CN105177493B - A kind of surface of hot working die arc-plasma auxiliary low pressure nitriding method - Google Patents

Abstract

The invention discloses a low-pressure nitriding method assisted by electric arc plasma on the surface of a hot work mold. Firstly, Ar ⁺ generated by arc-enhanced glow discharge is used to perform ion etching on the surface of the hot-working mold to remove oxides on the surface of the material. Then a certain flow of high-purity N ₂ , high-purity H ₂ , and high-purity Ar is continuously fed into the furnace to keep the temperature (300-600°C) and air pressure (0.2-1.0 Pa) constant in the furnace, and the workpiece transfer platform is connected to the negative pole of the pulse power supply , for plasma nitriding. The depth of the 2h nitriding layer is 15-40μm, the thickness of the compound layer in the nitriding layer is 0-3μm, the hardness is 1000-1300 HV _0.1 , the brittleness level is less than 1 level, and the porosity level is less than 1 level. In addition, the surface of the workpiece is effectively and real-time bombarded by argon ions to increase the diffusion channels of nitrogen atoms, accelerate the nitriding process, and finally obtain a high-strength and high-toughness nitriding surface layer.

Description

A Method for Arc Plasma Assisted Low Pressure Nitriding on the Surface of a Hot Work Die

technical field

The invention belongs to the field of material surface modification, and in particular relates to a low-pressure nitriding method assisted by electric arc plasma on the surface of a hot work mold, which is suitable for surface strengthening of hard alloy cutters, molds and metal parts.

Background technique

Plasma nitriding is an important chemical heat treatment technology, which has the advantages of low treatment temperature, fast speed, no pollution, good process controllability, etc., and can significantly improve the surface hardness and wear resistance of metal materials. Nitriding methods are usually divided into gas nitriding, liquid nitriding, solid nitriding and ion nitriding. Among them, ion nitriding has been widely used because of its high efficiency, low pollution, easy control, and small deformation of workpieces.

At present, the commonly used ion nitriding technologies include direct current ion nitriding, pulse direct current ion nitriding, active screen ion nitriding, hollow cathode plasma nitriding, ion implantation nitriding and so on.

In the DC ion nitriding process, the workpiece is placed in a vacuum container and connected to the negative electrode of the DC high voltage, and the anode is connected to the outer shell of the vacuum chamber, and the workpiece is nitrided in the low-temperature plasma generated by the DC glow discharge. . The workpiece is used as the cathode of the discharge system, and there are inevitably some difficult problems in the ion nitriding process. For example, M.OIzon-Dionysio studied the "corner effect" of DC ion nitriding and pointed out that the surface of the corners of the workpiece caused The morphology and organizational structure are different from other parts, resulting in uneven surface hardness. In addition, there are disadvantages such as surface arcing and hollow cathode effect.

In order to quickly quench the arc and improve the quality of nitriding workpieces, the development and application of pulse power supply is the biggest highlight in the development of ion chemical heat treatment technology in the past 30 years. The use of pulse power supply for ion chemical heat treatment has the characteristics of easy arc extinguishing, small hollow cathode effect, low reactive power loss, and easy independent control of process parameters, especially for some parts with special shapes, or need special process treatment, pulse power supply The advantages are more obvious. Ion nitriding treatment in a low-pressure plasma arc source can reduce the temperature by more than 100°C.

Luxembourg engineer Georges invented active screen ion nitriding technology, which solved the problems of direct current ion nitriding. Active screen ion nitriding treatment technology is to apply the cathode potential on a so-called active screen (metal screen) instead of on the workpiece to be processed, so it can completely avoid arcing on the surface of the workpiece, hollow cathode effect and edge effect And other issues. In 1987, Professor Conrad of the University of Wisconsin in the United States proposed the plasma source ion implantation technology, and then Professor Collins et al. proposed the plasma immersion ion implantation technology, which essentially added temperature assistance on the basis of the plasma source ion implantation technology, so that the implanted nitrogen element could Diffusion deep into the surface to increase the depth of the hardened layer.

