JPH0797656A - Cold forging steel - Google Patents

Abstract

PURPOSE:To provide a cold forging steel capable of keeping deformation resistance at the time of cold forging at a low value and excellent in hardenability after forming. CONSTITUTION:This steel has a composition consisting of 0.30-0.60% C, <=0.10% Si, 0.15-0.65% Mn, <=0.10% P, <=0.10% S, <=0.50% Cr, 0.05-0.40% Mo, 0.05-0.40% Ni, 0.0005-0.0035% B, 0.01-0.10% Ti, and the balance iron with inevitable impurities. Further, prescribed amounts of Cu, Nb, V, Pb, Te, Bi, and Ca can be added to this steel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cold forging steel used as a material for power transmission parts such as constant velocity joint outer races and gears in automobiles, construction machines and various industrial machines.

[0002]

2. Description of the Related Art In manufacturing power transmission parts such as constant velocity joint outer races and gears as described above, a large diameter steel bar is cold forged or warm forged into a predetermined shape, and then the surface is formed. Generally, induction hardening treatment or carburizing treatment is performed for hardening. In such manufacturing, particularly when cold forging is performed, it is required that the steel material has excellent cold workability. Further, cold workability includes deformability and deformation resistance, but low deformation resistance is the most important requirement for performing cold forging of the above parts.

As a method of lowering the deformation resistance during cold forging, elements such as C, Si, Mn, P, and Cr are reduced, and the decrease in hardenability due to the reduction of Si, Mn, and Cr is reduced by B. Has been proposed (for example, Japanese Patent Publication No. 1-38847 and Japanese Patent Laid-Open No. 2-38847).
14574, etc.). However, these techniques have a problem that the hardenability (particularly the induction hardenability) after molding deteriorates.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object thereof is to keep deformation resistance during cold forging low and to improve hardenability after forming. Is to provide an excellent cold forging steel.

[0005]

The present invention capable of achieving the above object means C: 0.30 to 0.60%, Si: 0.10.
% Or less, Mn: 0.15 to 0.65%, P: 0.10%
Below, S: 0.10% or less, Cr: 0.50% or less, M
o: 0.05 to 0.40%, Ni: 0.05 to 0.40
%, B: 0.0005 to 0.0035%, Ti: 0.0
It is a steel for cold forging having a gist that it contains 1 to 0.10% each, and the balance is iron and unavoidable impurities. If necessary, Cu, Nb, V, Pb, Te, Bi, C
It may contain a predetermined amount of a or the like.

[0006]

The present inventors examined the effects of various additive elements in order to develop a steel for cold forging that can meet the above requirements. As a result, when Ni is added, elements such as C, Si, Mn, P, and Cr in the steel can be further reduced, whereby the deformation resistance can be further reduced, and Si, Mn, and It has been found that the hardenability after molding (particularly the induction hardenability) can be improved despite the reduction of hardenability improving elements such as Cr.
And, in addition to the hardenability improving element and Ni as described above,
The inventors have found that a steel for cold forging having desired characteristics can be realized by appropriately adjusting chemical components such as Mo, B and Ti, and completed the present invention. In addition, in such cold forging steel, it is required that the grindability after quenching is good in addition to the reduction in deformation resistance and the improvement in hardenability described above. It was also found to be improved. The reasons for limiting the chemical components in the present invention are as follows.

C: 0.30 to 0.60% C is to secure the strength as a mechanical structural part,
It is necessary to contain 0.30% or more. However,
If the content exceeds 0.60%, the deformation resistance during cold forging becomes too high and quench cracking easily occurs, so the upper limit must be made 0.60%. Si: 0.10% or less Si is an element effective for deoxidizing steel, but its content is 0.10 because it is an element that enhances the deformation resistance during cold forging.
It must be less than or equal to%.

Mn: 0.15 to 0.65% Mn has the effect of rendering S harmless as MnS and improving ductility, and it is necessary to contain at least 0.15% in order to exert the effect. Also, the effect of improving hardenability can be obtained at the same time. However, excessive addition exceeding 0.65% impairs cold forgeability. P: 0.10% or less Since P is an element that enhances the deformation resistance during cold forging,
It was limited to 0.10% or less.

S: 0.10% or less Since S is an element that reduces the deformability during cold forging,
It was limited to 0.10% or less. Cr: 0.50% or less Cr is an element that has the effect of improving hardenability, but if added in excess, the deformation resistance during cold forging increases and the tool life decreases, so it is 0.50% or less. did.

Mo: 0.05 to 0.40% Mo is an element having the effect of improving hardenability, but if added in excess, the deformation resistance during cold forging increases and the tool life decreases. , Its content is 0.05-0.40
The range is%.

