WO2014038548A1 - Machine structure steel material having low heat-treatment deformation - Google Patents

Description

Machine structural steel with low heat treatment deformation Cross-reference of related applications

This application claims priority based on Japanese Patent Application No. 2012-193762 filed on September 4, 2012, the entire disclosure of which is incorporated herein by reference.

The present invention relates to machine structural steel used as power transmission parts such as gears and shafts used in automobiles, industrial machines, and the like, and more particularly to steel for machine structure with small heat treatment deformation.

It is known that deformation of a steel material (hereinafter referred to as “heat treatment deformation”) occurs due to heat treatment such as quenching. If there is such heat treatment deformation, the number of manufacturing processes will increase to correct the deformation, the defective part rate will increase if it cannot be corrected, or it will be caused by deformation when incorporated as a drive system part. There are adverse effects such as generating noise and vibration. Therefore, it is a very important problem in practice to keep the heat treatment deformation as small as possible.

Conventionally, this heat treatment deformation is considered to be influenced by many factors other than steel, such as part shape, influence of pre-heat treatment process, physical properties of refrigerants such as quenching oil, and non-uniform cooling. Has been. Therefore, attempts have been made to reduce heat treatment deformation by optimizing them in various ways. For example, as a material countermeasure, a method has been proposed in which a soft ferrite phase is precipitated in the core of a hardened steel material to reduce heat treatment strain (see, for example, Patent Document 1).

Also, as an approach from the cooling method, a method using pressurized gas cooling instead of conventional oil quenching has been proposed (for example, see Patent Document 2). In addition, a method for achieving uniform cooling of an object to be cooled using means for promoting or reducing the heat transfer coefficient has been proposed (for example, see Patent Document 3).

In Patent Document 3, the means for promoting the heat transfer coefficient is due to the convection of the coating material that promotes cooling provided in the portion where cooling is delayed or the coolant formed around the portion where cooling is delayed, The means for reducing the heat transfer rate is said to be glass wool or a heat insulating coating material covering a portion where cooling is likely to proceed.

JP 1997-111408 A JP 2008-121064 A JP 2010-174289 A

However, the conventional method proposed above cannot always be a general purpose means. This is because, for example, in the technique of Patent Document 1, a soft phase having a low strength may be introduced into a part, and in the technique of Patent Document 2, the heat treatment furnace itself has to be changed. This is because the technique of Patent Document 3 is not necessarily a general-purpose means, for example, it requires processing for individual heat-treated parts.

On the other hand, the present inventors have secured a sufficient steel material strength without relying on the generation of a ferrite structure that is soft and may reduce the strength of the component, and under a general quenching technique such as oil quenching, Even if the cooling of the steel becomes non-uniform, we have conducted intensive research on steel that can keep heat treatment deformation small. As a result, the inventors reduced the heat treatment deformation by controlling the chemical composition of the steel, the martensite transformation start temperature (Ms point), and the hardenability measured by the Jominy one-side quenching method to an appropriate range. It was found that it can be suppressed.

Therefore, an object of the present invention is to provide a steel material that is made of mechanical structural steel used as a power transmission component such as a gear or a shaft used in automobiles, industrial machines, and the like, and has less heat treatment deformation.

According to one aspect of the present invention, a steel material for mechanical structure with small heat treatment deformation, the steel material is in mass%,
C: 0.20 to 0.30%
Si: 0.10 to 1.50%,
Mn: 0.10 to 1.20%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 1.30-2.50%,
Cu: 0.30% or less,
Al: 0.008 to 0.300%,
O: 0.0030% or less,
N: 0.0020 to 0.0300%
A mechanical structural steel comprising the balance Fe and inevitable impurities,
The martensitic transformation start temperature (Ms point) of the steel material made of the steel is 460 ° C. or less,
Using the following formula (1), J1.5 of the hardness at a distance of 1.5 mm from the quenching end of the steel material and J9 of the hardness at a distance of 9 mm measured by the Jominy type one-end quenching method for the steel material. The calculated (J9 / J1.5) value is in the range of 0.70 to 0.85,
Furthermore, the value of (J11 / J1.5) calculated by the following equation (2) using J1.5 of hardness at a distance of 1.5 mm and J11 of hardness at a distance of 11 mm is 0.67 to 0.78. In the range of
A machine structural steel material with small heat treatment deformation is provided.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (distance from the quenching end measured by the Jominy type one-end quenching method. 5mm hardness) ... Formula (1)
(J11 / J1.5) = (hardness at a distance of 11 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (distance from the quenching end measured by the Jominy type one-end quenching method. (Hardness at 5 mm) (2)

