JPS622628B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface hardening treatment method for forming a carbonitride layer, particularly a carbonitride layer of Group Va elements, on the surface of an iron alloy material. The purpose of this is to form a carbonitride layer on the carbonitride layer.

The inventors first treated an iron alloy material containing 0.2% by weight or more of carbon with a molten salt bath, powder, gas, etc. containing Group Va elements of the periodic table to form a group Va element on the surface of the iron alloy material. We have developed a surface hardening treatment method that forms a carbide layer of group elements, and this method is widely used to extend the life of tools and molds.

In this method, group Va elements such as vanadium, niobium, or tantalum supplied from the outside and carbon in the iron alloy material are bonded together by thermal diffusion to form a carbide layer of group Va elements. One problem is that the amount of carbon in the base material directly under the carbide layer is consumed and reduced to form the carbide layer, and when the base material is subsequently quenched and hardened, the hardness of the part directly under the layer becomes smaller than that inside the base material. This means that there is a tendency for the value to decrease. For this reason, if a material surface-treated by the above method is used in applications where a large stress is applied, the portion immediately below the layer may deform, causing cracks in the layer or peeling of the layer. Also,
If the iron alloy material to be treated is a bar with a diameter of 1 mm or less, or if it is thin like the edge of a sharp knife, surface treatment will reduce the carbon content of the entire material.
It will be difficult to bake the entire material.

On the other hand, it has recently become known that a layer made of a nitrogen-containing carbide, ie, a carbonitride, has higher toughness than a carbide layer, and there is a tendency for a carbide coating to be used instead of a carbide coating. A gas method using titanium tetrachloride or the like is currently used as a method for carbonitride coating, but this requires measures for work hygiene, is troublesome, and requires expensive equipment.

Therefore, the present invention further develops the previously developed method for forming a carbide layer to form a Va layer on the surface of an iron alloy material.
An effective method has been developed for forming a surface layer made of group element carbonitride and an inner layer made of an iron alloy containing nitrogen as a solid solution.

That is, in the surface hardening treatment method of the present invention, the surface of an iron alloy material is subjected to nitriding treatment, and the nitrided material is subjected to thermal diffusion treatment in a treatment agent containing a group Va element. By combining carbon and nitrogen through chemical affinity at the treatment temperature, a layer consisting of carbonitride of group Va elements and a layer consisting of an iron alloy containing nitrogen as a solid solution are formed on the surface of the treated material. It is.

As the iron alloy material, one containing at least 0.2% by weight of carbon is used. This is because in order to form a high-quality carbonitride layer, 0.2% by weight is required in the iron alloy material.
This is because the above amount of carbon needs to be contained. Even if the carbon content is 0.2% by weight or less, carburizing may be performed prior to nitriding, during or after nitriding to reduce the amount of carbon on the surface before carbonitride formation. It may be increased to 0.2% by weight or more.

The nitriding treatment may be performed using any method such as gas nitriding, gas soft nitriding, salt bath soft nitriding, glow discharge nitriding, or the like. It is desirable that the nitrogen concentration of the nitrided layer is high, and the depth of the nitrided layer is desirably deep. When carburizing is performed after nitriding, the nitrogen in the material diffuses deep into the material during carburizing, reducing the amount of nitrogen on the surface of the material. The carburizing treatment should be carried out in a short period of time.

Carbonitride layer formation treatment can be performed by molten salt immersion method, molten salt electrolysis method, powder pack method, slurry method, fluidized bath furnace method, etc. Combines carbon and nitrogen. The treatment temperature is about 600°C or higher and below the melting point of the material, and practically 800°C to 1200°C is desirable. Processing time is about 30 minutes to 24 hours. In the electrolytic method, a cathode current density of about 0.01 to 3 A/cm ² is appropriate.

When the treatment temperature is increased and the treatment time is increased, the surface layer formed becomes thicker, but as the layer thickness increases, it is observed that fine hole-like defects tend to occur in the layer.
Decreases pitting resistance and wear resistance. The critical thickness at which defects are significantly observed cannot be definitively stated as it depends on the type of Group Va element, nitriding conditions, type of iron alloy material, and carbonitride layer forming treatment conditions, but it is 10 μm.
If it is less than m, the above defect problem will hardly occur.

When the treatment of the present invention is performed, a coating layer made of Group Va carbonitride having excellent wear resistance and toughness is formed on the surface of the iron alloy material. In addition, in the process of the present invention, nitrogen is used together with carbon in the base material to form the layer.
This is done by combining with Va group elements, so
The time required to obtain a given layer thickness is shorter than in the case of carbide layer formation. Furthermore, in the present invention, since a layer made of an iron alloy containing nitrogen as a solid solution is formed directly below the carbonitride layer, sufficient quenching hardness can be obtained even in the portion directly below the surface layer. Therefore, even a thin material can be sufficiently quenched and hardened to the base material.

Experimental Example 1 A JIS SKD61 specimen with a diameter of 20 mm (untreated specimen) and a specimen subjected to salt bath nitriding treatment (nitrided specimen) were prepared. The above salt bath nitriding treatment has a bath composition of 73% (NaCH + KCN), 15% KCl, 12%
The test was carried out under the condition of immersion in a Na ₂ CO ₃ salt bath at 560° C. for 2 hours. Note that in this example and the following examples, % is % by weight. Next, these specimens were immersed in a 1000°C molten borax bath containing 20% vanadium oxide (V ₂ O ₅ ) and 10% boron carbide (B ₄ C) for 30 minutes to 16 hours, and then taken out and cooled in oil. did. After washing off the adhering bath agent, the cross section was polished and the thickness of the layer formed on the surface was measured. The 8 μm and 6 μm thick layers were tested for 8 hours and 4 hours, respectively, on the nitrided specimens.
16 hours each in the untreated specimen.
It took twice as long, 8 hours. The hardness distribution measurement results of the cross section of the base material are shown in Figure 1.
In the untreated specimen shown in line B, a decrease in hardness was observed immediately below the formation layer (vanadium carbide layer), but in the nitrided specimen shown in line A, almost no such decrease in hardness was observed. Ta.

In addition, in the case of the nitrided specimen (borax bath treatment for 1 hour), cross-sectional X-ray microanalyzer analysis revealed C and N along with V in the layer as shown in Figure 2, which was determined by X-ray diffraction. The layer formed from the lattice constant was confirmed to be a carbonitride layer of vanadium, denoted V(C,N). The amount of nitrogen is 10
% has been reached. Further, a layer made of an iron alloy containing nitrogen as a solid solution was formed immediately below the carbonitride layer, and this corresponded to the portion where the hardness did not decrease as indicated by line A in FIG.

Experimental Example 2 S45C specimens with a diameter of 7 mm were ion-nitrided at 550°C for 3 hours in an atmosphere with a gas composition of H ₂ :N ₂ = 2:1 and a pressure of 5 torr, and an untreated S45C specimen.
The S45C specimen was immersed for 30 minutes to 16 hours in a molten borax bath at 900°C to which 20% Fe-V powder (containing 82% vanadium, -100 mesh) was added. Observation of the thickness in the cross section shows that the growth rate of the layer on the nitrided specimen is faster than that on the untreated specimen (approximately
1.5 times). In addition, the nitrided specimen has a surface layer made of V (C, N) and an inner layer made of an iron alloy containing nitrogen formed immediately below it, which reduces the hardness directly under the layer as in the untreated specimen. was hardly recognized.

Experimental Example 3 An untreated specimen and a nitrided specimen of SKD61 similar to those in Experimental Example 1 were prepared. And these, iron-
Niobium-tantalum (Fe-Nb-Ta) powder (5
% niobium, 11% tantalum, −100% mesh) in a molten borax bath at 1000 °C with the addition of 20%
Soaked for minutes to 4 hours. In this case too, 4μm, 5μm
It took 1 hour and 2 hours for the nitrided sample to form the layer, and 2 hours and 4 hours for the untreated sample, respectively.

When the nitrided specimen was subjected to thermal diffusion treatment for 30 minutes in the above bath, X-ray microanalyzer analysis revealed that the surface layer contained N as well as C, as shown in Figure 3. Confirmed. Ta
Both Nb and Nb show similar concentration changes, and when the X-ray diffraction results are taken together, the surface layer consists of carbonitrides represented by Nb and Ta (C, N), and an iron alloy containing nitrogen as a solid solution. It was determined that an inner layer was formed. As shown in FIG. 4, the hardness directly under the layer in the untreated specimen (line B) decreased, but no such decrease in hardness was observed in the nitrided specimen (line A).

Experimental Example 4 An SKD61 specimen nitrided in the same manner as in Experimental Example 1 was heated at 1000°C with the addition of 10% niobium oxide (Nb ₂ O ₅ ).
This was immersed in a molten borax bath and electrolytically treated for 2 hours at a cathode current density of 0.05 A/cm ² using the graphite container as a cathode and an anode. The formed layer has a smooth surface as shown in the micrograph in Figure 5, and is composed of Nb(C,N).
It was confirmed that it consists of carbonitrides. Furthermore, an inner layer made of an iron alloy containing nitrogen was formed directly below the carbonitride layer, which is the surface layer, and almost no decrease in hardness was observed immediately below the surface layer.

Experimental example 5 Bath composition is 73% (NaCN + KCNO), 15% KCl, 12
A _S45C specimen that had been nitrided in a salt _bath of 570°C for 90 minutes with 10% Fe-V powder (containing 82% vanadium, -
The sample was immersed for 30 minutes in a 1000°C bath containing barium chloride (BaCl ₂ ) added with 100 mesh. Analysis of the formed 3 μm thick layer using an X-ray microanalyzer revealed that it was a carbonitride layer represented by V (C, N) containing V, N and C, as shown in Figure 6. This was confirmed. Microscopic structure observation revealed that a structure indicating the presence of nitrogen was observed in the portion in contact with the base material layer, and almost no decrease in hardness was observed immediately below the surface layer.

Experimental example 6 SKD11 round bar specimen subjected to gas soft nitriding treatment at 570°C for 150 minutes in a mixed gas of 50% NH ₃ , 20% N ₂ , 15% H ₂ , 15% CO and untreated SKD11
A round bar specimen was placed in a stainless steel container with -100 mesh of Fe-V powder (containing 82% vanadium, -100 mesh).
10% potassium borofluoride (KBF ₄ )
Bury the container in a mixed powder and heat it in an atmospheric furnace.
Heated at 600°C for 16 hours. The container was taken out from the furnace and after air cooling, a test piece was taken out from the powder. When the thickness of the layer formed on the surface was measured, it was 2 to 3 μm for the nitrided piece and 0.7 μm for the untreated piece, and the nitrided piece was thicker. About the nitrided piece
When analyzed with a line microanalyzer, the seventh
As shown in the figure, the layer consists of V, N, and C.
It was confirmed that the layer was a V(C,N) carbonitride layer.

Experimental Example 7 An S45C round bar that had been gas nitrided in NH ₃ at 500°C for 60 hours and an untreated S45C round bar were buried in the same powder as in Experimental Example 6.
℃ for 16 hours. When the thickness of the layer formed on the surface was measured, it was 5 μm for the nitrided piece and 2.5 μm for the untreated piece, with the nitrided piece being thicker. As shown in Figure 8, the layer formed on the nitrided piece was also found to be composed of V, N, and C, confirming that the V(C,N) layer was formed on the outermost surface. It was done.

Experimental Example 8 Gas nitriding was performed under the same conditions as Experimental Example 7.
Fe-V (containing 82% vanadium, -
1000 mesh) using a mixed powder treatment agent with 5% ammonium chloride (NH ₄ Cl) added.
℃ for 5 hours. The thickness of the layer formed on the surface was measured and was 15 μm, which is the same as that of the untreated SK4 round bar treated in the same treatment agent.
11 μm, it was significantly thicker. As shown in Figure 9, a layer is formed from V, N, and C, and diffraction lines corresponding to VC and VN are observed in X-ray diffraction, and the surface layer is made of V(C,N) carbonitride. One thing was confirmed. Further, an inner layer made of an iron alloy containing nitrogen was formed immediately below the carbonitride layer, which is the surface layer, and almost no decrease in hardness was observed immediately below the surface layer.

Experimental Example 9 -Nitrided under the same conditions as Experimental Example 6 using a mixed powder of 100 mesh Fe-Nb-Ta (containing 51% niobium, 11% tantalum) and 10% _KBF4 .
The SK4 bar was treated at 1000°C for 5 hours. The thickness of the layer formed on the surface was 13μm, and the thickness of the layer formed on the surface of the untreated SK4 round bar treated under the same conditions was 11μm.
μm, and the growth rate of the layer was high by performing the nitriding treatment. The formed surface layer was composed of Nb, Ta, C, and N, as shown in FIG. 10, and it was confirmed that Nb and Ta (C, N) were formed. In addition, directly below the carbonitride layer,
A layer made of an iron alloy containing nitrogen as a solid solution was formed, and therefore, there was hardly any decrease in hardness immediately below the layer.

Experimental example 10 A mixed powder consisting of 40% alumina (Al ₂ O ₃ ), 55% Fe-V (containing 82% vanadium, -100 mesh), and 5% ammonium chloride (NH ₄ Cl) was dissolved in ethyl cellulose with ethyl alcohol. It was made into a slurry using a solvent. The slurry was applied to a thickness of 3 to 5 mm on SK4 gas nitrided under the same conditions as in Experimental Example 7, and then placed in a stainless steel container and heated at 1000° C. for 5 hours in an argon atmosphere. From the results of measuring the thickness of the layer formed on the surface, it was found that the growth rate of the layer on the nitrided specimen was approximately 1.5 times that of the untreated specimen treated under the same conditions. Analysis of the formed surface layer using an X-ray microanalyzer revealed that it was composed of V(C,N). Directly below this carbonitride layer, a layer made of an iron alloy containing nitrogen as a solid solution was formed, and therefore, almost no decrease in hardness was observed directly below the layer.