The above scheme has developed the nitriding process to a certain extent, but the ionized nitriding layer is shallow, and it is difficult to ensure a uniform layer for metal parts with complex structures, and the equipment is complicated and the initial investment is large. limit.

Plasma source assisted nitriding technology is to separate the generation of plasma from the workpiece at a lower pressure. A plasma generator is separately prepared in the furnace to ionize nitrogen-containing gas for nitriding. After summarizing and analyzing various ion source-assisted nitriding technologies, Zerwiec pointed out that in the ion source-assisted nitriding technology, most of the nitrogen ions enter the surface of the material through implantation, and the incident ions gradually lose energy, and finally stay in the material, causing the surface composition of the material, The structure and performance change, and excellent performance is obtained.

Invention content:

Aiming at the deficiencies of the current nitriding process, in order to control the thickness of the compound in the nitriding layer and improve the porosity of the compound layer, the present invention provides a low-pressure nitriding method assisted by arc plasma on the surface of a hot work mold, which adopts low pressure, pulse and nitriding Nitriding layers with high strength and toughness are prepared by passing Ar-H ₂ -N ₂ into nitrogen atmosphere.

The object of the present invention is achieved through the following technical solutions:

A method of arc plasma assisted low pressure nitriding on the surface of a hot work mold, comprising the following steps:

1) The workpiece is 4Cr5MoSiV1 hot-working die steel in different pre-treatment states. After ultrasonic cleaning and drying, it is placed in a low-pressure nitriding device, and the mechanical pump and molecular turbo pump are turned on in turn to evacuate to the background vacuum, and heated to 300-600 ℃, remove the residue in the vacuum chamber;

2) Keep the temperature in the reaction furnace at 300-500°C, the air pressure in the reaction furnace is 2.0×10 ^-2 -4.0×10 ^-3 Pa, the workpiece transfer platform is connected to the negative pole of the pulse power supply, the arc target is ignited, and the argon gas is passed through the reaction furnace. Keep the air pressure at 0.2-1.0Pa, and perform ion etching on the surface of the workpiece for 30-60min;

3) Continuously feed high-purity N ₂ , high-purity H ₂ and inert gas Ar into the reaction furnace to keep the temperature and air pressure in the reaction furnace constant. 60-120min plasma nitriding;

4) Then turn on the circulating cooling water system of the furnace body to cool for 60-120 minutes, the workpiece is cooled to room temperature with the furnace in a low vacuum state, turn on the vacuum furnace and take out the workpiece.

Further, the H13 hot work die steels in different pretreatment states described in step 1) are sandblasting state, grinding wheel grinding state, sandpaper polishing state (1000#), and mechanical polishing state.

Further, the heating described in step 1) is heated by an infrared electric heating tube, and the actual temperature in the chamber of the device is measured by a thermocouple.

Further, the workpiece transfer platform described in step 2) and step 3) is connected to the pulse power supply, the negative bias voltage is 300-500V, bipolar pulse is used, the pulse frequency is 10-20kHz, and the duty cycle is 0.8-1.0.

Further, the arc target current in step 2) is 80-85A.

Further, the flow rate of argon in step 2) is 180-200 mL/min.

Further, the ion etching in step 2) refers to the arc-enhanced glow discharge technology; the arc-enhanced glow discharge technology, the arc-enhanced glow discharge technology, is to generate high-density electrons through arc discharge, and the electrons and access Argon collides, ionizes Ar ⁺ , and etches the surface of the workpiece. The arc target adopts Ti target.

Further, the N ₂ flow rate in step 3) is 25-50 mL/min, the H ₂ flow rate is 25-50 mL/min, and the Ar flow rate is 80-120 mL/min.

Further, the temperature in step 3) is 300-500°C, and the air pressure is 0.2-1.0Pa.

Further, the reaction furnace adopts Metaplas-Domino mini equipment for the experiment.

Furthermore, the technical solution for realizing the object of the present invention follows the steps below:

(1) H13 steel workpieces in different pre-treatment states were selected, ultrasonically cleaned with acetone solution for 20 min, taken out, dried with a hair dryer, and placed in an arc plasma assisted nitriding device for nitriding treatment.