According to a preferred embodiment of the present invention, the steel material for mechanical structure having a small heat treatment deformation, the steel material is in mass%,
C: 0.20 to 0.30%
Si: 0.10 to 1.50%,
Mn: 0.10 to 1.20%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 1.30-2.50%,
Cu: 0.30% or less,
Al: 0.008 to 0.300%,
O: 0.0030% or less,
N: 0.0020 to 0.0300% is contained,
Furthermore, it contains one or two of Ni: 0.20 to 3.00% and Mo: 0.05 to 0.50%,
It is a steel material made of mechanical structural steel consisting of the balance Fe and inevitable impurities,
Furthermore, the martensitic transformation start temperature (Ms point) of this steel material is 460 ° C. or less,
Using the above formula (1), J1.5 of the hardness at a distance of 1.5 mm from the quenching end of the steel and J9 of the hardness at a distance of 9 mm measured by the Jominy one-end quenching method for this steel. The calculated (J9 / J1.5) value is in the range of 0.70 to 0.85,
Further, the value of (J11 / J1.5) calculated by the above equation (2) using J1.5 of the hardness at a distance of 1.5 mm and J11 of the hardness at a distance of 11 mm is 0.67-0. In the range of 78,
A machine structural steel material with small heat treatment deformation is provided.

According to another aspect of the present invention, there is provided a steel material for machine structural use having a small heat treatment deformation, the steel material being in mass%,
C: 0.20 to 0.30%
Si: 0.10 to 1.50%,
Mn: 0.10 to 1.20%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 1.30-2.50%,
Cu: 0.30% or less,
Al: 0.008 to 0.300%,
O: 0.0030% or less,
N: 0.0020 to 0.0300% is contained,
Further, Ti contains 0.020 to 0.200% and Nb: 0.02 to 0.20% of one or two,
It is a steel material made of mechanical structural steel consisting of the balance Fe and inevitable impurities,
Furthermore, the martensitic transformation start temperature (Ms point) of this steel material is 460 ° C. or less,
Using the above formula (1), J1.5 of the hardness at a distance of 1.5 mm from the quenching end of the steel material and J9 of the hardness at a distance of 9 mm measured by the Jominy one-end quenching method for this steel material. The calculated (J9 / J1.5) value is in the range of 0.70 to 0.85,
Furthermore, the value of (J11 / J1.5) calculated by the above equation (2) using the hardness J1.5 at a distance of 1.5 mm and the hardness J11 at a distance of 11 mm is 0.67-0. In the range of 78,
A machine structural steel material with small heat treatment deformation is provided.

According to another aspect of the present invention, there is provided a steel material for machine structural use having a small heat treatment deformation, the steel material being in mass%,
C: 0.20 to 0.30%
Si: 0.10 to 1.50%,
Mn: 0.10 to 1.20%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 1.30-2.50%,
Cu: 0.30% or less,
Al: 0.008 to 0.300%,
O: 0.0030% or less,
N: 0.0020 to 0.0300% is contained,
Furthermore, it contains one or two of Ni: 0.20 to 3.00% and Mo: 0.05 to 0.50%,
Further, Ti contains 0.020 to 0.200% and Nb: 0.02 to 0.20% of one or two,
It is a steel material made of mechanical structural steel consisting of the balance Fe and inevitable impurities,
Furthermore, the martensitic transformation start temperature (Ms point) of this steel material is 460 ° C. or less,
Using the above formula (1), J1.5 of the hardness at a distance of 1.5 mm from the quenching end of the steel and J9 of the hardness at a distance of 9 mm measured by the Jominy one-end quenching method for this steel. The calculated (J9 / J1.5) value is in the range of 0.70 to 0.85,
Further, the value of (J11 / J1.5) calculated by the above equation (2) using J1.5 of the hardness at a distance of 1.5 mm and J11 of the hardness at a distance of 11 mm is 0.67-0. In the range of 78,
A machine structural steel material with small heat treatment deformation is provided.

