Method for heat treatment of a pearlitic heat-resistant steel

Abstract

The application relates to a steel material surface modification treatment method, in particular to a pearlite heat-resistant steel heat treatment method, and solves the technical problem that a 2Cr3WMoV material is difficult to meet the performance requirements of high-speed operation of an aircraft fuel accessory. The pearlite heat-resistant steel heat treatment method comprises the following steps: step 1: pretreatment, quenching, heat preservation, air cooling or oil cooling of a 2Cr3WMoV-1 material rod, then tempering, heat preservation, water cooling or oil cooling, and obtaining a rod with a hardness HRC less than or equal to 32; then the rod is processed into a gear to be treated; then the rod is processed into a gear to be treated; step 2: carbonitriding is performed; step 3: subcritical quenching, cold treatment and tempering are performed, and the heat treatment of the gear to be treated is completed, so that the pearlite heat-resistant steel has higher hardness and wear resistance.

Description

TECHNICAL FIELD

[0001] The application relates to a surface modification treatment method of a steel material, in particular to a heat treatment method of a pearlite heat-resistant steel. BACKGROUND

[0002] 2Cr3WMoV-1 is a new type of pearlite heat-resistant steel, and is different from 2Cr3WMoV in GJB2294-1995 'Stainless Steel and Heat-Resistant Steel Bar Specification for Aviation' in the contents of C element, Mn element, Si element and Cr element, and the specific differences are shown in Table 1:

[0003] Table 1

[0004] Material Type C Mn Si Cr 2Cr3WMoV 0.16-0.24 0.25-0.6 ≤0.4 2.4-3.3 2Cr3WMoV-1 0.15-0.2 0.25-0.5 0.17-0.37 2.8-3.3

[0005] The 2Cr3WMoV material is mainly applied to forged gears to be treated, and through the heat treatment method of carburizing + quenching, a deep penetration layer, high hardness and wear resistance can be achieved, and the performance requirements of an aero-engine fuel accessory can be met, but the performance requirements of a high-speed operation of an aircraft fuel accessory cannot be met. In the prior art, no report about solving the related technical problems (hardness, wear resistance, etc.) of the pearlite heat-resistant steel (2Cr3WMoV-1) through heat treatment is found. SUMMARY

[0006] The application aims at solving the technical problem that the 2Cr3WMoV material cannot meet the performance requirements of a high-speed operation of an aircraft fuel accessory, and provides a heat treatment method of a pearlite heat-resistant steel, so that the pearlite heat-resistant steel has higher hardness and wear resistance.

[0007] The idea of the application is:

[0008] The round bar 2Cr3WMoV-1 which is better than the 2Cr3WMoV material is selected, the contents of C element, Mn element, Si element and Cr element in the round bar 2Cr3WMoV-1 are strictly controlled, the heat treatment method is changed on the basis of optimizing the 2Cr3WMoV material, the pretreatment, two-stage carbonitriding and intercritical quenching method are adopted, a carbonitriding layer with epsilon nitrogen carbide is formed on the surface of the gear processed by the round bar 2Cr3WMoV-1, compared with the chemical heat treatment of carburizing or / and nitriding, the gear processed by the round bar 2Cr3WMoV-1 has the characteristics of high wear resistance and small brittleness; meanwhile, the matrix grains of the gear are refined, and appropriate distribution of fine ferrite structure is obtained, so that the matrix has higher toughness, and the performance requirements of a high-speed operation of an aircraft fuel accessory are met.

[0009] In order to solve the above technical problems and realize the above application idea, the technical scheme adopted by the application is:

[0010] A heat treatment method of pearlitic heat-resistant steel, which is characterized by comprising the following steps:

[0011] Step 1: pretreatment

[0012] The bar of 2Cr3WMoV-1 material is quenched, and after holding, air cooling or oil cooling is performed; then tempering, holding, water cooling or oil cooling are performed, so as to obtain a bar with a hardness of HRC less than or equal to 32, and finally the bar is processed into a gear to be treated;

[0013] Step 2: carbonitriding

[0014] 2.1) determining the penetrant for carbonitriding;

[0015] 2.2) calculating the ratio of carbon atoms to nitrogen atoms of the carbonitriding layer of the gear to be treated obtained in step 1 according to the penetrant in step 2.1);

[0016] 2.3) performing two-stage carbonitriding on the gear to be treated obtained in step 1 by using the penetrant in step 2.1) and the ratio of carbon atoms to nitrogen atoms in step 2.2), so as to obtain a gear to be treated with a carbonitriding layer thickness of 0.35-0.5mm;

[0017] Step 3: subcritical quenching, cold treatment and tempering

[0018] 3.1) subcritical quenching the gear to be treated obtained in step 2.2);

[0019] 3.2) cold treatment of the gear to be treated obtained in step 3.1);

[0020] 3.3) tempering the gear to be treated obtained in step 3.2) to complete the heat treatment of the gear to be treated.

