JPS62139845A - Cold forged product - Google Patents

Abstract

PURPOSE:To reduce the deformation resistance of a cold forged product by cold forging stock contg. reduced amounts of elements which affect work hardening and specified amounts of elements which do not affect work hardness and improve hardenability so that the stock undergoes a small extent of work hardening. CONSTITUTION:The amounts of elements which affect work hardening is stock are reduce. For example, the amounts of C, Si and Mn are reduced to <=0.58% C, <=0.15%, especially <=0.1% Si and <=0.6% Mn. Elemenets which do not affect work hardness and improve hardenability are added to the stock so as to reduce the work hardenability. For example, one or more among >=0.1% Cr, >=0.15% Mo and >=0.001% B are added. The resulting stock is cold forged to obtain a cold forged product.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention relates to cold forged products used as mechanical structural parts for automobiles, electrical equipment, construction machinery, 1m industrial machinery, etc. be.

(Conventional technology) Previously, Complete Book of Automotive Engineering Volume 19a "Automobile Manufacturing Method"
(Published by Sankaido Co., Ltd. on April 20, 1981), as described in Item 2.8 Cold Forging (P49), the use of cold forged products for automobile parts is expanding. Such cold forged products include various products such as constant velocity forgings, drive shafts, gears, cams, retainers, sockets, housings, stays, and bushings.

This type of cold forged product is generally manufactured using a hydraulic or mechanical cold forging press, and requires a long life of the mold (tool).

For example, many drive shafts are formed by cold forging, and the cost of molds (tools) accounts for a high proportion of the cost of cold forged products. In particular, the rear extrusion punch that roughly forms the pole transfer surface of the drive shaft is in the most severe condition in terms of blood pressure, so it is desirable that the deformation resistance of the material be as small as possible.

Conventionally, this type of drive shaft material has been carbon steel (348C, 553C, etc.) and case hardened steel (S0M420H).
, SCr420H, etc.) have been used.

(Problems to be Solved by the Invention) However, when using such conventional materials, carbon steels such as 548C and 553C have to ensure surface hardness during induction hardening and also have carbon toughness. In order to ensure transfer fatigue strength in steel, it is not possible to reduce the carbon content, so even steel that has been spheroidized and annealed has considerable deformation resistance. There is a problem that the life is short, and furthermore, there is a problem that it is difficult to obtain a cold forged product with a large degree of processing or a complicated shape. In conventional steel, even if the amount of N2.02 is reduced by degassing etc. to improve workability, the load during processing is unlikely to be lower than the surface pressure strength of the cold forging die. It has been difficult to extend the life of the mold due to such impurity regulations.

This invention was made by focusing on the above-mentioned conventional problems, and it is possible to produce cold forging with less wear and tear on the mold during cold forging, and with which it is possible to obtain products with a large degree of processing or complex shapes. The purpose is to provide products.

[Structure of the Invention] (Means for Solving the Problems) The cold forged product according to the present invention reduces the content of elements that affect work hardening, and improves hardenability without affecting work hardening. It is characterized by being cold forged using a material with a small amount of work hardening that contains elements that cause

That is, in order to ensure the strength and toughness of the product, the cold forged product according to the present invention has a C content that is equal to or higher than that of conventional carbon steel or case hardened steel, and is an element that affects work hardening. For example, Cr is an element that reduces the content of Si and Mn compared to conventional carbon steel and case hardening steel, and improves hardenability without affecting work hardening.

It is made by cold forging using a material with a small amount of work hardening that contains appropriate amounts of Mo and B. It can significantly extend the life of cold forging dies, and can also be used to manufacture products with complex shapes. This makes it possible to improve dimensional accuracy.

A more preferable composition of the cold forged product according to the present invention is:
In weight%, C: 0.45-9.58%, Si: O, 15
%, Mn: 0, less than 60%, and Cr:
0.10-0.80%, MO: 0.15-0.30
%, B:O, OOl - 0.003%, and the remainder consists of Fe and inevitable impurities.

