JP2001262274A - High strength steel belt and its manufacturing method - Google Patents

Abstract

(57) [Problem] To provide a steel belt which has a high strength and is free from welding defects with an inexpensive steel composition not containing a large amount of alloying elements such as maraging steel, and a method for producing the same. SOLUTION: This steel belt is formed by welding a steel strip in a ring shape and then heat-treating the steel strip.
A steel belt satisfying the relationship of the following formula (1) with each content of V being defined and having a metal structure composed mainly of tempered martensite and having no welding defects, and a method for producing the steel belt. Disclose. 215 [Si] +110 [Cr] +115 [Mo] +114 [V] ≧ 400 (1) (in the formula, [] represents the content (% by mass) of each element)

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength steel belt which has a low content of alloying elements, can be provided at low cost, and has high strength and no welding defects, and a method for producing the same.

[0002]

2. Description of the Related Art A maraging steel is generally used as a steel belt having high strength and few welding defects. Maraging steel has a low carbon (≦ 0.03%), 18% Ni as a basic component, and further contains a large amount of alloying elements such as Co and Mo. This maraging steel is low carbon and therefore has good weldability, and is extremely useful as an age hardening type super-strength steel exhibiting high strength by precipitation of intermetallic compounds such as Ni and Mo by aging treatment. However, on the other hand, the cost is very high because a large amount of alloying elements is contained.

On the other hand, Japanese Unexamined Patent Publication No. Hei 5-171275 discloses an inexpensive aging precipitation type steel. However, in order to improve cold forgeability, this steel has a low C content and is mainly made of ferrite. Because of this structure, the strength level is as low as 1000 MPa or less in tensile strength at most, and lacks suitability as a steel belt requiring high strength.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an excellent steel belt which is low in cost, has high strength and has no welding defects, and a method for producing the same. Is to provide.

[0005]

The steel belt of the present invention which has solved the above-mentioned problems is a steel belt obtained by welding a steel strip in a ring shape and then heat-treating the steel strip.
0.45%, Si: 0.1 to 3.0%, Mn: 1.0 to
2.5%, Cr: 0.35 to 2.5% Mo: 0.25
1.5%, V: 0.1 to 0.8%
The gist lies in that the relationship of the following formula (1) is satisfied and the metal structure is mainly tempered martensite. 215 [Si] +110 [Cr] +115 [Mo] +114 [V] ≧ 400 (1) (in the formula, [] represents the content (% by mass) of each element)

[0006] The steel constituting the steel belt of the present invention may further include Cu ≦ 1.5% (not including 0%) as another element,
Ni ≦ 3.5% (excluding 0%), Al ≦ 1.5%
It may contain at least one element selected from the group consisting of (not including 0%), and in that case, it is necessary to satisfy the requirement of the following formula (2). 215 [Si] +110 [Cr] +115 [Mo] +114 [V] +100 [Cu] +60 [Ni + 2.2Al] ≧ 400 …… (2) (In the formula, [] indicates the content of each element (% by mass) Represents)

Further, the production method according to the present invention is an invention which is positioned as a production method for obtaining a steel belt satisfying the above requirements, wherein C: 0.002 to 0.20% by mass% and S:
i: 0.1 to 3.0%, Mn: 1.0 to 2.5%, C
r: 0.35 to 2.5% Mo: 0.25 to 1.5%, V
: After welding a steel strip containing 0.1 to 0.8% and satisfying the relationship of the above formula (1) in a ring shape, austenitizing, then quenching and tempering, and mainly tempering martensite. It has a gist in the place of the metal structure.

In carrying out the method of the present invention,
It is desirable that the steel before welding has a low carbon content from the viewpoint of weldability, and after welding, it is desirable to have a high carbon content in order to obtain high strength characteristics as a steel belt. Heating in a carburizing atmosphere to reduce the C content of the final steel belt to 0.05 to 0.4.
It is desirable to adopt a method of increasing to 5%.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors aimed at developing a high-strength steel belt having high strength and no welding defects without adding a large amount of alloying elements. As a result of intensive studies on the relationship of strength after tempering, the following findings were obtained.