[0021] Further, step 1 is specifically:

[0022] The bar of 2Cr3WMoV-1 material is quenched at a quenching temperature of 1050±10℃, holding for 60-90min, and after holding, air cooling or oil cooling is performed; after air cooling or oil cooling, tempering is performed at a tempering temperature of 700±10℃, holding for 60-90min, and after holding, water cooling or oil cooling is performed, so as to obtain a bar with a hardness of HRC less than or equal to 32, and then the bar is processed into a gear to be treated.

[0023] Further, in step 2.1), the penetrant comprises a carburizing agent, a diluent and ammonia;

[0024] The carburizing agent is C3H8, and the diluent is CH3OH.

[0025] Further, step 2.2) is specifically:

[0026] 2.2.1, calculating the content of carbon atoms in the carbonitrided layer of the gear to be treated obtained in step 1;

[0027] setting the carbon potential in the carbonitriding furnace, determining the flow rate of CH3OH according to the flow rate of C3H8, and calculating the content of carbon atoms in the carbonitrided layer of the gear to be treated obtained in step 1;

[0028] 2.2.2, calculating the content of nitrogen atoms in the carbonitrided layer of the gear to be treated obtained in step 1 according to the volumes of C3H8, CH3OH and NH3 gases in the carbonitriding furnace;

[0029] 2.2.3, obtaining the ratio of carbon atoms to nitrogen atoms in the carbonitrided layer according to the content of carbon atoms obtained in step 2.2.1 and the content of nitrogen atoms obtained in step 2.2.2.

[0030] Further, step 2.2.1 is specifically:

[0031] setting the carbon potential in the carbonitriding furnace to 0.9±0.1%, solidifying the flow rate of C3H8 to 0.3±0.1 L / min, and controlling the flow rate of CH3OH to 0.7-1 L / H through the control mode of oxygen probe+carbon potential control instrument, so that the content of carbon atoms in the carbonitrided layer of the gear to be treated obtained in step 1 is 0.8%-0.9%.

[0032] Further, step 2.2.2 is specifically:

[0033] 2.2.2.1, determining that the volume ratio of NH3 gas to CH3OH decomposition gas in the carbonitriding furnace is 2.3%;

[0034] 2.2.2.2, according to the flow rate of CH3OH 0.7-1 L / H in step 2.2.1 and the volume ratio 2.3% in step 2.2.2.1, calculating that the flow rate of NH3 is 0.43-0.61 L / min, so that the content of nitrogen atoms in the carbonitrided layer is 0.3%-0.4%.

[0035] Further, step 2.2.3 is specifically:

[0036] According to the content of carbon atoms 0.8%-0.9% in step 2.2.1 and the content of nitrogen atoms 0.3%-0.4% in step 2.2.2.2, the ratio of carbon atoms to nitrogen atoms in the carbonitrided layer is 2-3.

[0037] Further, step 2.3) is specifically:

[0038] 2.3.1, in the first stage of carbonitriding, C3H8, CH3OH and NH3 in step 2.1) are introduced, the carbon potential in the carbonitriding furnace is set to 0.9±0.1%, the flow rate of NH3 is controlled to be 0.45-0.6 L / min, the heating temperature is 830±10℃, and the holding time is 55-75 min, the carbon atoms and nitrogen atoms are penetrated into the gear to be treated obtained in step 1 according to the ratio obtained in step 2.2.3, and the ratio is selected to be 2.5; the ratio is 2.5;

[0039] 2.3.2, in the second stage of carbonitriding, the carbon potential in the carbonitriding furnace is reduced to 0.7±0.1%, the flow rate of NH3 is 0.45-0.6 L / min, the heating temperature is 830±10℃, and the holding time is 20-40 min, and a carbonitriding layer with a thickness of 0.35-0.5 mm is obtained.

[0040] Further, step 3.1) is specifically:

[0041] The gear to be treated obtained in step 2.3.2 is placed in an atmosphere furnace, the temperature of the atmosphere furnace is heated to 700±10℃, and the holding time is 2-3 hours, the atmosphere furnace is cooled to below 300℃, and the gear to be treated is taken out; then the gear to be treated is transferred into a salt furnace, and the heating temperature of the salt furnace is adjusted to 870±10℃, and the holding time is 10-15 min; finally, the gear to be treated is transferred into a nitrate salt tank or an alkali tank, and the heating temperature of the nitrate salt tank or the alkali tank is adjusted to 200±20℃, and the cooling time is 3-5 min, and the gear to be treated obtains a carbonitriding layer with ε nitrogen-carbon compound;

[0042] Alternatively, the gear to be treated obtained in step 2.3.2 is placed in an atmosphere furnace, the temperature of the atmosphere furnace is heated to 700±10℃, and the holding time is 2-3 hours, the atmosphere furnace is cooled to below 300℃, and the gear to be treated is taken out; then the gear to be treated is transferred into a salt furnace, and the heating temperature of the salt furnace is adjusted to 900±20℃, and the holding time is 7-12 min, and oil cooling is performed after holding, so that the gear to be treated obtains a carbonitriding layer with ε nitrogen-carbon compound.

[0043] Further, step 3.2) is specifically:

[0044] The gear to be treated obtained in step 3.1) is placed in an ice cooling machine, and the temperature of the ice cooling machine is adjusted to be less than or equal to -75℃, and the holding time is 1-2 h, and cold treatment is performed after holding;

[0045] Step 3.3) is specifically:

[0046] Put the gear to be treated obtained in step 3.2) into the oven, and set its temperature to 160±10 DEG C, and the holding time is greater than or equal to 2 hours, and after holding, air cooling is carried out, to obtain the gear to be treated with a carbonitriding layer of 0.35-0.5mm, a surface hardness of 56-62HRC, a center hardness of 35-43.5HRC, and a carbide grade of less than or equal to 5, and the heat treatment of the gear to be treated is completed.

[0047] Compared with the prior art, the beneficial effects of the technical scheme of the present application are:

[0048] (1) The heat treatment method of the pearlitic heat-resistant steel utilizes the gear to be treated processed by 2Cr3WMoV-1 material, changes the carbon atom and nitrogen atom ratio of the carbonitriding layer of the gear to be treated through carbonitriding, and then forms a carbonitriding layer with epsilon nitrogen carbide on the surface of the gear to be treated through two-stage carbonitriding and subcritical quenching, so as to obtain high wear resistance and fatigue resistance; meanwhile, the matrix grains of the gear to be treated are refined, and fine ferrite tissue is appropriately distributed, so that the gear to be treated has higher toughness and small deformation, and can meet the performance requirements of high-speed operation of aircraft fuel accessories.

[0049] (2) The heat treatment method of the pearlitic heat-resistant steel utilizes the gear to be treated processed by 2Cr3WMoV-1 material, reasonably determines the volume ratio of carburizing agent and ammonia, avoids black tissue defects and excessive residual austenite of the gear to be treated, improves the distribution of the carbonitriding layer of the gear to be treated, prevents the occurrence of adverse tissue, and makes the carbonitriding layer of the gear to be treated reach 0.35-0.5mm, the surface hardness reach HRC56-62, and the center hardness reach HRC35-43.5.

[0050] (3) The heat treatment method of the pearlitic heat-resistant steel utilizes the gear to be treated processed by 2Cr3WMoV-1 material, and when applied to an aircraft oil pump, the working rated speed of the aircraft oil pump can reach 12100r / min, the speed is high, the load is light, and short-time high-speed stable operation is realized. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 In the embodiment of the heat treatment method of the pearlitic heat-resistant steel, the pretreatment process curve of the gear to be treated is shown in the figure.

[0052] Figure 2 In the embodiment of the heat treatment method of the pearlitic heat-resistant steel, the two-stage carbonitriding process curve of the gear to be treated is shown in the figure.

[0053] Figure 3For the embodiment of the pearlitic heat-resistant steel heat treatment method of the present application, the to-be-processed gear is subjected to tempering and intercritical quenching to obtain a process curve diagram of the to-be-processed gear with a center hardness HRC of 35-39.

