A nitriding alloy for a piercing head and a method for producing the same

Abstract

The present application relates to a kind of head with nitriding alloy and its preparation method, with mass percentage, the head with nitriding alloy includes: C 0.19-0.23wt%, Si 0.17-0.35wt%, Ni 1.5-2.5wt%, Mo1.0-2.5wt%, W 2.0-3.5wt%, Co 1.0-2.0wt%, V 0.3-0.5wt%, the remainder is Fe and inevitable impurities.The present application is produced by reasonable chemical composition design and corresponding process, and high-performance head with nitriding alloy is produced, so that it can be rolled 250-300 branch perforated tube, and service life is extended.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of piercing head production, and particularly relates to a nitriding alloy for piercing head and a preparation method thereof. BACKGROUND

[0002] Seamless steel pipes are important products in the national economy of China and have been widely used in many industrial fields such as chemical industry, energy, construction, automobile and national defense. Main products include: gas cylinder accumulator pipe, oil casing, oil casing coupling, low and medium pressure boiler pipe, high pressure boiler pipe, pipeline pipe (including thick wall low temperature steel pipe for ocean oil and gas collection and transportation), oil cracking pipe, seamless steel pipe for fluid transportation, and seamless steel pipe for structure. At present, the seamless steel pipe mainly relies on piercing head materials for hot piercing forming.

[0003] The piercing head is a key tool for the production of seamless steel pipes, and its service environment is generally complex, such as high temperature difference, high load and strong friction. After the piercing head pierces the red-hot steel blank and circulates for many times, the surface will gradually appear cracking, nose collapse and size reduction due to high temperature friction and temperature change, which not only reduces the service life and piercing times of the piercing head, resulting in huge resource waste and unnecessary time cost, but also affects the quality of the produced steel pipe and the benefits of the manufacturer to some extent.

[0004] CN112077306A discloses a method for laser selective cladding to strengthen a seamless steel pipe piercing head and the obtained piercing head, comprising the following steps: (1) processing a U-shaped groove at the end of the piercing head to be strengthened, so that the U-shaped groove is circular, spiral or divergent; (2) cladding alloy material in the U-shaped groove by laser cladding; (3) processing the piercing head to a preset size and then performing surface oxidation treatment to obtain a piercing head with an oxidation layer on the surface, and completing the strengthening. The laser selective cladding strengthens the piercing head, the laser cladding high-temperature alloy layer can significantly improve the high-temperature strength of the piercing head, prevent plastic deformation and nose collapse, and the thick oxide skin formed in the area without laser cladding can effectively reduce the friction coefficient and heat conduction coefficient between the piercing head and the steel pipe blank during piercing, and prevent the surface temperature of the piercing head from rising; but the processing cost is high, and the friction is large during piercing, which increases the surface wear in the later stage and gradually causes size reduction.

[0005] Therefore, it is an urgent technical problem in the production of seamless steel pipes to develop a piercing head with good quality and long service life. SUMMARY

[0006] To solve the above technical problems, the present application provides a nose head nitriding alloy and a preparation method thereof, and through reasonable chemical composition design and corresponding process, the high-performance nose head nitriding alloy is produced, so that it can roll 250-300 perforated blank pipes, and the service life is prolonged.

[0007] To achieve the above technical effects, the present application adopts the following technical solutions:

[0008] In the first aspect, the present application provides a nose head nitriding alloy, which comprises, in mass percentage: C 0.19-0.23wt%, Si 0.17-0.35wt%, Ni 1.5-2.5wt%, Mo 1.0-2.5wt%, W 2.0-3.5wt%, Co 1.0-2.0wt%, V 0.3-0.5wt%, and the balance of Fe and inevitable impurities.

[0009] The nose head nitriding alloy provided by the present application adjusts the nose head alloy composition by adding tungsten, cobalt, vanadium and other elements, and combines the synergistic effect of multiple element content, so that the hardness of the nose head nitriding alloy is 270-320HB, the tensile strength is 850-900MPa, the yield strength is 500-600MPa, and the impact energy is ≥70J, so that it can roll 250-300 perforated blank pipes, and the service life of the nose head is prolonged.

[0010] In the present application, the mass percentage of C in the penetrator nitriding alloy is 0.19-0.23wt%, for example, it can be 0.195wt%, 0.20wt%, 0.205wt%, 0.21wt%, 0.215wt%, 0.22wt% or 0.225wt% and the like, the mass percentage of Si in the penetrator nitriding alloy is 0.17-0.35wt%, for example, it can be 0.18wt%, 0.20wt%, 0.22wt%, 0.24wt%, 0.26wt%, 0.28wt%, 0.30wt%, 0.32wt% or 0.34wt% and the like, the mass percentage of Ni in the penetrator nitriding alloy is 1.5-2.5wt%, for example, it can be 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt% or 2.4wt% and the like, the mass percentage of Mo in the penetrator nitriding alloy is 1.0-2.5wt%, for example, it can be 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2.0wt%, 2.2wt% or 2.4wt% and the like, the mass percentage of W in the penetrator nitriding alloy is 2.0-3.5wt%, for example, it can be 2.2wt%, 2.4wt%, 2.6wt%, 2.8wt%, 3.0wt%, 3.1wt%, 3.2wt%, 3.3wt% or 3.4wt% and the like, the mass percentage of Co in the penetrator nitriding alloy is 1.0-2.0wt%, for example, it can be 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt% or 1.9wt% and the like, the mass percentage of V in the penetrator nitriding alloy is 0.3-0.5wt%, for example, it can be 0.32wt%, 0.34wt%, 0.36wt%, 0.38wt%, 0.4wt%, 0.42wt%, 0.44wt%, 0.46wt% or 0.489wt% and the like, but not limited to the listed values, other values not listed in the value range are also applicable.

[0011] As a preferred technical solution of the present application, the total mass percentage of Ni+Mo in the penetrator nitriding alloy is 4.5-4.95wt%, for example, it can be 4.55wt%, 4.6wt%, 4.65wt%, 4.7wt%, 4.75wt%, 4.8wt% or 4.9wt% and the like, but not limited to the listed values, other values not listed in the value range are also applicable.

[0012] In the present application, by reasonably matching the use of nickel and molybdenum components, through narrow component control, the mechanical properties of the penetrator nitriding alloy are further improved, and the service life is prolonged.

[0013] Preferably, the mass percentage content of Co in the plug nitriding alloy is 1.5-2.0wt%, for example, it can be 1.55wt%, 1.6wt%, 1.65wt%, 1.7wt%, 1.75wt%, 1.8wt% or 1.9wt%, etc., but not limited to the listed values, and other values not listed within the value range are also applicable.

[0014] As a preferred technical solution of the present application, in the inevitable impurities, the mass percentage content of P is ≤0.025wt%, and the mass percentage content of S is ≤0.025wt%.

[0015] In the present application, the mass percentage content of P in the inevitable impurities is ≤0.025wt%, for example, it can be 0.024wt%, 0.022wt%, 0.020wt%, 0.015wt%, 0.010wt%, 0.009wt% or 0.005wt%, etc., and the mass percentage content of S in the inevitable impurities is ≤0.025wt%, for example, it can be 0.024wt%, 0.022wt%, 0.020wt%, 0.015wt%, 0.010wt%, 0.009wt% or 0.005wt%, etc., but not limited to the listed values, and other values not listed within the value range are also applicable.

[0016] As a preferred technical solution of the present application, the hardness of the plug nitriding alloy is 270-320HB, for example, it can be 275HB, 280HB, 285HB, 290HB, 295HB, 300HB, 305HB, 310HB or 315HB, etc., but not limited to the listed values, and other values not listed within the value range are also applicable.

[0017] Preferably, the tensile strength of the plug nitriding alloy is 850-900MPa, for example, it can be 855MPa, 860MPa, 865MPa, 870MPa, 875MPa, 880MPa, 885MPa, 890MPa or 895MPa, etc., but not limited to the listed values, and other values not listed within the value range are also applicable.

[0018] Preferably, the yield strength of the plug nitriding alloy is 500-600MPa, for example, it can be 510MPa, 520MPa, 530MPa, 540MPa, 550MPa, 560MPa, 570MPa, 580MPa or 590MPa, etc., but not limited to the listed values, and other values not listed within the value range are also applicable.

[0019] Preferably, the impact energy of the head with nitriding alloy is greater than or equal to 70J, for example, can be 72J, 74J, 76J, 78J, 80J or 85J, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0020] In the second aspect, the application provides a preparation method of the head with nitriding alloy as described in the first aspect, the preparation method comprising: sequentially melting and pretreating raw materials according to the formula amount, preparing an alloy head, and then performing nitriding treatment to prepare the head with nitriding alloy.

[0021] The preparation method provided by the application can not only enhance the strength of the head, meet the requirements of high strength, high hardness and high toughness under heavy load conditions, but also improve the surface wear resistance and prolong the service life.

[0022] As a preferred technical solution of the application, the pretreatment comprises sequentially performing an irregular casting blank, double annealing, hot die forging forming, isothermal spheroidizing annealing, welding a cladding layer, machining and heat treatment.

[0023] As a preferred technical solution of the application, the temperature of the double annealing is 900-950℃, for example, can be 905℃, 910℃, 915℃, 920℃, 925℃, 930℃, 935℃, 940℃ or 945℃, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0024] Preferably, the time of the double annealing is 2-3h, for example, can be 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h or 2.9h, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0025] Preferably, the temperature of the isothermal spheroidizing annealing is 920-970℃, for example, can be 925℃, 930℃, 935℃, 940℃, 945℃, 950℃, 955℃, 960℃ or 965℃, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0026] Preferably, the time of the isothermal spheroidizing annealing is 1-3h, for example, can be 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h or 2.8h, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0027] Preferably, the temperature of the heat treatment is 1000-1250℃, for example, it can be 1020℃, 1050℃, 1070℃, 1100℃, 1120℃, 1150℃, 1170℃, 1200℃ or 1220℃, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0028] Preferably, the time of the heat treatment is 2-3h, for example, it can be 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h or 2.9h, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0029] The other steps of the pre-treatment in the present application can use conventional processing parameters in the prior art, and are not specifically limited.

[0030] As a preferred technical solution of the present application, the nitriding treatment comprises: loading the furnace after raising the oxidation furnace to a first set temperature, then raising the temperature to a second set temperature and introducing helium gas for composite oxidation treatment, and holding at the second set temperature, and then discharging the furnace and air cooling.

[0031] Preferably, after the composite oxidation treatment, the thickness of the oxide film on the surface of the alloy top head is ≥0.8mm, for example, it can be 0.82mm, 0.84mm, 0.85mm, 0.86mm, 0.87mm, 0.88mm, 0.9mm or 0.94mm, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0032] As a preferred technical solution of the present application, the first set temperature is 325-375℃, for example, it can be 330℃, 335℃, 340℃, 345℃, 350℃, 355℃, 360℃, 365℃ or 370℃, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0033] As a preferred technical solution of the present application, the temperature raising rate for raising the temperature to the second set temperature is 70-80℃ / h, for example, it can be 72℃ / h, 74℃ / h, 76℃ / h, 78℃ / h or 79℃ / h, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0034] Preferably, the second set temperature is 850-950℃, for example, it can be 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃ or 940℃, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0035] Preferably, the holding time of the second set temperature is 5-7h, for example, can be 5.2h, 5.4h, 5.6h, 5.8h, 6h, 6.2h, 6.4h, 6.6h or 6.8h, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0036] The numerical range of the present application includes not only the above-mentioned listed point values, but also any point values between the above-mentioned numerical ranges which are not listed, and the present application does not exhaustively list the specific point values included in the range for the sake of brevity and simplicity.

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] The nitriding alloy for a plug provided by the present application adjusts the plug alloy composition by adding elements such as tungsten, cobalt, vanadium, etc., and cooperates with the synergistic effect of multiple element contents and nitriding treatment, so that the hardness of the nitriding alloy for a plug is 270-320HB, the tensile strength is 850-900MPa, the yield strength is 500-600MPa, and the impact energy is ≥70J, so that the nitriding alloy for a plug can roll 250-300 perforated raw pipes, thereby achieving the purpose of prolonging the service life of the plug. DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of the present application, the present application lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present application and should not be regarded as a specific limitation on the present application.

[0040] Embodiment 1

[0041] The present embodiment provides a nitriding alloy for a plug and a preparation method thereof. The nitriding alloy for a plug comprises, in mass percentage: C 0.21wt%, Si 0.25wt%, Ni 2.2wt%, Mo 2.5wt%, W 2.6wt%, Co 1.6wt%, V 0.4wt%, the balance being Fe and unavoidable impurities, wherein the unavoidable impurities comprise: P≤0.025wt%, S≤0.025wt%.

[0042] The preparation method comprises: sequentially melting, deformed billet, annealing at 920℃ for 2.5h, hot die forging, isothermal spheroidizing annealing at 950℃ for 2h, welding a cladding layer, machining, heat treatment at 1150℃ for 2.5h, to prepare an alloy plug, and then performing nitriding treatment to prepare the nitriding alloy for a plug.

[0043] The nitriding treatment includes: after the oxidation furnace is raised to 350 DEG C, the furnace is loaded, then the temperature is raised to 900 DEG C at a rate of 75 DEG C / h, helium is introduced for composite oxidation treatment, and the temperature is kept at 900 DEG C for 6h, then the furnace is unloaded and air cooled, the thickness of the surface oxide film of the alloy top head is 0.84mm.

[0044] Example 2

[0045] The example provides a nitriding alloy for a top head and a preparation method thereof, the nitriding alloy for the top head includes, in mass percentage: C 0.19wt%, Si 0.18wt%, Ni 2.3wt%, Mo 2.45wt%, W 2.0wt%, Co 1.5wt%, V 0.3wt%, the balance of Fe and inevitable impurities, in the inevitable impurities: P≤0.025wt%, S≤0.025wt%;

[0046] The preparation method includes: raw materials are sequentially subjected to melting, special-shaped casting blank, duplex annealing at 920 DEG C for 2.5h, hot die forging forming, isothermal spheroidizing annealing at 950 DEG C for 2h, welding cladding layer, mechanical processing, heat treatment at 1150 DEG C for 2.5h, to obtain the alloy top head, then nitriding treatment is carried out, to obtain the nitriding alloy for the top head;

[0047] The nitriding treatment includes: after the oxidation furnace is raised to 375 DEG C, the furnace is loaded, then the temperature is raised to 950 DEG C at a rate of 70 DEG C / h, helium is introduced for composite oxidation treatment, and the temperature is kept at 950 DEG C for 5h, then the furnace is unloaded and air cooled, the thickness of the surface oxide film of the alloy top head is 0.85mm.

[0048] Example 3

[0049] The example provides a nitriding alloy for a top head and a preparation method thereof, the nitriding alloy for the top head includes, in mass percentage: C 0.19wt%, Si 0.18wt%, Ni 2.3wt%, Mo 2.45wt%, W 2.0wt%, Co 1.5wt%, V 0.3wt%, the balance of Fe and inevitable impurities, in the inevitable impurities: P≤0.025wt%, S≤0.025wt%;

[0050] The preparation method includes: raw materials are sequentially subjected to melting, special-shaped casting blank, duplex annealing at 920 DEG C for 2.5h, hot die forging forming, isothermal spheroidizing annealing at 950 DEG C for 2h, welding cladding layer, mechanical processing, heat treatment at 1150 DEG C for 2.5h, to obtain the alloy top head, then nitriding treatment is carried out, to obtain the nitriding alloy for the top head;

[0051] The nitriding treatment includes: loading the oxidation furnace to 325℃, then heating to 850℃ at a rate of 80℃ / h, and passing in helium for compound oxidation treatment, and keeping at 850℃ for 7h, then discharging and air cooling, the thickness of the oxide film on the surface of the alloy top head is 0.82mm.

[0052] Example 4

[0053] The present embodiment provides a nitriding alloy for top head and a preparation method thereof, which is the same as example 1 except that the mass percentage of Ni is 1.5wt%.

[0054] Example 5

[0055] The present embodiment provides a nitriding alloy for top head and a preparation method thereof, which is the same as example 1 except that the mass percentage of Mo is 1.5wt%.

[0056] Example 6

[0057] The present embodiment provides a nitriding alloy for top head and a preparation method thereof, which is the same as example 1 except that the mass percentage of Co is 1.0wt%.

[0058] Example 7

[0059] The present embodiment provides a nitriding alloy for top head and a preparation method thereof, which is the same as example 1 except that the heating rate to 900℃ in the nitriding treatment is 90℃ / h.

[0060] Example 8

[0061] The present embodiment provides a nitriding alloy for top head and a preparation method thereof, which is the same as example 1 except that the heating rate to 900℃ in the nitriding treatment is 60℃ / h.

[0062] Example 9

[0063] The present embodiment provides a nitriding alloy for top head and a preparation method thereof, which is the same as example 1 except that the second set temperature in the nitriding treatment is 800℃.

[0064] Example 10

[0065] The present embodiment provides a nitriding alloy for top head and a preparation method thereof, which is the same as example 1 except that the second set temperature in the nitriding treatment is 1000℃.

[0066] Example 11

[0067] The embodiment provides a nitriding alloy for a piercing head and a preparation method thereof, wherein, except that the holding time of the second set temperature in the nitriding treatment is 3h, other conditions are the same as those in the embodiment 1.

[0068] Example 12

[0069] The embodiment provides a nitriding alloy for a piercing head and a preparation method thereof, wherein, except that the holding time of the second set temperature in the nitriding treatment is 9h, other conditions are the same as those in the embodiment 1.

[0070] Comparative Example 1

[0071] The comparative example provides a nitriding alloy for a piercing head and a preparation method thereof, wherein, except that the mass percentage content of the Co is 0.7wt%, other conditions are the same as those in the embodiment 1.

[0072] Comparative Example 2

[0073] The comparative example provides a nitriding alloy for a piercing head and a preparation method thereof, wherein, except that the mass percentage content of the Co is 2.4wt%, other conditions are the same as those in the embodiment 1.

[0074] Comparative Example 3

[0075] The comparative example provides a nitriding alloy for a piercing head and a preparation method thereof, wherein, except that the mass percentage content of the Mo is 0.5wt%, other conditions are the same as those in the embodiment 1.

[0076] Comparative Example 4

[0077] The comparative example provides a nitriding alloy for a piercing head and a preparation method thereof, wherein, except that the mass percentage content of the W is 1.0wt%, other conditions are the same as those in the embodiment 1.

[0078] Comparative Example 5

[0079] The comparative example provides a nitriding alloy for a piercing head and a preparation method thereof, wherein, except that the nitriding alloy for the piercing head does not contain the Co element, other conditions are the same as those in the embodiment 1.

[0080] Comparative Example 6

[0081] The comparative example provides a nitriding alloy for a piercing head and a preparation method thereof, wherein, except that the nitriding treatment is not performed, other conditions are the same as those in the embodiment 1.

[0082] The alloy piercing heads provided in the above embodiment and comparative examples are respectively subjected to performance inspection and piercing test, and the test results are shown in Table 1.

[0083] Table 1

[0084]

[0085]

[0086] The following points can be drawn from Table 1:

[0087] (1) The plug nitriding alloy and the preparation method thereof provided by embodiments 1-3 have excellent mechanical properties and wear resistance, the hardness of the prepared plug nitriding alloy is ≥300HB, the tensile strength is ≥860MPa, the yield strength is ≥570MPa, the impact energy is ≥71J, and the plug nitriding alloy can be rolled into 270 or more than 270 perforated pipes;

[0088] (2) It can be known from the comparison of embodiments 1 and 4-6 that when the content of alloying elements in the plug nitriding alloy is low, it is not conducive to improving the mechanical properties of the plug nitriding alloy;

[0089] (3) It can be known from the comparison of embodiments 1 and 7-12 that when the second temperature rising terminal temperature and the temperature rising rate of the nitriding treatment are too high or too low, the mechanical properties of the plug nitriding alloy will be adversely affected; when the second holding time of the nitriding treatment is too short, the work layer does not obtain a certain thickness of the compound layer with high chemical stability, which adversely affects the mechanical properties and wear resistance of the plug nitriding alloy;

[0090] (4) It can be known from the comparison of embodiments 1 and comparative examples 1-5 that when the content of Co, Mo or W exceeds the preferred range or does not contain Co element, the mechanical properties of the plug nitriding alloy will greatly decrease due to the fact that the above-mentioned elements can improve the strength, hardness and toughness of the alloy, thereby affecting the service life of the plug;

[0091] (5) It can be known from the comparison of embodiments 1 and comparative example 6 that when the nitriding treatment is not performed in the preparation process, the mechanical properties and wear resistance of the prepared plug nitriding alloy will greatly decrease, thereby affecting the service life of the plug and increasing the production cost.

[0092] The applicant declares that the above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought out by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A nitriding alloy for a piercing head, characterized by, The nitriding alloy for the plug comprises, in mass percentage: C 0.19-0.23wt%, Si 0.17-0.35wt%, Ni 1.5-2.5wt%, Mo 1.0-2.5wt%, W 2.0-3.5wt%, Co 1.5-2.0wt%, V 0.3-0.5wt%, the balance of Fe and inevitable impurities; The total mass percentage of Ni+Mo in the nitriding alloy for the plug is 4.7-4.95wt%; The nitriding alloy for the plug is prepared by the following preparation method: raw materials are sequentially subjected to smelting and pretreatment according to the formula amount, an alloy plug is prepared, and then nitriding treatment is performed to prepare the nitriding alloy for the plug; The nitriding treatment comprises the following steps: the oxidizing furnace is charged after being raised to a first set temperature, then the temperature is raised to a second set temperature and helium gas is introduced for composite oxidation treatment, and the temperature is kept at the second set temperature, and then the furnace is discharged for air cooling; the first set temperature is 325-375℃; the temperature raising rate to the second set temperature is 70-80℃ / h; and the second set temperature is 860-940℃.

2. The nosepiece nitriding alloy of claim 1 wherein, In the inevitable impurities, the mass percentage of P is ≤0.025wt%, and the mass percentage of S is ≤0.025wt%.

3. The nosepiece nitriding alloy of claim 1 wherein, The hardness of the nitriding alloy for the plug is 270-320HB.

4. The nosepiece nitriding alloy of claim 1 wherein, The tensile strength of the nitriding alloy for the plug is 850-900MPa.

5. The nosepiece nitriding alloy of claim 1 wherein, The yield strength of the nitriding alloy for the plug is 500-600MPa.

6. The nosepiece nitriding alloy of claim 1 wherein, The impact energy of the nitriding alloy for the plug is ≥70J.

7. A method of producing a nitriding alloy for a piercing head as claimed in any one of claims 1 to 6, characterized in that, The preparation method comprises the following steps: raw materials are sequentially subjected to smelting and pretreatment according to the formula amount, an alloy plug is prepared, and then nitriding treatment is performed to prepare the nitriding alloy for the plug; The nitriding treatment comprises the following steps: the oxidizing furnace is charged after being raised to a first set temperature, then the temperature is raised to a second set temperature and helium gas is introduced for composite oxidation treatment, and the temperature is kept at the second set temperature, and then the furnace is discharged for air cooling; the first set temperature is 325-375℃; the temperature raising rate to the second set temperature is 70-80℃ / h; and the second set temperature is 860-940℃.

8. The preparation method according to claim 7, characterized in that, The pretreatment comprises the following steps in sequence: special-shaped casting blank, double annealing, hot die forging forming, isothermal spheroidizing annealing, welding cladding layer, mechanical processing and heat treatment.

9. The production method according to claim 8, characterized by, The temperature of the double annealing is 900-950℃.

10. The preparation method according to claim 8, characterized in that, The time of the double annealing is 2-3h.

11. The preparation method according to claim 8, characterized in that, The temperature of the isothermal spheroidizing annealing is 920-970℃.

12. The method of claim 8, wherein, The time of the isothermal spheroidizing annealing is 1-3h.

13. The preparation method according to claim 8, characterized in that, The temperature of the heat treatment is 1000-1250℃.

14. The preparation method according to claim 8, characterized in that, The time of the heat treatment is 2-3h.

15. The preparation method according to claim 7, after the composite oxidation treatment, the thickness of the surface oxide film of the alloy plug is ≥0.8mm.

16. The preparation method according to claim 7, characterized in that, The holding time at the second set temperature is 5-7h.

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