WO2019026909A1

WO2019026909A1 - Method for manufacturing steel component, and steel component

Info

Publication number: WO2019026909A1
Application number: PCT/JP2018/028676
Authority: WO
Inventors: 中河原悠士
Original assignee: アイシン精機株式会社
Priority date: 2017-08-03
Filing date: 2018-07-31
Publication date: 2019-02-07
Also published as: JPWO2019026909A1

Abstract

Provided is a method for manufacturing a steel component in which it is possible to easily manufacture a steel component having suitable surface hardness. A quenching/tempering step is performed at least once using steel that contains, in percent by mass, 0.25-1.10% of C, 0.25-0.80% of Si, 0.80-3.00% of Mn, and 0.05-1.20% of Al, said step involving a quenching process and a tempering process being performed in the stated order at a temperature of at least the A1 transformation temperature and no more than 850°C. The quenching process includes a nitrogen-immersion quenching process to set the surface nitrogen concentration to at least 0.8%. Grain refining is performed after the quenching/tempering step.

Description

Method of manufacturing steel parts and steel parts

The present invention relates to a method of manufacturing steel parts and steel parts.

Steel parts such as gears and bearings used in transmissions of automobiles are manufactured by processing parts using chromium steel or chromium molybdenum steel and performing carburizing, quenching and tempering. In recent years, the demand for global warming prevention and resource saving through CO2 emission reduction is increasing, and weight reduction of a vehicle is called for further fuel efficiency improvement. For this reason, since steel parts are required to be miniaturized and load is increased, further strengthening is required. In addition, since steel parts used in automobiles reach environmental temperatures up to about 300 ° C., the hardness of the surface of the steel parts may be reduced, and pitting failure may occur. For this reason, in order to improve the resistance to pitting fatigue, steel parts excellent in temper softening resistance are required.

According to the technique described in Patent Document 1, a steel component obtained by carburizing, quenching and tempering a steel containing, by mass%, 0.7 to 1.0% of Si and 1.0 to 1.5% of Cr, from the surface Tempered to 300 ° C. with C content (hereinafter referred to as “surface C concentration”) at a portion of 50 μm depth to be 0.9 to 1.1% and the amount of retained austenite to be less than 30% (hereinafter, it is The hardness of a portion 50 μm deep from the surface of the steel part after “300 ° C. tempering” (hereinafter, referred to as “surface hardness”) has a Vickers hardness (hereinafter, referred to as “HV”). It is made to be 700 or more.

In the technology described in Patent Document 2, the surface hardness of the steel component after tempering at 300 ° C. is made to be HV700 or more by using a steel material containing Si + 0.2Cr + 0.01Mo in excess of 1.3%.

In the technology described in Patent Document 3, a steel containing an appropriate amount of Si, Mn, Cr, Mo, etc. is formed into a part shape, and the hardness after carburizing, tempering or carbonitriding, tempering is HRC 58 (equivalent to HV653) The steel parts are configured such that (surface hardness after quenching and tempering) − (surface hardness after tempering at 300 ° C.) is equal to or less than HV130.

In the technique described in Patent Document 4, it is proposed to reheat and harden after nitriding in the ferrite region to solve the problem that voids occur when the nitrogen concentration on the surface of the steel exceeds 0.8% in conventional carbonitriding. There is. Since nitrogen exceeding 0.8% can be solid-solved by this treatment, a high nitrogen concentration can be realized, and the upper limit of the nitrogen concentration is indicated. Moreover, in the technique described in Patent Document 5, it is shown that soft nitriding and induction hardening are combined for the same problem as Patent Document 4.

WO 2011/132722 Japanese Patent Laid-Open No. 2003-231943 JP 2006-97096 A Unexamined-Japanese-Patent No. 7-138696 International Publication No. 2014/192117

For example, when a steel part is used as a gear of an automobile, in order to ensure the tooth surface strength for preventing pitching fracture etc. in a steel gear, the surface hardness after tempering at 300 ° C. is preferably HV680 or more .