That is, if the amount of C is limited to secure the weldability and the alloy composition of the steel is controlled so that the amount of the alloying element satisfies the requirement of the above formula (1) or (2), the low-cost alloy composition However, the present invention has been found to be able to secure a high strength, not only to prevent a decrease in strength due to tempering, but also to increase strength.

In the following, the reason for determining the type of each element constituting steel and the content thereof in the present invention will be explained.

C: 0.05 to 0.45% C is an element essential for enhancing the hardenability and securing high strength, and also for turning the structure after quenching into tempered martensite. To make the most of
It must contain 0.05% or more of C in the state of the final steel belt. However, when the amount of C exceeds 0.45%, the toughness is greatly reduced and a tendency to become brittle occurs. The lower limit of the C content is more preferably 0.10 for making the structure tempered martensite and for achieving both high strength and toughness.
%, And a preferable upper limit is 0.40%.

Si: 0.10-3.0% Si is an element effective for deoxidation at the time of melting and strengthening of the matrix, and is also an element useful for promoting secondary hardening at the time of tempering. . In order to effectively exert such an effect, the content must be 0.10% or more. However, if the content is too large, the weldability is reduced and the toughness is adversely affected. Therefore, the content must be suppressed to 3.0% or less. . Si
A more preferred lower limit of the amount is 0.50%, and a more preferred upper limit is 2.50%.

Mn: 1.0 to 2.5% Mn not only acts as a deoxidizing agent at the time of melting, but also enhances hardenability and effectively acts to improve strength. In order to effectively exert such an effect, the content must be 1.0% or more. However, if the content is too large, the weldability when welding in a ring shape is reduced and the toughness is adversely affected.
%. A more preferred lower limit of Mn is 1.5%, and a more preferred upper limit is 2.3%.

Cr: 0.35 to 2.5% Cr is an element that enhances hardenability and contributes to improvement in strength, and is also an important element in increasing temper softening resistance. In order to effectively exert such an effect, the content must be 0.35% or more. However, if the content is too large, the weldability is impaired and the toughness is adversely affected, so the content must be suppressed to 2.5% or less. A more preferred lower limit of Cr is 1.0%, and a more preferred upper limit is 2.3%.

Mo: 0.25 to 1.5% Mo is an element effective for improving hardenability, and also has the effect of increasing the tempering softening resistance by secondary hardening. In order to effectively exert such an effect, it is necessary to contain 0.25% or more, but the effect is about 1.5%.
%, So further additions are economically useless. A more preferred lower limit of Mo is 0.50%, and a more preferred upper limit is 1.3%.

V: 0.1-0.8% V is an element effective in increasing the tempering softening resistance due to the secondary hardening. To effectively exhibit such an effect, V must be contained in an amount of 0.1% or more. Must. However, an excessive amount of V adversely affects weldability and toughness. Therefore, the V content should be suppressed to 0.8% or less. A more preferred lower limit of V is 0.2%, and a more preferred upper limit is 0.7%.

Cu: 1.5% or less Cu is an effective element that causes aging precipitation during tempering to increase the matrix strength. However, too much Cu adversely affects weldability. No. A particularly preferable Cu content is 0.5 to 1.3% in order to effectively exert the effect while avoiding the obstacle of Cu.