(2) Keep the temperature in the furnace at 500°C, the air pressure in the vacuum chamber is 4.0×10 ^-3 Pa, the workpiece transfer platform is connected to the pulse power supply, the arc target arc is ignited, and the argon gas is supplied, and the pressure in the furnace is kept at 0.2-1.0 Pa. Ion etching for 60min.

(3) Continuously feed a certain flow of high-purity N ₂ , high-purity H ₂ , and inert gas Ar into the furnace to keep the temperature and air pressure in the furnace constant. The workpiece transfer platform is connected to a pulse power supply, and the current of the arc target is kept constant for 120 minutes. Nitriding.

(4) Then turn on the circulating cooling water system of the furnace body to cool for 60 minutes. The workpiece is cooled to room temperature with the furnace in a low vacuum state, and the vacuum furnace is turned on and the workpiece is taken out.

The H13 hot work die steels in different pretreatment states described in step 1 are sandblasting state, grinding wheel grinding state, sandpaper polishing state (1000#), and mechanical polishing state.

The plasma etching in step 2 is an arc-enhanced glow discharge technology, and the workpiece is transferred to the platform and connected to a pulse power supply during the etching process. The collided Ar ⁺ etches the surface of the workpiece and removes the oxide on the surface.

The argon flow rate in step 2 was 190 mL/min.

In step 2 and step 3, the workpiece turntable is connected to the pulse power supply, the negative bias voltage is 300V, the pulse frequency is 20kHz, and the duty ratio is 0.8. The arc target adopts Ti target, the current of the arc target is 80-85A, and a baffle is attached in front of the target, and the evaporated Ti ions (or atoms) are deposited on the baffle, thereby colliding to generate Ar ⁺ .

During the nitriding process in step 3, the N ₂ flow rate is 50 mL/min, the H ₂ flow rate is 25 mL/min, and the Ar flow rate is 120 mL/min. During the nitriding process, Ar is introduced, and the pressure in the furnace is controlled at 1.0 Pa by controlling the flow rate of Ar.

In step 3, the nitriding temperature and air pressure are kept constant, the air pressure is 1.0 Pa, and the temperature is 500°C.

In step 3, the inert gas argon is passed through the nitriding process, which reduces the nitrogen concentration in the atmosphere, suppresses the generation of the compound layer, and reduces the hardness gradient; in addition, the surface of the workpiece is effectively bombarded and activated by argon ions to achieve the increase of nitrogen atoms The diffusion channel accelerates the nitriding process, and finally obtains a high-strength and high-toughness surface layer. The thickness of the compound layer in the nitriding layer is less than 0-3μm, the hardness is 1000-1300 HV _0.1 , the brittleness level is less than 1 level, and the porosity level is less than 1 level.

In step 3, the arc plasma assisted nitriding process changes the traditional glow discharge into a combination of glow discharge and arc discharge. The working pressure of nitriding is 1.0Pa. Input pulse power supply, the pulse frequency is as high as 20kHz, the arc extinguishing speed is fast, the energy of the arc point is small, no arc damage is caused to the surface of the parts, and the "hollow cathode effect" can be effectively suppressed.

Described reaction furnace adopts Metaplas-Domino mini type equipment for experiment.

The principle of plasma assisted nitriding technology of the present invention is:

Plasma source-assisted nitriding technology is to separate the generation of plasma from the workpiece and carry out at lower pressure. A plasma generator is separately prepared in the furnace to ionize nitrogen-containing gas for nitriding. Most of the nitrogen is injected. Entering the surface of the material, the incident ions gradually lose energy, and finally stay in the material, causing changes in the surface composition, structure and properties of the material, and obtaining excellent performance.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The arc plasma-assisted low-pressure nitriding technology of the present invention can improve the shortcomings of traditional ion nitriding. The arc discharge has a higher plasma density, requires less glow energy, and avoids damage to the workpiece surface. When the nitriding pressure is very low, the number of molecules per unit volume is small, the free path of iron ions is longer, and the probability of forming and depositing iron nitride FeN on the surface of the workpiece is low. At the same time, ions with higher kinetic energy bombard the surface to cause new formation. The compound layer is sputtered.