In Patent Documents 1 to 3, carburizing and quenching is performed on a base material at around 950 ° C. in manufacturing a steel component. In addition, even when the base material is quenched twice, the second quenching temperature is set to 850 ° C. or higher. When quenching is performed on the base material at 850 ° C. or more, austenite grains are coarsened, and thus the steel parts after quenching become coarser. In such a case, there is a risk that tooth surface strength may be insufficient when using steel parts as gears.

In the steel parts of Patent Documents 4 and 5, since the treatment temperature of the nitriding treatment is 500 to 600 ° C. and the treatment is at the A1 transformation point (723 ° C.) or less, the penetration and diffusion of N into the base material is slow. Processing takes a long time. In addition, since it is necessary to control the surface N concentration to be low in order to form a solid solution of nitride at the time of reheating after nitriding treatment, the treatment time is further extended. In addition, by setting the temperature at the time of reheating to 900 ° C. or more, decarbonization, denitrification, and coarsening of crystal grains are caused, and the durability of steel parts is lowered. Further, in Patent Documents 1 to 5, all steel parts contain rare elements such as Cr, Mo, Ni, and V in the base material, and since these are not easy to reuse, they have a large environmental load.

In view of the above situation, there is a need for a method of manufacturing steel parts that can easily manufacture steel parts having an appropriate surface hardness.

The characterizing features of the method for producing a steel component according to the present invention are, in mass%, C: 0.25 to 1.10%, Si: 0.25 to 0.80%, Mn: 0.80 to 3.00%, The steel containing Al: 0.05 to 1.20% is subjected to at least one quenching and tempering step in which a quenching treatment and a tempering treatment of A1 transformation point to 850 ° C. are sequentially applied to the steel, The treatment includes a carbonizing and quenching treatment to set the surface nitrogen concentration to 0.8% by mass or more, and the grain refining treatment is performed after the quenching and tempering step.

Cr, by performing a quenching and tempering process in which quenching and tempering are sequentially performed on the steel using a steel having C, Si, Mn, and Al as in the present configuration, and a crystal grain refining treatment Steel parts can be manufactured without using a rare element such as Mo and having a large environmental load. Moreover, the steel which has C, Si, Mn, and Al performed the quenching and tempering process containing A1 transformation point or more and 850 degrees C or less in the form including the nitroquenching process which makes surface nitrogen concentration 0.8 mass% or more Later, by performing grain refining processing, the grain size of the steel component is adjusted, and a steel component having an appropriate surface hardness can be easily manufactured.

Another feature is that shot peening with an arc height of 0.40 mmA or more is performed as the crystal grain refining process.

As in the present configuration, by performing shot peening with an arc height of 0.40 mmA or more as grain refining processing, it is possible to refine the crystal grains of the steel component, and a steel component having an appropriate surface hardness. Can be easily manufactured.

Another feature is that the quenching and tempering step is performed as the crystal grain refining process.

As in the present configuration, by performing a quenching and tempering step in which a quenching treatment and a tempering treatment of A1 transformation point or more and 850 ° C. or less are sequentially performed as grain refining treatment, the grain size of the steel component can be made finer. It is possible to easily produce a steel part having an appropriate surface hardness.

The characteristic features of the steel component of the present invention are, in mass%, C: 0.25 to 1.10%, Si: 0.25 to 0.80%, Mn: 0.80 to 3.00%, Al: 0 A base material having .05 to 1.20%, and a surface nitrogen concentration on the surface of the base material is 0.8 mass% or more, and (surface nitrogen concentration (mass%)-Si (mass%)-0 And a surface layer having 0.20 to 0.55% of (52 × Al (mass%)), and a half-value width is 7 deg or more.

According to the above configuration, it is possible to obtain an appropriate surface hardness in steel parts such as gears used for automobile parts and the like.

