JPH10102229A - Method for carburizing cylindrical steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form mild gradient carburized layers on the surfaces of the outer periphery and inner periphery of a steel. SOLUTION: A circular tube 4 hard to be subjected to carburization is set to the inside of a vessel 1, furthermore, a cylindrical steel 5 easy to be subjected to carburization compared to the circular tube 4 is arranged at the inside of the circular tube 4, moreover, at the cylinder inside and outer curcumferential side of the cylindrical steel 5 in the circular tube 4, carburizing agents 6 and 7 with different carburizing properties are housed dividedly into two layers above and below, furthermore, a carburizing agent for preventing decarburization is housed in the container on the outer peripheral side of the circular tube 4, and the container 1 is sealed up, which is heated in a furnace and is thereafter quenched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for carburizing a cylindrical steel material by carburizing a high alloy steel such as stainless steel using a solid carburizing method.

[0002]

2. Description of the Related Art Conventionally, a solid carburizing method called box carburizing and a gas carburizing method using CO as a carbon source have been used to harden a steel material surface. Among them, in the solid carburizing method, charcoal, coke, bone charcoal and the like stored in a container are used together with an accelerator and a diluent (coke or the like) added as necessary, instead of the gas containing CO used in the gas carburizing method. .

In addition, barium carbonate, sodium carbonate, or the like is used as the accelerator as a mixture with the carburizing agent, and the solid carburizing treatment is performed in an atmosphere at a high temperature of 830 to 950 ° C. or higher. The carburizing depth increases with the rise. The carburized part obtained by the carburizing treatment is subjected to forging annealing to be machine-finished.

In addition, the gas carburizing method has advantages that the carburizing concentration can be easily adjusted, carburizing can be performed uniformly, and direct quenching can be easily performed from the carburized state, as compared with the solid carburizing method.

On the other hand, even in high alloy steel such as stainless steel,
A method of obtaining a sufficiently thick carburized layer by the plasma carburizing (ion carburizing) method is described in the document "Plasma carburizing and its application", Masatomo Nakamura, Special Issue of Metals, '89 / 4, 198
9, p. 48-54.

[0006]

However, in the gas carburizing method, there is a problem that carburizing of high alloy steel such as stainless steel is difficult, and a sufficient carburized hardened layer cannot be obtained.

Further, in the above-mentioned plasma carburizing method, it is necessary to devise a masking jig to perform inclined carburizing, and it is particularly difficult to carburize the inner circumference of a long cylindrical steel material. However, there is a problem that a carburized hardened layer can be obtained at the inner periphery at the end, but a carburized hardened layer cannot be obtained at the inner periphery near the center.

The present invention has been made to solve the above-mentioned problem, and a carburizing agent of a different carburizing property is divided into two layers and brought into contact with a portion to be carburized of the steel material, so that the outer and inner peripheries of the steel material are separated. It is an object of the present invention to provide a method for carburizing a cylindrical steel material capable of forming a moderately inclined carburized layer on the surface of a steel sheet with a sufficient thickness.

[0009]

In order to achieve the above object, a method for carburizing a cylindrical steel material according to the first aspect of the present invention comprises disposing a hardly carburizing circular pipe in a container and placing the pipe in the circular pipe. A cylindrical steel material which is more easily carburized, and further, a carburizing agent having different carburizability is accommodated in the upper and lower layers of the cylindrical steel material in the cylinder and on the outer peripheral side thereof. A carburizing agent for preventing decarburization is accommodated in the container on the side, and the container is sealed, and then heated in a furnace and then quenched.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual view showing a method for carburizing a cylindrical steel material according to the present invention. In FIG. 1, reference numeral 1 denotes a closed state in an internal space 3 when an opening / closing lid 2 is attached to an upper opening so as to be openable and closable. Container.

In the container 1, a hardly carburizing circular tube 4 is first arranged so that the upper end is opened, and the lower end of the container 1 is brought into contact with the container bottom 1a. Then, a cylindrical steel material 5 which is a steel material such as stainless steel to be carburized is disposed near the center of the circular pipe 4. The cylindrical steel material 5 is made of a steel material that is easily carburized (has a high carburizing property) with respect to the circular pipe 4.
That is, the cylinder 4 is made of a material that is more difficult to carburize than the cylindrical steel material 5.