(2) The workpiece transfer platform is connected to the pulse power supply, using bipolar pulses, the frequency is as high as 20kHz, the arc extinguishing speed is fast, no arc damage is caused to the surface of the parts, and the "hollow cathode effect" can be effectively suppressed.

(3) The surface of the workpiece is effectively bombarded and activated by argon ions to increase the diffusion channels of nitrogen atoms, accelerate the nitriding process, avoid the formation of compound layers, and improve the thermal fatigue performance of the workpiece.

Description of drawings

Fig. 1 is the working schematic diagram of vacuum chamber;

Fig. 2 is the cross-sectional hardness gradient curve of H13 steel in the sandblasted state after arc plasma assisted nitriding treatment;

Fig. 3 is the metallographic photograph of the nitrided layer of the H13 steel cross-section in the blasted state;

Fig. 4 is a cross-sectional hardness gradient curve of H13 steel in the grinding state of grinding wheel after arc plasma assisted nitriding treatment;

Fig. 5 is the metallographic photograph of the nitriding layer of the H13 steel cross-section in the grinding state of the grinding wheel;

Fig. 6 is the hardness gradient curve of the cross section of H13 steel in the state of sandpaper grinding (1000#) after arc plasma assisted nitriding treatment;

Figure 7 is a metallographic photo of the nitrided layer of the H13 steel cross-section in the state of sandpaper grinding (1000#);

Fig. 8 is a curve diagram of the cross-section hardness gradient of mechanically polished H13 steel after arc plasma assisted nitriding treatment;

Fig. 9 is a metallographic photo of the nitrided layer of the H13 steel cross-section in the mechanically polished state.

detailed description:

The present invention will be further described below in conjunction with specific examples, but is not limited thereto.

Embodiment 1—workpiece surface blasting

(1) The workpiece is H13 steel that has been sandblasted, with a sandblasting particle size of 80 mesh and a roughness Ra of 1.4 μm. The workpiece is ultrasonically cleaned with acetone solution for 20 minutes, taken out and dried with a hair dryer, and placed in an arc plasma assisted nitriding device Carry out nitriding treatment in the vacuum chamber, turn on the mechanical pump and the molecular turbo pump in turn to evacuate to the background vacuum, heat to 600°C, and remove the residue in the vacuum chamber.

(2) Keep the temperature in the furnace at 500°C, the air pressure in the vacuum chamber is 4.0×10 ^-3 Pa, the workpiece transfer platform is connected to the negative electrode of the pulse power supply, the negative bias voltage is 300V, the pulse frequency is 20kHz, and the duty cycle is 0.8. The arc target is used to start the arc. The arc target uses a Ti target. The target current is 85A. There is a baffle in front of the target. The evaporated Ti ions are deposited on the baffle, thereby colliding to generate Ar ⁺ , etching the surface of the workpiece, and removing the oxide on the surface. The argon flow rate is 190 mL/min, the pressure in the furnace is kept at 1.0 Pa, and the surface of the workpiece is ion-etched for 60 min.

(3) Continuously feed constant flow of high-purity N ₂ , high-purity H ₂ , and inert gas Ar into the furnace. The flow rate of N ₂ is 50 mL/min, the flow rate of H ₂ is 25 mL/min, and the flow rate of Ar is 120 mL/min. The workpiece transfer platform is connected to the negative pole of the pulse power supply, the negative bias voltage is 300V, the pulse frequency is 20kHz, and the duty cycle is 0.8. The arc target current is 85A, the air pressure is kept at 1.0Pa, the temperature is 500°C, and plasma nitriding is carried out for 120min.

(4) Then turn on the cooling water circulation system of the furnace body to cool for 60 minutes. The workpiece is cooled to room temperature with the furnace under a vacuum of 1.0×10 ^-7 Pa. Then turn on the vacuum furnace and take out the workpiece. Figure 1 is a schematic diagram of the vacuum chamber.