These are conceptual diagrams which show an example of a hardening and tempering process. These are conceptual diagrams which show an example of a hardening and tempering process. These are conceptual diagrams which show an example of a hardening and tempering process. These are conceptual diagrams which show an example of 300 degreeC tempering.

Below, the manufacturing method of the steel component which concerns on this invention is demonstrated. Steel parts are used, for example, in gears, reduction gears, bearings and the like.

First Embodiment
For the base material of steel parts, as chemical components, C: 0.25 to 1.10%, Si: 0.25 to 0.80%, Mn: 0.80 to 3.00%, by mass as Al A steel having 0.05 to 1.20% is used. A steel component is manufactured by performing the hardening and tempering process in which a hardening process and a tempering process are sequentially given with respect to the said steel in multiple times.

In the present embodiment, the steel is subjected to at least one quenching and tempering step in which quenching treatment and tempering treatment of A1 transformation point to 850 ° C. are sequentially performed on the steel (first step), and after the quenching and tempering step A hardening and tempering process is further performed as a refinement process (second process). The example of the hardening process and tempering process with respect to steel is shown in FIG.1 and FIG.3. A hardening process and a tempering process are performed to steel as a 1st process. In the quenching treatment, low temperature and short-time carbonitriding is performed for 120 minutes at the A1 transformation point (723 ° C.) or more and 850 ° C. or less (800 ° C. in FIG. 1). Instead of carbonizing and quenching, carbonizing and nitriding may be performed. A hardening process and a tempering process are performed with respect to steel materials as a 2nd process following a 1st process. In the second step, quenching is performed at the A1 transformation point (723 ° C.) or more and 850 ° C. or less (780 ° C. in FIG. 3), followed by tempering.

The temperings of the first and second steps shown in FIGS. 1 and 3 are both at 150 ° C. for 120 minutes, and the quenching of the second step shown in FIG. 3 is 5 minutes. The temperature and time of quenching and tempering in the first step and the second step can be appropriately adjusted. The hardening and tempering process on the steel may be performed three or more times.

Adjust the surface nitrogen concentration (hereinafter referred to as “surface N concentration”) by adjusting the chemical composition of the steel, the conditions for nitrocarburizing, and the surface carbon concentration (hereinafter referred to as “surface C concentration”) when carburizing is also performed. 0.8% to 1.5% by mass, and the sum of surface N concentration and surface C concentration (hereinafter referred to as “surface (N + C) concentration”) is 1.5 to 2.5% by mass. . Here, the surface C concentration and the surface N concentration are the ratio of the mass to the base material in the portion where the carbon and nitrogen become the highest concentration in the vicinity of the surface of the steel (the depth from 200 m to the surface) . In addition, the surface (N + C) concentration refers to the ratio of the mass to the base material in the portion where nitrogen is the highest concentration and the portion where carbon is the highest concentration in the vicinity of the surface of the steel (the depth from 200m to the surface). It is the sum of the ratio of mass to base material.

By using a steel containing C, Si, Mn, and Al, and performing the quenching and tempering process a plurality of times in which the quenching treatment and the tempering treatment are sequentially applied to the steel, it is rare like Cr and Mo, and the environmental load Steel parts can be manufactured without using large elements. Moreover, the steel which has C, Si, Mn, and Al performs the quenching and tempering process including the quenching process of A1 transformation point or more and 850 degrees C or less two or more times, and carries out the nitriding quenching processing which makes surface N concentration 0.8 mass% or more By performing processing so as to contain, the amount of retained austenite in the steel component is adjusted and the crystal grains are refined. As a result, the half value width of the steel component can be adjusted, and a steel component having an appropriate surface hardness can be easily manufactured. The surface hardness of steel parts decreases as the amount of retained austenite increases. Moreover, the surface hardness after tempering at 300 ° C. becomes higher as the crystal size becomes finer. As a result, it is possible to obtain an appropriate surface hardness as a steel material used for gears of automobiles and the like.