Subsequently, different types (carburizing) of carburizing agents 6 and 7 are accommodated in the upper and lower outer layers of the cylindrical steel material 5 in the circular pipe 4 inside and outside the cylinder. Here, as the carburizing agent 6 on the upper layer side, activated carbon as a weak carburizing agent or a mixture of a smaller amount of an accelerator than the carburizing agent 7 is used.
As the lower layer carburizing agent 7, a mixture of activated carbon and an accelerator is used.

Next, in the container 1 on the outer peripheral side of the circular pipe 4, a carburizing agent 8 for preventing decarburization as charcoal or a carburizing agent having low carburizing property is accommodated, and the container 1 is covered with an opening / closing lid 2. After sealing the inside, this is heated in a furnace, and after this heating, the cylindrical steel material 5 is taken out and quenched and tempered.

Here, the carburizing conditions are set to, for example, 9
6 hours at 80 ° C, quenching immediately after carburizing protection (air cooling)
After the carburizing, tempering is performed twice at 520 ° C. for 1.5 hours.

Therefore, SUS420J2 (outer peripheral portion, inner peripheral portion), low carbon SKD11 similar steel (outer peripheral portion), SUS31
FIG. 2 shows the carbon concentration distribution of each steel material 6 (outer peripheral portion) measured at a depth of 0.1 mm from the carburized surface by the carburizing process. FIG. 2 shows carburizing agent 6
FIG. 4 is a graph showing a carbon concentration distribution centered on the boundary between the carburizing agent 7 and the carburizing agent 7, and a gentle gradient carburizing is performed in a range of about 20 to 30 mm from the boundary to the side of the carburizing agent 6 with weak carburization. It could be confirmed.

FIG. 3 shows a carburized layer hardness distribution. According to this, in SUS420J2, a Vickers hardness of up to about 750 is obtained at a depth of about 500 microns from the carburized surface, while an SUS316 air-cooled material has a hardness of about 50 microns from the carburized surface. Hardness up to about 450 has been obtained. That is, a sufficiently hardened surface hardened layer is obtained by carburization.

Therefore, according to the method for carburizing a cylindrical steel material according to the present invention, the toughness at the carburizing boundary is improved as compared with the conventional case, and the breakage at that portion can be reduced. Therefore, this carburizing method is suitable for the production of parts such as punched parts which require abrasion resistance and toughness even if the contact resistance of the hardened part is slightly lowered.

[0018]

As described above, according to the first aspect of the present invention, a hardly carburizing circular pipe is provided in a container, and a more easily carburizing cylindrical steel material is disposed in the circular pipe. A carburizing agent having a different carburizing property is accommodated in the upper and lower layers of the cylindrical steel material inside the circular pipe on the inner and outer peripheral sides thereof, and a carburizing agent for preventing decarburization is further contained in the container on the outer peripheral side of the circular pipe. Contain
Since the container was sealed and then quenched after heating in the furnace, the carburizing agent of a different type of carburizing property was divided into two layers and brought into contact with the carburizing scheduled portion of the steel material, so that the steel material was contacted. In addition to forming a gentle inclined carburized layer with sufficient thickness on the outer and inner surfaces of the steel, the toughness at the carburized boundary can be improved, and the effect that breakage at a part of this can be avoided beforehand is obtained. .

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a method for carburizing a cylindrical steel material according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a carbon concentration distribution of a cylindrical steel material by a method of carburizing a cylindrical steel material according to the present invention.

FIG. 3 is a characteristic diagram showing a hardness distribution of a carburized layer of a cylindrical steel material according to the method for carburizing a cylindrical steel material of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Container 4 Circular pipe 5 Cylindrical steel material 6, 7 Carburizing agent

Claims (1)

[Claims] 1. A hardly carburizing circular pipe is installed in a container, and a more easily carburizable cylindrical steel material is arranged in the circular pipe. In the upper and lower layers, carburizing agents having different carburizing properties are accommodated, and further, a carburizing agent for preventing decarburization is accommodated in the container on the outer peripheral side of the circular pipe, and the container is sealed. A method for carburizing a cylindrical steel material, wherein the method is followed by quenching after heating.