JPS592741B2 - Boronitriding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for heat treating steel coated with a solid borening agent under nitriding conditions.

BACKGROUND ART Nitriding has been widely used and achieved results as a surface treatment method for improving the wear resistance and corrosion resistance of various sliding members and solving the problems of galling and seizure.

However, when carbon steel and low alloy steel (excluding nitrided steel) are nitrided using the nitriding method, a hardened layer with high hardness cannot be obtained and the hardened layer is shallow, so the surface treatment effect by nitriding is not very effective. Ta.

Also, recently, a boronic treatment method has been implemented as a surface treatment. The borening treatment method has the advantage of being able to obtain a hardened layer with high hardness in a short time, but since it is treated at a high temperature above the As transformation point, the deformation of the material after the treatment, especially in long-axis parts, is significant. Deformation occurred and the internal hardness tended to decrease. For this reason, when direct quenching or reheating quenching is performed after the borening treatment to increase the internal hardness, the deformation of the material becomes even greater, making processing in subsequent steps difficult. In order to eliminate these drawbacks of nitriding and borening, the present invention provides a method for obtaining a sufficient hardening layer for carbon steel and low alloy steel (excluding nitriding steel) and minimizing bending of the material. The object of the present invention is to provide a surface treatment method. That is, the present invention provides carbon steel and low-alloy steel (excluding nitriding steel) by embedding carbon steel and low-alloy steel (excluding nitriding steel) in a solid boring agent and surface-treating the material under nitriding treatment conditions. This makes it possible to obtain a hardened layer with small deformation, high hardness, and sufficient depth even for steels such as steel (excluding steel).

The present invention will be explained below based on Examples.

FIG. 1 shows a cross-sectional structure of a gas nitriding furnace.

151 is a steel material to be surface treated, 2 is a solid borourant,
Boron carbide (B4C) is used as a boron supplying agent, and borax (Na) is used as a borizing accelerator.

B4O7) are mixed at a ratio of 8:2. 3 is a case for storing the steel material 1 embedded in solid borizing agent 2, 4 is a nitriding case that makes case 3 a 20 nitriding atmosphere, 5 is an ammonia gas inlet provided on one side of the nitriding case 4, and 6 is a nitriding case. An ammonia gas outlet is provided on one side of the case 4, T is a furnace that covers the entire nitriding case 4, and 8 is a heater that heats the inside of the furnace 7.

25 The steel material 1 covered with the solid boring agent 2 is heated to 500 to 500 ml by the heater 8 in a nitrogen atmosphere using ammonia gas.
By heating to 80°C and holding for 10 hours or more,
It has been found that nitrogen and boron diffuse into the surface of the steel material 1, forming highly hard nitrides and borides, and that a sufficient hardened layer with the required hardness can be obtained.

For material SCM3 material diameter 50φ length 1000mm (
1) In the case of gas nitriding treatment (processing conditions: 510°C, 50°C
(2) In the case of borosilication treatment (treatment 35 conditions:
900°C, 5 hours), (3) Boronitriding treatment (processing conditions: 510°C, 50°C using the equipment shown in Figure 1)
Regarding the time retention), FIG. 2 shows the relationship between the distance from the surface of the material and the hardness, and FIG. 3 shows the relationship between the distance from one end of the material and the amount of deformation thereof.

In FIG. 2, when comparing the hardness within a range of 0.31 mm from the surface of the material, the hardness is highest in the case of borening treatment, followed by boronitriding treatment and gas nitriding treatment. Although high hardness is desirable for wear resistance, on the other hand, heat treatment at high temperatures such as boring treatment causes large deformation of the material and also reduces the internal hardness of the material itself.

In the case of the boronitriding method of the present invention, although the temperature conditions and holding time are the same as those of the gas nitriding method, the temperature within 0.3 mm from the surface is approximately 300 H due to the difference in the borizing atmosphere.
It is as high as v.

FIG. 3 shows the amount of bending deformation of the SCM 3 after each surface treatment is completed.

(The amount of deformation refers to the maximum amount of change when the material is placed on a flat surface and rotated.) There is almost no deformation in the boronitriding and nitriding methods of the present invention, and in the case of the boronitriding method according to the present invention, A large deformation of up to 0.8 mm occurred. In this example, borax was used as a borons accelerator, but the time required for the boronitriding process can be shortened by appropriately adding carbonates, halides, etc. . As mentioned above, the boronitriding method does not increase the hardness as much as the boronic method, but it has the required stable hardness and the amount of deformation is small. Satisfactory results were also obtained for steels such as carbon steel or low alloy steel (excluding nitrided steel), which had previously been difficult to obtain.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a gas nitriding furnace. 1: Steel material, 2: Solid borourant, 3: Case, 4: Nitriding case, 5: Ammonia gas inlet, 6: Ammonia gas outlet, 7: Furnace, 8: Heater.

Claims (1)

[Claims] 1. Place carbon steel or low alloy steel (excluding nitrogen steel) embedded in a solid boring agent in a gas nitriding furnace, and heat the furnace in a nitrogen atmosphere at a temperature of 500 to 580°C for 10 hours or more. A boronitriding method characterized by air cooling after holding.