[0054] Figure 4 For the embodiment of the pearlitic heat-resistant steel heat treatment method of the present application, the to-be-processed gear is subjected to tempering and intercritical quenching to obtain a process curve diagram of the to-be-processed gear with a center hardness HRC of 39-45. DETAILED DESCRIPTION

[0055] A pearlitic heat-resistant steel heat treatment method, comprising the following steps:

[0056] Step 1: Pretreatment

[0057] As shown in Figure 1 , the bar stock of 2Cr3WMoV-1 material is quenched at a quenching temperature of 1050±10℃ for 60-90min, and then subjected to air cooling or oil cooling after the holding; then the bar stock is tempered at a tempering temperature of 700±10℃ for 60-90min, and then subjected to water cooling or oil cooling after the holding to obtain a bar stock with a hardness HRC less than or equal to 32, and finally the bar stock is processed into a to-be-processed gear.

[0058] Step 2: Carbonitriding

[0059] Since the 2Cr3WMoV-1 material contains a large number of alloying elements, in order to avoid the to-be-processed gear processed from the bar stock of 2Cr3WMoV-1 material from having black structure defects, excessive residual austenite, and decreased surface hardness, it is necessary to reasonably determine the volume ratio of carburizing agent to ammonia gas so that carbon atoms and nitrogen atoms in the carbonitriding layer are infiltrated in a certain proportion, and the specific determination method is as follows:

[0060] 2.1) Determine the carburizing agent for carbonitriding;

[0061] During the carbonitriding process, the volume ratio of the carburizing agent (gas) to ammonia gas (NH3) should be selected according to the material of the part, the structure and properties of the carburized layer, and the type of carbonitriding temperature. In this embodiment, the carburizing agent includes carburizing agent, diluent and ammonia gas; preferably the carburizing agent is C3H8, and the diluent is CH3OH;

[0062] 2.2) According to the carburizing agent in step 2.1), calculate the ratio of carbon atoms to nitrogen atoms in the carbonitriding layer of the to-be-processed gear obtained in step 1;

[0063] 2.2.1, calculate the content of carbon atoms in the carbonitriding layer;

[0064] The carbon potential in the carbonitriding furnace is set to 0.9±0.1%, the flow rate of solidified C3H8 is 0.3±0.1L / min, the flow rate of CH3OH is controlled to 0.7-1L / H by the control mode of oxygen probe+carbon potential control instrument, and the content of carbon atoms in the carbonitriding layer is 0.8%-0.9%.

[0065] 2.2.2. According to the volume of C3H8, CH3OH and NH3 gas in the carbonitriding furnace, the content of nitrogen atoms in the carbonitriding layer is calculated.

[0066] 2.2.2.1. Generally, the volume ratio of NH3 gas to the gas in the carbonitriding furnace is set to 2-12%, and the volume ratio of NH3 gas to the volume of CH3OH decomposition gas in the carbonitriding furnace is determined to be 2.3% in the present application.

[0067] 2.2.2.2. According to the flow rate of CH3OH of 0.7-1L / H in step 2.2.1 and the volume ratio of 2.3% in step 2.2.2.1, the flow rate of NH3 can be calculated.

[0068] In the present embodiment, when the flow rate of CH3OH is 1L / H, the flow rate of decomposition gas is 26.7L / min, and the flow rate of NH3 is 26.7×2.3%=0.61L / min. In actual production, the flow rate of CH3OH is 0.7-1L / H, and the flow rate of NH3 is

[0069] Minimum flow rate of NH3: 0.7×0.61=0.43L / min

[0070] Maximum flow rate of NH3: 1×0.61=0.61L / min

[0071] Since the minimum scale of the float flowmeter is 0.05L / min, it is convenient for on-site operation, and therefore the flow rate of NH3 is controlled to 0.45-0.6L / min by the float flowmeter.

[0072] According to the calculated flow rate of NH3 of 0.43-0.61L / min, the content of nitrogen atoms in the carbonitriding layer is 0.3%-0.4%.

[0073] 2.2.3. According to the content of carbon atoms of 0.8%-0.9% in step 2.2.1 and the content of nitrogen atoms of 0.3%-0.4% in step 2.2.2.2, the ratio of carbon atoms to nitrogen atoms in the carbonitriding layer is 2-3.