Ni: 3.5% or less Ni is also an element effective for aging precipitation during tempering to increase the matrix strength. However, too much Ni deteriorates the weldability. No. Ni
The Ni content is particularly preferably in the range of 2.0 to 3.3% in order to effectively exhibit the effect while avoiding the obstacles described above. 215 [Si] +110 [Cr] +115 [Mo] +114 [V] ≧ 400 ... (1) 215 [Si] +110 [Cr] +115 [Mo] +114 [V] +100 [Cu] +60 [Ni + 2.2Al] ≧ 400 …… (2)

In the present invention, secondary hardening after tempering is performed by adjusting the relationship between the amounts of the respective elements so as to satisfy the requirements of the above formula (1) or (2) in addition to the amounts of the respective alloying elements. Can increase the softening resistance. In particular, a steel satisfying the requirement of the above formula (2) exhibits a strength increasing effect due to aging precipitation in addition to an increase in softening resistance, and is preferable in achieving higher strength.

The constituent elements of the steel belt according to the present invention are as described above, and the balance is substantially Fe, but in addition, trace amounts of S, P, N, O, etc. which are inevitably mixed. Of course, other elements can be positively contained as long as the above-mentioned characteristics of the present invention are not impaired. Included in the scope. Examples of elements that can be positively added include, for example, Ti, Nb and the like, which have a toughness improving effect.

In the steel belt of the present invention, in addition to the above chemical components, it is necessary that the metal structure be a structure mainly composed of tempered martensite, that is, austenite is formed by heat treatment after welding, and then quenching and tempering are performed. By
It is very important to have a metal structure mainly composed of tempered martensite. The reason is that the tempered martensite-based metal structure has both excellent strength and toughness, and in the case of a structure-based material such as ferrite, bainite, or pearlite, even if the chemical composition satisfies the prescribed requirements, However, the levels of strength and toughness intended in the present invention cannot be obtained. For this reason, the metal structure of the steel constituting the steel belt of the present invention must have a tempered martensite-based structure, but not all of the steel structure has to be a tempered martensite structure. If the amount is about 30% or less, preferably 10% or less, a bainite structure may be contained in a small amount.

Next, the manufacturing method of the present invention is positioned as a method of manufacturing a high-strength steel belt satisfying the above requirements, and its basic method is to use a steel strip as a raw material, weld it in a ring shape, It is characterized in that the main constituent of the metal structure is tempered martensite by performing quenching and tempering treatment after austenitizing by heat treatment.
The preferred component composition of the steel strip used here, the types and contents of all the elements except C in the steel belt finally obtained as it is, and accordingly, the above formulas (1) and (2)
The relational expression expressed by the above also applies substantially to the raw material strip.

However, as for the C content, since a high level of weldability is required at the stage of the raw steel strip, the C content is set to 0.1%.
It is necessary to use one that falls within the range of 002 to 0.20%. Incidentally, C is not only an important element for enhancing the hardenability and turning the structure after quenching into tempered martensite, but also an element indispensable for securing high strength. Therefore, it is desirable to keep it as low as possible before welding. Moreover, when carrying out the production method of the present invention, the amount of C can be increased after welding by performing the heating for austenitization performed after welding in a carburized atmosphere, so that only the weldability is improved. Considering this, it is desirable to keep the carbon content in the steel strip before welding as low as possible.
However, since it is not easy to reduce the C content to less than 0.002% in the steel making stage, considering the practicality, the lower limit of the C content in the raw steel strip stage may be considered to be about 0.002%.

On the other hand, it is important that the upper limit of the C content at the raw steel strip stage is kept within a range that does not impair the upper limit, particularly from the viewpoint of weldability. This is an indispensable requirement for ensuring the weldability. By the way, C content in steel before welding is 0.20%
In the case of exceeding, welding defects due to poor weldability (specifically, welding cracks, pore defects, poor fusion, etc.) are likely to occur, and these welding defects are difficult to heal even in the subsequent heat treatment process, It remains substantially as a defect in the product steel belt. Therefore, the C content of the steel strip used as the raw material steel is 0.002% or more and 0.20% or more.
% Or less, more preferably 0.18% or less.

