JPH0978127A - Production of high strength and high toughness axial parts for mechanical structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce axial parts for mechanical structures excellent in fatigue characteristics and toughness by subjecting a steel contg. specified amount of C, Mn, Cr, B, Ti and Al and in which the contents of Si, P, S and O are regulated to cold working and induction hardening to control its hardness. SOLUTION: A steel for induction hardening having a compsn. contg., by weight, 0.30 to 0.55% C, <=0.15% Si, 0.20 to 1.50% Mn, 0.05 to 0.30% Cr, 0.0005 to 0.0035% B, 0.01 to 0.05% Ti, 0.01 to 0.06% Al, <=0.030% P, <=0.035% S and <=0.0020% O and furthermore contg. prescribed amounts of Pb, Bi, Te, Ca, Nb, Ta, Hf and Zr is subjected to hot rolling to regulate its structure into a ferritic-pearlitic one. This hot rolled steel is subjected to cold working to harden the whole body or a part to 220 to 300 HV hardness. Furthermore, this worked product is subjected to induction hardening to regulate its surface to the hardening ratio (t)/R=0.4 to 0.7 ((t) denotes the depth of the hardened layer to 50% martensite hardness and R denotes the radius of the parts).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a spindle, a joint, a shaft, etc., which are shaft-shaped parts made of steel for machine structure, and particularly to a shaft structure for machine structure excellent in fatigue characteristics and toughness. The present invention relates to a method of manufacturing a component.

[0002]

2. Description of the Related Art A spindle, which is a shaft-shaped component for machine structure,
Since joints, shafts and the like are required to have excellent fatigue strength, they are often subjected to induction hardening after being manufactured into a predetermined shape. In this way, as the steel for machine structure to obtain the final quality by induction hardening treatment,
A medium carbon steel containing C: 0.40 to 0.60% is generally used, and has been manufactured into a predetermined shape by hot working. However, since the dimensional accuracy is poor only by hot working and the subsequent cutting is required, cold working excellent in material yield and dimensional accuracy has recently been adopted. On the other hand, in this cold working, JIS
Since the deformation resistance is high and the cold working tool life becomes a problem when the medium carbon steel is rolled as it is, it is necessary to perform annealing and spheroidizing annealing in order to improve the cold workability. It's a problem.

In recent years, it has been desired to reduce the weight of automobiles and the like for the purpose of reducing fuel consumption and exhaust gas, and to increase the strength of mechanical structural parts accompanying the increase in output of engines. As a method for improving the fatigue strength of induction-hardened machine structural parts, a method of increasing the depth of hardened layer, surface layer hardness, and core hardness is known. In order to increase the depth of the hardened layer, it is necessary to lengthen the heating time for induction hardening, but if heated for a long time, the crystal grains become coarse, the surface compressive residual stress decreases, and the surface hardness decreases. There is a problem that the fatigue strength decreases. Therefore, it is possible to increase the hardenability and deepen the hardened layer depth by adding an alloying element, but the strength of the raw material is increased, and problems such as cold working occur. Further, in order to increase the surface hardness, C
It is desirable to increase the content, but problems such as cold working occur. Further, addition of alloying elements is effective for increasing the hardness of the core, but it becomes a very expensive steel material, the strength of the material increases, and problems such as cold workability occur.

[0004]

The present invention focuses on the above-mentioned conventional problems and applies cold working and induction hardening to remarkably improve fatigue properties and toughness without causing the above problems. An object of the present invention is to provide a method for manufacturing a shaft-shaped component for an excellent high strength and high toughness mechanical structure.

[0005]

The method for manufacturing a shaft-shaped component for a machine structure according to the present invention is C: 0.30 to 05 in weight%.
5%, Si: 0.15% or less, Mn: 0.20 to 1.5
0%, Cr: 0.05-0.30%, B: 0.005-
0.0035%, Ti: 0.01 to 0.05%, Al:
0.01-0.06%, P: 0.030% or less, S:
0.035% or less, O: 0.0020% or less, balance Fe
In order to improve cold workability, P: 0.015% or less, S: 0.010% or less, N:
It is regulated to 0.010% or less, and Pb: 0.01 to 0.20%, Bi: 0.
01-0.20%, Te: 0.005-0.10%, C
a: 0.0003 to 0.010% of one kind or two or more kinds are added, and Nb:
0.01-0.30%, Ta: 0.01-0.30%,
Hf: 0.01 to 0.30%, Zr: 0.01 to 0.3
When manufacturing shaft-shaped parts for machine structures using steel containing 0% of 1 type or 2 or more types, the ferrite / pearlite structure is adjusted by hot rolling and the hardness is wholly or partly cold-worked. It is cured to 220 to 300 HV, and the surface is further cured layer ratio t / R = 0.4 to 0.7 (t: effective cured layer depth,
R: radius of parts) is characterized by induction hardening, and the desired portion can be obtained by carrying out this method.