[0074] 2.3) 2Cr3WMoV-1 material contains a variety of carbide-forming elements with high content. In order to avoid the appearance of unfavorable structures such as network, block, and angular structures in the carbonitrided layer of the gear to be processed, C3H8, CH3OH and NH3 are added according to the ratio of carbon atoms to nitrogen atoms in step 2.2.3 to perform two-stage carbonitriding on the gear to be processed obtained in step 1 to obtain a carbonitrided layer with a thickness of 0.35-0.5mm. Specifically, Figure 2 As shown:

[0075] 2.3.1. In the first carbonitriding stage, under the action of high carbon potential and high temperature, C3H8, CH3OH and NH3 prepared in step 2.1) are introduced into the carbonitriding furnace, and the gear to be treated is kept warm for a long time for strong carbonitriding, so that carbon atoms and nitrogen atoms are infiltrated into the matrix of the gear to be treated in a certain ratio. In this embodiment, preferably, the ratio of carbon atoms to nitrogen atoms is selected to be 2.5; the carbon potential in the carbonitriding furnace is set to 0.9%±0.1%, the flow rate of NH3 is 0.45-0.6 L / min, the heating temperature is 830±10°C, and the temperature is kept warm for 55-75 minutes. Carbon atoms and nitrogen atoms are infiltrated into the gear to be treated obtained in step 1, and a high-concentration carbonitriding layer of 0.35-0.4 mm is obtained;

[0076] 2.3.2. In the second stage of carbonitriding, the carbon potential in the carbonitriding furnace is reduced to 0.7±0.1%, the flow rate of NH3 is 0.45-0.6 L / min, the heating temperature is 830±10℃, and the temperature is kept for 20-40 minutes to obtain a gear to be treated with a carbonitriding layer thickness of 0.35-0.5 mm.

[0077] Since the first stage of carbonitriding is a strong infiltration, the carbon concentration on the surface of the infiltration layer is about 0.9%±0.1%. The second stage reduces the carbon potential to 0.7±0.1%. The short-term "trace" infiltration method is adopted. On the one hand, the carbon atoms and nitrogen atoms on the surface of the infiltration layer diffuse to the core of the gear to be processed, so that the concentration gradient gradually slows down, thereby improving the distribution of carbides and nitrides in the infiltration layer of the gear to be processed and preventing the emergence of unfavorable structures; on the other hand, trace amounts of carbon atoms and nitrogen atoms infiltrate into the parts of the gear to be processed with low local content, avoiding the appearance of "soft spots" in the infiltration layer.

[0078] Step 3: Tempering and sub-temperature quenching

[0079] In GJB2294-1995, "Specification for Stainless Steel and Heat-Resistant Steel Bars for Aviation," the quenching temperature for 2Cr3WMoV is 1030-1080°C, while the 2Cr3WMoV-1 material standard recommends a quenching temperature of 900-950°C. In line with the requirements of this standard and based on the carbonitriding quenching process commonly used for structural steel and stainless steel, the present invention selects a sub-temperature quenching method, namely 870±10°C or 900±20°C. This forms a carbonitriding layer containing ε nitrogen and carbon compounds on the surface of the gear to be treated, achieving higher wear resistance than the carburized layer. Simultaneously, it refines the matrix grains of the gear to be treated, resulting in a properly distributed fine ferrite structure, achieving higher toughness and reducing deformation of the gear to be treated.

[0080] 3.1) If Figure 3 As shown, the gear to be processed obtained in step 2.3.2 is placed in an atmosphere furnace, heated to 700±10°C, kept warm for 2-3 hours, and then cooled to below 300°C before being taken out of the furnace; the gear to be processed is then transferred to a salt furnace, heated to 870±10°C, and kept warm for 10-15 minutes; finally, the gear to be processed is transferred to an alkali tank or a nitrate salt tank, and the heating temperature of the alkali tank or the nitrate salt tank is adjusted to 200±20°C, cooled for 3-5 minutes, and air-cooled, so that the gear to be processed obtains a carbonitrided layer having ε nitrogen-carbon compounds and a center hardness HRC of 35-39;

[0081] Or, as Figure 4 As shown, in order to improve the center hardness of the gear to be processed, the gear to be processed obtained in step 2.3.2 can also be placed in an atmosphere furnace, the atmosphere furnace temperature is heated to 700±10℃, kept warm for 2-3 hours, and the atmosphere furnace is cooled to below 300℃ and taken out of the furnace; then the gear to be processed is transferred to a salt furnace, and the salt furnace is heated to a temperature of 900±20℃, kept warm for 7-12 minutes, and oil-cooled after keeping warm, so that the gear to be processed obtains a carbonitriding layer with ε nitrogen-carbon compounds, and the center hardness HRC is 39-45.

[0082] 3.2) Place the gear to be treated obtained in step 3.1) in a freezer and adjust the temperature of the freezer to be less than or equal to -75°C for 1-2 hours, then perform the cold treatment.

[0083] 3.3) The gear to be treated obtained in step 3.2) is placed in an oven at 160±10°C for 2 hours or longer, followed by air cooling to obtain a gear to be treated having a carbonitrided layer of 0.35-0.5 mm, a surface hardness of 56-62 HRC, a center hardness of 35-43.5 HRC, and a carbide grade of ≤5. This provides the gear to be treated with increased wear resistance and toughness, and minimizes deformation, thereby meeting the performance requirements of high-speed operation of aircraft fuel accessories.

Claims

1. A heat treatment method for a pearlitic heat-resistant steel, characterized by, The method comprises the following steps: Step 1: pretreatment The bar of 2Cr3WMoV-1 material is quenched, and then is kept for a certain time, and then is air-cooled or oil-cooled; then the bar is tempered, and then is kept for a certain time, and then is water-cooled or oil-cooled, so that the bar with a hardness of HRC less than or equal to 32 is obtained, and finally the bar is processed into a gear to be treated; the 2Cr3WMoV-1 material mainly comprises, in percentage by mass, 0.15%-0.2% of C element, 0.25%-0.5% of Mn element, 0.17%-0.37% of Si element and 2.8%-3.3% of Cr element; Step 2: carbonitriding is performed 2.1) the carbonitriding agent is determined; 2.2) according to the carbonitriding agent in step 2.1), the ratio of carbon atoms to nitrogen atoms in the carbonitrided layer of the gear to be treated obtained in step 1 is calculated; 2.3) the gear to be treated obtained in step 1 is subjected to two-stage carbonitriding by using the carbonitriding agent in step 2.1) and the ratio of carbon atoms to nitrogen atoms in step 2.2), so that the gear to be treated with a carbonitrided layer with a thickness of 0.35-0.5 mm is obtained: 2.3.1, in the first-stage carbonitriding, C3H8, CH3OH and NH3 in step 2.1) are introduced, the carbon potential in the carbonitriding furnace is set to 0.9±0.1%, the flow rate of NH3 is controlled to be 0.45-0.6 L / min, the heating temperature is 830±10℃, the holding time is 55-75 min, the ratio of carbon atoms to nitrogen atoms is selected to be 2.5 according to the ratio obtained in step 2.2, and the gear to be treated obtained in step 1 is penetrated; 2.3.2, in the second-stage carbonitriding, the carbon potential in the carbonitriding furnace is reduced to 0.7±0.1%, the flow rate of NH3 is 0.45-0.6 L / min, the heating temperature is 830±10℃, the holding time is 20-40 min, and the gear to be treated with a carbonitrided layer with a thickness of 0.35-0.5 mm is obtained; Step 3: subcritical quenching, cold treatment and tempering are performed 3.1) the gear to be treated obtained in step 2.2) is subjected to subcritical quenching; 3.2) the gear to be treated obtained in step 3.1) is subjected to cold treatment; 3.3) the gear to be treated obtained in step 3.2) is subjected to tempering, and the heat treatment of the gear to be treated is completed.

2. The heat treatment method of the sorbite heat-resistant steel according to claim 1, characterized in that, Step 1 is specifically: The bar of 2Cr3WMoV-1 material is quenched at a quenching temperature of 1050±10℃, and then is kept for 60-90 min, and then is air-cooled or oil-cooled; after air-cooling or oil-cooling, the bar is tempered at a tempering temperature of 700±10℃, and then is kept for 60-90 min, and then is water-cooled or oil-cooled, so that the bar with a hardness of HRC less than or equal to 32 is obtained, and then the bar is processed into a gear to be treated.

