JPH0523775A - Manufacture of steel parts - Google Patents

Abstract

PURPOSE:To manufacture the steel parts whose wear resistance and fatigue strength are excellent by performing a carburizing treatment to a steel stock. and thereafter, forming a die lubricating film at a lower temperature than a carburizing treatment temperature, executing plastic working at a higher temperature than a quenching temperature, and quenching the stock. CONSTITUTION:After performing a surface hardening treatment to a steel stock, a plastic working lubricating film is formed on the surface of the steel stock at a lower temperature than the surface hardening treatment temperature. Subsequently, plastic working is executed by a plastic working die at a higher temperature than a quenching temperature, and thereafter, quenching is executed. In such a way, lubrication to the plastic working die becomes satisfactory enough and by preventing generation of uneven abrasion, a service life of the die can be extended. Also, a variance of dimensions caused by generation of uneven abrasion becomes small and the quality of steel parts can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical structure of parts such as various kinds of gears, various kinds of shafts, various kinds of retainers, etc., which are obtained by subjecting a steel material to a surface hardening treatment to improve wear resistance and fatigue strength. The present invention relates to a method for manufacturing a steel part used for manufacturing a steel part by plastic working.

[0002]

2. Description of the Related Art Conventionally, the above-mentioned various parts for machine structure are
It was often manufactured by cutting steel material, but in recent years it is also often manufactured by plastic working such as forging and rolling, and thermomechanical processing that combines plastic working and heat treatment. Many laws are being adopted.

Such a thermomechanical treatment method includes (1) a thermomechanical treatment method involving machining before transformation, depending on the time of machining.
It can be classified into three types, (2) a thermomechanical treatment method involving working during transformation and (3) a thermomechanical treatment method involving machining after transformation. There are forging quenching that involves plastic working at austenite temperature and quenching and ausforming that involves plastic working at metastable austenite temperature and then quenching. The work heat treatment during transformation in (2) above is pearlite. Alternatively, there are isoforming in which plastic working is applied and quenching is performed during bainite transformation, and sub-zero working is performed where plastic working is performed during martensite transformation. There are patenting for which plastic working is performed later and malform for which plastic working is performed on martensite.

Of these, the work heat treatment method before transformation (1) is useful as a treatment technique for significantly improving the strength and toughness of steel by improving hardenability and refining crystal grains and precipitates. It has become.

However, in such a thermomechanical treatment method,
Since there is a limit to the improvement of wear resistance and fatigue strength of the surface, surface hardening treatment is also performed.

FIG. 1C and FIG. 5 illustrate a manufacturing process of a steel part in which surface hardening treatment and thermomechanical treatment before transformation are combined. For example, after carburizing and then performing plastic working, for example, forging (for example, tooth profile forging), hold for the required time, and then quench, to manufacture steel parts with excellent wear resistance and fatigue strength by plastic working. It is something you do.

[0007]

However, in such a conventional method for manufacturing a steel part, since the forging (for example, tooth profile forging) is performed while maintaining the heating temperature in the carburizing step, Since the material is in a high temperature state throughout the entire process, it is not possible to form a lubrication film for the forging die on the surface of the steel material, and therefore the load on the forging die increases, which causes uneven wear on the forging die. However, there is a problem in that the life of the forging die is shortened due to the occurrence of defects and the dimensional accuracy of the steel parts may vary.

Although it is not unthinkable to directly spray the lubricant to the forging die inside the forging machine, the sprayed lubricant may be accumulated in the portion of the forging die, resulting in deterioration of processing accuracy. Therefore, there is a problem that there is a possibility that there is a possibility that there is a possibility that there is also a problem.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned conventional problems, and the lubrication of a plastic working die is sufficiently improved to prevent uneven wear, thereby extending the die life. It is an object of the present invention to provide a method for manufacturing a steel part, which is capable of improving the quality of the steel part by reducing unevenness in dimensions due to occurrence of uneven wear.

[0010]

A method of manufacturing a steel part according to the present invention is characterized in that after a surface hardening treatment is performed on a steel material, the surface of the steel material is plasticized at a temperature lower than the surface hardening treatment temperature. The invention relates to a method for producing such a steel part, which is characterized in that a work-type lubrication film is formed, the temperature is higher than the quenching temperature, and the work is performed by plastic working with a plastic working die, followed by quenching. The above configuration is used as means for solving the above-mentioned conventional problems.

In the method for manufacturing a steel part according to the present invention, as a steel material, carbon steel for machine structure established as JIS SC material, JIS SCr material, SCM material, S
A low alloy steel for machine structure, which is established as an NC material, an SNCM material, an SMn material, or the like, and those in which the component amounts are appropriately adjusted or added to these are used.

When the surface hardening treatment is performed on such a steel material, carburizing or carbonitriding treatment is adopted, but the present invention is not limited to these.

Next, a plastic working type lubricating film is formed on the steel material after the surface hardening treatment. At this time, if the temperature of the steel material is too high, it becomes difficult to form the lubricating film. When a graphite film is used as the lubricating film, the temperature of the steel material is set to about 150 to 200 ° C. to perform the graphite coating.