In cold forged products with such components, C is an element necessary to ensure the strength and toughness of the cold forged products and to improve wear resistance, and for this purpose, 0.45 %
It is more desirable to contain more than 0.5.
It is more desirable to keep it at 8% or less. Also, Si is an element that acts as a deoxidizing agent during steel melting, but it is an element that affects work hardening and reduces cold forgeability due to work hardening. Therefore, it is particularly desirable to reduce the Si content as much as possible by obtaining a substitute effect for Si with other additive components or by melting using a melting method that can reduce the oxygen content. More preferably, it is less than 0.10%.
n is an element that acts as a deoxidizing and desulfurizing agent during melting, but like St, this is also an element that affects work hardening and reduces cold forgeability due to work hardening. It is desirable to suppress the Mn content to the minimum necessary amount, such as by obtaining a substitutive effect for Mn by using an additive component or by melting means that can reduce the oxygen and sulfur content, and more preferably less than 0.60%. 40
Furthermore, Cr.

Mo and B are elements that have little effect on work hardening and are effective for improving hardenability, and are effective elements for compensating for the decrease in hardenability caused by reducing the St and Mn contents. . In order to obtain such an effect, Cr
is 0.10% or more, Mo is 0.15% or more, B is 0.0
It is particularly desirable to add one or more of these in an amount of 0.1% or more. However, adding a large amount will reduce toughness and workability, so Cr is 0.8% or more.
It is particularly desirable that MO be 0.30% or less, and B be 0.003% or less.

Note that if B is added instead of Cr, it is possible to further reduce the deformation resistance, but if the spheroidized annealed structure remains, the hardenability of B will decrease, so it is not recommended to add the standard process last. In addition, it is more desirable to limit S to 0.030% or less in order to improve the amount of processing, and it is also more desirable to limit P to 0.030% or less.

Cold forged products made from such steel have a significantly lower amount of work hardening of the material, and the deformation resistance during cold forging is much lower than conventional ones, so there is less wear and tear on the cold forging dies (tools). It is possible to significantly reduce the amount of heat and extend the life of the product, and it is also possible to produce a cold forged product with a large degree of processing or a complex shape, and even with high dimensional accuracy.

(Example 1) Using steel with the components shown in Table 1 as a material, test steel N of the present invention example
o, 1 (Hardness before molding HBD5.20-5.25)
With a forming load of 800 to 840 tons, and comparative example test steel No. 2 (hardness before forming HBD 4.60
~5.10) were each cold forged with a forming load of 860 to 900 tons, and at this time, the drive shafts were manufactured by forming in the order of forward extrusion → upsetting → backward extrusion.

Table 1 As a result, the life of the cold forging die was the fiNo.

In the conventional case using No. 2, the limit was about 15,000 shots, while in the case of the present invention example using test steel No. We have not confirmed any wear and tear that would have an impact.

(Example 2) Using steels (No. 3, No. 4) with the composition shown in Table 2 as raw materials, we investigated the change in deformation resistance depending on the amount of cold forging after spheroidizing annealing. The results shown in the figure were obtained.

As shown in Figure 1 of Table 2, 1□2, in the case of No. 3 according to the present invention, the deformation of the cold forged product during cold forging was greater than in the comparative cases of No. 4. It is clear that the increase in resistance is much smaller. When the amount of Cr was reduced by adding B in place of Cr in an amount that would maintain the same hardenability, the deformation resistance was further reduced and even better results were obtained.

C Effect of the Invention] As explained above, the cold forged product according to the present invention reduces the content of elements that affect work hardening, and also contains elements that do not affect work hardening and improve hardenability. Because it is made by cold forging using a material with a small amount of work hardening, the work hardness during cold forging is extremely low, and the deformation resistance of the cold forged product can be made small. , it is possible to significantly extend the life of cold forging molds (tools), and it is a remarkable achievement that it is possible to produce cold forged products with complex shapes, high dimensional accuracy, and low cost. In addition, the added amount of elements that affect work hardening such as Si and Mn is reduced compared to the conventional case, and the resulting decrease in hardenability is reduced to affect work hardening of Cr and other elements. By adjusting the hardenability by adding hardenability-improving elements that do not affect the hardenability of the steel, it is possible to keep the hardenability constant, making it easier to manage the manufacturing process. Excellent effects can also be obtained.

[Brief explanation of drawings]

FIG. 1 is a graph showing an example of the results of investigating changes in deformation resistance depending on the amount of cold plastic working.

Claims (1)

[Claims] (1) Cold forged using a material with a small amount of work hardening that reduces the content of elements that affect work hardening and also contains elements that do not affect work hardening and improve hardenability. A cold forged product characterized by: