Quenching and tempering method for peritectic steel large forged circle

Abstract

The invention discloses a quenching and tempering treatment method for a peritectic steel large forged circle, and relates to the technical field of forged circle machining and manufacturing, the quenching and tempering treatment method comprises the following steps: step S1, pretreatment: carrying out temperature programming gradient open fire preheating on a steel ingot; s2, forging forming is conducted, specifically, the steel ingot obtained after preheating treatment is hoisted to a forging press to start forging forming; and S3, heat treatment is conducted, specifically, heat treatment is conducted on the peritectic steel large forged circle formed through forging. The quenching and tempering treatment method for the peritectic steel large forged circle is simple and easy to implement and low in energy consumption; the peritectic steel large forged circle treated through the quenching and tempering process is smooth in surface, free of defects, high in yield, better in mechanical property, more excellent in corrosion resistance and long in service life.

Description

Technical Field

[0001] The invention relates to the technical field of forged circle processing and manufacturing, in particular to a quenching and tempering method for large peritectic steel forged circles. Background Art

[0002] Peritectic steel refers to the process in which the grains grow from the inside out during the metal crystallization process, and at the same time, there is another phase of metal on the surface that is mutually dissolved with it, forming a peritectic alloy. Due to its excellent properties such as high strength, high hardness, high wear resistance and high toughness, it is widely used in the manufacture of high-strength and high-wear-resistant parts such as cutting tools, molds, and bearings. With the further expansion of its application scope, people have higher and higher requirements for its performance, and the market demand is increasing.

[0003] Quenching and tempering treatment is an indispensable process in the preparation of alloy steel. This process can adjust the performance and material of steel to a great extent. The strength, plasticity and toughness of the steel after quenching and tempering treatment are good, and it has good comprehensive mechanical properties. Therefore, it is widely used in the heat treatment of steel. As one of the common alloy steel materials, it is very necessary to perform quenching and tempering treatment on peritectic steel forgings in order to improve their comprehensive properties. However, there are few reports on the existing quenching and tempering treatment processes for peritectic steel forgings. The only reported processes often have complex processes, long production cycles, high energy consumption, and the surface defects of the forged forgings are prone to cracking, resulting in defects such as material scrapping or loss.

[0004] In order to solve the above problems, a Chinese invention patent with authorization announcement number CN113355596B discloses a tempering treatment process for alloy steel forgings, wherein the alloy steel forgings include the following chemical components in percentage by mass: C=0.40-0.45%, Si=0.20-0.35%, Mn=0.6-0.8%, P≤0.01%, S≤0.01%, Cr=0.4-0.6%, Ni=0.6-0.9%, Mo=0.1-0.3%, Hf-Fe=0.01-0.03%, Zr-Fe=0.01-0.03%, Be=0.02-0.04%, Gd=0.01-0.03%, and the balance is iron; and a preparation method thereof includes step S1, open flame heating treatment before forging; step S2, forging; and step S3, heat treatment. The alloy steel forged round quenching and tempering treatment process provided by the invention is simple, easy to operate and control, and has low energy consumption; the alloy steel forged round treated by the quenching and tempering treatment process has a smooth surface without defects, a high qualified rate of finished products, better mechanical properties, and better comprehensive performance. However, the qualified rate of forged rounds made by this process needs to be further improved, and the mechanical properties need to be further improved. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a tempering treatment method for large forged peritectic steel circles. The treatment method is simple, easy to implement and has low energy consumption. The large forged peritectic steel circles treated by the tempering treatment process have a smooth surface without defects, a high yield rate, better mechanical properties, better corrosion resistance and a long service life.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a quenching and tempering method for large forged peritectic steel rounds, comprising the following steps:

[0007] Step S1, pretreatment: preheating the steel ingot with a programmed temperature gradient open flame;

[0008] Step S2, forging: hoisting the preheated steel ingot onto a forging press to start forging;

[0009] Step S3, heat treatment: heat treatment is performed on the forged peritectic steel large forging circle.

[0010] Preferably, the pre-programmed temperature rise gradient open flame preheating in step S1 is specifically as follows: heating from room temperature to 420-470°C at a heating rate of 1-3°C / min, keeping warm for 0.5-1h, then heating to 500-600°C at a heating rate of 3-5°C / min, keeping warm for 10-15min, then heating to 750-850°C at a heating rate of 5-8°C / min, keeping warm for 0.1-0.3h, then heating to 950-1050°C at a heating rate of 8-10°C / min, keeping warm for 0.2-0.5h; finally heating to 1210-1260°C at a rate of 10-12°C / min, keeping warm for 1-3h.

[0011] Preferably, the steel ingot in step S1 comprises the following components in weight percentage: C: 0.1%-0.18%, Si: 0.15%-0.45%, Mn: 0.75%-1%, Cr: 0.1%-0.3%, Ni: 0.5%-0.7%, Ta: 0.01%-0.03%, Nb: 0.1-0.3%, W: 0.01%-0.03%, rare earth elements: 0.01%-0.03%, Ga: 0.01%-0.03%, B: 0.001%-0.003%, and the balance is Fe and unavoidable impurities.

[0012] Preferably, the rare earth element is at least one of Sc, Y, La and Ce.

[0013] Preferably, the forging ratio of the forging forming in step S2 is 4-6, the soaking temperature is 1190-1240, the heating rate is ≤80°C / h, the soaking time is 3-5 hours, the start forging temperature is 1160-1180°C, the final forging temperature is 870-950°C, and the number of upsetting times is ≥4 times.

[0014] Preferably, the heat treatment in step S3 includes normalizing, annealing and tempering performed sequentially.

[0015] Preferably, the normalizing treatment is carried out at a temperature of 880-940° C. for a time of 0.5-1.2 h, followed by cooling in air.

[0016] Preferably, the quenching is step isothermal quenching, specifically: first keep warm at 840-910°C for 40-60min, then immediately transfer to a 580-620°C furnace for 25-45min, and then cool to room temperature at an average cooling rate of 28-34°C / second.

[0017] Preferably, the quenching is any one of water quenching and air quenching.

[0018] Preferably, the tempering treatment is a two-stage tempering treatment, the temperature of the first stage tempering treatment is 600-720°C, the insulation time is 0.8-1.2h, and the temperature of the second stage tempering treatment is 160-200°C, the insulation time is 1-2h. DETAILED DESCRIPTION

[0019] The preferred embodiments of the present invention will be described in detail below.

[0020] A quenching and tempering method for a large peritectic steel forging circle comprises the following steps:

[0021] Step S1, pretreatment: preheating the steel ingot with a programmed temperature gradient open flame;

[0022] Step S2, forging: hoisting the preheated steel ingot onto a forging press to start forging;

[0023] Step S3, heat treatment: heat treatment is performed on the forged peritectic steel large forging circle.

[0024] Preferably, the pre-programmed temperature rise gradient open flame preheating in step S1 is specifically as follows: heating from room temperature to 420-470°C at a heating rate of 1-3°C / min, keeping warm for 0.5-1h, then heating to 500-600°C at a heating rate of 3-5°C / min, keeping warm for 10-15min, then heating to 750-850°C at a heating rate of 5-8°C / min, keeping warm for 0.1-0.3h, then heating to 950-1050°C at a heating rate of 8-10°C / min, keeping warm for 0.2-0.5h; finally heating to 1210-1260°C at a rate of 10-12°C / min, keeping warm for 1-3h.

[0025] Preferably, the steel ingot in step S1 comprises the following components in weight percentage: C: 0.1%-0.18%, Si: 0.15%-0.45%, Mn: 0.75%-1%, Cr: 0.1%-0.3%, Ni: 0.5%-0.7%, Ta: 0.01%-0.03%, Nb: 0.1-0.3%, W: 0.01%-0.03%, rare earth elements: 0.01%-0.03%, Ga: 0.01%-0.03%, B: 0.001%-0.003%, and the balance is Fe and unavoidable impurities.

[0026] Preferably, the forging ratio of the forging forming in step S2 is 4-6, the soaking temperature is 1190-1240, the heating rate is ≤80°C / h, the soaking time is 3-5 hours, the start forging temperature is 1160-1180°C, the final forging temperature is 870-950°C, and the number of upsetting times is ≥4 times.

[0027] Preferably, the heat treatment in step S3 includes normalizing, annealing and tempering performed sequentially.

[0028] Preferably, the normalizing treatment is carried out at a temperature of 880-940° C. for a time of 0.5-1.2 h, followed by cooling in air.

[0029] Preferably, the quenching is step isothermal quenching, specifically: first keep warm at 840-910°C for 40-60min, then immediately transfer to a 580-620°C furnace for 25-45min, and then cool to room temperature at an average cooling rate of 28-34°C / second.

[0030] Preferably, the quenching is any one of water quenching and air quenching.

[0031] Preferably, the tempering treatment is a two-stage tempering treatment, the temperature of the first stage tempering treatment is 600-720°C, the insulation time is 0.8-1.2h, and the temperature of the second stage tempering treatment is 160-200°C, the insulation time is 1-2h.

[0032] Due to the application of the above technical scheme, the patent of the present invention has the following advantages compared with the prior art: the present invention makes the treatment method simple and easy with low energy consumption through the reasonable selection of the composition formula of the steel ingot and the tempering treatment process parameters; the surface of the large forged circle of peritectic steel treated by the tempering treatment process is smooth and defect-free, the yield rate is high, the mechanical properties are better, the corrosion resistance is more excellent, and the service life is long.

[0033] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0034] Example 1

[0035] A quenching and tempering method for a large peritectic steel forging circle comprises the following steps:

[0036] Step S1, pretreatment: preheating the steel ingot with a programmed temperature gradient open flame;

[0037] Step S2, forging: hoisting the preheated steel ingot onto a forging press to start forging;

[0038] Step S3, heat treatment: heat treatment is performed on the forged peritectic steel large forging circle.

[0039] The pre-programmed temperature-increasing gradient open flame preheating described in step S1 is specifically as follows: heating from room temperature to 420°C at a heating rate of 1°C / min, keeping warm for 0.5h, then heating to 500°C at a heating rate of 3°C / min, keeping warm for 10min, then heating to 750°C at a heating rate of 5°C / min, keeping warm for 0.1h, then heating to 950°C at a heating rate of 8°C / min, keeping warm for 0.2h; finally heating to 1210°C at a rate of 10°C / min, keeping warm for 1h.

[0040] The steel ingot in step S1 includes the following components in weight percentage: C: 0.1%, Si: 0.15%, Mn: 0.75%, Cr: 0.1%, Ni: 0.5%, Ta: 0.01%, Nb: 0.1, W: 0.01%, rare earth elements: 0.01%, Ga: 0.01%, B: 0.001%, and the balance is Fe and unavoidable impurities; the rare earth element is Sc.

[0041] The forging ratio of the forging forming in step S2 is 4, the soaking temperature is 1190, the heating rate is ≤80°C / h, the soaking time is 3 hours, the start forging temperature is 1160°C, the final forging temperature is 870°C, and the number of upsetting times is ≥4 times.

[0042] The heat treatment in step S3 includes normalizing, annealing and tempering in sequence; the temperature of the normalizing treatment is 880°C, the time is 0.5h, and then cooled in air; the quenching is step isothermal quenching, specifically: first keep warm at 840°C for 40min, then immediately transfer to a 580°C furnace and keep warm for 25min, and then cool to room temperature at an average cooling rate of 28°C / second; the quenching is water quenching; the temperature of the second stage tempering treatment is 160°C, and the holding time is 1h.