The H13 steel in the sandblasted state has a hardness gradient curve after the above-mentioned 500°C arc plasma assisted nitriding is shown in Figure 2. The surface hardness is 1192.0 HV _0.2 , and the depth of the nitriding layer is between 15-20 μm in 2 hours. There is no vein-like distribution of nitride in the middle diffusion layer, and the nitride level is level 1, as shown in Figure 3.

The mechanically ground H13 steel has an original roughness of 1.4 μm, and the roughness after nitriding is still 1.4 μm. After sandblasting, the surface has a large lattice distortion, the dislocation density increases, and the bombardment effect of Ar ⁺ on the surface is not good. Obviously, the thickness of the compound layer under the metallographic microscope (500×) is about 3 μm. The indentation test shows that the brittleness of the surface layer is good, there are no obvious cracks around the indentation, and the brittleness grade is level 1.

Embodiment 2—workpiece surface grinding wheel grinding

(1) The workpiece is H13 steel in the grinding state of the grinding wheel, with a roughness Ra of 0.8 μm. The workpiece is ultrasonically cleaned with acetone solution for 20 minutes. After taking it out, it is dried with a hair dryer, and placed in an arc plasma assisted nitriding device for nitriding treatment. Turn on the mechanical pump and the molecular turbo pump to evacuate to the background vacuum, heat to 600°C, and remove the residue in the vacuum chamber.

(2) Keep the temperature in the furnace at 500°C, the air pressure in the vacuum chamber is 4.0×10 ^-3 Pa, the workpiece transfer platform is connected to the negative electrode of the pulse power supply, the negative bias voltage is 300V, the pulse frequency is 20kHz, and the duty cycle is 0.8. The arc target is used to strike the arc. The arc target uses a Ti target. The target current is 85A. There is a baffle in front of the target. The evaporated Ti ions are deposited on the baffle, thereby colliding to generate Ar ⁺ , etching the surface of the workpiece, and removing the oxide on the surface. The argon flow rate is 190 mL/min, the pressure in the furnace is kept at 1.0 Pa, and the surface of the workpiece is ion-etched for 60 min.

(3) Continuously feed constant flow of high-purity N ₂ , high-purity H ₂ , and inert gas Ar into the furnace. The flow rate of N ₂ is 50 mL/min, the flow rate of H ₂ is 25 mL/min, and the flow rate of Ar is 120 mL/min. The workpiece transfer platform is connected to the negative pole of the pulse power supply, the negative bias voltage is 300V, the pulse frequency is 20 kHz, and the duty cycle is 0.8. The arc target current is 85A, the air pressure is kept at 1.0Pa, the temperature is 500°C, and plasma nitriding is carried out for 120min.

(4) Then turn on the cooling water circulation system of the furnace body to cool for 60 minutes, the workpiece is cooled to room temperature with the furnace under a vacuum state of 1.0×10 ^-7 Pa, turn on the vacuum furnace and take out the workpiece.

The hardness gradient curve of _H13 steel in grinding wheel grinding state is shown in Fig. 4 after the above 500 ^o C arc plasma assisted nitriding. Between 30-35 μm, there is no vein-like distribution of nitride in the diffusion layer in the nitrided layer, and the nitride level is level 1, as shown in Figure 5.

The H13 steel in the state of grinding wheel grinding has an original roughness of 0.80 μm. Due to the bombardment of Ar ⁺ during the nitriding process, the roughness after nitriding is 0.90 μm, and the thickness of the compound layer under the metallographic microscope (500×) is about 2 μm. The indentation test shows that the brittleness of the surface layer is good, and there are no obvious cracks around the indentation, and the brittleness grade is level 1.

Embodiment 3—workpiece surface sandpaper grinding

(1) The workpiece is sandpaper-polished (1000#) H13 steel, with a roughness of Ra 0.35 μm. The workpiece is ultrasonically cleaned with acetone solution for 20 minutes. After taking it out, it is dried with a hair dryer and placed in an arc plasma assisted nitriding device for nitriding For nitrogen treatment, turn on the mechanical pump and molecular turbo pump in turn to evacuate to the background vacuum, heat to 600°C, and remove the residue in the vacuum chamber.

