JPS59232267A - Surface treatment of iron and steel material - Google Patents

Abstract

PURPOSE:To prevent the decrease in the hardness of an iron or steel base material right under a boriding layer by subjecting preliminarily the surface of the base material to a nitriding treatment when a concd. Si layer is formed at the boundary between the boriding layer and the base material in the stage of subjecting the surface of the base material to a boriding treatment. CONSTITUTION:The surface of an iron or steel material is nitrided by a gas nitriding, gas soft nitriding, salt bath soft nitriding or glow discharge method to form an Fe-N solid soln. layer and an Fe-N compd. layer having 5-30mu thickness. Said material is then dipped in a B-contg. molten salt bath or is treated by an electrolyzing, powder or gas method, by which the surface is borided. The boriding layer contg. boron and having excellent resistance to wear, seizure and molten Al is formed on the surface of the iron or steel member. The formation of a concd. Si layer right under the boriding layer and consequent decrease in the hardness of the iron or steel base material right under the boriding layer are obviated according to the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface treatment of steel materials, particularly to poron immersion treatment.

Ferrous boride (F) is applied to the surface of the steel material by applying poron treatment.
It is known that the wear resistance, seizure resistance, and molten aluminum resistance of steel materials can be improved by forming a boron-immersed layer such as eB, FexB).

However, the steel material has a high silicon (Sl) content, and when subjected to poron immersion treatment, silicon is enriched directly under the boron immersion layer due to the formation of an immersion poron layer, and a ferrite phase that is not hardened during quench hardening of the base material is generated. When a steel material is used in an application where a large stress is applied when a softened portion exists directly under the impregnated poron layer, problems such as settling and layer peeling occur during use, which shortens the life of the material.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a surface treatment method for forming a boron-immersed layer in which the hardness of the base material directly under the boron-immersed layer of a steel material containing silicon does not decrease.

Therefore, in contrast to the boron-immersion treatment, the present invention is advantageous in that the surface of the steel material that forms a silicon-concentrated layer at the boundary between the poron-immersion layer and the base material is nitrided in advance, and then the poron-immersion treatment is performed. This is to achieve the above objectives.

In the present invention, the nitriding treatment may be any method such as gas nitriding, gas soft nitriding, salt bath soft nitriding, glow discharge nitriding, etc. Processing conditions may be according to conventional methods, 450°C to 600°C.
, about 10 minutes to 2 hours. As for the structure to be formed, in addition to the Fe-N solid solution layer, it is desirable that an Fe-N compound layer with a thickness of about 5 μm to 30 μm is formed. When performing Poron dipping treatment after nitriding, the nitrogen in the material diffuses deep into the material during Poron dipping treatment, reducing the nitrogen on the surface of the material. It should be done in such a way that it will be high. In addition, the borax (borax) treatment applied to nitrided steel materials
The immersion method involves immersing the steel material in a molten bath of a substance containing poron (B) such as Na2B404), the electrolytic method involving electrolysis, and the embedding of the material in powder such as potassium borofluoride (K B F4 ). A powder method, a gas method performed in a gas atmosphere containing B, etc. may be used. The treatment temperature is approximately 600° C. or higher and lower than the melting point of the material, preferably approximately 800 to 1200° C. in practice. Processing time is 3
It is about 0 minutes to 5 hours.

The steel material in the present invention has a property of forming an 81 concentrated layer at the boundary between the boron-immersed layer and the base material if it is simply subjected to the poron-immersed treatment. Such steel materials include 5KD4.5KD5.5KD61.5KD62.5
UP6.5UP7, Si such as cast iron.

This applies to those with a content of 0.3 to 3%.

According to the present invention, by performing nitriding treatment in advance during the boron-immersion treatment, a boron-immersion layer containing nitrogen (N) and having excellent wear resistance, seizure resistance, and bath-melting aluminum resistance is formed on the surface of the steel material. In addition, even when the silicon content of the steel material is high, no ferrite phase is generated directly below the layer, and the hardness of the base material directly below the impregnated poron layer does not decrease.

Due to the presence of N, the boron-immersed layer formed according to the present invention has Fe2(B, N) or Fe(B,
N), Fe, (B, N) o layer, and this layer is different from the layer obtained by simply performing boron immersion treatment according to the conventional method.