[0043] Example 2

[0044] A quenching and tempering method for a large forged peritectic steel round is basically the same as that in Example 1, except that the pre-programmed temperature rise gradient open flame preheating in step S1 is specifically as follows: heating from room temperature to 430°C at a heating rate of 1.5°C / min, keeping warm for 0.6h, then heating to 530°C at a heating rate of 3.5°C / min, keeping warm for 12min, then heating to 770°C at a heating rate of 6°C / min, keeping warm for 0.15h, and then heating to 770°C at a heating rate of 8.5°C / min. The heating rate is increased to 980°C and kept at this temperature for 0.3h; finally, the temperature is increased to 1230°C at a rate of 10.5°C / min and kept at this temperature for 1.5h; the steel ingot in step S1 comprises the following components by weight percentage: C: 0.12%, Si: 0.25%, Mn: 0.8%, Cr: 0.15%, Ni: 0.55%, Ta: 0.015%, Nb: 0.15%, W: 0.015%, rare earth elements: 0.015%, Ga :0.015%,B:0.0015%,the balance is Fe and inevitable impurities; the forging ratio of the forging in step S2 is 4.5, the soaking temperature is 1210, the heating rate is ≤80℃ / h, the soaking time is 3.5 hours, the start forging temperature is 1165℃, the final forging temperature is 890℃, and the number of upsetting times is ≥4 times; the heat treatment in step S3 includes normalizing treatment, annealing treatment and tempering treatment performed in sequence; the temperature of the normalizing treatment is 900℃, the time is for 0.7h, and then cooled in air; the quenching is step isothermal quenching, specifically: first keep warm at 870℃ for 45min, then immediately transfer to a 590℃ furnace and keep warm for 30min, and then cool to room temperature at an average cooling rate of 30℃ / sec; the quenching is air quenching; the tempering treatment is a two-stage tempering treatment, the temperature of the first stage tempering treatment is 640℃, the holding time is 0.9h, the temperature of the second stage tempering treatment is 175℃, and the holding time is 1.2h.

[0045] Example 3

[0046] A quenching and tempering method for a large forged peritectic steel round is basically the same as that in Example 1, except that the pre-programmed temperature rise gradient open flame preheating in step S1 is specifically as follows: heating from room temperature to 450°C at a heating rate of 2°C / min, keeping warm for 0.8h, then heating to 550°C at a heating rate of 4°C / min, keeping warm for 13min, then heating to 800°C at a heating rate of 6.5°C / min, keeping warm for 0.2h, and then heating to 800°C at a heating rate of 9°C / min. The temperature is raised to 1000°C at a heating rate of 11°C / min and kept at this temperature for 0.35h; finally, the temperature is raised to 1240°C at a rate of 11°C / min and kept at this temperature for 2h; the steel ingot in step S1 comprises the following components by weight percentage: C: 0.15%, Si: 0.3%, Mn: 0.85%, Cr: 0.2%, Ni: 0.6%, Ta: 0.02%, Nb: 0.2%, W: 0.02%, rare earth elements: 0.02%, Ga: 0 .02%, B: 0.002%, the balance is Fe and unavoidable impurities; the forging ratio of the forging in step S2 is 5, the soaking temperature is 1220, the heating rate is ≤80℃ / h, the soaking time is 4 hours, the start forging temperature is 1170℃, the final forging temperature is 930℃, and the number of upsetting times is ≥4 times; the heat treatment in step S3 includes normalizing treatment, annealing treatment and tempering treatment in sequence; the temperature of the normalizing treatment is 920℃, the time is 0. 9h, and then cooled in air; the quenching is step isothermal quenching, specifically: first keep warm at 890℃ for 50min, then immediately transfer to a 600℃ furnace and keep warm for 35min, and then cool to room temperature at an average cooling rate of 32℃ / second; the quenching is water quenching; the tempering treatment is a two-stage tempering treatment, the temperature of the first stage tempering treatment is 690℃, the holding time is 1h, and the temperature of the second stage tempering treatment is 180℃, and the holding time is 1.5h.

[0047] Example 4

[0048] A quenching and tempering method for a large forged peritectic steel round is basically the same as that in Example 1, except that the pre-programmed temperature rise gradient open flame preheating in step S1 is specifically as follows: heating from room temperature to 460°C at a heating rate of 2.5°C / min, keeping warm for 0.9h, then heating to 590°C at a heating rate of 4.5°C / min, keeping warm for 14min, then heating to 850°C at a heating rate of 7.5°C / min, keeping warm for 0.25h, and then heating to 850°C at a heating rate of 9.5°C / min. The temperature is raised to 1040°C at a heating rate of 11.5°C / min and kept at this temperature for 0.45h; finally, the temperature is raised to 1250°C at a rate of 11.5°C / min and kept at this temperature for 2.5h; the steel ingot in step S1 comprises the following components by weight percentage: C: 0.17%, Si: 0.42%, Mn: 0.95%, Cr: 0.25%, Ni: 0.65%, Ta: 0.025%, Nb: 0.25%, W: 0.025%, rare earth elements: 0.025% , Ga: 0.025%, B: 0.0025%, the balance is Fe and inevitable impurities; the forging ratio of the forging in step S2 is 5.5, the soaking temperature is 1230, the heating rate is ≤80℃ / h, the soaking time is 4.5 hours, the start forging temperature is 1175℃, the final forging temperature is 930℃, and the number of upsetting times is ≥4 times; the heat treatment in step S3 includes normalizing treatment, annealing treatment and tempering treatment performed in sequence; the temperature of the normalizing treatment is 930℃, The time is 1.1h, and then cooled in the air; the quenching is step isothermal quenching, specifically: first keep warm at 900℃ for 55min, then immediately transfer to a 610℃ furnace and keep warm for 43min, and then cool to room temperature at an average cooling rate of 33℃ / second; the quenching is air quenching; the tempering treatment is a two-stage tempering treatment, the temperature of the first stage tempering treatment is 710℃, the holding time is 1.1h, and the temperature of the second stage tempering treatment is 195℃, and the holding time is 1.8h.

[0049] Example 5

[0050] A quenching and tempering method for a large forged peritectic steel round is basically the same as that in Example 1, except that the pre-programmed temperature rise gradient open flame preheating in step S1 is specifically as follows: heating from room temperature to 470°C at a heating rate of 3°C / min, keeping warm for 1h, then heating to 600°C at a heating rate of 5°C / min, keeping warm for 15min, then heating to 850°C at a heating rate of 8°C / min, keeping warm for 0.3h, and then heating to 850°C at a heating rate of 10°C / min, keeping warm for 0.3h. The temperature is raised to 1050°C at a rate of 12°C / min and kept at this temperature for 0.5h; finally, the temperature is raised to 1260°C at a rate of 12°C / min and kept at this temperature for 3h; the steel ingot in step S1 comprises the following components by weight percentage: C: 0.18%, Si: 0.45%, Mn: 1%, Cr: 0.3%, Ni: 0.7%, Ta: 0.03%, Nb: 0.3%, W: 0.03%, rare earth elements: 0.03%, Ga: 0.03 %, B: 0.003%, the balance is Fe and inevitable impurities; the forging ratio of the forging in step S2 is 6, the soaking temperature is 1240, the heating rate is ≤80℃ / h, the soaking time is 5 hours, the start forging temperature is 1180℃, the final forging temperature is 950℃, and the number of roughening times is ≥4 times; the heat treatment in step S3 includes normalizing, annealing and tempering in sequence; the normalizing temperature is 940℃, the time is 1.2h, and then cooled in air; the quenching is step isothermal quenching, specifically: first keep warm at 910℃ for 60min, then immediately transfer to a 620℃ furnace for 45min, and then cool to room temperature at an average cooling rate of 34℃ / second; the quenching is water quenching; the tempering is a two-stage tempering, the temperature of the first stage tempering is 720℃, the holding time is 1.2h, and the temperature of the second stage tempering is 200℃, and the holding time is 2h.

[0051] Comparative Example 1

[0052] A method for quenching and tempering a large forged round peritectic steel is basically the same as Example 1, except that Ta and Ga are not added, annealing is used instead of quenching, the annealing temperature is 520° C., and the annealing time is 1 hour.

[0053] Comparative Example 2

[0054] A method for tempering a large forged round of peritectic steel is basically the same as Example 1, except that W and rare earth elements are not added, and the pre-programmed temperature gradient open flame preheating in step S1 is specifically: the steel ingot is heated with open flame in five stages, heating one stage at 350°C for 2 minutes; heating two stages at 450°C for 1 minute; heating three stages at 600°C for 2 minutes; heating four stages at 800°C for 1 minute; heating five stages at 1000°C for 1 hour.

[0055] In order to further illustrate the beneficial technical effects of each product, the performance of the peritectic steel large forged round products obtained by the quenching and tempering treatment method of the peritectic steel large forged round involved in each example is tested. The test method refers to the current national standard of my country or the conventional method in this field. The corrosion resistance is the salt spray corrosion resistance test of the peritectic steel large forged round obtained by the quenching and tempering treatment method of each example of the peritectic steel large forged round. The test temperature is 35°C, and a 5% mass concentration of sodium chloride aqueous solution is sprayed in the test box to simulate the accelerated corrosion of the environment. The peritectic steel large forged round has a tolerance time (i.e., the time to remain unrusted) of more than 500 hours, which is qualified for corrosion resistance, otherwise it is unqualified. The test results are shown in Table 1.