(2) Keep the temperature in the furnace at 500°C, the air pressure in the vacuum chamber is 4.0×10 ^-3 Pa, the workpiece transfer platform is connected to the negative electrode of the pulse power supply, the negative bias voltage is 300V, the pulse frequency is 20kHz, and the duty cycle is 0.8. The arc target is used to start the arc. The arc target uses a Ti target. The target current is 85A. There is a baffle in front of the target. The evaporated Ti ions are deposited on the baffle, thereby colliding to generate Ar ⁺ , etching the surface of the workpiece, and removing the oxide on the surface. The argon flow rate is 190 mL/min, the pressure in the furnace is kept at 1.0 Pa, and ion etching is performed on the surface of the workpiece for 60 min.

(3) Continuously feed constant flow of high-purity N ₂ , high-purity H ₂ , and inert gas Ar into the furnace. The flow rate of N ₂ is 50 mL/min, the flow rate of H ₂ is 25 mL/min, and the flow rate of Ar is 120 mL/min. The workpiece transfer platform is connected to the negative pole of the pulse power supply, the negative bias voltage is 300V, the pulse frequency is 20kHz, and the duty cycle is 0.8. The arc target current is 85A, the air pressure is kept at 1.0Pa, the temperature is 500°C, and plasma nitriding is carried out for 120min.

(4) Then turn on the cooling water circulation system of the furnace body to cool for 60 minutes, the workpiece is cooled to room temperature with the furnace under a vacuum state of 1.0×10 ^-7 Pa, and the vacuum furnace is turned on and the workpiece is taken out.

The hardness gradient curve of H13 steel in the sandpaper ground state (1000#) after the above-mentioned 500°C arc plasma assisted nitriding is shown in Figure 6. The surface ground state increases the diffusion channel, and the depth of the nitriding layer increases after 2 hours, between 30-35 μm , the surface hardness is 1312.4HV _0.2 In the nitrided layer, there is no vein-like distribution of nitrides in the diffusion layer, and the nitride level is level 1, as shown in Figure 7.

Sandpaper polished state (1000#) H13 steel, the original roughness is 0.35μm, due to the bombardment of Ar ⁺ during the nitriding process, the roughness after nitriding is 0.65μm, the thickness of the compound layer under the metallographic microscope (500×) is about 1 μm. The indentation test shows that the brittleness of the surface layer is good, and there are no obvious cracks around the indentation, and the brittleness grade is level 1.

Embodiment 4—workpiece surface grinding and polishing

(1) The workpiece is mechanically polished H13 steel with a roughness of Ra0.05μm. The workpiece is ultrasonically cleaned with acetone solution for 20 minutes. After taking it out, it is dried with a hair dryer and placed in an arc plasma assisted nitriding device for nitriding treatment. Turn on the mechanical pump and the molecular turbo pump to evacuate to the background vacuum, heat to 600°C, and remove the residue in the vacuum chamber.

(2) Keep the temperature in the furnace at 500°C, the air pressure in the vacuum chamber is 4.0×10 ^-3 Pa, the workpiece transfer platform is connected to the negative electrode of the pulse power supply, the bias voltage is -300V, the pulse frequency is 20kHz, and the duty cycle is 0.8. The arc is struck by the arc target. The arc target uses a Ti target. The current of the arc target is 85A. There is a baffle in front of the target. The evaporated Ti ions are deposited on the baffle, thereby colliding to generate Ar ⁺ , etching the surface of the workpiece, and removing the oxidation on the surface. thing. The argon flow rate is 190 mL/min, the pressure in the furnace is kept at 1.0 Pa, and ion etching is performed on the surface of the workpiece for 60 min.

(3) Continuously feed constant flow of high-purity N ₂ , high-purity H ₂ , and inert gas Ar into the furnace. The flow rate of N ₂ is 50 mL/min, the flow rate of H ₂ is 25 mL/min, and the flow rate of Ar is 120 mL/min. The workpiece transfer platform is connected to the negative pole of the pulse power supply, the bias voltage is -300V, the pulse frequency is 20kHz, and the duty cycle is 0.8. The arc target current is 85A, the air pressure is kept at 1.0Pa, and the temperature is 500°C for 120min plasma nitriding.

(4) Then turn on the cooling water circulation system of the furnace body to cool for 60 minutes, the workpiece is cooled to room temperature with the furnace under a vacuum state of 1.0×10 ^-7 Pa, turn on the vacuum furnace and take out the workpiece.

The mechanically polished H13 steel has a hardness gradient curve after arc plasma assisted nitriding at 500°C as shown in Figure 8. The penetration rate of the polished state is lower than that of the ground state. The hardness is 1255.2 HV _0.2 In the nitrided layer, there is no vein-like distribution of nitrides in the diffusion layer, and the nitride level is level 1, as shown in Figure 9.

The mechanically polished H13 steel has an original roughness of 0.05 μm, and due to the bombardment of Ar ⁺ during the nitriding process, the roughness after nitriding is 0.40 μm, and the thickness of the compound layer under the metallographic microscope (500×) is about 1 μm. The indentation test shows that the brittleness of the surface layer is good, and there are no obvious cracks around the indentation, and the brittleness grade is level 1.

Claims (5)

1. a kind of surface of hot working die arc-plasma auxiliary low pressure nitriding method, it is characterised in that comprise the following steps：

1）Workpiece is the H13 of different pre-treatments state（4Cr5MoSiV1）Clean, dry up through ultrasonic wave, be placed in low pressure nitriding device In, unlatching mechanical pump, molecule turbine pump are evacuated to base vacuum successively, are heated to 600 DEG C of 300-, remove residual in vacuum chamber Stay thing；

2）Keep reacting 300-500 DEG C of in-furnace temperature, air pressure is 2.0 × 10 in reacting furnace^-2 -4.0×10^-3 Pa, workpiece turn flat Platform connects pulse power negative pole, electric arc target striking, leads to argon gas, and air pressure keeps 0.2-1.0Pa in reacting furnace, and workpiece surface is carried out Ion etching 30-60min；Described workpiece turns platform and connects pulse power negative pole, and back bias voltage is 300-500V, and use is bipolar Pulse, pulse frequency 10-20kHz, dutycycle 0.8-1.0；

3）High-purity N is continuously passed through into reacting furnace₂, high-purity H₂ With inert gas Ar, keep reaction in-furnace temperature and air pressure permanent Fixed, workpiece turns platform and connects pulse power negative pole, and electric arc target current 80-85A keeps constant, carries out 60-120min plasmas and oozes Nitrogen；Described workpiece turns platform and connects pulse power negative pole, and back bias voltage is 300-500V, using bipolar pulse, pulse frequency 10-20kHz, dutycycle 0.8-1.0；Described N₂ Flow is 25-50mL/min, H₂ Flow is 25-50mL/min, Ar Flow is 80-120 mL/min；Described temperature is 300-500 DEG C, air pressure 0.2-1.0Pa；

4）Later on body of heater recirculating cooling water system cools down 60-120min, and workpiece cools to room with the furnace under low vacuum state Temperature, open vacuum drying oven and take out workpiece.

2. a kind of surface of hot working die arc-plasma auxiliary low pressure nitriding method according to claim 1, its feature It is, step 2）Described electric arc target current is 80-85A.

3. a kind of surface of hot working die arc-plasma auxiliary low pressure nitriding method according to claim 1, its feature It is, step 2）Described argon flow amount is 180-200 mL/min.

4. a kind of surface of hot working die arc-plasma auxiliary low pressure nitriding method according to claim 1, its feature It is, step 2）Described ion etching refers to using electric arc enhancing glow discharge technique.

5. a kind of surface of hot working die arc-plasma auxiliary low pressure nitriding method according to claim 4, its feature It is, electric arc enhancing glow discharge technique, is that high density electronics is produced by arc discharge, electronics is with being passed through argon gas collision, electricity Separate out Ar⁺, workpiece surface is performed etching；Electric arc target uses Ti.