[0006]

The induction hardening steel used as a raw material in the method of manufacturing a shaft-shaped component for a machine structure according to the present invention has a good cold workability by reducing the Si content and has an increased hardenability. In order to secure a sufficient induction hardening depth and further improve the toughness of the induction hardening portion, B is added, and the tendency of crystal grain coarsening is prevented by adding Al. Then, this induction hardening steel is hot-rolled to adjust to a ferrite-pearlite structure having excellent cold workability and toughness, and the core hardness is hardened to 220 to 300 HV by cold working. By performing the treatment so as to obtain the optimum hardened layer depth by quenching, it has become possible to manufacture a shaft-shaped component for a mechanical structure having excellent fatigue properties and toughness. Hereinafter, the reasons for limiting the component range of the induction hardening steel used as a raw material in the method for manufacturing a machine structural component according to the present invention will be described.

C: 0.30 to 0.55% C is an element necessary for ensuring the strength of mechanical structural parts, and is 0.30 in order to obtain sufficient surface hardness particularly by induction hardening. % Or more is required. But,
If it is too large, quench cracking tends to occur during induction hardening, so the content was limited to 0.55% or less.

Si: 0.15% or less Si is an amount contained as a deoxidizing agent at the time of melting, but since it deteriorates the cold workability, it is 0.15% or less in order to improve the cold workability. Limited to.

Mn: 0.20 to 1.50% Mn is an element that acts as a desulfurizing agent at the time of melting, and is an element that improves hardenability. If less than 0.20%,
Due to induction hardening, a sufficient hardened layer depth cannot be obtained, and the fatigue characteristics of the product deteriorate significantly. Also, 1.50
If it exceeds%, the cold workability deteriorates like Si. Therefore, it is set to 0.20 to 1.50%.

Cr: 0.05% to 0.30% Cr is an element that improves hardenability, and it is necessary to add 0.05% or more to obtain a sufficient hardened layer depth by induction hardening. is there. However, if it is too large, quench cracking is likely to occur during induction hardening, so the content was limited to 0.30% or less.

B: 0.0005 to 0.0035% B is an element added to secure the necessary induction hardening depth, and is also an element for improving the toughness of martensite in the induction hardened part, and such an effect is obtained. 0.00 to get
It is necessary that the content be at least 05%. However, as the amount increases, the effect saturates, and the adverse effect of deterioration of hot workability appears, so the content was made 0.0035% or less.

Ti: 0.01 to 0.05% Ti is an element added to fix N and ensure the improvement of hardenability by adding B. It is necessary that the content be 01% or more. However, if the content is too large, the toughness is reduced. Therefore, the content is limited to 0.05% or less.

Al: 0.01 to 0.06% Al is an element necessary for deoxidation.
It is an element that is effective in preventing the tendency of crystal grains to coarsen due to addition, refining the crystal grains during induction hardening of B-added steel, improving the strength, and significantly reducing the strain after induction hardening. In order to obtain various effects, it is contained by 0.01% or more. However, if the amount is too large, the crystal grains become coarser and the toughness of the steel decreases, so 0.0
It was limited to 6% or less.

P: 0.030% or less If the P content is too large, the toughness is impaired and the cold workability is deteriorated. Therefore, it is preferable to regulate the content to 0.030% or less, more preferably 0.015% or less. Good.

S: 0.035% or less If the S content is too large, the cold workability is deteriorated, so that
It is preferable to regulate to 035% or less, and more desirably to 0.010% or less. However, if the S content is too low, the machinability is deteriorated. Therefore, when the machinability improving element described later is not added, it is necessary to add S in an amount not deteriorating the cold workability. It is desirable to regulate the range to 0.020.

N: 0.010% or less If the N content is too large, the deformation resistance increases and the cold workability deteriorates. Therefore, it is desirable to control the content to 0.010% or less.

O: 0.0020% or less If the O content is too large, the amount of inclusions in the steel increases and the cold workability deteriorates. Therefore, it is desirable to control the content to 0.0020% or less.

Pb: 0.01 to 0.20%, Bi: 0.
01-0.20%, Te: 0.005-0.10%, C
a: 0.0003 to 0.010% of one or more Pb, Bi, Te and Ca are effective elements for improving the machinability, and the S content is considerably increased in order to improve the cold workability. Since it is effective in compensating for the decrease in machinability when it is suppressed, it may be appropriately added within the above range if necessary.

Nb: 0.01 to 0.30%, Ta: 0.
01 to 0.30%, Hf: 0.01 to 0.30%, Z
r: 0.01 to 0.30% of one or more Nb, Ta, Hf, and Zr are elements that contribute to refining the crystal grains and improving the toughness, so they are added in the above range as necessary. Also good.