Examples related to the present invention will be described below along with comparative examples.

Example 1 A specimen of J-5SKD61 (silicon content 1.0%) with a diameter of 20 mm and a thickness of 5 mm was subjected to tuftride treatment (soft crab treatment) to form a rat layer on the surface. The formed specimens were mixed with a bath of 11 FL and 1 O of ferromanganese.
%, 1000'C with addition of ferroaluminum IOX
The sample was immersed in a borax bath for 1 and 4 hours, then taken out and cooled in oil, and the adhering treatment agent was washed off with hot water.

After cutting the specimen, cross-sectional observation revealed that a coating layer of about 25 μm thick was formed on the nitrided specimen treated for 1 hour, and about 45 μm thick on the nitrided specimen treated for 4 hours. Note that a coating layer of the same thickness was also formed on each specimen that had not been nitrided.

As a result of X-ray microanalyzer analysis, it was confirmed that, for example, in a nitrided specimen treated for one hour, the coating layer was composed of Fe, B, and N, as shown in FIG.

Combined with the X-ray diffraction results, the coating layer is Fe2(B, N)
It was confirmed that this was a boron-soaked layer. Furthermore, N was also detected in the base material directly below the coating layer.

FIG. 2 shows the results of measuring the hardness of the base material directly under the coating layer on specimens treated for 4 hours, where line A is the nitrided specimen and line B is the unnitrided specimen.

As is known from the figure, when boron immersion treatment is applied to a specimen that has not been nitrided, the hardness of the base material directly under the coating layer is Hv 45.
However, in the case where the boron immersion treatment was applied to the sample which had been previously nitrided according to the present invention, the hardness of the base material directly under the layer was HV650, which was almost the same as that in the deep part of the base material.

Example 2 A specimen of J-5SKD5 (silicone content 0.4%) with a diameter of 15mm and a thickness of 5mm, a specimen on which a nitride layer was formed on the surface by ta-hydride treatment was prepared. Prepare 40 boron carbide (B4C) powder for the total amount of bath.
% in a borax bath at 1000°C, and after holding for 4 hours, it was taken out and cooled in oil.

When cross-sectional observation was performed in the same manner as in Example 1, it was found that a coating layer with a thickness of about 80 μm was formed in both the nitrided and non-nitrided specimens.

As a result of X-ray microanalyzer analysis, X-ray diffraction, and base material hardness measurements, the specimens that were not nitrided showed:
A strong immersed Poron layer between FeB, Fe, and B was confirmed, but a dark S5- layer was observed at the boundary between the immersed Poron layer and the steel base metal, indicating that a ferrite phase with low hardness was formed. was.

In the pre-nitrided sample of the present invention, the coating layer was a poron immersion layer, but N was present in the layer and it was similar to Fe (B, N) and Few (B, N). Furthermore, no ferrite phase was observed at the boundary between the impregnated boron layer and the matrix, and the hardness of the matrix below the layer surface was almost the same as the hardness inside, and was not reduced by the impregnated boron treatment.

As explained above, when a steel material according to the present invention is previously nitrided and then subjected to a boron-immersion treatment, the hardness of the base material immediately below the boron-immersion layer decreases if only the boron-immersion treatment is performed. Even in the case of steel materials, the hardness of the base material does not decrease, and a practically sufficient thickness of the boron-immersed layer is formed.

Therefore, the steel material treated according to the present invention has excellent wear resistance, seizure resistance, and molten aluminum resistance, and has S1
Even steel materials with a high content can be suitably used in applications where large stresses are applied.

[Brief explanation of the drawing]

Fig. 1 shows the results of Xi microanalyzer ``v'-analysis of a boron-soaked layer formed on a steel material by the method of the present invention, and Fig. 2 shows a material treated by the method of the present invention and a conventional method. It is a figure which shows the measurement result of the base material hardness of the straight F of the boron immersion layer.

Claims (1)

[Claims] The steel material that forms a silicon-enriched layer at the boundary between the poron layer and the base material is subjected to a nitriding treatment in advance and then subjected to a post-boron treatment to form a silicon-concentrated layer on the surface of the steel material. A method for surface treatment of steel materials, characterized by forming.