According to another aspect of the present invention, there is provided a steel material for machine structural use having a small heat treatment deformation, the steel material being in mass%,
C: 0.20 to 0.30%
Si: 0.10 to 1.50%,
Mn: 0.10 to 1.20%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 1.30-2.50%,
Cu: 0.30% or less,
Al: 0.008 to 0.300%,
O: 0.0030% or less,
N: 0.0020 to 0.0300%
Ni: 0 to 3.00%,
Mo: 0 to 0.50%
Ti: 0 to 0.200%,
Nb: 0 to 0.20%
Comprising the balance Fe and inevitable impurities,
The steel material has a martensitic transformation start temperature (Ms point) of 460 ° C. or less,
The ratio of the hardness J9 at a distance of 9 mm from the quenching end of the steel material to the hardness J1.5 at a distance of 1.5 mm from the quenching end of the steel material when measured by the Jomini type one-end quenching method ( J9 / J1.5) is in the range of 0.70 to 0.85, and the distance from the quenching end of the steel to the hardness J1.5 at a distance of 1.5 mm from the quenching end of the steel A steel material for machine structure having a ratio of hardness J11 at 11 mm (J11 / J1.5) in the range of 0.67 to 0.78 is provided.

According to a preferred aspect of the present invention, the steel material does not substantially contain Ni, Mo, Ti and Nb or contains an inevitable impurity level.

According to a preferred aspect of the present invention, the steel material includes one or two of Ni: 0.20 to 3.00% and Mo: 0.05 to 0.50% in mass%.

According to a preferred aspect of the present invention, the steel material includes one or two of Ti: 0.020 to 0.200% and Nb: 0.02 to 0.20% by mass%.

According to a preferred aspect of the present invention, the steel material is, by mass%, one or two of Ni: 0.20 to 3.00% and Mo: 0.05 to 0.50%, and Ti. : 0.020 to 0.200%, and Nb: 0.02 to 0.20%.

The present invention will be specifically described below. In addition, "%" of each component shows the mass%.

The steel material for mechanical structure with small heat treatment deformation according to the present invention is, in mass%, C: 0.20 to 0.30%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.20%, P: 0.030% or less, S: 0.030% or less, Cr: 1.30 to 2.50%, Cu: 0.30% or less, Al: 0.008 to 0.300%, O: 0.00. 0030% or less, N: 0.0020 to 0.0300%, Ni: 0 to 3.00%, Mo: 0 to 0.50%, Ti: 0 to 0.200%, Nb: 0 to 0.20% Comprising the balance Fe and inevitable impurities, preferably consisting essentially of these elements and inevitable impurities, more preferably consisting only of these elements and inevitable impurities (Consisting of).

C: 0.20 to 0.30%
C is an element necessary for securing the strength after quenching and tempering of steel or the strength of the core after carburizing, quenching and tempering as mechanical structural parts, and is adjusted to a predetermined range in order to reduce heat treatment deformation. There is a need. If the C content is less than 0.20%, the strength cannot be ensured, and if it exceeds 0.30%, deformation due to heat treatment becomes too large. Therefore, the C content is set to 0.20 to 0.30%, preferably 0.22 to 0.27%.

Si: 0.10 to 1.50%
Si is an element necessary for deoxidation and is an effective element for imparting necessary strength and hardenability to steel. However, if the Si content is less than 0.10%, the effect cannot be obtained, and if it exceeds 1.50%, the machinability is lowered. Therefore, the Si content is 0.10 to 1.50%, preferably 0.20 to 1.00%.

Mn: 0.10 to 1.20%
Mn is an element necessary for ensuring hardenability. However, if the Mn content is less than 0.10%, sufficient effect on hardenability cannot be obtained, and if it exceeds 1.20%, the machinability is lowered. Therefore, the Mn content is 0.10 to 1.20%, preferably 0.20 to 0.80%, and more preferably 0.20 to 0.55%.

P: 0.030% or less P is an unavoidable element contained in scrap, but segregates at the grain boundary and lowers properties such as impact strength and bending strength. Therefore, the P content is 0.030% or less (including 0%), and typically exceeds 0 and is 0.030% or less.