3. The heat treatment method of the sorbite heat-resistant steel according to claim 2, characterized in that, Step 2.2) is specifically: 2.2.1, the content of carbon atoms in the carbonitrided layer is calculated; The carbon potential in the carbonitriding furnace is set, the flow rate of CH3OH is determined according to the flow rate of C3H8, and the content of carbon atoms in the carbonitrided layer of the gear to be treated obtained in step 1 is calculated; 2.2.2, the content of nitrogen atoms in the carbonitrided layer of the gear to be treated obtained in step 1 is calculated according to the volumes of C3H8, CH3OH and NH3 in the carbonitriding furnace; 2.2.3, according to the carbon atom content obtained in step 2.2.1 and the nitrogen atom content obtained in step 2.2.2, the ratio of carbon atoms to nitrogen atoms in the carbonitrided layer is obtained.

4. The method of heat treatment of a pearlitic heat-resistant steel according to claim 3, characterized in that, Step 2.2.1 is specifically: The carbon potential in the carbonitriding furnace is set to 0.9±0.1%, the flow rate of solidified C3H8 is 0.3±0.1L / min, the flow rate of CH3OH is controlled to be 0.7-1L / H by the control mode of oxygen probe+carbon potential control instrument, and the carbon atom content in the carbonitrided layer of the gear to be treated obtained in step 1 is 0.8%-0.9%.

5. The method of heat treatment of a pearlitic heat-resistant steel according to claim 4, characterized in that, Step 2.2.2 is specifically: 2.2.2.1, the volume ratio of NH3 gas to CH3OH decomposition gas in the carbonitriding furnace is determined to be 2.3%; 2.2.2.2, according to the flow rate of CH3OH in step 2.2.1 being 0.7-1L / H and the volume ratio in step 2.2.2.1 being 2.3%, the flow rate of NH3 is calculated to be 0.43-0.61L / min, and the nitrogen atom content in the carbonitrided layer is 0.3%-0.4%.

6. The method of heat treatment of a pearlitic heat-resistant steel according to claim 5, characterized in that, Step 2.2.3 is specifically: According to the carbon atom content of 0.8%-0.9% in step 2.2.1 and the nitrogen atom content of 0.3%-0.4% in step 2.2.2.2, the ratio of carbon atoms to nitrogen atoms in the carbonitrided layer is obtained.

7. The method of heat treatment of a pearlitic heat-resistant steel according to claim 6, characterized in that, Step 3.1) is specifically: The gear to be treated obtained in step 2.3.2 is placed into an atmosphere furnace, the temperature of the atmosphere furnace is heated to 700±10℃, and the temperature is maintained for 2-3 hours, and the atmosphere furnace is cooled to below 300℃ before being taken out of the furnace; then the gear to be treated is transferred into a salt furnace, and the salt furnace is heated to a temperature of 870±10℃, and the temperature is maintained for 10-15min; finally, the gear to be treated is transferred into a nitrate salt tank or an alkali tank, and the heating temperature of the nitrate salt tank or the alkali tank is adjusted to 200±20℃, and the temperature is cooled for 3-5min, and air cooling is performed, so that the gear to be treated obtains a carbonitrided layer with ε nitrogen-carbon compound; Alternatively, the gear to be treated obtained in step 2.3.2 is placed into an atmosphere furnace, the temperature of the atmosphere furnace is heated to 700±10℃, and the temperature is maintained for 2-3 hours, and the atmosphere furnace is cooled to below 300℃ before being taken out of the furnace; then the gear to be treated is transferred into a salt furnace, and the salt furnace is heated to a temperature of 900±20℃, and the temperature is maintained for 7-12min, and oil cooling is performed after the temperature is maintained, so that the gear to be treated obtains a carbonitrided layer with ε nitrogen-carbon compound.

8. The method of heat treatment of a pearlitic heat-resistant steel according to claim 7, characterized in that, Step 3.2) is specifically: The gear to be treated obtained in step 3.1) is placed into an ice cooler, and the temperature of the ice cooler is adjusted to be less than or equal to -75℃, and the temperature is maintained for 1-2h, and cold treatment is performed after the temperature is maintained; Step 3.3) is specifically: The gear to be treated obtained in step 3.2) is placed into an oven, and the temperature of the oven is set to 160±10℃, and the temperature is maintained for greater than or equal to 2 hours, and air cooling is performed after the temperature is maintained, so that the gear to be treated obtains a carbonitrided layer with a thickness of 0.35-0.5mm, a surface hardness of 56-62HRC, a center hardness of 35-43.5HRC, and a carbide grade of ≤5, and the heat treatment of the gear to be treated is completed.

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