When a steel strip having a C content of about 0.15% or more is used as a raw steel, a high strength can be ensured by forming a tempered martensite structure in a subsequent heat treatment step. If the C content is less than the 0.15% level, it will be difficult to obtain the level of strength intended in the present invention only by controlling the metallographic structure. Therefore, heating for austenitization is performed in a carburizing atmosphere. In this way, the carburization is carried out at the same time, and the C content as the final steel belt is reduced to 0.
It is indispensable to increase to 15% level or more.

As is clear from the above, in the steel strip stage before welding, it is desirable that the C content is as small as possible in order to ensure excellent weldability.
C content is 0.3-0.4% due to the need to ensure high strength
In order to satisfy these two requirements at the same time, it is necessary to use a steel strip with a low carbon content to ensure excellent weldability and perform heat treatment after welding in a carburizing atmosphere. A method of increasing the amount of C by performing is recommended as the most effective method.

The types and contents of the elements other than the above-mentioned C constituting the raw material strip are not substantially changed by heat treatment or carburizing treatment, so that the composition of the steel material constituting the steel belt is not changed. The contained elements shown in the section and the preferred contents thereof, and the relational expressions shown in the above formulas (1) and (2) apply as they are.

The specific conditions for the heat treatment for carrying out the production method of the present invention are not particularly limited as long as the metal structure as the final steel belt can be made mainly of tempered martensite, and it is also dependent on the chemical composition of the steel used. It is not appropriate to determine uniformly because it changes. However, as an example of a standard condition, the heating condition for austenitization is 9%.
At a temperature of 00 to 1150 ° C, and a tempering condition of 400 to 60
A range of 0 ° C. is common.

[0030]

EXAMPLES Next, the structure and operation and effect of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and can be adapted to the spirit of the preceding and following examples. Of course, the present invention can be implemented with modifications within the scope, and all of them are included in the technical scope of the present invention.

Example 1 Steel No. 1 shown in Table 1 was used. 1 to 29 were smelted by a vacuum smelting furnace and then cast, and then forged into a round bar having a diameter of 5 mm. Then, after annealing, pickling and lubrication treatment, a 0.5 mm thick steel strip was formed by cold rolling. Butt welding was performed on each of the obtained steel strips, and the occurrence of cracks in the welds was visually checked. Furthermore, each steel strip is heated to 1100 ° C.
After tempering at 500 ° C. for 2 hours, the hardness of the obtained steel belt was measured, and the results shown in Table 1 were obtained. In addition, it was confirmed that the chemical composition of the obtained steel belt was not substantially changed from the chemical composition of Table 1 used as the raw material strip. The metal structure of each of the obtained belts was mainly tempered martensite.

[0032]

[Table 1]

In Table 1, steel No. Examples 1 to 15 satisfy all the requirements of the present invention, and have no weld cracks and have a desired hardness of Hv450 or more. On the other hand, steel No. 16, 18, 20, 22,
In Nos. 24 and 25, since the amounts of C, Bi, Mn, Cr, Mo, and V did not reach the specified values, respectively, the hardness did not reach the target level. In addition, steel No. 17,19,21,23,2
Nos. 6 and 28 had C, Si, Mn, Cr, V and Cu contents exceeding the specified values, respectively. In No. 29, the amounts of Ni and Al exceeded the specified values, and cracks occurred during welding. In addition, steel No. No. 27 does not reach the target hardness level because the value represented by the expression (1) has not reached 400.

Example 2 Steel No. 1 having the chemical composition shown in Table 2 was used. 1 to 27 were smelted by a vacuum smelting furnace, cast and then forged into a round bar having a diameter of 5 mm. Then, after annealing, pickling and lubrication treatment, a 0.5 mm thick steel strip was formed by cold rolling. Next, butt welding was performed on each steel strip, and the occurrence of cracks in the welded portions was visually checked. Further, each was heated to 920 ° C. in a carburizing atmosphere to austenite, and after quenching, tempered at 500 ° C. for 2 hours. The hardness of each of the obtained belts was measured, and the results shown in Table 2 were obtained. In addition,
The metal structure of each of the obtained belts was mainly tempered martensite.

[0035]

[Table 2]

In Table 2, steel No. Examples 1 to 14 satisfy all the requirements of the present invention, have no weld cracks, and have a required hardness of Hv450. On the other hand, steel No. 16, 18, 20, 22,
Sample No. 23 has insufficient hardness because the amounts of Si, Mn, Cr, Mo, and V have not reached the specified values. Further, steel No. 15 has a weld crack because the C content after carburizing and quenching exceeds a specified value. In addition, steel No. 17,1
9, 21, 24, and 26 represent Si, Mn, Cr,
The amounts of V and Cu exceed the specified values. 27 is Ni
Since the Al content and the Al content exceed the specified values, welding cracks are generated in each case. Furthermore, steel No. In No. 25, the target level hardness was not obtained because the value of the expression (2) was less than 400.

[0037]

The present invention is constituted as described above. By specifying the chemical composition and the metal structure of the steel material, the invention uses a maraging steel with an inexpensive steel composition not containing many alloying elements. It has become possible to provide a steel belt having comparable strength and no welding defects. Further, according to the manufacturing method of the present invention, a high-strength steel belt can be easily manufactured while securing excellent weldability. Therefore, the steel belt can be used very effectively for power transmission of various driving devices including, for example, automobiles and ships, and various industrial machines.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C21D 9/50 101 C21D 9/50 101B C22C 38/38 C22C 38/38 38/58 38/58 (72) Inventor Satoshi Abe 2, Nadahama-Higashi-cho, Nada-ku, Kobe-shi Kobe Steel Works, Ltd.Kobe Works (72) Inventor Yoshitake Matsushima 2nd Nadahama-Higashi-cho, Nada-ku, Kobe City Kobe Steel Works, Ltd. Hide 1 Toyota Town, Toyota City, Aichi Prefecture F-term in Toyota Motor Corporation (reference) 4K042 AA23 AA24 CA05 CA06 CA08 CA10 CA13 DA01 DA02 DC02 DC04

Claims (4)

[Claims] 1. A steel belt heat-treated after welding a steel strip in a ring shape, wherein C: 0.05 to 0.4 in mass%.
5%, Si: 0.1 to 3.0%, Mn: 1.0 to 2.5
%, Cr: 0.35 to 2.5% Mo: 0.25 to 1.5
%, V: 0.1 to 0.8%, and the following formula
A high-strength steel belt that satisfies the relationship of (1) and is characterized in that a main structure is tempered martensite. 215 [Si] +110 [Cr] +115 [Mo] +114 [V] ≧ 400 (1) (in the formula, [] represents the content (% by mass) of each element) 2. The method according to claim 1, further comprising Cu ≦ 1.5% (0%).
%), Ni ≦ 3.5% (not including 0%),
2. The high-strength steel belt according to claim 1, wherein the high-strength steel belt includes at least one element selected from the group consisting of Al ≦ 1.5% (excluding 0%) and satisfies the requirement of the following formula (2). . 215 [Si] +110 [Cr] +115 [Mo] +114 [V] +100 [Cu] +60 [Ni + 2.2Al] ≧ 400 …… (2) (In the formula, [] indicates the content of each element (% by mass) Represents) 3. C: 0.002 to 0.20 by mass%
%, Si: 0.1 to 3.0%, Mn: 1.0 to 2.5
%, Cr: 0.35 to 2.5% Mo: 0.25 to 1.5
%, V: 0.1 to 0.8%, and after welding a steel strip made of steel satisfying the relationship of the above formula (1) into a ring shape,
A method for producing a high-strength steel belt, comprising obtaining the high-strength belt according to claim 1 or 2, wherein the metal structure is mainly tempered martensite by quenching and tempering after austenitization. 4. The method according to claim 3, wherein the austenitization is performed in a carburizing atmosphere to increase the C content to 0.05 to 0.45%.