S: 0.030% or less S is an element that improves machinability, but generates MnS that is a non-metallic inclusion and lowers the toughness and fatigue strength in the transverse direction. Therefore, the S content is 0.030% or less (including 0%), and typically exceeds 0 and is 0.030% or less.

Cr: 1.30-2.50%
Cr is an element necessary for ensuring hardenability. However, if the Cr content is less than 1.30%, a sufficient effect on hardenability cannot be obtained. Therefore, the Cr content is set to 1.30 to 2.50%, preferably 1.50 to 2.25%.

Ni: 0.20 to 3.00%
Ni is an optional element that improves hardenability and toughness, and in order to obtain the effect, addition of 0.20% or more is preferable. However, if the Ni content exceeds 3.00%, the workability is remarkably lowered and the cost is increased, so the content is made 3.00% or less. Therefore, the Ni content is set to 0.20 to 3.00%.

Mo: 0.05 to 0.50%
Mo is an optional element that improves hardenability and toughness, and 0.05% or more is preferable for obtaining the effect. However, if the Mo content exceeds 0.50%, the workability decreases. Therefore, the Mo content is set to 0.05 to 0.50%.

Cu: 0.30% or less Cu is an inevitable element contained from scrap, but has aging properties and an effect of increasing strength. However, when the Cu content exceeds 0.30%, the hot workability is lowered. Therefore, the Cu content is set to 0.30% or less (including 0%), and typically exceeds 0 and is set to 0.30% or less.

Al: 0.008 to 0.300%
Al is an element used as a deoxidizing material, and also binds to N and precipitates as AlN as will be described later, thereby bringing about an effect of suppressing grain coarsening. In order to obtain this effect, 0.008% or more of Al needs to be added. On the other hand, if Al is added in excess of 0.300%, large alumina inclusions are formed, and fatigue characteristics and workability are deteriorated. Therefore, the Al content is set to 0.008 to 0.300%, preferably 0.014 to 0.200%.

O: 0.0030% or less O is an element inevitably contained in steel. However, if O exceeds 0.0030%, workability and fatigue strength are reduced due to an increase in oxide. Therefore, the content of O is set to 0.0030% or less (including 0%), preferably 0.0020% or less (including 0%). Also, typically, it exceeds 0 and is 0.0030% or less, and desirably exceeds 0 and is 0.0020% or less.

N: 0.0020 to 0.0300%
N is an element that finely precipitates as AlN or Nb nitride in the steel and has an effect of preventing the coarsening of crystal grains. In order to obtain the effect, it is necessary to add 0.0020% or more of Ni. However, if the Ni content exceeds 0.0300%, nitrides increase and fatigue strength and workability deteriorate. Therefore, the N content is set to 0.0020 to 0.0300%, preferably 0.0020 to 0.0200%. However, particularly in steel containing 0.020% or more of Ti, the N content is set to 0.0020 to 0.0100% in order to avoid a decrease in fatigue strength due to excessive TiN formation.

Ti: 0.020 to 0.200%
Ti is an optional element that combines with C in the steel to form carbides finely and has the effect of preventing grain coarsening. To obtain this effect, 0.020% or more of Ti is added. It is preferable to do. On the other hand, if the Ti content exceeds 0.200%, the machinability is impaired. Therefore, the Ti content is set to 0.020 to 0.200%.

Nb: 0.02 to 0.20%
Nb is an arbitrary element that forms carbides or nitrides and has an effect of preventing grain coarsening. In particular, nano-order sized NbC or Nb (C, N) finely dispersed in steel suppresses the growth of crystal grains. If the Nb content is less than 0.02%, the effect cannot be obtained. If the Nb content exceeds 0.20%, the amount of precipitates becomes excessive and workability deteriorates. Therefore, the Nb content is 0.02 to 0.20%, preferably 0.02 to 0.12%.

Furthermore, the reasons for limiting the Ms point and the hardenability measured by the Jominy one-side quenching method other than the reasons for limiting the above components will be described.