Ni: 0.05 to 0.40% Ni is an element that improves the hardenability without increasing the deformation resistance as much as Si, Mn, and Cr, and the addition of Si is limited to reduce the deformation resistance. It is added to complement the deterioration of hardenability due to lack of Mn and Cr. It is also an element that also has the effect of improving notch toughness. The effect of addition is obtained from 0.05%, but the addition of more than 0.40% is not preferable because it increases the deformation resistance and increases the cost.

B: 0.0005 to 0.0035% B is for compensating for the hardenability deterioration due to the deficiency of Si, Mn, Cr, Mo, etc. whose addition amount is limited in order to reduce the deformation resistance during cold forging. Added to. Addition effect is 0.0005%
However, if it exceeds 0.0035%, the effect is saturated.

Ti: 0.01 to 0.10% Ti fixes N to prevent the formation of BN and exerts the effect of improving hardenability of B. The effect is exhibited from 0.01%, but the addition exceeding 0.10% is not preferable because it causes a decrease in deformability due to the generation of inclusions.
The present invention comprises the above elements as basic components and the balance iron and unavoidable impurities.
b, V, Pb, Te, Bi, Ca, etc. may be added.
The contents when these elements are added are as follows.

Cu: 0.05 to 0.40% As described above, Cu is an element effective for improving the grindability after quenching.
It is necessary to add more than 05%. However, 0.40
If added in excess of%, cracking may occur during slabbing and should be avoided.

Nb: 0.01 to 0.10% and / or V: 0.01 to 0.10% Nb and V are both effective elements for crystal refining, and in order to exert their effect. 0.01 alone or total
% Or more must be added. However, if the added amount exceeds 0.10%, the effect is saturated.

Pb: 0.01 to 0.20%, Te: 0.
01 to 0.10%, Bi: 0.01 to 0.10%, and Ca: 0.0005 to 0.0050%, one or more selected from the group consisting of Pb, Te, Bi, and Ca. Although it is a property improving element, it is also an element that reduces the deformability during cold forging, so the addition range is set as described above in consideration of both machinability improvement and deformability reduction.

The present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the present invention, and any modification of the present invention can be made without departing from the spirit of the preceding and following paragraphs. It is included in the technical scope.

[0018]

Example A test material having the chemical composition shown in Table 1 was melted in a small melting furnace (150 kg / charge), a dummy billet was prepared, and rolled into a steel bar having a diameter of 25 mm. Then, in order to investigate the cold forgeability, a spheroidizing annealing treatment (730 ° C. ×
[Holding] for 4 hours → gradual cooling to 680 ° C. at 10 ° C./hour and then cooling was performed, and a compression test piece (diameter: 20 mm × length: 30 mm) was produced by machining.

[0019]

[Table 1]

A constrained compression test was conducted using a 300 ton press using the above compression test piece. At this time, the test piece with a height of 30 mm was constrained and compressed to a height of 12 mm (compression processing rate: 60
%) Processed and examined for deformation resistance. The results are shown in Table 2.

As for the examination of hardenability, a cylindrical test piece having a diameter of 20 mm and a length of 70 mm was prepared by machining, and induction hardening treatment was performed. The processing condition is 8
Using a high frequency oscillator of 0 KHz (output; 150 Kw),
It was moved (12 mm / sec) in the coil on the ring, rapidly heated, and then rapidly cooled with an aqueous solution of a water-soluble quenching agent. The central portion of this test piece was cut, the cross-sectional hardness was measured, and the outermost surface hardness, the effective hardened layer depth (distance from the outermost surface to Hv = 500) and the austenite grain size were investigated. The results are also shown in Table 2.

[0022]

[Table 2]

As a test for confirming the effect of improving notch toughness with or without addition of Ni, No. 1 as a Ni-added steel and No. 13 as a comparative steel among the test materials shown in Table 1 were taken,
Diameter: 25m steel bar (850 ℃ × 30min, OQ)
→ After quenching and tempering under the condition of (500 ° C. × 120 min, WQ), a JIS No. 3 V notch Charpy impact test piece was prepared by machining, and an impact test was performed at room temperature, 0 ° C., and -25 ° C. humidity. The results are shown in Table 3.

[0024]

[Table 3]

Next, as a confirmation test of the effect of improving the grindability by Cu, as the Cu-added steel among the test materials shown in Table 1,
No. 4, No. 19, No. 1 as a Cu-free steel was taken, diameter: 105 mm steel bar was rolled, and a test piece with a diameter: 100 mm x length: 215 mm was prepared, then induction hardening and tempering treatment was performed, and grinding was performed. The test was conducted. The grinding conditions are as follows. Then, the grindability was evaluated by the number of grindings up to that point, when the life of the grindstone was defined as when the finished surface became defective due to crushing or clogging during grinding. The results are shown in Table 4.