[0056] Table 1

[0057] project Yield Strength tensile strength Corrosion resistance unit MPa MPa — Example 1 867 1080 qualified Example 2 872 1083 qualified Example 3 875 1085 qualified Example 4 881 1090 qualified Example 5 885 1096 qualified Comparative Example 1 850 1045 Failure Comparative Example 2 841 1030 Failure

[0058] It can be seen from Table 1 that the peritectic steel large forged rounds treated by the tempering treatment method of the peritectic steel large forged rounds in the embodiment of the present invention have higher yield strength and tensile strength and better corrosion resistance. The combined use of Ta, Ga, W and rare earth elements, and the selection of preheat treatment and heat treatment processes are beneficial to improving the above properties.

[0059] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A quenching and tempering method for large peritectic steel forgings, characterized in that: The steps include: Step S1, pretreatment: preheating the steel ingot with a programmed temperature gradient open flame; Step S2, forging: hoisting the preheated steel ingot onto a forging press to start forging; Step S3, heat treatment: heat treatment is performed on the forged peritectic steel large forging circle.

2. The quenching and tempering method of large peritectic steel forgings according to claim 1, characterized in that: The pre-programmed temperature rise gradient open flame preheating described in step S1 is specifically as follows: heating from room temperature to 420-470°C at a heating rate of 1-3°C / min, keeping warm for 0.5-1h, then heating to 500-600°C at a heating rate of 3-5°C / min, keeping warm for 10-15min, then heating to 750-850°C at a heating rate of 5-8°C / min, keeping warm for 0.1-0.3h, then heating to 950-1050°C at a heating rate of 8-10°C / min, keeping warm for 0.2-0.5h; finally heating to 1210-1260°C at a rate of 10-12°C / min, keeping warm for 1-3h.

3. The quenching and tempering method of large peritectic steel forgings according to claim 1, characterized in that: The steel ingot in step S1 includes the following components in weight percentage: C: 0.1%~0.18%, Si: 0.15%~0.45%, Mn: 0.75%~1%, Cr: 0.1%~0.3%, Ni: 0.5%~0.7%, Ta: 0.01%~0.03%, Nb: 0.1-0.3%, W: 0.01%~0.03%, rare earth elements: 0.01%~0.03%, Ga: 0.01%~0.03%, B: 0.001%~0.003%, and the balance is Fe and unavoidable impurities.

4. The quenching and tempering method of large peritectic steel forgings according to claim 3, characterized in that: The rare earth element is at least one of Sc, Y, La and Ce.

5. The quenching and tempering method of large peritectic steel forgings according to claim 1, characterized in that: The forging ratio of the forging in step S2 is 4-6, the soaking temperature is 1190-1240, the heating rate is ≤80°C / h, the soaking time is 3-5 hours, the start forging temperature is 1160-1180°C, the final forging temperature is 870-950°C, and the number of upsetting times is ≥4 times.

6. The quenching and tempering method of peritectic steel large forging round according to claim 1, characterized in that: The heat treatment in step S3 includes normalizing, annealing and tempering performed in sequence.

7. The quenching and tempering method of large peritectic steel forgings according to claim 6, characterized in that: The normalizing treatment is performed at a temperature of 880-940° C. for a time of 0.5-1.2 h, followed by cooling in air.

8. The quenching and tempering method of peritectic steel large forging round according to claim 6, characterized in that: The quenching is step isothermal quenching, specifically: first keep the temperature at 840-910°C for 40-60min, then immediately transfer to a 580-620°C furnace and keep the temperature for 25-45min, and then cool to room temperature at an average cooling rate of 28-34°C / second.

9. The quenching and tempering method of peritectic steel large forging round according to claim 6, characterized in that: The quenching is any one of water quenching and air quenching.

10. The quenching and tempering method of peritectic steel large forging round according to claim 6, characterized in that: The tempering treatment is a two-stage tempering treatment, the temperature of the first stage tempering treatment is 600-720°C, the insulation time is 0.8-1.2h, and the temperature of the second stage tempering treatment is 160-200°C, the insulation time is 1-2h.