Ms point: 460 ° C. or less In the steel material according to the present invention, it is necessary to regulate the martensite transformation start temperature (Ms point) to 460 ° C. or less in order to reduce the heat treatment deformation of the steel material. The reason why heat treatment deformation can be reduced by restricting the Ms point to 460 ° C. or less is that, even when the parts are not cooled when quenched, the martensitic transformation occurs in the temperature range where the cooling performance of the refrigerant is high. This is because it can be avoided, and as a result, it can be suppressed that the martensitic transformation time largely deviates depending on the parts. Therefore, the Ms point is restricted to 460 ° C. or lower, but preferably the Ms point is restricted to 450 ° C. or lower. In this case, the heat treatment deformation means bending of the shaft-shaped part, falling of the gear teeth, or twisting.

Value of (J9 / J1.5): 0.70 to 0.85
Value of (J11 / J1.5): 0.67 to 0.78
The ratio of the hardness J9 at a distance of 9 mm from the quenching end of the steel material to the hardness J1.5 at a distance of 1.5 mm from the quenching end of the steel material (J9 / J1.5) is in the range of 0.70 to 0.85, and the hardness at a distance of 11 mm from the quenching end of the steel relative to the hardness J1.5 at a distance of 1.5 mm from the quenching end of the steel When the ratio of J11 (J11 / J1.5) is in the range of 0.67 to 0.78, the heat treatment deformation of the steel material can be kept small. The heat treatment deformation referred to here is the bending of the shaft-shaped part, the gear teeth falling or twisting after quenching, and the change in the dimension (length, diameter, thickness, etc.) of the part before and after quenching. Although the mechanism by which heat treatment deformation is suppressed by controlling the Jominy hardenability within an appropriate range has not yet been fully elucidated, heat treatment deformation can be achieved even if Jominy hardenability is too low or too high. It has been experimentally confirmed by the present inventors that this increases. Without being bound by theory, in steels with Jominy hardenability in this range, bainite transformation occurs moderately prior to martensitic transformation in the quenching cooling process, increasing the strength of the steel material and deforming to some extent. It is considered that the deformation due to heat treatment is suppressed because the martensitic transformation starts from the difficult state. On the other hand, if the hardenability is too low, the bainite transformation occurs excessively, so that the heat treatment deformation increases due to the influence of the bainite transformation itself, and if the hardenability is too high, the bainite structure relaxes the heat treatment deformation. It is considered that the deformation due to heat treatment is also increased due to the small amount.

After the steel material is processed into a part by the limitation of steel components, the Ms point, and the hardenability limit measured by the Jominy one-side quenching method as described above, quenching and carburizing and quenching are performed to harden the part. The heat treatment deformation when performed can be reduced. As a result, the present invention has beneficial effects such as improvement of component yield, simplification and abolition of component correction processes, and omission of gear tooth grinding for noise and vibration countermeasures. Can do.

The steel material according to the present invention will be specifically described based on the following examples.

In order to obtain mechanical structural steels used as power transmission parts such as gears and shafts used in automobiles and industrial machines, the No. of the invention examples shown in Table 1 were obtained. Steel consisting of 1 to 23, the remainder Fe and unavoidable impurities was melted in a vacuum induction melting furnace to obtain a 100 kg steel ingot.

As in the above-described examples of the present invention, as a structural steel used as a power transmission component such as a gear or a shaft used in automobiles or industrial machines, the comparative example No. 2 shown in Table 2 was used. Steel consisting of 1 to 16 component compositions, the balance Fe and unavoidable impurities was melted in a vacuum induction melting furnace to obtain a 100 kg steel ingot.

First, these ingots of the present invention and comparative examples were heated at 1250 ° C. for 5 hours and then forged into a steel bar having a diameter of 32 mm. Next, normalizing was performed by heating and holding at 900 ° C. for 1.5 hours and then air cooling. Subsequently, a test piece having a diameter of 20 mm and a length of 80 mm was produced from a steel bar having a diameter of 32 mm, and a groove having a depth of 5 mm, a width of 8 mm, and a length of 80 mm was applied to the side surface of the test piece. When quenching was performed by this groove processing, the cooling rate was varied greatly depending on the portion in the test piece. Moreover, the length of the test piece was measured after the groove processing. Further, the radius and groove width were measured at each position of 2 mm, 20 mm from the end of the test piece, and 40 mm which is the center of the test piece length. Then, after carburizing these test pieces at 930 ° C., the temperature was lowered to 850 ° C. in the furnace, and further maintained for 1 hour, and then quenched into a quenching oil at 60 ° C. After quenching, the specimens that were sufficiently cooled were measured for the bend and length of the specimen and the radius and groove width at each position of 2 mm, 20 mm from the specimen edge, and 40 mm, which is the center of the specimen length.

