower roller rollers, tool bits for tunnel excavation, shanks, disc cutters, chisel tools, and soil cutters for soil agitation of soil improvement machines. it is obvious.

Further, the bucket teeth, the ripper points, the end bits, and the cutting edges, which are frequently used for the rock excavation work and require tempering softening resistance, use the above-mentioned tempering parameters to obtain HRC45 by tempering at 600 ° C. It is clear that cracking, chipping, and breakage defects can be prevented by properly adding alloying elements so as to have the above hardness, more preferably at least HRC50, and further increasing the toughness by adding Al and Ni in combination. is there.

Furthermore, as is clear from the impact test results of Examples 4 and 5, the toughness improved by the combined addition of Al and Ni leads to the strengthening of the grain boundary strength (former austenite grain boundary) and the delay resistance. It is extremely effective in improving track shoe bolts, which may cause breakage. It is known that delayed fracture of bolts frequently occurs in bolts using quenched and tempered steel of HRC 40 or more, and easily occurs in steel with remarkable temper embrittlement, so it does not contain much alloying elements. , B of S35C in Table 4 whose hardenability has been improved is often used, but its Charpy impact value is HRC40 hardness of 7 to 11 kgf.
m / cm ² is not sufficient as compared with the effect of improving the Charpy impact value by the combined addition of Al and Ni in the present invention. HRC41 or more due to the suppression of temper brittleness and the remarkable improvement in grain boundary strength of the present invention. And the Charpy impact value is the expression log
(Charpy impact value (kgf · m / cm ² ))>-0.0
By satisfying the relationship of 263 × HRC + 2.225, it is clear that a higher tensile bolt can be manufactured.

In addition, as shown in FIG. 40 has a remarkable Charpy impact value even in hardness HRC60, and SCM4 assuming a gear
Since the toughness is extremely higher than that of the 20H carburized and quenched tempered material (see Example 5), the steel of the present invention containing 0.45 to 1.2% by weight of carbon to which Al and Ni are added in combination is used. After gear processing, induction hardening or tempering or an appropriate well-known quenching and tempering treatment is applied, and the surface hardness is HRC5.
Clearly, five or more gears can be manufactured cheaper than conventional carburized and tempered gears. In order to increase the bearing pressure resistance of the gear, the surface hardness should be HRC5.
It is more preferable that the average particle diameter is 8 or more, and it is further preferable that the cementite particles having an average particle diameter of 1 μm or less are dispersed in the surface layer.

Further, as is clear from the impact test results of Examples 4 and 5, 5 kgf · m / cm is also obtained in the quenched and tempered steel and the carburized and tempered steel in which the carbon concentration is in the high concentration range of up to 1.2% by weight. ^Since it exhibits a Charpy impact value of ² or more, it is clear that the present invention can be applied to members such as taps, press dies, chisels, shearing shear blades, saw blades and blades.

(Embodiment 7: Form 2 of application example of high hardness and high toughness steel) In this embodiment, high tensile strength steel plate and wear resistance in construction and civil engineering machines where the above-mentioned high hardness and high toughness steel is expected to be applied. Focusing on the fact that cold cracking and reheat cracking of steel sheets, etc. are caused by the embrittlement of the former austenite grain boundaries of the base material due to welding heat, this high hardness and high toughness steel is effective in preventing these weld cracks. Make it clear.

With the development of higher tensile strength steel plates for welding and wear-resistant welded steel plates, measures to prevent cold cracking in the base metal after welding become important, and standards based on the chemical composition of these steel plates have been established. . In our company, 50kg
For high-strength steels of f / mm ² or more and wear-resistant welding steels using the same, the standard value PH of Nippon Steel Corporation calculated by the weight% of each element is: PH = C + Mn / 10 + Cr / 15 + Mo / 6 + 3V +
The steel plate components are adjusted so that 40P + 100B is 1.0 or less,
From this relational expression, P that significantly causes grain boundary embrittlement promotes weld cracking extremely remarkably, so that P is regulated to 0.01% by weight or less, and the amount of B for ensuring the hardenability of the steel material is It is carefully controlled and the amount of carbon is limited to 0.1 to 0.3% by weight.

