CN115433896B - Method for rapidly obtaining tissue ultra-fine high-hardness nitriding layer on carburized alloy steel or high-carbon alloy steel surface layer - Google Patents

Abstract

The invention relates to a method for quickly obtaining a nitrided layer with superfine structure and high hardness on the surface layer of carburized alloy steel or high-carbon alloy steel. The invention relates to a method for obtaining a nitrided layer on the surface layer of carburized alloy steel or high-carbon alloy steel. The invention aims to solve the problems of difficult and slow nitriding on the surface of carburizing alloy steel or high-carbon alloy steel at low temperature and easy occurrence of thick vein-like structure in high-temperature nitriding. Methods: 1. pretreatment; 2. low-temperature nitriding; 3. high-temperature diffusion; 4. repeated low-temperature nitriding and high-temperature diffusion; 5. low-temperature nitriding. The invention is used for quickly obtaining superfine structure and high hardness nitrided layer on the surface layer of carburized alloy steel or high carbon alloy steel.

Description

A method for rapidly obtaining ultra-fine structure on the surface of carburized alloy steel or high carbon alloy steel Hardness Nitriding Layer Method

technical field

The invention relates to a method for obtaining a nitrided layer on the surface layer of carburized alloy steel or high-carbon alloy steel.

Background technique

After 1990, with the development of machinery and aviation, the reliability requirements for engine transmission components became higher and higher, and it was found that most of the failures of these transmission components occurred on the surface. Previous research results have shown that wear, corrosion, and micropitting may be the main reasons for the failure of alloy steel substrates in the future. Therefore, in order to ensure that the bearings, gears and other transmission components maintain structural integrity for a long time in harsh environments, it is necessary to further improve their surface comprehensive properties, such as high hardness, good wear resistance and long rolling contact fatigue life. Nitriding for bearing parts with complex shapes is one of the most effective and flexible technologies to achieve surface hardening. The nitriding temperature is low and efficient, and can avoid deformation while obtaining high surface hardness. However, the depth of the conventional nitriding layer is small, and the limited bearing capacity is not conducive to the improvement of fatigue performance.

Dual-phase treatment (combination of other heat treatment and nitriding) is currently the most commonly used hardening method for alloy steel, especially gear and bearing steel, which can greatly improve surface hardness and wear resistance. The dual-phase treatment process is mainly divided into two types according to the different steel types: for traditional carburizing steel, a dual-phase composite process of carburizing and nitriding is proposed; for high-carbon steel, full hardening (solution quenching + high temperature tempering) is proposed. Dual phase process combined with nitriding. Since the surface of carburized steel or the surface of medium and high carbon steel contains a large amount of carbon atoms, the carbon atoms introduced before nitriding will hinder the subsequent nitriding process, resulting in a large activation energy for the diffusion of N atoms during low temperature nitriding. If the amplitude increases, it will take extra time to ensure the thickness of the nitrided layer, which will undoubtedly reduce the production efficiency and increase the production cost. High-temperature nitriding can improve the diffusion ability of N atoms and shorten the nitriding time, but it is easy to induce the formation of vein-like or even network-like compounds during the nitriding process, resulting in the deterioration of the structure of the nitriding layer, which is not conducive to the improvement of fatigue performance. Therefore, there is an urgent need to develop a method that can not only eliminate the tendency of vein-like structure in the process of high-temperature nitriding, but also solve the problem of difficult and slow nitriding on the surface of high-carbon or carburized steel, and quickly form high-temperature nitriding with a certain thickness. The process method of hard nitriding layer.

Contents of the invention

The present invention aims to solve the problems of difficult and slow nitriding at low temperature on the surface of existing carburizing alloy steel or high carbon alloy steel, and easy occurrence of coarse and large veins during high temperature nitriding, and provides a method for carburizing alloy steel or high carbon alloy steel. A method for quickly obtaining an ultra-fine structure and high-hardness nitriding layer on the steel surface.

A method for quickly obtaining an ultra-fine structure and high-hardness nitriding layer on the surface of carburized alloy steel or high-carbon alloy steel, which is carried out according to the following steps:

1. Preparing the alloy steel for heat treatment to obtain the quenched alloy steel;

The alloy steel is carburized alloy steel or high carbon alloy steel;

2. Under the conditions of nitriding furnace and temperature of 380℃～480℃, the quenched alloy steel is subjected to low-temperature nitriding, and the nitriding layer after nitriding is composed of a diffusion layer and a compound layer with a thickness of ≤2 μm, and a primary nitriding is obtained. Alloy steel after nitrogen;

3. Under the conditions of inert protective gas, voltage of 500V-750V and air pressure of 50Pa-350Pa, the temperature of the nitriding furnace is raised to 480°C-580°C, and then the temperature of the nitriding furnace is 480°C-580°C. Diffusion of alloy steel after nitrogen at high temperature for 0.5h to 2h;

4. Repeat step 2 and step 3 successively to obtain the alloy steel after the diffusion treatment;

5. Under the condition of nitriding furnace and temperature of 380℃～480℃, the alloy steel after diffusion treatment is subjected to low-temperature nitriding, and the nitriding layer after nitriding is composed of a diffusion layer and a compound layer with a thickness of ≤2μm, that is The invention provides a method for rapidly obtaining a super-fine structure and high-hardness nitrided layer on the surface layer of carburized alloy steel or high-carbon alloy steel.

The beneficial effects of the present invention are:

1. The present invention uses the quenched structure of carburized alloy steel and high-carbon alloy steel instead of the modulated structure as the initial state, and performs low-temperature nitriding and high-temperature diffusion in a nitriding furnace. Utilizing the phenomenon that surface nitriding and core tempering are carried out simultaneously in the nitriding process, a high-temperature diffusion stage is added after low-temperature nitriding, and N atoms have an "interpolation" effect on the pre-introduced C atoms. Atoms diffuse toward the core, which can reduce the resistance of subsequent nitriding and greatly improve the efficiency of nitriding. The core is tempered at high temperature at the same time, which shortens the production cycle and prevents the formation of veins. Because plasma nitriding can produce surface nanometerization under certain conditions in the quenched state structure, the present invention makes the formed nitrided layer structure uniform and fine grain size by controlling the nitriding conditions.

2. The thickness of the nitrided layer obtained by the present invention on the surface layer of carburized or high-carbon alloy steel is 2 to 3 times that of the traditional process at the same time. The structure of the nitriding layer is uniform and only consists of a diffusion layer, without a thick compound layer (thickness ≤ 2 μm), and no coarse intergranular vein structure. The surface hardness is ≥1250HV _0.1 , and the hardness distribution gradient is gentle, which is beneficial to the improvement of wear resistance and fatigue performance. The surface is dense, and the nitride clusters are uniform, small and ≤200nm in size, which is beneficial to the reduction of surface roughness.

3. This method can realize nitriding and diffusion stages only by changing the temperature and atmosphere in the furnace in the same equipment, and at the same time complete the high-temperature tempering of the core, with simple operation and low equipment requirements; it is suitable for both carburizing alloy steel and High carbon alloy steel, widely used. Therefore, this method has important engineering application value.

The invention is used for a method for quickly obtaining a super-fine structure and high-hardness nitrided layer on the surface layer of carburized alloy steel or high-carbon alloy steel.

Description of drawings

Fig. 1 is the traditional dual-phase hardening process curve of comparative experiments 1 and 2;

Fig. 2 is the process curve of the method for quickly obtaining the superfine structure and high hardness nitriding layer in embodiment one;

Fig. 3 is the XRD pattern of the alloy steel surface after primary nitriding prepared in step 2 of Example 1, ○ is α′, ● is γ′-Fe ₄ N, ▼ is MN, ◆ is ε-Fe _2～3 N;

Fig. 4 is the cross-sectional SEM figure of the nitriding layer in the alloy steel after the primary nitriding prepared by embodiment one step two;

Fig. 5 is the sectional metallographic diagram of nitriding layer, (a) is the alloy steel that obtains nitriding layer on the surface of comparative experiment 1, (b) obtains the alloy steel of nitriding layer on the surface of embodiment 1;

Fig. 6 is the hardness-depth curve of nitriding layer, and 1 is the alloy steel that obtains nitriding layer on the surface of comparative experiment 1, and 2 is the alloy steel that obtaining nitriding layer on the surface of embodiment 1;

Fig. 7 is the surface topography figure of nitriding layer, (a) is the alloy steel that obtains nitriding layer on the surface of comparative experiment 1, (b) is the alloy steel that obtains nitriding layer on the surface of comparative experiment 2, (c) is embodiment Alloy steel with a nitrided layer on the surface;

Fig. 8 is the SEM of the section of the nitriding layer, (a) the alloy steel obtained from the nitriding layer on the surface of (a) comparative experiment 2, (b) the alloy steel obtained from the nitriding layer on the surface of Example 1;

Fig. 9 is the process curve of the method for quickly obtaining ultra-fine microstructure and high hardness nitriding layer in embodiment 2;

Fig. 10 is the cross-sectional metallographic diagram of the nitriding layer, (a) is the alloy steel obtained from the nitriding layer on the third surface of the comparative experiment, and (b) is the alloy steel obtained from the nitriding layer on the surface of the second embodiment;

Fig. 11 is a cross-sectional SEM image of a nitrided layer in an alloy steel prepared in Example 2 with a nitrided layer on its surface.

Detailed ways

The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

Specific embodiment one: a kind of method described in this embodiment mode obtains the superfine microstructure high-hardness nitriding layer fast on the surface layer of carburized alloy steel or high carbon alloy steel, it is carried out according to the following steps:

1. Preparing the alloy steel for heat treatment to obtain the quenched alloy steel;

The alloy steel is carburized alloy steel or high carbon alloy steel;

2. Under the conditions of nitriding furnace and temperature of 380℃～480℃, the quenched alloy steel is subjected to low-temperature nitriding, and the nitriding layer after nitriding is composed of a diffusion layer and a compound layer with a thickness of ≤2 μm, and a primary nitriding is obtained. Alloy steel after nitrogen;

3. Under the conditions of inert protective gas, voltage of 500V-750V and air pressure of 50Pa-350Pa, the temperature of the nitriding furnace is raised to 480°C-580°C, and then the temperature of the nitriding furnace is 480°C-580°C. Diffusion of alloy steel after nitrogen at high temperature for 0.5h to 2h;

4. Repeat step 2 and step 3 successively to obtain the alloy steel after the diffusion treatment;

5. Under the condition of nitriding furnace and temperature of 380℃～480℃, the alloy steel after diffusion treatment is subjected to low-temperature nitriding, and the nitriding layer after nitriding is composed of a diffusion layer and a compound layer with a thickness of ≤2μm, that is The invention provides a method for rapidly obtaining a super-fine structure and high-hardness nitrided layer on the surface layer of carburized alloy steel or high-carbon alloy steel.

In Step 3 of this embodiment, raise the temperature in the nitriding furnace to 480°C-580°C, but not higher than the austenitization temperature, and keep it warm for 0.5-2 hours, so that N atoms can fully diffuse into the interior under high temperature conditions, reducing Nitrogen content near the surface, while high temperature tempering occurs in the core.

In the third step of this embodiment, the introduction of nitrogen-containing gas and dilute gas H ₂ that can react with solid-dissolved N atoms in steel is reduced or stopped, and the inert gas argon is introduced at the same time, which can prevent the nitrogen from the surface, and the diffusion temperature is lower than that of traditional alloy steel. In the high temperature tempering temperature range, the total diffusion time is controlled within the time range of traditional high temperature tempering of alloy steel.

The nitriding temperature and time in Step 5 of this embodiment can be determined according to the thickness, structure and surface hardness of the nitriding layer.

The beneficial effects of this embodiment are:

1. In this embodiment, the quenched structure of carburized alloy steel and high-carbon alloy steel is used as the initial state instead of the modulated structure, and low-temperature nitriding and high-temperature diffusion are carried out in a nitriding furnace. Utilizing the phenomenon that surface nitriding and core tempering are carried out simultaneously in the nitriding process, a high-temperature diffusion stage is added after low-temperature nitriding, and N atoms have an "interpolation" effect on the pre-introduced C atoms. Atoms diffuse toward the core, which can reduce the resistance of subsequent nitriding and greatly improve the efficiency of nitriding. The core is tempered at high temperature at the same time, which shortens the production cycle and prevents the formation of veins. Because plasma nitriding can produce surface nanometerization under certain conditions in the quenched state structure, the present invention makes the formed nitrided layer structure uniform and fine grain size by controlling the nitriding conditions.

2. In this embodiment, the thickness of the nitrided layer obtained on the surface layer of carburized or high-carbon alloy steel is 2 to 3 times that of the traditional process at the same time. The structure of the nitriding layer is uniform and only consists of a diffusion layer, without a thick compound layer (thickness ≤ 2 μm), and no coarse intergranular vein structure. The surface hardness is ≥1250HV _0.1 , and the hardness distribution gradient is gentle, which is beneficial to the improvement of wear resistance and fatigue performance. The surface is dense, and the nitride clusters are uniform, small and ≤200nm in size, which is beneficial to the reduction of surface roughness.

3. This method can realize nitriding and diffusion stages only by changing the temperature and atmosphere in the furnace in the same equipment, and at the same time complete the high-temperature tempering of the core, with simple operation and low equipment requirements; it is suitable for both carburizing alloy steel and High carbon alloy steel, widely used. Therefore, this method has important engineering application value.

Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the preliminary heat treatment described in step 1 is one or a combination of solution quenching, carburizing quenching and secondary quenching; and the preparatory The cooling method in the heat treatment process is water quenching, oil quenching, gas quenching, gas-liquid composite quenching or air cooling. Others are the same as in the first embodiment.

Embodiment 3: This embodiment differs from Embodiment 1 or Embodiment 2 in that: after preparatory heat treatment in step 1, use sandpaper to polish and remove surface scale, and then ultrasonically clean in acetone or alcohol for 5 minutes to 20 minutes. Others are the same as in the first or second embodiment.

Embodiment 4: This embodiment differs from Embodiments 1 to 3 in that the compound layers described in Step 2 and Step 5 are composed of γ′-Fe ₄ N and ε-Fe _2˜3 N. Others are the same as the specific embodiments 1 to 3.

Embodiment 5: This embodiment differs from Embodiments 1 to 4 in that: the low-temperature nitriding time in step 2 is greater than or equal to the high-temperature diffusion time in step 3. Others are the same as the specific embodiments 1 to 4.

Embodiment 6: This embodiment differs from Embodiment 1 to Embodiment 5 in that the inert protective gas described in step 3 is argon. Others are the same as those in Embodiments 1 to 5.

Embodiment 7: This embodiment is different from Embodiment 1 to Embodiment 6 in that: in step 4, step 2 and step 3 are repeated once or more in sequence. Others are the same as those in Embodiments 1 to 6.

Embodiment 8: The difference between this embodiment and one of Embodiments 1 to 7 is that the low-temperature nitriding described in step 2 and step 5 is gas nitriding, vacuum nitriding or plasma nitriding; When the low-temperature nitriding is plasma nitriding, it is carried out according to the following steps: in a nitrogen-containing atmosphere, the temperature is 380°C-480°C, the voltage is 500V-750V, and the pressure is 200Pa-350Pa, the plasma nitriding treatment 0.5h～8h. Others are the same as those in Embodiments 1 to 7.

Embodiment 9: This embodiment differs from Embodiment 1 to Embodiment 8 in that: the low-temperature nitriding temperature in step five is less than or equal to the low-temperature nitriding temperature in step two. Others are the same as those in Embodiments 1 to 8.

Embodiment 10: This embodiment differs from Embodiments 1 to 9 in that the nitrogen-containing atmosphere is a mixed atmosphere of diluent gas and nitrogen-containing gas, wherein the volume ratio of nitrogen-containing gas to diluent gas is less than or equal to 3:1; the nitrogen-containing gas is nitrogen or ammonia; the diluting gas is hydrogen or argon; or the diluting gas is hydrogen or argon, and the diluting gas contains a volume fraction of ≤1% Carbon-containing gas, the carbon-containing gas is methane, acetylene, propane, carbon monoxide, carbon dioxide, gaseous acetone, alcohol or benzene. Others are the same as the specific embodiments 1 to 9.

Adopt the following examples to verify the beneficial effects of the present invention:

Embodiment 1, in conjunction with Fig. 2 specific description:

A method for quickly obtaining an ultra-fine structure and high-hardness nitriding layer on the surface of carburized alloy steel or high-carbon alloy steel, which is carried out according to the following steps:

1. The alloy steel was solid-dissolved for 0.5h at a temperature of 1100°C, then air-cooled to room temperature, polished with sandpaper to remove the surface scale, and then ultrasonically cleaned in acetone for 10 minutes to obtain the quenched alloy steel;

The alloy steel is high carbon alloy steel M50;

2. In the nitriding furnace, under the conditions of a nitrogen-containing atmosphere, a temperature of 450°C, a voltage of 600V, and a pressure of 250Pa, the quenched alloy steel is plasma nitrided for 2 hours, and the nitrided layer after nitriding is formed by diffusion Layer composition, to obtain alloy steel after primary nitriding;

The nitrogen-containing atmosphere is a mixed atmosphere of hydrogen and nitrogen, wherein the volume of nitrogen and hydrogen is 1:3;

3. Under the conditions of inert protective gas, voltage of 680V and air pressure of 80Pa, the temperature of the nitriding furnace is raised to 530°C, and then the alloy steel after the first nitriding is diffused at high temperature for 2 hours at a temperature of 530°C;

The inert protective gas is argon;

4. Repeat step 2 and step 3 for 2 times to obtain alloy steel after diffusion treatment;

5. In the nitriding furnace, under the conditions of a nitrogen-containing atmosphere, a temperature of 450°C, a voltage of 600V, and an air pressure of 250Pa, the alloy steel after diffusion treatment was treated with plasma nitriding for 2 hours, cooled with the furnace, and after nitriding The nitrided layer is composed of a diffusion layer, and the thickness of the nitrided layer is 109 μm, and the alloy steel with a nitrided layer obtained on the surface is obtained;

The nitrogen-containing atmosphere is a mixed atmosphere of hydrogen and nitrogen, wherein the volume of nitrogen and hydrogen is 1:3.

After nitriding in Step 2 and Step 5, γ′-Fe ₄ N and ε-Fe _2-3 N are formed on the surface, but no compound layer is formed.

Contrast experiment 1, the traditional two-phase hardening process curve, combined with Figure 1 to illustrate: the difference between this comparative experiment and embodiment 1 is that steps 2 to 5 are cancelled, and the quenched state The alloy steel was tempered for 2 hours, and the tempering was repeated 3 times, and then in the nitriding furnace, the plasma nitriding treatment was carried out for 8 hours under the conditions of a nitrogen-containing atmosphere, a temperature of 450°C, a voltage of 600V and a pressure of 250Pa; The nitrogen-containing atmosphere is a mixed atmosphere of hydrogen and nitrogen, wherein the volume of nitrogen and hydrogen is 1:3. Others are the same as in Embodiment 1.

Contrast experiment 2, the traditional two-phase hardening process curve, combined with Figure 1 to explain in detail: the difference between this comparative experiment and comparative experiment 1 is: in the nitriding furnace, in the nitrogen-containing atmosphere, the temperature is 530°C, the voltage is 600V and the pressure is Under the condition of 250Pa, plasma nitriding treatment for 8h. Others are the same as the comparative experiment 1.

In the comparison test, several times of high-temperature tempering were carried out after quenching, and the modulated structure was used as the initial structure before nitriding. In Example 1, the quenched structure is directly used as the initial structure before nitriding, and a high-temperature diffusion stage is added in the middle of the nitriding stage at 450°C. The temperature and total time of the diffusion stage are the same as those of the removed tempering process.

Embodiment 2, specifically described in conjunction with FIG. 9:

A method for quickly obtaining an ultra-fine structure and high-hardness nitriding layer on the surface of carburized alloy steel or high-carbon alloy steel, which is carried out according to the following steps:

1. The alloy steel gear is carburized for 4 hours under the condition of vacuum and temperature of 900°C, then oil quenched to room temperature, polished with sandpaper to remove the surface scale, and then ultrasonically cleaned in acetone for 10 minutes to obtain the quenched alloy steel;

The alloy steel gear is a carburized alloy steel 18CrNiM07-6 gear;

2. In the nitriding furnace, under the conditions of a nitrogen-containing atmosphere, a temperature of 450°C, a voltage of 600V, and a pressure of 250Pa, the quenched alloy steel is plasma nitrided for 2 hours, and the nitrided layer after nitriding is formed by diffusion Layer composition, to obtain alloy steel after primary nitriding;

The nitrogen-containing atmosphere is a mixed atmosphere of hydrogen and nitrogen, wherein the volume of nitrogen and hydrogen is 1:3;

3. Under the conditions of inert protective gas, voltage of 650V and air pressure of 100Pa, the temperature of the nitriding furnace is raised to 530°C, and then the alloy steel after primary nitriding is diffused at high temperature for 2 hours at a temperature of 530°C;

The inert protective gas is argon;

4. Repeat step 2 and step 3 for 2 times to obtain alloy steel after diffusion treatment;

5. In the nitriding furnace, under the conditions of a nitrogen-containing atmosphere, a temperature of 450°C, a voltage of 600V, and an air pressure of 250Pa, the alloy steel after diffusion treatment was treated with plasma nitriding for 2 hours, cooled with the furnace, and after nitriding The nitriding layer is composed of a diffusion layer and a compound layer with a thickness ≤ 2 μm, and the thickness of the nitriding layer is 120 μm, so as to obtain an alloy steel with a nitrided layer on the surface;

The nitrogen-containing atmosphere is a mixed atmosphere of hydrogen and nitrogen, wherein the volume of nitrogen and hydrogen is 1:7.

After nitriding in step 2, γ′-Fe ₄ N and ε-Fe _2~3 N are formed on the surface, but no compound layer is formed.

Comparative experiment 3, traditional dual-phase hardening process curve: the difference between this comparative experiment and embodiment 2 is that steps 2 to 5 are omitted, and the quenched alloy steel is tempered for 2 hours in a vacuum furnace at a temperature of 530°C. And repeat the tempering 3 times, then in the nitriding furnace, under the conditions of a nitrogen-containing atmosphere, a temperature of 450°C, a voltage of 600V and an air pressure of 250Pa, plasma nitriding treatment for 8h; the nitrogen-containing atmosphere is hydrogen Mixed atmosphere with nitrogen, where the volume of nitrogen and hydrogen is 1:3. Others are the same as the second embodiment.

In comparative test 3, several times of high-temperature tempering were carried out after quenching, and the modulated structure was used as the initial structure before nitriding. In Example 2, the quenched structure is directly used as the initial structure before nitriding, and a high-temperature diffusion stage is added in the middle of the nitriding stage at 450°C. The temperature and total time of the diffusion stage are the same as those of the removed tempering process.

Figure 1 is the traditional dual-phase hardening process curves of comparative experiments 1 and 2; specifically, solution quenching plus three high-temperature tempering, the nitriding stage is one-stage, and the temperature is 450°C or 530°C;

Figure 2 is the process curve of the method for quickly obtaining ultra-fine structure and high hardness nitriding layer in Example 1; specifically, the pretreatment stage is solution quenching, and three diffusion stages at high temperature of 530°C are added in the low temperature nitriding stage at 450°C;

Fig. 3 is the XRD pattern of the alloy steel surface after primary nitriding prepared in step 2 of Example 1, ○ is α′, ● is γ′-Fe ₄ N, ▼ is MN, ◆ is ε-Fe _2～3 N; It can be seen from the figure that nitrides γ′-Fe ₄ N and ε-Fe _2~3 N are formed on the surface.

Fig. 4 is the cross-sectional SEM image of the nitriding layer in the alloy steel after the primary nitriding prepared in step 2 of Example 1; as can be seen from the figure, the nitriding layer is only composed of a diffusion layer, and no nitride γ'-Fe ₄ N and A compound layer composed of ε-Fe _2～3 N.

Fig. 5 is the cross-sectional metallographic diagram of the nitriding layer, (a) is the alloy steel that obtains the nitriding layer on the surface of the comparative experiment one, and (b) is the alloy steel obtaining the nitriding layer on the surface of the embodiment one; As can be seen from the figure, the comparative experiment The thickness of the nitrided layer after the nitriding temperature is 450°C in the traditional dual-phase hardening process is 37 μm. However, the thickness of the nitrided layer after treatment in Example 1 is 109 μm, which is 2.95 times the thickness of the nitrided layer obtained by the traditional dual-phase hardening process.

Fig. 6 is the hardness-depth curve of nitriding layer, and 1 is the alloy steel that obtains nitriding layer on the surface of comparative experiment 1, and 2 is the alloy steel that obtaining nitriding layer on the surface of embodiment 1; As can be seen from the figure, the obtained nitriding layer in embodiment 1 The surface hardness of the nitrogen layer is 1250HV _0.1 , the hardness gradient is gentler, and the depth of the hardened layer reaches 2.3 times of that obtained by the comparative experiment-traditional process.

Fig. 7 is the surface topography figure of nitriding layer, (a) is the alloy steel that obtains nitriding layer on the surface of comparative experiment 1, (b) is the alloy steel that obtains nitriding layer on the surface of comparative experiment 2, (c) is embodiment 1. Alloy steel with a nitriding layer on the surface; it can be seen from the figure that the nitride clusters on the surface of the sample after the traditional dual-phase hardening process with a nitriding temperature of 450°C are uniform in size, but there are some holes, Poor compactness. According to the comparison experiment, the size of nitride clusters on the surface of the sample after the traditional two-phase hardening process with the nitriding temperature of 530 ° C is uneven, and some clusters have been coarsened. After the process in Example 1, the surface of the sample is dense, and the nitride clusters on the surface are uniform, small and the size is ≤200nm.

Fig. 8 is the section SEM of nitriding layer, (a) the alloy steel that obtains nitriding layer on the surface of (a) comparative experiment two, (b) is the alloy steel that obtaining nitriding layer on the surface of embodiment one; As can be seen from the figure, through comparative experiment nitriding temperature A compound layer appeared on the surface of the nitriding layer of the sample after the traditional two-phase hardening process at 530°C, and a vein-like structure was formed under the compound layer. After the process of Example 1, the surface of the nitriding layer of the sample has no compound layer, and the nitriding layer is only composed of a diffusion layer, with a uniform structure and no vein-like structure.

Figure 9 is the process curve of the method for quickly obtaining ultra-fine structure and high hardness nitriding layer in Example 2; the pretreatment stage is carburizing and quenching, and three diffusion stages at high temperature of 530°C are also added in the 450°C low temperature nitriding stage;

Fig. 10 is the cross-sectional metallographic diagram of the nitrided layer, (a) is the alloy steel obtained with the nitrided layer on the third surface of the comparative experiment, and (b) is the alloy steel obtained with the nitrided layer on the surface of the second embodiment; as can be seen from the figure, after comparison Experiment 3 After the traditional two-phase hardening process with a nitriding temperature of 450 ° C, the nitriding layer is located above the carburizing layer, and the thickness is only 44 μm. After the process in Example 2, the nitriding layer is also located above the carburizing layer, and the thickness can reach 120 μm. Compared with the traditional process, the thickness of the nitriding layer is nearly doubled, and the thickness of the carburizing layer is also slightly increased.

Fig. 11 is a cross-sectional SEM image of the nitriding layer in the alloy steel prepared in Example 2 with a nitriding layer on the surface; it can be seen from the figure that a thinner compound layer is formed above the diffusion layer, and its thickness is ≤ 2 μm.

Claims (8)

1. a kind of method that obtains structure superfine high hardness nitriding layer fast at carburizing alloy steel or high-carbon alloy steel surface layer, it is characterized in that it is carried out according to the following steps: 1. Preparing the alloy steel for heat treatment to obtain the quenched alloy steel; The alloy steel is carburized alloy steel or high carbon alloy steel; 2. Under the conditions of nitriding furnace and temperature of 380 ℃ ~ 480 ℃, the quenched alloy steel is subjected to low temperature nitriding, and the nitriding layer after nitriding is composed of a diffusion layer and a compound layer with a thickness of ≤ 2 μm to obtain a primary nitriding Alloy steel after nitrogen; 3. Under the conditions of inert protective gas, voltage of 500V~750V and air pressure of 50Pa~350Pa, the temperature of the nitriding furnace is raised to 480°C~580°C, and then the temperature of the nitriding furnace is 480°C~580°C. Diffusion of alloy steel after nitrogen at high temperature for 0.5h~2h; 4. Repeat step 2 and step 3 successively to obtain the alloy steel after the diffusion treatment; 5. Under the conditions of nitriding furnace and temperature of 380°C~480°C, the alloy steel after diffusion treatment is subjected to low-temperature nitriding, and the nitriding layer after nitriding is composed of a diffusion layer and a compound layer with a thickness ≤ 2 μm, that is Complete the method of quickly obtaining ultra-fine structure and high hardness nitrided layer on the surface layer of carburized alloy steel or high carbon alloy steel; The compound layer described in step 2 and step 5 is composed of γ´-Fe ₄ N and ε-Fe _2~3 N; The low-temperature nitriding described in step 2 and step 5 is gas nitriding, vacuum nitriding or plasma nitriding; Under the conditions of atmosphere, temperature 380℃~480℃, voltage 500V~750V and air pressure 200Pa~350Pa, plasma nitriding treatment 0.5h~8h; The nitrogen-containing atmosphere is a mixed atmosphere of dilution gas and nitrogen-containing gas, wherein the volume ratio of nitrogen-containing gas to dilution gas is less than or equal to 3:1. 2. a kind of method according to claim 1 in carburizing alloy steel or high-carbon alloy steel surface layer obtains microstructure superfine high-hardness nitriding layer fast, it is characterized in that the preparatory heat treatment described in step 1 is solid solution One or a combination of quenching, carburizing quenching and secondary quenching; and the cooling method in the preparatory heat treatment process is water quenching, oil quenching, gas quenching, gas-liquid composite quenching or air cooling. 3. A kind of method according to claim 2 on the surface layer of carburized alloy steel or high carbon alloy steel to obtain superfine microstructure and high hardness nitrided layer rapidly, it is characterized in that after step 1 preliminary heat treatment, use sandpaper to polish and remove the surface Oxidized skin, and then ultrasonic cleaning in acetone or alcohol for 5min~20min. 4. A kind of method according to claim 1 in carburized alloy steel or high-carbon alloy steel surface layer obtains microstructure superfine high-hardness nitriding layer fast, it is characterized in that the low-temperature nitriding time in step 2 is greater than or equal to step 2. Three medium and high temperature diffusion time. 5. a kind of method according to claim 1 in carburizing alloy steel or high-carbon alloy steel surface layer obtains structure ultrafine high hardness nitriding layer rapidly, it is characterized in that the inert shielding gas described in step 3 is argon gas. 6. a kind of method according to claim 1 in carburizing alloy steel or high-carbon alloy steel surface layer obtains structure ultrafine high hardness nitriding layer fast, it is characterized in that step 2 and step 3 are repeated successively in step 4 Do it one or more times. 7. A kind of method according to claim 1 in carburizing alloy steel or high-carbon alloy steel surface to obtain microstructure superfine high-hardness nitriding layer fast, it is characterized in that the low-temperature nitriding temperature in step 5 is less than or equal to Low temperature nitriding temperature in step two. 8. A method for rapidly obtaining a microstructure and high-hardness nitriding layer on the surface of carburized alloy steel or high-carbon alloy steel according to claim 1, wherein the nitrogen-containing gas is nitrogen or ammonia ; The diluent gas is hydrogen or argon; or the diluent gas is hydrogen or argon, and the diluent gas contains a carbon-containing gas with a volume fraction ≤ 1%, and the carbon-containing gas is methane, acetylene, Propane, carbon monoxide, carbon dioxide or gaseous acetone, alcohol, benzene.