For bending after heat treatment, hold both ends of the test piece with V block, and measure the maximum and minimum displacement on the circumference of the center of the test piece with a dial gauge when the test piece is rotated once. The difference between the maximum displacement and the minimum displacement was obtained by dividing by 2. In this measurement, the displacement of the bottom portion of the groove existing on the circumference of the test piece was ignored. In addition, as an index of heat treatment deformation, a difference in length of the test piece before and after the heat treatment was obtained, and the absolute value thereof was evaluated. Furthermore, the radius before and after the heat treatment at each position of the total three locations of 2 mm, 20 mm from the end of the test piece, and 40 mm which is the center of the length of the test piece, and the groove width dimension measurement result, After obtaining the dimensional change amount of the groove width, the values obtained by subtracting the minimum value from the maximum value among the dimensional change amounts at the three locations are defined as the radius change amount and the groove width change amount, respectively. It was evaluated as an index of deformation.

In addition, a test piece having a diameter of 3 mm and a length of 10 mm is determined from the steel bar having a diameter of 32 mm after the above normalization, and the Ms point, which is the martensitic transformation start temperature of the steel material, is measured using a fully automatic transformation recording measuring device. did. The Ms point in the present embodiment is measured and measured under the condition that the cooling process of the component is assumed. In the present embodiment, the above-described grooved test piece having a diameter of 20 mm has an oil temperature of 60 ° C. Assuming oil quenching, the cooling rate during quenching was measured at 30 ° C./s. For the measurement of the hardenability of steel by the Jominy type one-end quenching method, a test piece was prepared from the above-described forged steel bar with a diameter of 32 mm, and “steel hardenability test method (one end) specified in JIS G 0561”. The test was conducted under the conditions according to the quenching method) and evaluated.

Table 3 shows the Ms point measured for the steel of the present invention, J1.5 of the hardness at a distance of 1.5 mm, J9 of the hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method, and Each value of the hardness J11 at a distance of 11 mm, and the obtained (J9 / J1.5) value and (J11 / J1.5) value are shown. Further, the bending (unit: mm) evaluated after quenching the above test piece, the absolute value of the difference in length of the test piece before and after the heat treatment (unit: mm), and the radius change of the test piece before and after the heat treatment determined by the above method An amount (unit: mm) and a groove width change amount (unit: mm) are shown. Invention Example No. As shown in Table 3, in the steel material consisting of 1 to 23, the martensite transformation start temperature, that is, the Ms point is in the range of 388 to 444 ° C., and (J9 / J1.5) of this steel material is represented by the following formula (1 ) Is in the range of 0.72 to 0.85, the value of formula (2) shown below in (J11 / J1.5) is in the range of 0.67 to 0.78, and the bend after heat treatment Is 0.005 to 0.030 mm, the absolute value of the difference in length of the test piece before and after heat treatment is 0.003 to 0.023 mm, and the amount of change in radius before and after heat treatment is 0.002 to 0.008 mm. The change in groove width before and after the heat treatment was 0.011 to 0.024 mm.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (1)
(J11 / J1.5) = (hardness at a distance of 11 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (a distance of 1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (2)

Similarly, Table 4 shows the measured Ms point of the steel of the comparative example, J1.5 of the hardness (HRC) at a distance of 1.5 mm from the quenching end measured by the Jomini type one-end quenching method, and the hardness at a distance of 9 mm. Jominy hardenability which is J9 of thickness (HRC) and J11 of hardness (HRC) at a distance of 11 mm, and the obtained values of (J9 / J1.5) and (J11 / J1.5) are shown. . Further, the bending of the test piece after quenching (unit: mm), the absolute value of the difference in length of the test piece before and after the heat treatment (unit: mm), and the radius change of the test piece before and after the heat treatment determined by the above method The amount (unit: mm) and the groove width change amount (unit: mm) are shown.