Hardening and tempering treatment is sequentially performed on a steel containing, by mass%, Si: 0.25 to 0.80%, Mn: 0.80 to 3.00%, Al: 0.05 to 1.20% The surface C concentration: 0.25 to 1.10% by mass and the surface N concentration: 0.8 to 1.5% by mass by performing the quenching and tempering step to be applied a plurality of times, and the amounts and sizes of MnSiN 2 and AlN And optimize the crystal grain size until the half width becomes 7.00 deg or more.

When the contents of surface C concentration, surface N concentration, Mn, and Si are increased to refine the crystal grains, the diffusion of C and N and the movement of dislocations are suppressed by the interaction between atoms, so the softening resistance of the steel increases. It is considered to be a thing. Further, by increasing the surface N concentration to refine the crystal grains, a large amount of Fe 4 N precipitates uniformly and finely at the time of tempering at 300 ° C., and therefore, it is considered that the softening resistance of the steel part is enhanced.

By increasing the content of Si, Mn, and Al in the steel and increasing the surface N concentration after carbonitriding, N diffusion is suppressed and MnSiN 2 and AlN are precipitated in large amounts to gasify N, H Generation of voids due to For this purpose, each element is in the above range, and (surface N concentration (mass%)-Si (mass%)-0.52 x Al (mass%)) <0.60 (%) It is required to meet In addition, it is considered effective to suppress the generation of voids by quenching treatment at a low temperature for a short time of 120 minutes at the A1 transformation point (723 ° C.) or more and 850 ° C. or less.

Second Embodiment
In the present embodiment, the steel is subjected to at least one quenching and tempering step in which quenching treatment and tempering treatment of A1 transformation point to 850 ° C. are sequentially performed on the steel (first step), and after the quenching and tempering step A shot peening process is performed as a miniaturization process (second step). A hardening process and a tempering process are performed to steel as a 1st process. In the quenching treatment, low temperature and short-time carbonitriding is performed for 120 minutes at the A1 transformation point (723 ° C.) or more and 850 ° C. or less (800 ° C. in FIG. 1). Instead of carbonizing and quenching, carbonizing and nitriding may be performed. As a second step, a shot peening treatment with an arc height of 0.40 mmA or more is performed following the first step.

The steel containing C, Si, Mn, and Al is subjected to at least one quenching and tempering step in which a quenching treatment and a tempering treatment are sequentially applied to the steel, and thereafter shot peening is performed to obtain Cr and Mo Thus, steel parts can be manufactured without using an element that is rare and has a large environmental impact. In addition, steels having C, Si, Mn, and Al are subjected to a hardening and tempering process including a hardening treatment including A1 transformation point to 850 ° C. or less, and then shot peening as grain refining treatment to obtain steel parts. The amount of retained austenite is adjusted to refine the crystal grains. As a result, the half value width of the steel component can be adjusted, and a steel component having an appropriate surface hardness can be easily manufactured.

Hereinafter, the present invention will be specifically described by way of examples. In addition, these Examples are for demonstrating this invention, Comprising: The scope of the present invention is not limited.

After soaking the steel ingot having the chemical components shown in Table 1 below, rolling and normalizing were performed, and then a test piece of a round bar of φ8 × 12 mm was processed. As shown in FIG. 1, FIG. 3 and Table 2 below, in the inventive examples 1 to 5 and the comparative example 9, the hardening and tempering step was repeated twice in the first step and the second step. In the first step, the quenching and tempering step (hereinafter referred to as quenching and tempering A) shown in FIG. 1 was performed, and in the second step, the quenching and tempering step (hereinafter referred to as quenching and tempering C) shown in FIG. . In quenching and tempering A, the test piece is subjected to nitriding at 800 ° C. for 120 minutes, oil quenching at 65 ° C., and thereafter at 150 ° C. for 120 minutes in a vacuum furnace with controlled NH 3 concentration. A tempering process was performed. In quenching and tempering C, water quenching was performed at room temperature after being held at 780 ° C. for 5 minutes in an electric furnace in air atmosphere, and then tempering was performed at 150 ° C. for 120 minutes. In the case of Invention 5, quenching and tempering C was further performed after the second step (third step).