Core hardness and hardened layer ratio: In the present invention, a steel having the above chemical composition is used as a material, but a material having a low hardness is used so that cold working is easy. However, in this state, sufficient hardness cannot be obtained even if induction hardening is performed due to insufficient hardness of the core. Therefore, cold extrusion, cold working such as rolling is used to harden the material,
The fatigue strength can be improved by increasing the core hardness, but at this time, if it is less than 220 HV, the core hardness is low and the desired fatigue strength cannot be obtained. Further, if cold working is performed until it exceeds 300 HV, the tool life during cold extrusion and rolling becomes a problem, so 2
It is necessary to cure it to 20 to 300 HV. Furthermore, after this, induction hardening is performed, but it is sufficient that the hardened layer ratio t / R, which is the ratio of the hardened layer depth t up to 50% martensite hardness and the component radius R, is less than 0.4. Fatigue strength cannot be obtained. Further, even if it exceeds 0.7, the compressive residual stress decreases, and the increase in fatigue strength saturates. From this, t / R
= 0.4-0.7, induction hardening is required.

[0021]

EXAMPLES The effects of the present invention will be described with reference to examples. After the steel having the chemical composition shown in Table 1 was melted, slab rolling and product rolling were performed to manufacture a rolled material having a diameter of 40 mm. Then, the rolled material is cold-extruded by cold extrusion, and a part of it is a circumferential notch (1 mmR notch, depth 1 mm).
An impact test piece having a notch bottom diameter of 15 mm was prepared. In addition, a part of both ends was subjected to serration processing by rolling to prepare a torsion test piece (parallel part diameter 25 mm).
At that time, the tool life during cold extrusion was investigated. The tool life was set to 1 for the conventional steel (No. 15). Subsequently, the impact test piece prepared was subjected to induction hardening treatment under the conditions shown in Table 2,
An impact test was conducted to determine the impact value. Further, the torsion test piece was subjected to induction hardening treatment under the conditions shown in Table 3 and a torsion fatigue test was performed. In the torsional fatigue test, a sine wave torque of 2 Hz was applied, and the torque value at the number of repeated fractures of 2 × 10 ⁵ was taken as the torsional fatigue strength. The above results are shown in Tables 4 and 5.

It can be seen that all the samples produced by the method of the present invention exhibit high fatigue strength and impact value. In Comparative Example 10, the tool life is excellent because the C content of the material is small, but sufficient torsional fatigue strength cannot be obtained because the surface hardness after induction hardening is low. In Comparative Example 11, the Mn content of the material is small, the induction hardening depth is insufficient, and the hardened layer ratio t / R is 0.
Since it is 4 or less, the torsional fatigue strength is low. In Comparative Example 12, the Mn content of the material is sufficient and the induction hardening depth is sufficient, but the hardened layer ratio t / R becomes 0.7 or more, the surface layer residual compression stress decreases, and the torsional fatigue strength also decreases. are doing. Furthermore, the tool life is shortened because the Mn content is high. In Comparative Example 13, the tool life is shortened due to the large Si content of the material, and the impact value of the induction hardened material is also reduced. In Comparative Example 14, since the C content of the material is large, the impact value of the induction hardened material is low. Comparative Examples 15 and 16 are steels corresponding to JIS standards S40C and S48C, but the torsional fatigue strength is improved by cold working, but a sufficient hardened layer depth cannot be obtained, and compared with the samples according to the present invention. The torsional fatigue strength and impact value are low.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

[0028]

As is clear from the above description, in the present invention, cold working and induction hardening are applied to manufacture a shaft-shaped component for a high strength and high toughness mechanical structure having excellent fatigue properties and toughness. It is possible and the parts are most suitable for spindles, joints and shafts.

Claims (6)

[Claims] 1. In weight%, C: 0.30 to 0.55.
%, Si: 0.15% or less, Mn: 0.20 to 1.50
%, Cr: 0.05 to 0.30%, B: 0.0005
~ 0.0035%, Ti: 0.01-0.05%, A
1: 0.01 to 0.06%, P: 0.030% or less,
S: 0.035% or less, O: 0.0020% or less,
When manufacturing a shaft-shaped component for machine structure using induction hardening steel containing a steel, a ferrite-pearlite structure is adjusted by hot rolling, and a hardness of 220 to
It is cured to 300 HV and the surface is further cured at a layer ratio of t / R
A method for manufacturing a shaft-shaped component for machine structure, characterized by induction hardening to 0.4 to 0.7 (t: depth of hardened layer up to 50% martensite hardness, R: component radius). 2. A method for manufacturing a shaft-shaped component for machine structure, wherein P in claim 1 is restricted to 0.015% or less. 3. A method for manufacturing a shaft-shaped component for machine structure, wherein S according to claim 1 or 2 is restricted to 0.010% or less. 4. A method for manufacturing a shaft-shaped component for a machine structure, characterized in that N in any one of claims 1 to 3 is restricted to 0.010% or less. 5. Pb: 0.01 to 0.20 in% by weight.
%, Bi: 0.01 to 0.20%, Te: 0.005
An induction hardening steel containing one or more of 0.10% and Ca: 0.0003 to 0.010% is used. Production method. 6. Nb: 0.01 to 0.30 in weight%.
%, Ta: 0.01 to 0.30%, Hf: 0.01 to
An induction hardening steel containing one or more of 0.30% and Zr: 0.01 to 0.30% is used. Production method.