No. in the above invention example. For 1 to 23, the composition range excluding unavoidable impurities other than Fe, Ni, and Mo of steel materials is shown in Table 1, Ms point is set to 388 to 444 ° C. below 460 ° C., and measured by Jomini type one-end quenching method By appropriately controlling the hardenability to be performed, the value of (J9 / J1.5) calculated from the equation (1) is calculated within the range of 0.72 to 0.85 from the equation (2) ( By setting the value of J11 / J1.5) in the range of 0.67 to 0.78, the bending of the test piece after the heat treatment is reduced to a small range of 0.005 to 0.030 mm, and the test piece before and after the heat treatment is further reduced. The absolute value of the difference in length is in a small range of 0.003 to 0.023 mm, the change in radius before and after heat treatment is in a small range of 0.002 to 0.008 mm, and the change in groove width before and after heat treatment is 0. .Small range from 011 to 0.024mm It could be.

In contrast, No. in the above comparative example. In Table 2, the composition ranges excluding inevitable impurities other than Fe, Ni, and Mo of steel materials 1 to 16 are shown in Table 2. 2, No. The remaining 14 cases, excluding 16 2 cases, were out of the composition range of the present invention. These No. The steels of Comparative Examples 1 to 16 have a value (J9 / J1.5) of 0.70 to 0. 0 determined by the formula (1) and the formula (2) from the hardness measured by the Jomini type one-end quenching method. It is out of the range of 85, and the value of (J11 / J1.5) is out of the range of 0.67 to 0.78. In addition, these No. Of the 1 to 16 comparative steels, 9 have a measured Ms point above 460 ° C. In Comparative Examples 1 to 16, the bending of the test piece after the heat treatment is 0.050 to 0.090 mm, and all are larger than the steel of the inventive example. In addition, these No. In the steels of Comparative Examples 1 to 16, any one or more of the absolute value of the difference in length of the test pieces before and after the heat treatment, or the radius change amount and the groove width change amount before and after the heat treatment is the value of the present invention. Bigger than steel. Therefore, among the comparative examples, the bending of the test piece after the heat treatment, the absolute value of the difference in length of the test piece before and after the heat treatment, and the radius change amount and the groove width change amount before and after the heat treatment are all the same as the steel of the present invention example. There was no one equivalent.

The Ms point satisfies the claims of the present invention, and the values of (J9 / J1.5) and (J11 / J1.5) satisfy the claims of the present invention. In Nos. 1 to 23, the bending of the test piece after the heat treatment, the absolute value of the difference in the length of the test piece before and after the heat treatment, and the radius change amount and the groove width change amount before and after the heat treatment are substantially smaller than those in the comparative example. Deformation is suppressed. The steel material of the present invention is used after being tempered after being subjected to heat treatment with hardening for hardening parts such as carburizing and quenching.

From the above, after the steel material was processed into parts by the limitation of the steel components and the Ms point which is the martensitic transformation start temperature and the limitation of the hardenability measured by the Jominy one-side quenching method, carburizing and quenching was performed. For example, the heat treatment deformation when the heat treatment with hardening for hardening the parts is performed can be reduced. As a result, the steel material according to the present invention is a steel material applicable to power transmission parts such as gears and shafts used in automobiles and industrial machines.

Claims (4)