As shown in FIG. 1 and Table 2 below, in Comparative Examples 10 to 12, only the hardening and tempering A (one hardening and tempering step) was performed as the first step.

As shown in FIG. 1, FIG. 2 and Table 2 below, in Inventive Examples 6 to 8 and Comparative Example 13, the second step is carried out by performing hardening and tempering A (see FIG. 1) once as the first step. Shot peening was done. In Comparative Example 14, a quenching and tempering step (hereinafter, referred to as quenching and tempering B) shown in FIG. 2 was performed as a first step, and shot peening was performed as a second step. In quenching and tempering B, the test piece is subjected to carbonitriding treatment at 800 ° C. for 120 minutes, oil quenching treatment at 120 ° C., and then tempering at 150 ° C. for 120 minutes in a vacuum furnace with controlled NH 3 concentration. I did the processing. The NH 3 concentration in the quenching and tempering step in the first step of each of Inventive Examples 1 to 8 and Comparative Examples 9 to 14 was controlled (high concentration, medium concentration, low concentration) as shown in Table 2.

The C concentration distribution and N concentration distribution from the surface of each test piece are measured by EPMA (Electron Probe Micro Analyzer), and the highest concentration in the vicinity of each surface (the depth from the surface to 200 μm) is the surface C concentration, surface N It was the concentration. These measurements were performed after the first step in the invention examples 1 to 8 and the comparative examples 9 to 13, and were performed after the second step only for the comparative example 14. These are shown in the evaluation 1 of Table 3 below.

The outermost surface of each test piece was measured by an X-ray residual stress measuring apparatus (μ-X360 manufactured by Pulstec Industrial Co., Ltd.) to calculate the amount of retained austenite and the half width. Measurement conditions are: incident angle: 35 ° C., collimator diameter: φ 1.0 mm, X-ray intensity: 30 kV / 1 mA, X-ray wavelength: Kα 2.29093 Å, Kβ 2.08480 Å, measurement distance: 39 mm, diffraction surface: 211 surface, and did. These measurements are performed after the second step in the invention examples 1 to 4 and 6 to 8 and the comparative examples 9 and 13 to 14, after the third step in the invention example 5, and after the first step in the comparative examples 10 to 12. The These are shown in the evaluation 1 of Table 3 below.

The test pieces of Inventive Examples 1 to 8 and Comparative Examples 9 to 14 were subjected to tempering at 300 ° C. for 240 minutes for evaluation as shown in FIG. The hardness distribution from the surface was measured with a micro Vickers hardness meter (load: 300 gf) before 300 ° C. tempering (time C in FIG. 4) and after 300 ° C. tempering (time D in FIG. 4). In each measured hardness distribution, the hardness at a position of 50 μm from the surface was taken as the surface hardness before and after 300 ° C. tempering. Moreover, the hardness of the position of 0.2 mm from the surface was confirmed from the hardness distribution measured after 300 degreeC tempering. Furthermore, the vicinity of the surface of the cross section of the test piece was observed with an optical microscope to confirm the presence or absence of generation of a void. These are shown in evaluation 2 and evaluation 3 of Table 3 below.

