JPS60135519A - Production of blank material for cold forging - Google Patents

Abstract

PURPOSE:To produce a blank material for cold forging which has good spheroidized structure, decreased hardness and good moldability by subjecting successively the blank steel material to warm forging, cooling, reheating, holding at a constant temp. and slow cooling under specific conditions. CONSTITUTION:A carbon steel represented by JIS S48C is used as a steel material. The billet of such steel material is heated up to the surface temp. between the Ac1 transformation (720 deg.C) and Ac2 transformation (770 deg.C) and is subjected to warm forging, thereby forming a blank material for a joint outer. Such blank material is air cooled to about 400-600 deg.C below the Ar1 transformation temp. and is reheated to the temp. range (about 720-735 deg.C) higher by about 15 deg.C than said temp. from the Ac1 transformation point, by which the fine carbide is solutionized. The blank material is further held at a constant temp. for about 30- 60min within said temp. range and is slowly cooled down to the Ar1 transformation temp. or below at a cooling rate of about 8-10 deg.C/hr to accelerate the spheroidization of the carbide and to form the coarser grains of the carbide.

Description

[Detailed description of the invention] The present invention relates to a method of manufacturing a material for cold forging.

Conventionally, when manufacturing a constant velocity joint outer for an automobile, for example, a material for cold forging is obtained from a steel material by warm forging, and then the material is subjected to final forming by cold forging to obtain a joint outer. In the above-mentioned warm forging, the temperature of the steel material is At
Y, Ac, transformation is carried out at a temperature within the temperature range of, for example, 750°C, and then slowly cooled or kept at a constant temperature of about 650°C for spheroidizing annealing, so the material has a spheroidal structure. However, since the carbide is too fine, the hardness is high (as a result, the die is subject to severe wear in the next cold forging process, resulting in a short life span).

In view of the above, an object of the present invention is to provide a manufacturing method that includes a heat treatment step capable of spheroidizing the structure of the material and reducing the hardness of the material, and in which the temperature of the steel material is between Ac and A.
In the second step, warm forging is performed in a temperature range for C3 transformation to form a material for cold forging;
, cooling the material to below the transformation temperature;
Reheating from the transformation temperature to a temperature range approximately 15°C higher than that temperature and maintaining the temperature constant in that temperature range for a predetermined time; and slowly cooling the material. .

An example in which the present invention is applied to the production of a joint outer material in a constant velocity joint will be described below.
The drawing shows the lunar temperature changes in each J] degree.
As the steel material, carbon steel specified by JIS 548C is used.

First, a billet made of carbon steel is heated to a temperature (e.g., 750°C) whose surface temperature is Ac and between the transformation (720°C) and the Aca transformation (770°C) (line a in the figure).
).

The billet heated to the above temperature is warm-forged to form the outer material (line h in the figure).

2. The material is Ar, and is air-cooled to 400 to 600°C below the transformation temperature (line C in the figure).

After air cooling, the above material is heated to Ac, 720 to 735 from the transformation temperature.
The sample is reheated to a temperature range of 0.degree. C. to dissolve fine carbides (line d in the figure).

The material is kept at a constant temperature in the above temperature range for 30 to 60 minutes (line e) in the figure, and then gradually cooled to below the transformation temperature at a cooling rate of 8 to b to promote the spheroidization of carbides and reduce the coarseness of the carbides. (line f in the figure)
).

By maintaining the above constant temperature and subsequent slow cooling operation, the spheroidized carbide is made into an appropriate size and the area of the ferrite part is expanded (
This can improve formability in cold forging. In addition, since the reheating temperature is low (・, the depth of the decarburized layer is several 10
It is possible to suppress it to tr.

The hardness of the material obtained through the above steps is HRB 77~
83, and in the case of the conventional method, the I'lRB was 85 to 9o for the same carbon steel, so it is clear that the hardness is significantly reduced.

When a joint outer was formed by cold forging the above material, it was confirmed that the forming load was small, there was little wear and tear on the mold, and there was no cracking or forging cracking in the joint outer.

As mentioned above, by using warm forging in combination, the reheating temperature can be lowered, and the time required for constant temperature maintenance and subsequent slow cooling can be shortened, making it possible to shorten the length of the annealing furnace and make it more compact. It becomes possible to improve production efficiency by combining the annealing furnace in series with a warm forging machine.

As described above, according to the present invention, it is possible to obtain a material for cold forging that has a spheroidized structure and reduced hardness and has good formability, thereby eliminating problems such as wear and tear on the mold. I can do it. In addition, production efficiency can be improved because warm forging, reheating, constant temperature holding, and subsequent spheroidizing annealing by slow cooling are performed in a series. Furthermore, since reheating to maintain a constant temperature is carried out once the material is below the Ar transformation temperature, it is possible to use the residual heat after warm forging for reheating, which is effective in saving energy. It is.

[Brief explanation of drawings]

The drawing is a graph showing the relationship between material temperature and time in each process. −6=

Claims (1)

[Claims] a step of performing warm forging to form a material for cold forging in a state where the temperature of the steel material is in the temperature range of A c + and A c + transformation; a step of cooling the material to below the Ar transformation temperature; For cold forging, the method comprises: reheating the material from the AC1 transformation temperature to a temperature range approximately 15° C. higher than that temperature and maintaining the temperature constant in that temperature range for a predetermined time; slowly cooling the material; How the material is manufactured.