WO2007043316A1

WO2007043316A1 - Steel material and process for producing the same

Info

Publication number: WO2007043316A1
Application number: PCT/JP2006/318885
Authority: WO
Inventors: Yoshimi Usui; Yutaka Sato; Masahiko Igarashi; Wataru Yanagita; Hideo Watanabe; Satoru Nakamyo
Original assignee: Honda Motor Co., Ltd.; Sanyo Special Steel Co., Ltd.
Priority date: 2005-10-11
Filing date: 2006-09-22
Publication date: 2007-04-19
Also published as: JP2007107029A; US20090110589A1; CN101283111A

Abstract

A steel material of 85 to 95 HRB exhibiting a ratio of area occupied by ferrite of 30% or higher, which steel material comprises given amounts of C, Si, Mn, S, Ti, Cr, Al and B and the balance of iron and unavoidable impurities, is subjected to induction hardening. After the hardening, the surface of the steel material exhibits an HV value of 640 to 730. When t refers to the effective hardening depth, namely, the distance from the surface to a region exhibiting an HV value of 392 and r refers to the radius of the steel material, the hardened layer ratio, t/r, is 0.4 or higher.

Description

Specification

Steel material and manufacturing method thereof

Technical field

[0001] The present invention relates to a steel material and a method for manufacturing the steel material, and more particularly to a steel material suitable as a material for a drive shaft and a method for manufacturing the steel material.

Background art

[0002] A drive shaft that constitutes a traveling engine of an automobile is generally manufactured from a steel material. This type of steel material is required to be relatively easy to cut. On the other hand, it is necessary that the shear stress to break when applying the torsional torque to ensure the durability of the drive shaft is high, in other words, the torsional strength is high. For example, JIS-S40C equivalent material is selected as the steel material to obtain such a drive shaft.

[0003] By the way, with the recent growing interest in environmental protection, emissions of CO, NOx, etc.

2

Various investigations have been made to improve the fuel efficiency of a vehicle that reduces the amount of fuel. Attempts have been made to reduce weight by reducing the dimensions of the components of automobiles.

[0004] Same steel strength When manufacturing a small-sized drive shaft, the strength and the like usually decrease. Therefore, there is a demand for a steel material that can ensure sufficient strength even when a small-sized drive shaft is manufactured.

[0005] In response to this need, for example, Patent Document 1 discloses that a drive shaft is composed of a steel material in which the composition ratio, surface hardness, martensite ratio, and hardening depth ratio of constituent elements satisfy predetermined values. Has been proposed.

[0006] Further, Patent Document 2 discloses a steel for induction hardening in which the structure area ratio of ferrite with respect to contained C and the crystal grain size of ferrite are not more than a predetermined value. According to Patent Document 2,

The induction hardening steel is said to be suitable as a drive shaft material.

[0007] Patent Document 1: Japanese Patent Laid-Open No. 10-36937

Patent Document 2: JP 2002-69566 A Disclosure of the invention

[0008] A general object of the present invention is to provide a steel material having excellent characteristics even when a small-sized member is formed.

[0009] A main object of the present invention is to provide a method for producing a steel material for producing the steel material.

According to one embodiment of the [0010] present invention, the mass ^{_{0/0, C:. 0.47~0}} 52%, Si:. 0.03~0 1 5%, Mn:.. 0 6~0 7%, S : 0.005 to 0.03%, Ti: 0.025 to 0.04%, Cr: 0.05 to 0.3%, Mo: 0.04 to 0.09%, A1: 0.02 to 0.04%, B: 0.0005 to 0.004%, the balance being iron and Inevitable impurities,

Surface Vickers hardness is 640-730,

A steel material having a hardened layer ratio tZr of 0.4 or more is provided, where the effective hardened depth t is the distance of surface force to reach the part showing 392 in Vickers hardness and the radius is r.

[0011] By setting the hardness and the hardened layer ratio in this way, the hardness and the strength are ensured.

. This is because a substance having a high hardness generally has a high strength. Also, since the hardness is not excessively large, toughness is ensured and brittle fracture is less likely to occur.

[0012] By making the above-mentioned component composition ratio as described above, a steel material having excellent machinability can be obtained.

[0013] N in this steel material is preferably 0.01% by mass or less. In this case, BN and TiN are difficult to generate. Therefore, it is possible to avoid that the hardness proceeds excessively and the workability and machinability are deteriorated while quenching proceeds without being hindered.

[0014] According to another embodiment of the present invention, the distance from the surface Vickers hardness of 640 to 730 and the surface force Vickers hardness of 392 to the effective hardening depth t and the radius where rZ is a method of manufacturing a steel material with tZr of 0.4 or more,

Mass ^{_{0/0, C:. 0.47~0}} 52%, Si:. 0.03~0 15%, Mn:. 0.6~0 7%, S:. 0 005~0.03%, Ti: 0.025~0.04%, Cr : 0.05 to 0.3%, A1: 0.02 to 0.04%, B: 0.0005-0.004%, the balance is iron and unavoidable impurities, the ferrite occupied area ratio is 30% or more, B scale Rockwell Provided is a method for producing a steel material having a hardness of 85 to 95 and subjecting the steel material to induction hardening. That is, by subjecting the raw material steel having the above-mentioned component 'composition ratio to induction hardening, a steel material having excellent hardness and strength and good machinability can be obtained.

[0016] By using a steel material exhibiting such characteristics, it is possible to produce a member having excellent strength even with a small size. However, this steel material is very easy to process because it has good machinability and high compositional deformability. Also, because it has excellent toughness

Cracks are less likely to occur during processing.

Furthermore, since this steel material has high torsional strength, it can be suitably used as a material for a long shaft member, for example, a drive shaft.

[0018] As described above, by configuring the steel material by setting the components, composition ratio, hardness, and hardened layer ratio, a steel material having excellent strength, particularly torsional strength, and good machinability can be obtained. . Brief Description of Drawings

FIG. 1 is an overall schematic side view along the longitudinal direction of a drive shaft that also has steel force according to the present embodiment.

[FIG. 2] FIG. 2 is a graph showing the relationship between the surface force distance and the hardness of the drive shaft of FIG.

FIG. 3 is a chart showing the components and composition ratios of each steel material.

FIG. 4 is a chart showing various characteristics of the steel material shown in FIG.

FIG. 5 is a graph showing the relationship between the hardened layer ratio rZt and the shear stress in the steel materials according to each example.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the steel material and the manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an overall schematic side view of the drive shaft 10 along the longitudinal direction. The drive shaft 10 is a long solid body, and the diameter of the measurement site indicated by reference numeral 12 in FIG. 1 is 28 mm.

Here, the steel material that is the material of the drive shaft 10 is C, in addition to iron and inevitable impurities.

Contains Si ゝ Mn, S, Ti, Cr ゝ Mo, Al, B.

[0023] C ensures the strength and hardness of the drive shaft 10 after quenching and tempering. The composition ratio is set to 0.47-0.52% (numbers are% by mass, the same shall apply hereinafter). If it is less than 0.4%, it will be difficult to ensure hardness. On the other hand, if it exceeds 0.52%, the hardness will increase excessively, making it difficult to carry out plastic deformation or cutting, and will also show brittle fracture, resulting in a decrease in strength. In particular, the deformability in cold working is reduced.

Si is an element useful for deoxidation of the drive shaft 10 and is contained in the drive shaft 10 at a ratio of 0.03 to 0.15%. Less than 03%, the deoxidation effect is poor. On the other hand, if it exceeds 0.15%, the hardness will increase excessively, making it difficult to perform plastic deformation or cutting. In particular, the deformability in cold working is reduced.

[0025] Mn improves the induction hardenability of the drive shaft 10. That is, due to the presence of Mn, when induction hardening is performed on the drive shaft 10, the hardness is significantly increased as compared with that before the quenching. The composition ratio of Mn to ensure this effect is set to 0.6 to 0.7%. If it exceeds 0.7%, the hardness will increase excessively, making it difficult to perform plastic deformation or cutting. In particular, the deformability in cold working is reduced.

[0026] S is a component that forms MnS together with Mn in the structure of the drive shaft 10, thereby improving the machinability of the drive shaft 10. The composition ratio of S is set to 0.005 to 0.03%. If it is less than 0.005%, it is difficult to improve machinability, and if it exceeds 0.03%, the deformability particularly during cold working is reduced.

[0027] Ti plays a role in capturing free N in the drive shaft 10. When free N is trapped in this way, the effect of adding B described later becomes more remarkable. The composition ratio of Ti is set to 0.025 to 0.04%. If it is less than 0.25%, the effect of capturing free N is poor. On the other hand, if it exceeds 0.04%, Ti will be present excessively, so that machinability and deformability during cold heating are reduced.

[0028] Cr is a component that improves the hardenability of the drive shaft 10. In other words, the presence of Cr significantly increases the hardness of the drive shaft 10 after quenching. The composition ratio of Cr is set to 0.05-5.3%. If it is less than 0.05%, it is difficult to obtain this effect. On the other hand, if it exceeds 0.3%, Cr concentrates in the cementite. It prevents carbon from dissolving in the steel material when it is put.

[0029] Mo is an element useful for improving the grain boundary strength of the drive shaft 10 after quenching, and particularly for improving the torsional strength. The Mo composition ratio is set to 0.04-0.09%. If it is less than 0.04%, it is difficult to improve the grain boundary strength. On the other hand, if it exceeds 0.09%, the hardness will increase excessively, making it difficult to perform plastic deformation or cutting. In particular, the deformability during cold working is reduced.

[0030] B is a component that improves the grain boundary strength. In addition, the hardenability of the drive shaft 10 is improved. This effect is reduced when N is present in excess. This is because BN is generated from B and surplus N. Therefore, as described above, this effect is ensured by capturing N with a predetermined amount of Ti.

[0031] The composition ratio of B is set to 0.0005 to 0.004% (5 to 40 ppm). If it is less than 5 ppm, the effect of improving the grain boundary strength is poor. If it exceeds 40 ppm, the hardenability will be reduced.

[0032] A1, like Si, is a component that contributes to deoxidation. When the composition ratio of A1 is less than 0.02%, the deoxidation effect is poor. In addition, if A1 is present excessively, oxide impurities such as Al 2 O increase.

twenty three

In addition, as a result, fatigue characteristics and deformability at the time of plastic deformation are reduced. For this reason, the upper limit of A1 is set to 0.04%.

[0033] Here, if free N is excessively present in the drive shaft 10, it binds to B to form BN as described above, and as a result, hardenability and the like deteriorate. In addition, when TiN is formed by combining with Ti, the hardness increases excessively, making it difficult to process and lowering the toughness. In the present embodiment to avoid such a situation, the composition ratio of N existing in the drive shaft 10 is set to 0.01% or less.

[0034] When the structure of the drive shaft 10 is observed, the occupied area ratio of the ferrite existing in the structure is 30% or more. In other words, if the total field of view is 100%, ferrite occupies 30% or more. Due to the presence of ferrite in this proportion, the drive shaft 10 after quenching exhibits excellent toughness.

[0035] Furthermore, the hardness of the surface of the drive shaft 10 is B scale Rockwell hardness (H).

RB

When expressed, it is 85-95. By setting the surface hardness within this range, quenching and quenching The strength of the drive shaft 10 after the returning process is ensured.

[0036] The drive shaft 10 is manufactured, for example, by subjecting a cylindrical workpiece made of a steel material having the above-mentioned component 'composition ratio to a turning process or a rolling process.

Next, the drive shaft 10 is quenched and tempered.

[0038] In the present embodiment, an induction hardening method in which heating is performed with a high frequency is employed as the quenching. That is, first, the surface of the drive shaft 10 is rapidly heated by the high-frequency induction current, and then the cooling liquid is jetted onto the surface to perform rapid cooling. The quenching conditions may be, for example, a heating time of 1 to 5 seconds when the frequency and output of the induced current are approximately 1 to 40 kHz and 50 to about LOOkW.

[0039] Next, the drive shaft 10 is tempered in a temperature range of about 150 ° C to 200 ° C. As a result, residual stress is removed from the drive shaft 10 and the drive shaft 10 is prevented from undergoing secular change or cracking.

[0040] The picker hardness (H) of the surface of the drive shaft 10 subjected to the quenching and tempering treatment as described above is 640 to 730. High hardness steels generally have higher strength.

V

If the hardness is of this level, the toughness may not be sufficient.

[0041] Further, in the drive shaft 10, the hardness decreases in the radial direction, that is, from the surface to the inside, as shown in FIG. In the present embodiment, the hardness of the drive shaft 10 is measured from the surface side in this way, and the distance (depth) to the part indicated by 392 in H is calculated.

V

Effective hardened layer depth t. For example, since the diameter of the measurement site 12 is 28 mm as described above, 14 mm on the horizontal axis of the graph in FIG. 2 represents the center in the radial direction at the measurement site 12.

[0042] When the radius of the drive shaft 10 is r, the cured layer ratio tZr, which is the ratio of the effective cured layer depth t to the radius r, is 0.4 or more. If it is less than 0.4, the thickness of the effective hardened layer is not sufficient, so that the torsional strength of the drive shaft 10 is reduced.

[0043] That is, by setting the surface H to 640 to 730 and the cured layer ratio tZr to 0.4 or more,

V

A drive shaft 10 having excellent strength and toughness is obtained.

[0044] In the above-described embodiment, the drive shaft 10 is exemplified as the steel material.

1S The final product is not limited to this. Even if it is a counter member to be used.

Example 1

[0045] Using a vacuum melting furnace, an ingot of a steel material having a composition ratio shown in Fig. 3 was prepared. Next, this ingot was heated to 950 ° C and subjected to hot forging force to produce a cylindrical workpiece having a diameter of 27 mm. The temperature at the end of forging was set to be between Ac3 point and 880 ° C.

[0046] Then, the cylindrical workpiece was observed with an optical microscope, and the occupied area ratio of ferrite was obtained. On the other hand, H at a depth of 7-8mm from the surface

B was measured.

[0047] From this cylindrical workpiece, a small cylindrical workpiece having a diameter of 14 mm and a length of 21 mm was cut out. Thereafter, upsetting was performed on this small cylindrical workpiece in the cold working temperature range, and the upsetting rate until cracking occurred was obtained.

[0048] Further, for the cylindrical workpiece, using ST20E (trade name of a cutting tool manufactured by Sumitomo Electric), a cutting speed of 150mZ, a cutting depth of 0.5mm, and a feed speed of 0.2mmZrev. A cutting test was conducted under the conditions, and the wear amount of ST20E after 12 minutes was measured.

[0049] Further, a drive shaft 10 having the shape shown in Fig. 1 is produced from the cylindrical workpiece, and the drive shaft 10 is subjected to induction hardening and tempering treatment under various conditions to obtain an effective hardened layer depth t. The hardened layer ratio tZr was varied. Thereafter, a static torsion test was performed on each drive shaft 10.

[0050] For comparison, the same experiment was performed on the steel material having the composition / component ratio shown in FIG.

[0051] The above results are also shown in FIG. From this Fig. 4, it can be seen that by using a steel material with a specified composition, composition ratio, ferrite occupation area ratio, and hardness, it has excellent deformability, good machinability, and high torsional strength. It becomes a part to become.

Here, the relationship between the hardened layer ratio tZr and the shear stress in the steel materials according to the respective examples is shown as a graph in FIG. Higher shear stress means higher static torsional strength. The broken line in FIG. 5 represents the relationship between the hardened layer ratio and the shear stress in the S40C equivalent material.

[0053] From FIG. 5, it is clear that the steel materials according to each Example have a higher static torsional strength than S40C equivalent materials.

Claims

The scope of the claims

[1] in a weight ^{_{0/0, C:. 0.47~0}} 52%, Si:. 0.03~0 15%, Mn:. 0.6~0 7%, S: 0.

Contains 005 to 0.03%, Ti: 0.025 to 0.04%, Cr: 0.05 to 0.3%, Mo: 0.04 to 0.09%, A1: 0.02 to 0.04%, B: 0.0005 to 0.004%, balance iron and inevitable Impurities,

Surface Vickers hardness is 640-730,

A steel material characterized in that the hardened layer ratio tZr is 0.4 or more, where the effective hardened depth t is the distance of the surface force to reach the part showing 392 in Vickers hardness and the radius is r.

[2] The steel material according to claim 1, wherein N is 0.01% or less by mass%.

[3] The steel material according to claim 1, wherein the steel material is a drive shaft (10).

[4] This is a method of manufacturing a steel material in which tZr is 0.4 or more when the effective hardening depth t and radius are the distance from the surface to the part showing 392 in the Vickers hardness of 640 to 730 and the surface to Vickers hardness 392. And

Mass ^{_{0/0, C:. 0.47~0}} 52%, Si:. 0.03~0 15%, Mn:. 0.6~0 7%, S:. 0 005~0.03%, Ti: 0.025~0.04%, Cr : 0.05 to 0.3%, Mo: 0.04 to 0.09%, A1: 0.02 to 0.04%, B: 0.0005 to 0.004%, balance iron and inevitable impurities, 30% ferrite occupation area ratio As mentioned above, the manufacturing method of the steel materials characterized by performing induction hardening with respect to the raw material steel whose Rockwell hardness of B scale is 85-95.

[5] The method for manufacturing a steel material according to claim 4, wherein the raw material steel is formed into a drive shaft (10) and subjected to induction hardening.