(Grinding test conditions) Grinding material: induction hardening and tempering material (diameter: 100 mm x length: 215 mm) Grinding stone: WA (alumina type) Grinding wheel rotation speed: 1500 rpm Complex material rotation speed: 100 rpm Traverse speed: 540 mm / min Depth of cut: 5 μm Cutting allowance: 300 μm Cutting oil: Pinolol

[0027]

[Table 4]

From the above results, the following can be considered. Specimen No. 1 (inventive steel) and the sample material No. Comparing 2 (comparative steel), the test material No. In No. 2, C is too low, the outermost surface hardness is low, and the effective hardened layer depth is shallow. On the other hand, sample material No. 3 shows a case where C is too high, but it is understood that the deformation resistance is significantly higher than that of sample material No. 1.

Specimen No. No. 4 is a steel of the present invention showing an example of Cu addition. Although the deformation resistance, the effective hardened layer depth, and the surface hardness are almost the same as those of No. 1, it is understood that the grindability is excellent as shown in Table 4.

Specimen No. No. 5 is a comparative steel in which Si is too high, but has a deformation resistance of the test material No. It can be seen that it is too high as compared with No. 1 steel of the present invention. Also, the test material No. No. 6 is a comparative steel in which the Mn content is too low, the outermost surface hardness is low, and the effective hardened layer depth is shallow. Further, the test material No. 7 is Mn
Although the content of comparative steel is too high, the deformation resistance is
o. It can be seen that it is significantly higher than that of No. 1 steel of the present invention.

Specimen No. No. 8 is a comparative steel containing an excessive amount of P, but it can be seen that the deformation resistance is higher than that of the steel of the present invention. Also, the test material No. No. 9 is a comparative steel in which S is excessively contained, and the deformation resistance is almost the same as that of the present invention, but the crack occurrence rate in the constrained compression test is No. It is inferior to 1.

Specimen No. Although 10 is a comparative example in which Cr is excessively contained, the deformation resistance of the steel of the present invention is N.
o. It is much higher than the one. Specimen No. 11 is M
The o content is too low, the outermost surface hardness is low, and the effective hardened layer depth is shallow. On the other hand, the sample material No. No. 12 shows the case where the Mo content is too high, but the deformation resistance is No. Higher than 1.

Specimen No. In No. 13, the Ni content is too low, the outermost surface hardness is low, and the effective hardened layer depth is shallow. On the other hand, the sample material No. No. 14 shows the case where the Ni content is too high, but the deformation resistance is the test material No. Significantly higher than 1. Specimen No. No. 15 is the case where B is not added, but the outermost surface hardness is low because it is not baked, and the effective hardened layer depth is shallow. On the other hand, the test material No. No. 16 shows the case where the Ti content is too low, but the outermost surface hardness is low due to no quenching, and the effective hardened layer depth is shallow.

Specimen No. Nos. 17, 18, and 19 show the cases where fine elements such as Nb and V were added, respectively. The deformation resistance, the outermost surface hardness, and the effective hardened layer depth almost equal to 1 are shown. In particular, the austenite grain size has been further refined.

Specimen No. Nos. 20, 21, 22, and 23 are steels of the present invention to which machinability improving elements such as Pb, Te, Bi, and Ca are added, respectively. The deformation resistance, the outermost surface hardness, and the effective hardened layer depth almost equal to 1 are shown.

On the other hand, from the results of the Charpy impact test in Table 3, the steel of the present invention containing Ni shows a higher value at any test temperature than the comparative steel containing no Ni. Further, the grinding results in Table 4 show that the Cu-added steel exhibits excellent specific grindability as compared with the Cu-free steel.

[0037]

EFFECTS OF THE INVENTION The present invention is constructed as described above, and it is possible to realize a cold forging steel which can maintain a low deformation resistance during cold forging and is excellent in hardenability after forming. Further, such cold forging steel is most suitable as a material for power transmission components, such as constant velocity joint outer races and gears, which are induction hardened after cold forging.

Claims (4)

[Claims] 1. C: 0.30 to 0.60% (meaning weight%; the same applies hereinafter), Si: 0.10% or less, Mn: 0.1
5 to 0.65%, P: 0.10% or less, S: 0.10%
Below, Cr: 0.50% or less, Mo: 0.05 to 0.4
0%, Ni: 0.05 to 0.40%, B: 0.0005
Steel for cold forging, characterized in that each of the alloys contains 0.0035% to 0.0035% Ti: 0.01 to 0.10%, and the balance is iron and inevitable impurities. 2. The steel for cold forging according to claim 1, which further contains Cu: 0.05 to 0.40%. 3. The steel for cold forging according to claim 1, which further contains Nb: 0.01 to 0.10% and / or V: 0.01 to 0.10%. 4. Pb: 0.01 to 0.20%, T
e: 0.01 to 0.10%, Bi: 0.01 to 0.10.
% And Ca: One or more selected from the group consisting of 0.0005 to 0.0050%.
The steel for cold forging according to any one of to 3.