JP2000144243A - Manufacture of driving transmission mechanism parts excellent in contact fatigue life strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the pitting fatigue strength of driving transmission mechanism parts such as gears used for automobile transmission, etc., by subjecting a steel stock of specific composition to rough forming, to carburizing and quenching, then to high-frequency heating at specific temperature, and immediately to working and providing specific required physical properties. SOLUTION: A steel stock, having a composition which consists of, by weight, 0.1-0.3% C, 0.01-0.15% Si, 0.3-1.5% Mn, 0.3-1.5% Cr, 0.01-0.06% S, 0.001-0.01% Ca, <=0.003% O, and the balance Fe, etc., and in which the value of Ca/O is regulated to 0.5-3.5, is used. The steel stock is subjected to rough forming, to carburizing and quenching, to high-frequency heating to 200-600 deg.C for 1-5 min, and immediately to working of 10-60%. By this procedure, slack quenched layer, compressive residual stress at surface, and surface roughness Rmax are regulated to <15 μm, >=25 kgf/mm2, and >=2.5 μm, respectively. Moreover, the relationship between the value β' given by making the X-ray diffraction half-width made to dimensionless by the half-width after annealing of the steel stock and the surface roughness Rmax is regulated so that β'>=2.29-0.401 n (Rmax) is satisfied. Further, retained austenite is regulated to <=10%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to sliding parts such as automobiles and machine tools, and more particularly to high-strength steel gears used in automobile transmissions and the like, as well as to drive transmission parts which are subject to contact fatigue. Things.

[0002]

2. Description of the Related Art A drive transmission system component represented by a gear is often subjected to carburizing, quenching and tempering to harden the surface after being formed by hot forging. In automobiles, it is required to reduce the size of parts in order to reduce the weight.Parts used in a drive system are required to have a large load during use, and are also required to improve bending fatigue and pitting fatigue life generated when parts come into contact with each other. I have.

Regarding the improvement of bending fatigue, "Transactions of the Japan Society of Mechanical Engineers, C, 55, 520, 3034 (1989)"
As reported in Japanese Patent Application Laid-Open No. H11-260, measures have been taken to impart a compressive residual stress by performing shot peening after carburizing, quenching and tempering. However, the mechanism by which the pitching life occurs is unknown, and various countermeasures have been proposed. As disclosed in Japanese Patent Application Laid-Open No. 1-264727, a method has been proposed in which shot peening is performed after heat treatment to impart a compressive residual stress. However, JP-A-3-10741
No. 8 also states that shot peening reduces pitching fatigue. Further, since shot peening roughens the surface, it also has a noise problem during drive transmission.

[0004] As a steel material having excellent pitting fatigue properties, "Special Steel Vol. 44, No. 3, pp. 39-48 (1995)"
Various steel materials have been reported. In each case, the composition of alloy elements is adjusted for the purpose of controlling the depth and hardness of the grain boundary oxide layer and the incompletely quenched layer generated during carburization. But,
The grain boundary oxidized layer and the incompletely quenched layer originally have initial defects and are softened layers, so that even if component adjustment is performed, characteristics are difficult to obtain. Further, the addition of the alloy component causes an increase in cost.

[0005] As described above, with regard to the pitting fatigue characteristics of the drive transmission system components under a high load, industrially useful techniques for improving the fatigue strength have not been found yet.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the pitting fatigue strength of a drive transmission system component such as a gear used for an automobile transmission.

[0007]

Means for Solving the Problems The present inventors have conducted research on the above-mentioned problems and found the following new findings.
In a roller pitting test, which is a standard pitting performance evaluation test, it was found that the pitting life was significantly improved by abrasion of an incompletely quenched layer (softened portion) generated during carburizing. The cause of abrasion is that the bainite structure of the incompletely quenched layer is embrittled by processing strain imparted by shot peening or the like. The reason that the pitting life is improved by the wear is that the initial cracks generated in the incompletely quenched layer and the grain boundary oxidized portion therein are removed by the wear, and the pitting generation is suppressed.
This is because the contact area increases due to the wear and the actual surface pressure decreases.

Various investigations have been made on the conditions under which the incompletely quenched layer is worn. As a method of applying processing strain to embrittle the incomplete quenching layer, a method of performing shot peening after carburizing quenching and tempering is immediately imagined,
The number of processes increases. The present inventors have disclosed in
Japanese Patent No. 232642 proposes a method of carburizing and quenching and thereafter performing tempering warm forging using heating during tempering. However, by using this processing method, it is possible to reduce the processing strain without increasing the number of steps. Can be added.
However, when the amount of wear increases, the shape of the part is damaged. Further, when the incompletely quenched layer is deepened to increase the wear amount, the grain boundary oxidation is also deepened, and the bending fatigue is reduced. Therefore, extreme wear must be avoided.

[0009] The present inventors have also found that pitting occurs from MnS inclusions as a starting point from a roller pitting test using a test piece from which an incompletely quenched layer has been removed by grinding. During hot rolling, MnS exists in a form stretched in the axial direction. Many of the sliding parts such as gears come into contact in the circumferential direction, so that the contact load moves in the direction perpendicular to the direction in which MnS extends. As the contact load moves along the circumferential direction, a tensile stress is generated on the surface, and MnS stretched in the axial direction receives a tensile load in the perpendicular direction. When the contact load moves on the surface, MnS has low interfacial adhesion to the ground iron, and hard MnS does not deform but deforms the ground iron. Has reached. And, it was found that the pitting life was improved by suppressing the stretching of MnS. Furthermore, it was also found that the pitting life was similarly improved by using a steel material having a reduced S content in steel and a small MnS content.

Based on these findings, an incompletely quenched layer serving as a wear layer is provided to such an extent that the influence on bending fatigue life and the like is small, and the occurrence of pitting is suppressed, and MnS is reduced even when the wear layer disappears during use. Stretch-suppressed matrix or M
It has been found that the appearance of a base layer having a small amount of nS makes it possible to improve the pitting life, and the following means have been clarified, leading to the present invention.

That is, the present invention provides: (1) C: 0.1 to 0.3%, Si:
0.01-0.15%, Mn: 0.3-1.5%, C
r: 0.3 to 1.5%, S: 0.01 to 0.06%, C
a: 0.001 to 0.01%, O: 0.003% or less,
However, after roughly forming a steel material containing Ca / O: 0.5 to 3.5, the balance being Fe and unavoidable impurities, carburizing and quenching are performed, and then high-frequency heating is performed at 200 to 600 ° C. for 1 to 5 minutes. Immediately thereafter, the incompletely quenched layer is less than 15 μm, the compressive residual stress on the surface is 25 kgf / mm ² or more, and the surface roughness Rmax is 2.5 μm.
In addition to the above, the relationship between the value β ′ obtained by rendering the half-width of X-ray diffraction non-dimensional by the half-width after annealing of the steel material and the surface roughness Rmax is β ′ ≧ 2.29−0.40 ln (Rmax). And a method for manufacturing a drive transmission system component having excellent contact fatigue life strength, wherein the retained austenite is 10% or less.

(2) C: 0.1 to 0.1% by weight.
3%, Si: 0.01 to 0.15%, Mn: 0.3 to
1.5%, S: less than 0.01%, Cr: 0.3 to 1.5
%, And after roughly forming a steel material comprising the balance of Fe and unavoidable impurities, carburizing and quenching are performed, and then 200 to 6%.
High frequency heating to 00 ° C for 1 to 5 minutes and immediately 10 to 60%
15 um
Less than 25 kgf / mm ² or more, surface roughness Rmax is 2.5 μm or more, and the half-width of X-ray diffraction is made dimensionless by the half-width after annealing. '
And β ′ ≧ 2.29−0.40
A method of manufacturing a drive transmission system component having excellent contact fatigue life strength, wherein ln (Rmax) and retained austenite are 10% or less.

(3) Mo: 0.1 to
A drive transmission system component excellent in contact fatigue life strength according to (1) or (2), wherein a steel material further containing one or more of 1.0% and Ni: 1.0% or less is used. Manufacturing method.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
C is an element added to secure the strength required as a part, particularly the strength of the core, but if it is less than 0.1%, such effects cannot be sufficiently obtained, and it exceeds 0.3%. And 0.1% to 0.3% because the toughness decreases.

[0015] Si is used as a deoxidizing material at the time of melting and needs to be 0.01% or more. However, it is an element that forms a grain boundary oxide layer during carburization, and when added in a large amount, the properties of carburizing steel such as bending fatigue are significantly deteriorated, so that the content is set to 0.15% or less. Mn is used as a deoxidizing material and a desulfurizing material at the time of melting, and is an element necessary for ensuring strength, toughness, and hardenability, and is required to be 0.3% or more. However, when the content exceeds 1.5%, a hard structure of bainite or martensite is formed in a cooling process after hot rolling, and the material is not suitable for machining such as cutting and grinding.

Cr is an element necessary for ensuring hardenability and mechanical performance, and is required to be 0.3% or more. But,
If this element also exceeds 1.5%, it becomes a hard structure of bainite or martensite in the cooling process after hot rolling, and is not suitable for machining such as cutting and grinding. In order to improve the pitting life of the combined parts during use due to the wear of the incompletely quenched layer, it is necessary to impart processing strain to embrittle and wear the incompletely quenched layer.

Many of the drive transmission system components are heated to an austenite region, hot forged, and finished to a predetermined shape by cutting. Thereafter, in order to harden the surface, the steel sheet is heated to the austenite region again and carburizing, quenching and tempering are performed. In this manufacturing process, heating to the austenite region is performed twice. In this step, in order to apply processing strain to the incompletely quenched layer at the time of carburization to cause abrasion, it must be provided after carburizing, quenching and tempering. On the other hand, in the process of performing warm forging during tempering after carburizing and quenching a steel material, heating to the austenite region only needs to be performed once, and an incompletely quenched layer that gives work strain during warm forging remains. Become.

Since the heating temperature is lower in the warm forging than in the hot forging, a material which has been appropriately set up, bent or otherwise roughly formed is generally used. Therefore, in the present invention, carburizing and quenching are performed after the steel material is roughly formed. The as-hardened case is heated to perform tempering because of its low toughness. If this temperature is lower than 200 ° C., the softening of the steel material is not so much observed and the hot forgeability is impaired, and recrystallization occurs at a temperature exceeding 600 ° C., so that the heating temperature is 200 ° C. or higher and 600 ° C. or lower. .

Since a high frequency is used as the heating means, it is easy to raise the temperature of the steel material in a short time and the generation of oxide scale can be suppressed. A heating time of 1 minute or more is required to uniformly heat the steel material. Heating for more than 5 minutes requires a long heating time, and should be avoided in order to prevent heating efficiency and the generation of oxide scale. For the processing rate, 6
If the processing exceeds 0%, cracks occur due to insufficient ductility. 10
% Processing cannot impart strength, and the processing strain applied to the incompletely quenched layer is small and does not wear.

If the wear layer is too deep, there is a possibility that the shape accuracy of the part is reduced and noise and vibration problems occur. Further, when the incompletely quenched layer is deep, the grain boundary oxide layer is also deepened to reduce bending fatigue.
If the incompletely quenched layer does not have a compressive residual stress, when the parts come into contact with each other, a crack is generated in the incompletely quenched layer due to the tensile stress on the surface where abrasion occurs, leading to pitching. Therefore, a compressive residual stress of 25 kgf / mm ² or more is required.

In order for the incompletely quenched layer to be embrittled by the hot forging at the time of tempering, it is necessary to impart processing strain at the time of the hot forging. As a measure, the X-ray diffraction half width is used in consideration of not damaging the surface, and the dimension is made dimensionless by the latter half width of the steel used so that there is no difference between measuring instruments and standard samples. The obtained value β ′ was used.
Further, in order to cause abrasion, a convex portion serving as a starting point of abrasion is required on the surface. Therefore, the surface roughness Rma after tempering warm forging
x needs to be 2.5 μm or more. However, even if there is a projection, abrasion does not occur unless the processing strain is small and brittle.
Therefore, the relationship between Rmax and β ′ is β ′ ≧ 2.29−
It is necessary to satisfy 0.40 ln (Rmax).

Further, if the amount of retained austenite is large, plastic deformation does not occur and abrasion does not occur. In order to suppress the occurrence of pitting even if the incompletely quenched layer is lost due to abrasion, in the first invention, a matrix layer in which the stretching of MnS, which is the starting point of pitting after wear, is suppressed, is provided. To form a base layer having a small amount of MnS.

In the first invention, in order to suppress MnS stretching, it is necessary to control MnS morphology by adding Ca. In the drive transmission system parts, machining such as grinding is performed to remove thermal strain and secure product accuracy. S is effective for machinability in cutting and grinding, and 0.01%
It is necessary to contain the above. However, if it exceeds 0.06%, the working limit during forging is significantly reduced, so the upper limit is made 0.06%.

Ca is an element necessary for suppressing the stretching of MnS, and is required to be 0.001% or more. However, 0.
Even if the content exceeds 01%, the effect is saturated and the economy is impaired, so the upper limit is made 0.01%. O increases the amount of inclusions in the steel and deteriorates fatigue strength characteristics such as rotational bending fatigue.

As a measure for suppressing the stretching of MnS, it is necessary to suppress the generation of hard inclusions which lower the deformability and become the starting point of pitching. Specifically, MnS is converted to (Mn, Ca) S and (Mn, Ca) S by adding Ca.
It is effective to use + calcium aluminate.
In order to convert MnS into (Mn, Ca) S and (Mn, Ca) S + calcium aluminate, it is necessary to maintain Ca / O (calcium / oxygen) at a predetermined ratio and control the reaction system.

When Ca / O is less than 0.5, hard CaO.
6Al ₂ O _{3 and the} like are generated and serve as a starting point of pitting. When Ca / O exceeds 3.5, hard CaS is also generated and the pitting fatigue life is reduced. Therefore, Ca / O is set to 0.5 to 3.5. In the second invention, S is set to less than 0.01% in order to reduce MnS. Compared to a conventional part that has been heated to the austenite region and has been carburized, the present invention in which tempering is performed after carburizing and quenching has a small thermal strain, and it is assumed that the part is used as a part as forged. The crack origin during tempering warm forging is MnS which is a hard inclusion. Therefore, in order to prevent cracking during tempering warm forging, it is better that MnS is small, and that the amount of S in steel is small, so that cracking can be suppressed.

Cr alone is not enough to ensure hardenability, and at least one of elements such as Mo and Ni is contained as necessary. Mo is contained in an amount of 0.1% or more in order to provide hardenability equal to or higher than that of conventional steel. However, if the content exceeds 1.0%, the effect is saturated and the economy is impaired, so the content is set to 1.0% or less.
Further, even if Ni is contained in excess of 1.0%, the effect is saturated and the economy is impaired, so the content is set to 1.0% or less.

[0028]

EXAMPLE Steels having the chemical compositions shown in Tables 1 and 4 were melted, then ingoted, then slab-rolled and bar-rolled to produce a diameter of 70 mm (rolling ratio of 50). ,
It was rolled into round bars of 28 mm and 27 mm. Subsequently, each rolled material was normalized at 925 ° C.

Each material was placed in a carburizing gas atmosphere at 930 ° C.
Heating for 5 hours → oil quenching at 130 ° C. Thereafter, in order to perform tempering and warm forging, the steel sheet was heated and held at a predetermined temperature by a high frequency and extruded into a round bar having a diameter of 26 mm. The heating time was 3 minutes in total, 1 minute for temperature rise and 2 minutes for holding. The extrusion reduction area, which represents the processing rate during tempering warm forging, is 36 mm in diameter.
It becomes 48% when extruding using the rolled material. In addition, using rolled materials having diameters of 30 mm, 28 mm, and 27 mm, the area reduction rates are 25%, 14%, and 7%, respectively. The tempering warm forging was performed at a constant speed of 150 mm / s using a compression tester of a hydraulic servo type having a load capacity of 50 tonf. Although the mold surface roughness is 0.5 to 1 μm, extrusion using a mold having a surface roughness of 3 to 4 μm was also performed in order to examine the effect of the extruded material surface roughness.