For example, when the steel part is an automobile gear, in the invention examples 1 to 8, the half hardness is 7 deg or more, and the surface hardness after tempering at 300 ° C. is HV 680 or more to prevent pitting fracture and the like. Tooth surface strength can be secured. Further, in the invention examples 1 to 8, since the hardness at the position of 0.2 mm from the surface after tempering at 300 ° C. is HV600 or more, the spalling can be suppressed. Furthermore, in the invention examples 1 to 3, since the surface hardness before tempering at 300 ° C. is less than HV 660, the tooth contact is improved, and the generation of noise and the contact can be suppressed. Further, in the invention examples 5 to 8, since the half width is 7.65 or more and the hardness after tempering at 300 ° C. is HV 700 or more, the tooth surface strength can be improved.

Furthermore, in Inventive Examples 1 to 8, a void-free structure was obtained under an environment where the surface N concentration is 0.8% by mass or more. As described above, according to Inventive Examples 1 to 8, the material having small environmental load and easy to obtain is used, and the surface N concentration is immersed at 0.8 mass% or more at the A1 transformation point (723 ° C.) or more and 850 ° C. or less. A steel part such as a gear having an appropriate hardness can be obtained by performing a quenching and tempering process including a nitriding and quenching process at least once and performing a grain refining process after the quenching and tempering process. Here, the grain refining process is a further quenching and tempering process or shot peening with an arc height of 0.40 mmA or more. The test pieces of the invention examples 1 to 8 have a surface N concentration of 0.8 mass% or more, and (surface N concentration (mass%)-Si (mass%)-0.52 x Al (mass%)) Contains a surface layer of 0.20 to 0.55%.

In Comparative Example 9, the surface N concentration was lower than 0.8% by mass, and Si, Mn, and Al were small, so the surface hardness after tempering at 300 ° C. was as low as HV 660 or less, and generation of voids was observed.

In Comparative Example 10, the surface hardness after tempering at 300 ° C. is as low as HV 650 or less because the crystal grains are coarse (the half width is small at less than 7 deg). In Comparative Example 11, the surface N concentration is low, the amount of Si, Mn, and Al is small, and the crystal grain is coarse (half width less than 7 deg is small), so the surface hardness after tempering at 300 ° C. is HV 650 or less and low. The occurrence of voids was observed. In Comparative Example 12, since (Surface N concentration (mass%)-Si (mass%)-0.52 × Al (mass%)) is 0.60 (%) and is high, generation of voids is recognized The Further, in Comparative Examples 10 to 12, the amount of retained austenite on the surface is 62% by mass and 52% by mass since the quenching and tempering step is performed once. It is as high as 71% by mass, resulting in a decrease in surface hardness after tempering at 300 ° C. (HV 665 or less).

In Comparative Examples 13 and 14, since the arc height value in the shot peening in the second step is small, the half width is smaller than 7 deg and the surface hardness after tempering at 300 ° C. is low.

The present invention can be widely used for automobile parts and machine parts.

Claims

Steel having, by mass%, C: 0.25 to 1.10%, Si: 0.25 to 0.80%, Mn: 0.80 to 3.00%, Al: 0.05 to 1.20% Using at least one quenching and tempering step where quenching treatment and tempering treatment of A1 transformation point to 850 ° C. are sequentially applied to the steel, and the quenching treatment is performed with a surface nitrogen concentration of 0.8 mass% or more The manufacturing method of steel components which performs a grain refinement process after the said hardening and tempering process including the nitro-quenching process which is said to be.
The manufacturing method of the steel component of Claim 1 which performs shot peening whose arc height is 0.40 mmA or more as said crystal grain refinement | miniaturization process.
The manufacturing method of the steel component of Claim 1 which performs the said hardening and tempering process as said crystal grain refinement process.
Mother with C: 0.25 to 1.10%, Si: 0.25 to 0.80%, Mn: 0.80 to 3.00%, Al: 0.05 to 1.20% by mass% And surface nitrogen concentration on the surface of the base material is 0.8 mass% or more, and (surface nitrogen concentration (mass%)-Si (mass%)-0.52 × Al (mass%)) And a surface layer of 0.20 to 0.55%, and a half value width of 7 deg or more.