In this case, when the carburizing treatment is performed as the surface hardening treatment, after the carburizing treatment, the steel material is once cooled to room temperature or near room temperature, and then 150 to 20.
It may be reheated to 0 ° C and then coated with graphite, or 150 to 20
Graphite coating may be performed after cooling to 0 ° C.

In this forging-type lubricating film, not only graphite but also other W-based or Mo-based solid lubricants can be used.

In this way, after the plastic working type lubricating film is formed on the surface of the steel material which has been subjected to the surface hardening treatment, the temperature is made higher than the quenching temperature and then the plastic working type is used to perform the plastic working to a predetermined shape ( By forging, rolling, upsetting, etc.) and then quenching, steel parts with excellent wear resistance and fatigue strength are manufactured by plastic working.

FIGS. 1A and 2 show an embodiment of the present invention, which is 900 to 1 for a steel material.
After carburizing at about 050 ° C, cool it to room temperature and then heat it to 150-20
Graphite coating is performed at a temperature of about 0 ° C., then secondary heating is performed to bring the steel material to a temperature of about 900 to 1050 ° C., followed by forging, and then 800 to 900.
After holding at about ℃ for an appropriate time, quenching is performed, and if necessary, tempering is performed to make steel parts.

FIGS. 1B and 3 show another embodiment of the present invention.
150 ~ 200 after carburizing at 1050 ℃
After cooling to a temperature of about ℃, graphite coating is performed, the steel material is heated to a temperature of about 900 to 1050 ° C, forged, and then held at about 800 to 900 ° C for an appropriate time, and then quenched. Carry out tempering if necessary to make steel parts.

[0019]

The method of manufacturing a steel part according to the present invention has the above-mentioned structure. Therefore, a steel part having excellent wear resistance and fatigue strength can be obtained, and a lubricating action for a plastic working die can be obtained. As a result, it becomes sufficiently favorable to prevent uneven wear of the plastic working type and to extend the life, and the product quality is also improved.

[0020]

FIG. 4 shows an embodiment of the present invention, and shows an example in which a gear is manufactured by the steps shown in FIGS. 1B and 3.

In this embodiment, the steel material is JIS S
It is made of Cr420 steel, and as shown in FIG.
The steel material 1 is charged into the carburizing furnace 2 and subjected to carburizing treatment at 950 ° C. for 5 hours and then cooled in the cooling furnace 3, and then the graphite water tank 4
At 180 ° C., graphite coating is performed on the surface of the steel material 1 to form a mold lubrication film made of graphite, and then it is fed into the heating furnace 5 and heated to 950 ° C., and then tooth profile forging processing is performed by the forging machine 6. After making the gear-shaped component material 7, put it in the temperature holding tank 8 and 850
After maintaining the temperature at ℃, and then putting it in the quenching tank 9 for quenching, it was tempered at 170 ° C to obtain a steel part made of gears.

The steel parts (gear) thus obtained are
It is excellent in wear resistance and fatigue strength due to the use of surface-hardened steel material, and because the lubrication action with the forging die of the forging machine 6 is sufficiently good, it is biased to the forging die. It has become stable and highly accurate with no dimensions such as wear and other defects. In the conventional case, quality variation was about 3σ ± 0.1.
It was possible to keep it within the range of σ ± 0.05, and it was possible to improve the quality, and at the same time, it was possible to extend the mold life from about 2000 times to about 6000 times.

[0023]

In the method for manufacturing a steel part according to the present invention, after the surface hardening treatment is performed on the steel material, the surface of the steel material is subjected to plastic working type lubrication at a temperature lower than the surface hardening treatment temperature. Since the coating is formed, the temperature is higher than the quenching temperature, plastic working is performed by the plastic working die, and then quenching is performed, so it is excellent in wear resistance and fatigue strength by using the steel material that has undergone the surface hardening treatment. Steel parts can be manufactured, lubrication of the plastic working die is sufficiently good, and uneven wear can be prevented to extend the life of the die. The dimensional variation due to the occurrence of wear is remarkably reduced, which brings about an excellent effect that it is possible to further improve the quality of steel parts.

[Brief description of drawings]

FIG. 1 is a process explanatory view illustrating a method for manufacturing a steel part by carburizing forging and quenching according to the present invention ((A) and (B) in FIG. 1) and the related art ((C) in FIG. 1).

FIG. 2 is an explanatory view showing an embodiment of a method for manufacturing a steel part according to the present invention.

FIG. 3 is an explanatory view showing another embodiment of the method for manufacturing a steel part according to the present invention.

FIG. 4 is a schematic explanatory view of manufacturing equipment used for carrying out the method for manufacturing a steel component according to the present invention.

FIG. 5 is an explanatory view showing a conventional method for manufacturing a steel part.

[Explanation of symbols]

 1 Steel material 2 Carburizing furnace 3 Cooling furnace 4 Graphite water tank 5 Heating furnace 6 Forging machine 7 Parts material 8 Temperature holding tank 9 Quenching tank

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C23C 30/00 C 7217-4K

Claims (1)

Claims: 1. A steel material is subjected to a surface hardening treatment, and then a plastic working lubrication film is formed on the surface of the steel material at a temperature lower than the surface hardening treatment temperature, followed by quenching. A method for manufacturing a steel part, which comprises performing a plastic working with a plastic working die at a temperature higher than the temperature and then quenching.