For example, since the bucket wear-resistant steel plates shown in Table 4 are used by being fillet-welded to the bottom surface of the bucket, the carbon content is controlled to 0.3% by weight or less, and Since the composition is regulated to prevent the occurrence of welding cracks, there is a problem that sufficient wear resistance cannot be obtained, but in the present embodiment, Fe-0.45C-0.21Si.
-1.2Mn-0.5Ni-0.15Cr-0.018
P-0.0011B (PH = 1.41) and 0.2
Two types of quenched and tempered steel sheets (hardness: about HRC54, thickness 15 m) of steel (PH = 1.48) with 6 wt% Al added.
m, width 70 mm, length 600 mm) was welded to the bottom surface of the bucket at room temperature at the two corners of the longitudinal direction with fillet CO ₂ and the weld cracks were investigated. As a result, 2 out of 5 cracks were observed in the Al-free steel. Although it occurred, it was found that there was no crack in 20 of the Al-added steels.

Further, for the purpose of removing residual stress, the buckets welded with them were heated to 500 ° C. for 30 minutes and then air-cooled to room temperature, and as a result of investigating cracks in the welded portion, as a result, the remaining 3 steels in the Al-free steel were It was found that cracking occurred in all, whereas no cracking was observed in the Al-added steel. Therefore, the upper limit PH of the high-strength steel sheet to which 0.15 wt% or more of Al and 0.3 wt% or more of Ni are added
The value is PH = 1.4 to 1.48, and the P content is 0.0
When limited to 2% by weight or less, the amount of carbon added is about 0.
Since the upper limit is 6% by weight, the appropriate amount of carbon is 0.1 to 0.
It can be seen that it is 6% by weight.

[Brief description of drawings]

FIG. 1 is a graph showing influences of various alloy elements on an Ac3 temperature line of a FeSi-based alloy.

FIG. 2 is a graph showing the tempering hardness of various wear resistant steels.

FIG. 3 is a graph (1) showing the relationship between hardness and impact value of various tempered steels.

FIG. 4 is a graph (2) showing the relationship between hardness and impact value of various tempered steels.

FIG. 5 is a graph showing the results of preliminary experiments investigating the relationship between the Charpy impact value and the carbon content.

6 is a schematic diagram of No. 1-No. It is a graph which shows and compares the measured value (hardening temperature 870 degreeC) of the tempering hardness of 9 and the calculated value.

7 is a schematic diagram of No. 10-No. It is a graph which shows and compares the measured value (hardening temperature 870 degreeC) of the tempering hardness of 22 and a calculated value.

8 is a schematic diagram of No. 23-No. It is a graph which shows and compares the measured value (hardening temperature 900 degreeC) of the tempering hardness of 29, and a calculated value.

9 is a schematic diagram of No. 30-No. It is a graph which compares and shows the measured value (hardening temperature 950 degreeC) of the tempering hardness of 33, and a calculated value.

10 is a schematic diagram of No. 34-No. It is a graph which compares and shows the measured value (hardening temperature 900 degreeC) of the tempering hardness of 38, and a calculated value.

11 is a schematic diagram of No. 47-No. It is a graph which shows the relationship between the tempering hardness of 49 and a Charpy impact value.

12 is a schematic diagram of No. It is a graph which shows the relationship between the tempering temperature of 10, 12, 47, and a Charpy impact value.

FIG. 13 is a graph showing carburizing and quenching conditions.

FIG. 14 is a hardness distribution diagram of a Charpy test piece after carburizing, quenching, and tempering.

15 (a) and 15 (b) show that the surface carbon concentration is 1.
The surface-hardened layer structure is carburized at 1000 ° C. for 2 hours so as to be 1% by weight and 1.3% by weight, then cooled to room temperature, and subjected to reheating quenching and tempering treatment at 850 ° C. for 1 hour.

FIG. 16 is a schematic view of quenched and tempered steel of S45C (H
9 is a graph showing the relationship between the hardness and wear ratio of various steels when the gouging wear amount in v500) is 1.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) // C21D 1/06 C21D 1/06 A 6/00 6/00 L W 101 101Z 9/00 9/00 B E 9 / 22 9/22 9/32 9/32 A 9/42 9/42 F term (reference) 2D058 BA01 4K028 AA01 AB01 AB06 4K042 AA12 AA18 AA20 AA24 AA25 BA02 BA03 BA04 CA02 CA03 CA04 CA05 CA06 CA07 CA08 CA09 CA10 CA12 CA13 DA01 DA02 DB01 DC02 DD02

Claims (24)

[Claims] 1. At least C: 0.15-0.60 wt%, Si: 0.05-1.8 wt%, Cr: 0.1
In steel containing 3.5% by weight, Mo is 0.1 to 0.1%.
In the range of 1.7% by weight and with the formula Mo (% by weight) = 1.7
-0.5xSi (weight%) is added as an upper limit, and V: 0.10 to 0.40 weight% and W: 0.
Either one or both of 1 to 1.0% by weight is added, and Mn, Ni, Co, Cu, Al, Ti,
Quenched and tempered martensitic steel containing one or more alloy elements of B, Nb, Zr, Ta, Hf, Ca, and unavoidable impurity elements such as P, S, N, O, and the balance being substantially Fe. High hardness and high toughness steel. 2. Si: 0.8 to 1.60% by weight, Cr:
High hardness and high toughness according to claim 1, wherein B is added in an amount of 0.0005 to 0.005% by weight, and Mo is limited to 0.1 to less than 1.0% by weight and Mo: 0.5 to 1.3% by weight. steel. 3. The formula 26.2 ≦ 5.8 × (Si (wt%)
+ Al (wt%)) +2.8 x Cr (wt%) +11 x M
o (wt%) + 25.7 x V (wt%) + 7.5 x W
The high hardness and high toughness steel according to any one of claims 1 to 3, wherein the alloy addition amount is adjusted in a relationship of (wt%) ≤36.2. 4. A steel containing at least C: 0.10 to 1.20% by weight and Si: 0.05 to 1.8% by weight, wherein a part of Si is 0.15 to 1.6% by weight. While replacing with Al, 0.3 to 2.5 wt% of Ni was added, and Mn, Cr, Mo, V, W, Co, Cu,
Quenched and tempered martens containing at least one alloy element of Ti, B, Nb, Zr, Ta, Hf, Ca, and unavoidable impurity elements such as P, S, N, O, and the balance being substantially Fe. High hardness and high toughness steel characterized by being a site structure steel. 5. The high hardness and high toughness steel according to claim 4, wherein Cr is contained in the range of 0.1 to 3.5% by weight. 6. When Mo is in the range of less than 1.7% by weight, S
With respect to the addition of i and Al, the formula Mo (wt%) = 1.7-
The high hardness and high toughness steel according to claim 4 or 5, wherein the upper limit is the relationship of 0.5 x (Si (wt%) + Al (wt%)). 7. V: 0.05 to 0.40% by weight, W:
The high hardness and high toughness steel according to claim 4, wherein either one or both of 0.1 to 1.0% by weight is added. 8. Al: 0.15 to 0.75% by weight, N
i: either of 0.3 to 2.0% by weight and 0.0005 to 0.005% by weight of B added, or both of them. High hardness and high toughness steel described in Crab. 9. The formula 21.2 ≦ 5.8 × (Si (wt%)
+ Al (wt%)) +2.8 x Cr (wt%) +11 x M
o (wt%) + 25.7 x V (wt%) + 7.5 x W
The high hardness and high toughness steel according to any one of claims 4 to 8, wherein the alloy addition amount is adjusted in a relationship of (wt%) ≤ 41.2. 10. At least C: 0.25 to 0.55% by weight, Si: less than 0.8% by weight, Cr: 3.5 to 5.5.
In the steel containing 10% by weight, Mo is added in the range of 0.3 to 1.0% by weight, and V: 0.10 to 0.
One or both of 40% by weight and W: 0.1 to 1.0% by weight is added, and Mn, Ni, Co and C are further added.
A baked alloy containing at least one alloy element of u, Al, B, Ti, Nb, Zr, Ta, Hf, and Ca, and unavoidable impurity elements such as P, S, N, and O, and the balance being substantially Fe. High hardness and high toughness steel characterized by having a quenched and tempered martensitic structure. 11. 0.1 to 1.0% by weight of Al and 0.
The high hardness and high toughness steel according to claim 10, wherein 3 to 2.5% by weight of Ni is added to improve temper softening resistance and toughness. 12. The formula 21.2 ≦ 3 × (Si (weight) + A
l (wt%)) + 2.8 × Cr (wt%) + 11 × Mo
The high hardness and high toughness steel according to claim 11, wherein the alloy addition amount is adjusted in a relationship of (wt%) + 25.7 × V (wt%) + 7.5 × W (wt%) ≦ 41.2. 13. The high hardness and high toughness steel according to claim 1, wherein 1 to 20% by weight of Co is added. 14. The high hardness and high toughness steel according to claim 1, wherein the total amount of one or more of Nb, Ti, Zr, Ta and Hf is 0.005 to 0.2% by weight. 15. A temperature of 600 ° C. or higher after quenching treatment
Hardness HRC50 ~ 6 by high temperature tempering
0, Charpy impact value 5 kgf ・ m / cm ^TwoAnd above
The high hardness and high toughness steel according to any one of claims 1 to 14. 16. A tempered martensitic steel that has been tempered after quenching has a hardness of HRC4.
5 or more, the expression log (Charpy impact value kgf · m / cm ² ) ≧ −0.0263 in the hardness range of HRC45 to 55.
× HRC + 2.225, and HR
Charpy impact value is 6kgf ・ m above C55
/ Cm < ² > or more, The high hardness and high toughness steel in any one of Claims 1-14 characterized by the above-mentioned. 17. The high hardness and high toughness steel according to claim 1, wherein the hardness is HRC52 or higher and the Charpy impact value is 6 kgf · m / cm ² or higher. Tracked parts using track steel for track-type vehicles, which are track bushes, track links, upper and lower roller rollers for tracks, and track shoes. 18. The high-hardness, high-toughness steel according to claim 1, wherein the hardness is HRC50 or more and the Charpy impact value is 8 kgf · m / cm ² or more. An earth and sand wear resistant component characterized by being a shank for tunnel excavation using site steel, a disc cutter for tunnel excavation, a chisel tool, a stirring blade for soil improvement, etc. 19. The high hardness and high toughness steel according to claim 1, wherein the hardness is HRC 40 or more, and the Charpy impact value is the expression log (Charpy impact value k.
gf · m / cm ² ) ≧ −0.0263 × HRC + 2.2
A fastening bolt used in a construction machine, characterized by using a quenched and tempered martensitic steel satisfying the relationship of 25. 20. The high according to claim 1.
Hardness and high toughness steel is processed into a gear shape and then carburized and quenched.
The surface carbon concentration is 0.6 to 1.0 weight due to the return process.
%, The surface carburizing depth is 0.4 mm or more, and its hardness is H
Charpy adjusted to RC55-64 and having equivalent depth
Impact value of test piece is 8kgf · m / cm ^TwoBe above
High toughness gears characterized by. 21. After machining the high hardness and high toughness steel according to any one of claims 1 to 16 into a gear shape, and then carburizing the surface carbon amount to 0.8 to 1.3% by weight, Once A
It is cooled to 1 transformation temperature or less, and further subjected to reheating quenching and tempering treatment to disperse cementite having a surface carburizing hardened layer depth of 0.4 mm or more and an average particle diameter of 1 μm or less in the hardened layer. The hardness is adjusted to HRC59-65, and the impact value of the Charpy test piece having the equivalent depth is 4
A high toughness and high surface pressure resistant gear characterized by having a kgf · m / cm ² or more. 22. After the high hardness and high toughness steel according to any one of claims 1 to 16 is processed into a gear shape, induction hardening and tempering is performed to adjust the surface hardness to HRC52 to 64, and the hardening depth thereof. Is equivalent to the impact value of the Charpy test piece is 5 kgf · m / cm ² or more, a high toughness gear. 23. A high-hardness, high-toughness steel according to any one of claims 1 to 16 is hardened and tempered to obtain 50 kgf.
/ Mm ² or more of high tension and / or hardness of HRC 50 or more, and is used by welding to a bucket, bulldozer blade, etc., and is used as a wear-resistant steel plate. 24. Less than 3.5 wt% Cr, 60
Formula 26.2 ≦ 5.8 × (Si (wt%) + Al (wt%)) + 2.8 × Cr (wt%) + 11 × Mo (wt%) so that HRC50 or more by tempering at 0 ° C. +25.7 x V (wt%) +7.5 x W (wt%)
The alloy addition amount is adjusted to satisfy the relation of ≦ 41.2.
A sand-and-sand wear-resistant component used for earth and sand excavation, such as a ripper point, an end bit, a bucket tooth, an edge, a disk cutter for tunnel excavation, which is characterized by using the high hardness and high toughness steel according to any one of 14 above.