A small roller test piece having a diameter of 26 mm and a width of 28 mm used in a roller pitching test was machined from the extruded round bar having a diameter of 26 mm. In the roller pitching test, a fatigue test is performed by combining this small roller test piece with a large roller having a diameter of 130 mm. The large roller is made of rolled SCr420 material with a diameter of 70 mm and a diameter of 150 mm
After forging to 130mm in diameter, 18mm in width, R150
Machined into a predetermined shape with a crowning of mm,
Then heated at 930 ° C x 5 hours in a carburizing gas atmosphere → 13
Oil quenching at 0 ° C. → tempering at 200 ° C. × 1 hour.

The surface residual stress, half width, and retained austenite of each small roller test piece were measured. Since the X-ray half width is likely to have an error depending on the measuring machine and the standard sample, the dimension is made dimensionless by the value of the annealed material of each test piece. The annealing conditions were as follows.
The temperature was gradually cooled to ° C. As a pitting life evaluation, a roller pitting fatigue test was performed by combining a small roller test piece and a large roller. The test conditions were as follows:
The test was performed at 00 rpm, a slip ratio of 40%, and an automatic transmission oil as a lubricant at an oil temperature of about 80 ° C. The set surface pressure in the roller pitting test was set at 300 kgf / mm ² , and the point at which the area ratio of pitting generated on the small roller became 3% or more was evaluated as the fatigue life by the number of rotations up to that point.

An Ono-type rotary bending fatigue test was performed to evaluate bending fatigue. The above-mentioned rolled material having a diameter of 70 mm is formed into
It was rolled to 2 mm and then normalized at 925 ° C. Each material was heated in a carburizing gas atmosphere at 930 ° C. × 5 hours → oil quenching at 130 ° C., and then heated and held at 250 ° C. by high frequency for tempering and warm forging, and extruded into a round bar having a diameter of 10 mm. . The extrusion area reduction rate is 31%. A round bar having a diameter of 15 mm and a length of 90 mm was joined to both ends of the extruded round bar having a diameter of 10 mm and a length of 30 mm by friction welding to prepare a rotary bending test piece having a parallel portion having a diameter of 10 mm.

As an example for the first invention or the third invention, a roller pitting test was performed using steel materials A to K shown in Table 1. Steel materials A to E are examples of the present invention. In the steel materials F to K, Ca, O and Ca / O are out of a predetermined range,
Steel material K contains a large amount of Si. Table 2 shows the temperature during tempering forging, the area reduction rate, the depth of the incompletely quenched layer after forging, the MnS length in the rolling direction, the surface roughness, the residual stress, and the like.
The dimensionless half width, the amount of residual γ, and the fatigue life in a roller pitting test are shown. As for the residual stress, a negative value indicates the compressive residual stress, and a positive value indicates that of the tensile stress. The depth of the incompletely quenched layer and the MnS length were measured from the cross-sectional structure of the small roller.

In the examples of Nos. 1 to 13 of the present invention, no pitching occurred even 10 ⁷ times.
It was described as "× 10 ³ times. In Nos. 1 to 11, the surface roughness of the mold used at the time of warm forging is 0.5 to 1 μm. On the other hand, No. 12 and No. 13 are cases where warm forging was performed using a mold having a surface roughness of 3 to 4 μm, and the surface roughness Rmax after forging was No. 1 to 11 It is coarser than. Further, β ′ given due to a small area reduction rate during warm forging is smaller than in the cases of Nos. 1 to 7. However, beta 'to the surface roughness Rmax after forging is large is within a predetermined range, pitching up to 10 ⁷ times did not occur.

Nos. 14 to 25 are comparative examples. No.14 ~
Reference numeral 18 denotes a case where a steel material whose MnS is not shape-controlled is used, and MnS is longer than that of the present invention. Therefore, after the incompletely quenched layer was worn, a parent phase in which MnS was not shape-controlled appeared, so that the roller pitting fatigue life was short. No. 19 was also a case where a steel material whose MnS was not shape-controlled was used, but no pitting occurred because the incompletely quenched layer was deep and the generation of wear did not end. However, deeper wear leads to lower product accuracy,
The limits vary by product. In addition, it was presumed that the incompletely quenched layer was deep and the grain boundary oxide layer was also deep, so that bending fatigue was low.

[0036] As rotating bending fatigue test results Ono-type in Table 3, showing the fatigue limit stress also be fatigue 10 ⁷ times without breaking. Nos. 26 to 30 are examples of the present invention, and No. 31 is a comparative example using steel material K. Since the steel material K contains a large amount of Si, the grain boundary oxide layer is deep, and it can be seen that the bending fatigue life of the comparative example is nearly 30% lower than that of the inventive example. No. 20 is a case where the working ratio at the time of tempering warm forging is low, and the applied working strain is small and the dimensionless half width β ′ is smaller than a predetermined lower limit. Pitting life because wear did not occur in the roller pitting test does not reach the 10 ⁷ times.

In No. 21, tempering warm forging is performed after grinding after carburizing and quenching until the incomplete quenched layer disappears. There was no incompletely quenched layer to be a wear layer, and no pitting life was obtained because no wear occurred. In No. 22, a material obtained by rolling a rolled material having a diameter of 70 mm into a round bar having a diameter of 26 mm was used, and only tempering was performed without carburizing quenching and warm forging. Since work strain is not applied, the residual stress is a tensile, beta 'also pitting life is below the predetermined lower limit value does not reach the 10 ⁷ times.

For No. 23, after carburizing and quenching to reduce the surface roughness after forging, polishing was performed to reduce Rmax to 1.0 or less,
Thereafter, tempering warm forging was performed. Since the surface roughness after forging was small, no abrasion occurred and the pitting life was short. N
o.24 grind the surface layer about 10μm after tempering warm forging,
This is a case where a surface with a high residual γ inside comes out. Since the surface layer was not plastically deformed and abrasion did not occur, the pitting life was short.

No. 25, in which the heating temperature at the time of tempering warm forging was set to 150 ° C. However, since the material was not sufficiently softened by heating, extrusion molding was not possible with a 50 tonf compression tester. As an example for the second invention or the third invention, a roller pitching test was performed using steel materials L to T shown in Table 4. Steel materials L to Q are steels for the present invention, and steel materials RT are comparative examples and contain a large amount of sulfur.

Table 5 shows the temperature during tempering and forging, the area reduction rate,
The graph also shows the depth of the incompletely quenched layer after forging, surface roughness, residual stress, dimensionless half width, residual γ amount, and fatigue life in a roller pitting test. As for the residual stress, a negative value indicates the compressive residual stress, and a positive value indicates that of the tensile stress. In Table 5, Nos. 32 to 44 are examples of the present invention, and Nos. 45 to 5
3 is a comparative example. In the present invention example, 10 ⁷
Pitching was not reached in times.

In Nos. 32 to 42, the surface roughness of the mold used during warm forging is 0.5 to 1 μm. On the other hand, No. 43 and No. 44 have a surface roughness of 3 to 4 μm.
This is a case where warm forging was performed using a m mold, and the surface roughness Rmax after forging was larger than that of Nos. 32-42. Further, β ′ given due to a small area reduction rate during warm forging is smaller than that of Nos. 32-42. But,
For the surface roughness Rmax after forging is large beta 'is within a predetermined range, pitching up to 10 ⁷ times did not occur.

Nos. 45 to 47 show the cases where steel R, steel S and steel T containing a large amount of sulfur in the steel were used. Since the surface where stretched MnS was present after abrasion of the incompletely quenched layer appeared, pitting was performed. Life was short. No. 48 is a case where the working ratio at the time of tempering warm forging was low, β ′ after forging was smaller than a predetermined lower limit, and no pitting life was obtained because no abrasion occurred.