% By mass
C: 0.20 to 0.30%
Si: 0.10 to 1.50%,
Mn: 0.10 to 1.20%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 1.30-2.50%,
Cu: 0.30% or less,
Al: 0.008 to 0.300%,
O: 0.0030% or less,
N: 0.0020 to 0.0300% is contained,
It is a steel for machine structure consisting of the balance Fe and inevitable impurities,
The martensitic transformation start temperature (Ms point) of the steel material made of the steel is 460 ° C. or less,
The following formula (1) is used by using J1.5 of the hardness at a distance of 1.5 mm from the quenching end of the steel material and J9 of the hardness at a distance of 9 mm measured by the Jominy-type one-end quenching method for the steel material. The value of (J9 / J1.5) calculated by is in the range of 0.70 to 0.85,
Further, using the hardness J1.5 at a distance of 1.5 mm and the hardness J11 at a distance of 11 mm, the value of (J11 / J1.5) calculated by the following equation (2) is 0.67 to 0.78. In the range of
Machine structural steel with small heat treatment deformation.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (distance from the quenching end measured by the Jominy type one-end quenching method. (Hardness of 5mm) …… Formula (1)
(J11 / J1.5) = (hardness of a distance of 11 mm from the quenching end measured by the Jomini-type one-end quenching method) ÷ (distance from the quenching end measured by the Jomini-type one-end quenching method. (Hardness of 5mm) …… Formula (2) % By mass
C: 0.20 to 0.30%
Si: 0.10 to 1.50%,
Mn: 0.10 to 1.20%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 1.30-2.50%,
Cu: 0.30% or less,
Al: 0.008 to 0.300%,
O: 0.0030% or less,
N: 0.0020 to 0.0300% is contained,
Furthermore, it contains one or two of Ni: 0.20 to 3.00% and Mo: 0.05 to 0.50%,
It is a steel for machine structure consisting of the balance Fe and inevitable impurities,
The martensitic transformation start temperature (Ms point) of the steel material made of the steel is 460 ° C. or less,
The following formula (1) is used by using J1.5 of the hardness at a distance of 1.5 mm from the quenching end of the steel material and J9 of the hardness at a distance of 9 mm measured by the Jominy-type one-end quenching method for the steel material. The value of (J9 / J1.5) calculated by is in the range of 0.70 to 0.85,
Further, using the hardness J1.5 at a distance of 1.5 mm and the hardness J11 at a distance of 11 mm, the value of (J11 / J1.5) calculated by the following equation (2) is 0.67 to 0.78. In the range of
Machine structural steel with small heat treatment deformation.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (distance from the quenching end measured by the Jominy type one-end quenching method. (Hardness of 5mm) …… (1)
(J11 / J1.5) = (hardness of a distance of 11 mm from the quenching end measured by the Jomini-type one-end quenching method) ÷ (distance from the quenching end measured by the Jomini-type one-end quenching method. (Hardness of 5mm) …… (2) % By mass
C: 0.20 to 0.30%
Si: 0.10 to 1.50%,
Mn: 0.10 to 1.20%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 1.30-2.50%,
Cu: 0.30% or less,
Al: 0.008 to 0.300%,
O: 0.0030% or less,
N: 0.0020 to 0.0300% is contained,
Furthermore, it contains one or two of Ti: 0.020-0.200% and Nb: 0.02-0.20%,
It is a steel for machine structure consisting of the balance Fe and inevitable impurities,
The martensitic transformation start temperature (Ms point) of the steel material made of the steel is 460 ° C. or less,
With respect to the steel material, J1.5 of the hardness at a distance of 1.5 mm from the quenching end of the steel material measured by the Jominy type one-end quenching method and J9 of the hardness at a distance of 9 mm are used according to the following formula (1). The calculated (J9 / J1.5) value is in the range of 0.70 to 0.85,
Further, using the hardness J1.5 at a distance of 1.5 mm and the hardness J11 at a distance of 11 mm, the value of (J11 / J1.5) calculated by the following equation (2) is 0.67 to 0.78. In the range of
Machine structural steel with small heat treatment deformation.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (1)
(J11 / J1.5) = (hardness at a distance of 11 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (a distance of 1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (2) % By mass
C: 0.20 to 0.30%
Si: 0.10 to 1.50%,
Mn: 0.10 to 1.20%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 1.30-2.50%,
Cu: 0.30% or less,
Al: 0.008 to 0.300%,
O: 0.0030% or less,
N: 0.0020 to 0.0300% is contained,
Furthermore, it contains one or two of Ni: 0.20 to 3.00% and Mo: 0.05 to 0.50%,
Furthermore, it contains one or two of Ti: 0.020-0.200% and Nb: 0.02-0.20%,
It is a steel for machine structure consisting of the balance Fe and inevitable impurities,
The martensitic transformation start temperature (Ms point) of the steel material made of the steel is 460 ° C. or less,
With respect to the steel material, J1.5 of hardness at a distance of 1.5 mm from the quenching end of the steel material measured by the Jominy type one-end quenching method and J9 of hardness at a distance of 9 mm are used according to the following formula (1). The calculated (J9 / J1.5) value is in the range of 0.70 to 0.85,
Further, using the hardness J1.5 at a distance of 1.5 mm and the hardness J11 at a distance of 11 mm, the value of (J11 / J1.5) calculated by the following equation (2) is 0.67 to 0.78. In the range of
Machine structural steel with small heat treatment deformation.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (1)
(J11 / J1.5) = (hardness at a distance of 11 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (a distance of 1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (2)