Experimental example 11 Alumina (Al ₂ O ₃ ) 60%, Fe-V38.8%,
A mixed powder consisting of 1.2% NH ₄ Cl was placed in a fluidized tank furnace, and the mixed powder was brought into a fluidized state with argon gas introduced from the bottom of the tank. SKD61 rods subjected to salt bath nitriding treatment and untreated SKD61 rods were charged into this fluidized bath furnace in the same manner as in Experimental Example 1, and after being held at 1000° C. for 8 hours, they were taken out and air-cooled and quenched. The thickness of the layer formed on this surface was 10 μm for the nitrided specimen.
The thickness of the untreated specimen was 8 μm. Nitriding treatment
The SKD61 rod has V(C,
A carbonitride layer of N) was formed. A layer made of a nitrogen-containing iron alloy was formed immediately below this carbonitride layer, and therefore, almost no decrease in hardness was observed immediately below the layer.

Experimental example 12 A standard thread cutting tap made of SKH9 with a pitch of 8 mm in diameter was heated to 1025 mm in a molten borax bath containing 30% V ₂ O ₅ and 15% B ₄ C.
℃ for 1 hour to form a vanadium carbide layer on the surface. Thereafter, the base material was heated in a vacuum furnace at 1190°C for 30 minutes, and the base material was quenched and hardened by gas cooling.

In addition, the standard thread cutting tap bath composition above is 53%.
560 in a salt bath of NaCNO, 12% KCl, 35% _CaCl2
After performing salt bath soft nitriding treatment at ℃ for 20 minutes, the same treatment as above was performed in a molten borax bath to form a vanadium carbonitride layer on the surface, and the base material was quenched and hardened.

When thread cutting was performed on SK45C material, the lifespan of commercially available nitrided taps was approximately 1,500 (number of holes drilled), and the lifespan of taps with the carbide layer formed was approximately 2,500.
There were approximately 3,000 taps on which the carbonitrided layer was formed. In this example as well, it can be seen that according to the present invention, a layer made of an iron alloy containing nitrogen is also formed in the portion immediately below the surface layer, and sufficient quench hardening can be performed.

As explained above, in the present invention, an iron alloy material is nitrided in advance, a group Va element is supplied from the outside, and the group Va element is combined with nitrogen and carbon in the material through thermal diffusion. A surface layer made of a carbonitride of group elements and a layer made of an iron alloy containing nitrogen are formed, and a carbonitride layer with a good surface condition is formed on the material. In addition, sufficient quench hardening can be performed on the portion immediately below the forming layer. Furthermore, processing can be carried out in a short time. The present invention can be applied to cutting tools and the like to greatly improve tool life.

[Brief explanation of the drawing]

1 and 4 are diagrams showing the hardness of the base metal portion of the iron alloy material treated according to the present invention in Experimental Example 1 and Experimental Example 3, FIG. 2, FIG. 3, FIG. 6, Figures 7, 8, 9, 10, and 11 are experimental examples 1, 3, 5, and 6, respectively.
Figures 7, 8, 9, and 10 show the results of X-ray microanalyzer analysis of the surface portion of the iron alloy material treated according to the present invention. This is a micrograph (400x) showing a cross section.

Claims (1)

[Claims] 1. After nitriding the surface of an iron alloy material containing 0.2% by weight or more of carbon, the iron alloy material has a Va.
A thermal diffusion treatment is performed using a treatment agent containing group elements,
A surface hardening treatment for an iron alloy material, characterized by forming a surface layer made of carbonitride of group Va elements of the periodic table on the surface of the iron alloy material, and an inner layer made of an iron alloy containing nitrogen as a solid solution immediately below the surface layer. Method. 2. The surface hardening method for iron alloy materials according to claim 1, wherein the thermal diffusion treatment is carried out in a molten salt bath treatment agent containing a Group Va element and a borate. 3. The surface hardening treatment method for iron alloy material according to claim 1, wherein the thermal diffusion treatment is performed by immersing the iron alloy material in a molten salt bath containing Group Va elements. 4 The above thermal diffusion treatment uses an iron alloy material as a cathode in a molten salt bath containing Group Va elements, and the cathode current density is
3. The method for surface hardening of iron alloy materials according to claim 2, wherein the surface hardening treatment is carried out by electrolytic treatment at 0.01 to 3 A/cm ² . 5 The above thermal diffusion treatment is performed by embedding the iron alloy material in a powder treatment agent containing Group Va elements, applying a slurry powder treatment agent to the iron alloy material, or performing powder treatment containing Group Va elements. 2. A method for surface hardening treatment of an iron alloy material according to claim 1, which is carried out by placing the agent in a fluidized state and inserting and removing the iron alloy material therein.