In No. 49, tempering warm forging is performed after grinding until the incomplete quenched layer disappears after carburizing and quenching. Since there was no incompletely quenched layer and no abrasion occurred, the pitting life was short. In No. 50, a material obtained by rolling a rolled material having a diameter of 70 mm into a round bar having a diameter of 26 mm was used, and only tempering was performed after carburizing and quenching without warm forging. Since no processing strain is given, the residual stress is tensile,
β 'is also below the lower limit and the pitting life is 1
Not reached 0 ⁷ times.

For No. 51, after carburizing and quenching to reduce the surface roughness after forging, polishing was performed to reduce Rmax to 1.0 or less.
Thereafter, tempering warm forging was performed. Since the surface roughness after forging was small, no abrasion occurred and the pitting life was short. N
No. 52 is a case where the surface layer was ground by about 10 μm after tempering warm forging, and a phase having a high residual γ inside appeared on the surface. Since the surface layer was not plastically deformed and abrasion did not occur, the pitting life was short.

No. 53 is the case where the heating temperature during the tempering warm forging was 150 ° C., but the material could not be softened sufficiently by heating, so that extrusion molding could not be carried out with a 50 tonf compression tester.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

[Table 4]

[0050]

[Table 5]

[0051]

According to the present invention, after carburizing and quenching, working is performed by using the heating of tempering to apply a working strain to the carburized layer, whereby the surface is worn during use and the pitting life is greatly improved. Can be. This means that it is possible to increase the load applied to the drive transmission system components, or to reduce the size and weight of the components themselves. It has a great effect.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/00 301 C22C 38/00 301N 38/18 38/18 38/60 38/60 (72) Inventor Seiji Ito 12 Nakamachi, Muroran-shi, Hokkaido F-term in Muroran Works, Nippon Steel Corporation (reference) 3J030 AC10 BC02 BC10 CA10 4K032 AA05 AA08 AA11 AA12 AA16 AA26 AA29 AA31 CA01 4K042 AA18 BA01 BA03 CA03 CA06 CA08 DA06

Claims (3)

[Claims] C: 0.1 to 0.3% Si: 0.01 to 0.15% Mn: 0.3 to 1.5% Cr: 0.3 to 1.5% S by weight% : 0.01-0.06% Ca: 0.001-0.01% O: 0.003% or less However, Ca / O: 0.5-3.5 is contained, and the balance consists of Fe and unavoidable impurities. After the steel material is roughly formed, carburizing and quenching are performed, and then 200 to 60
Immediately after the high frequency heating at 0 ° C. for 1 to 5 minutes and the processing of 10 to 60%, the incompletely quenched layer is less than 15 μm, the compressive residual stress on the surface is 25 kgf / mm ² or more, and the surface roughness Rmax is 2 0.5 μm or more, and the relationship between β ′ and the surface roughness Rmax obtained by rendering the half-width of the X-ray diffraction dimensionless by the half-width after annealing the steel is β ′ ≧ 2.29-0.40 l.
A method of manufacturing a drive transmission system component having excellent contact fatigue life strength, wherein n (Rmax) and retained austenite are 10% or less. 2. In% by weight, C: 0.1 to 0.3% Si: 0.01 to 0.15% Mn: 0.3 to 1.5% S: less than 0.01% Cr: less than 0.01% After roughly forming a steel material containing 3 to 1.5% and the balance being Fe and unavoidable impurities, carburizing and quenching are performed, and then 200 to 60%.
Immediately after the high frequency heating at 0 ° C. for 1 to 5 minutes and the processing of 10 to 60%, the incompletely quenched layer is less than 15 μm, the compressive residual stress on the surface is 25 kgf / mm ² or more, and the surface roughness Rmax is 2 0.5 μm or more, and the relationship between β ′ and the surface roughness Rmax obtained by rendering the half-width of the X-ray diffraction dimensionless by the half-width after annealing the steel is β ′ ≧ 2.29-0.40 l.
A method of manufacturing a drive transmission system component having excellent contact fatigue life strength, wherein n (Rmax) and retained austenite are 10% or less. 3. The steel material according to claim 1, further comprising one or more of the following: Mo: 0.1 to 1.0% Ni: 1.0% or less. Method for producing a drive train component having excellent contact fatigue life strength.