High-strength steel cylindrical barrel for underwater pressure equipment and integrated forging manufacturing method thereof

Abstract

This invention proposes a high-strength steel cylindrical body for underwater pressure-resistant equipment and its integrated forging manufacturing method. The steps are as follows: electric arc furnace smelting, ladle refining furnace refining, vacuum degassing refining, vacuum casting, electroslag remelting, forging, rough machining, performance heat treatment, and finish machining. The product manufacturing is completed through the above steps. This invention uses a new integrated forging process, combining double vacuum treatment with electroslag remelting, and performing performance heat treatment after forging to ensure excellent metallurgical quality of the cylinder body, eliminate longitudinal welds, and ensure that the various performance characteristics of the cylinder body meet the technical requirements and are uniform and stable. The product is finally delivered in a finished state, which can precisely control the dimensions and form and position tolerances of the cylinder body and facilitate assembly.

Description

Technical Field

[0001] This invention belongs to the field of underwater high-performance metal materials and their processing technology, and particularly relates to a high-strength steel cylindrical body for underwater pressure-resistant equipment and its integrated forging manufacturing method. Background Technology

[0002] Chromium-nickel-molybdenum-vanadium series high-strength steel is a commonly used high-strength special steel for underwater pressure equipment in my country. It has the characteristics of high strength, high toughness, good weldability, and excellent resistance to seawater corrosion. It has good shipbuilding process adaptability and is widely used in the manufacture of underwater pressure equipment.

[0003] Currently, the supply of chromium-nickel-molybdenum-vanadium-based high-strength steel in China is limited to quenched and tempered hot-rolled steel plates. Manufacturing cylindrical bodies for underwater pressure equipment requires processes such as hot-rolled steel plate blanking, beveling, cold bending, longitudinal welding, weld inspection, and finishing. Using chromium-nickel-molybdenum-vanadium-based high-strength steel plates for cylindrical body manufacturing presents several technical challenges: 1. After cold bending, the strength of the quenched and tempered hot-rolled steel plate exhibits varying lower limits, making it difficult to meet design requirements; 2. The rolled cylindrical body contains one or more longitudinal welds, resulting in welding stress, and the large workload of welding and weld inspection prolongs the manufacturing cycle; 3. Manufacturing is difficult for small-diameter, thick-walled cylindrical bodies, especially those with diameters less than 2m and wall thicknesses greater than 100mm with large curvature. Summary of the Invention

[0004] This invention addresses the problems of existing steel plate rolled cylindrical bodies having one or more longitudinal welds and reduced mechanical properties. It proposes an integrated forging method for high-strength steel cylindrical bodies used in underwater pressure-resistant equipment. The method utilizes a novel integrated forging process, combining double vacuum treatment with electroslag remelting to ensure excellent metallurgical quality of the cylindrical body. Furthermore, post-forging heat treatment ensures that the cylindrical body's various performance characteristics meet technical requirements and are uniformly stable. The resulting product is delivered in a precision-machined state, allowing for accurate control of the cylindrical body's dimensions and form tolerances, facilitating assembly.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] An integrated forging method for a high-strength steel cylindrical body for underwater pressure-resistant equipment, characterized by comprising the following steps:

[0007] (1) Electric arc furnace smelting: High-quality steel materials and ferroalloys are selected and fed into the electric arc furnace. Ultra-high power graphite electrodes are used to melt the furnace materials. Oxygen blowing is carried out to assist melting during the melting process. Then, dephosphorization and decarburization operations are carried out respectively to perform rough steelmaking and rough adjustment of chemical composition.

[0008] (2) Steel ladle refining furnace (LF furnace): When the molten steel is poured into the LF furnace, slag is removed. During the steel pouring process, ferromanganese, ferrosilicon, aluminum ingots, etc. are added for reduction. After the steel is poured, the power is supplied to raise the temperature and slag-forming materials and ferroalloys are added. Aluminum powder or silicon-calcium powder is used for slag deoxidation. After the slag deoxidation state is good, samples are taken for analysis and the composition is fine-tuned.

[0009] (3) Vacuum degassing: A vacuum degassing furnace is used to degas the molten steel. Argon gas is introduced to ensure that the vacuum degree does not exceed 80 Pa. After the vacuum treatment is completed, the power is supplied to raise the temperature.

[0010] (4) Vacuum casting: A vacuum casting system is used. Before casting, the ingot plate, refractory materials, etc. are dried and the molten steel is diverted from the outlet. During the casting process, the argon flow rate is controlled to avoid the molten steel surface being exposed. Casting is then carried out to obtain a steel ingot.

[0011] (5) Electroslag remelting: The steel ingot is electroslag remelted in an electroslag furnace to obtain electroslag ingots;

[0012] (6) Forging: The electroslag ingot is transferred to a forging press for free forging to obtain a forging billet;

[0013] (7) Rough machining: The forging billet is rough machined using a CNC vertical lathe to obtain a cylindrical body;

[0014] (8) Performance heat treatment: The cylindrical body performance heat treatment is completed by using a high-precision resistance heat treatment furnace and water tank; the performance heat treatment process is quenching and tempering; after the quenching heat treatment is completed, it is transferred to the water tank, and the transfer time is no more than 2.5 min, followed by rapid water cooling; then tempering heat treatment is performed, and after the tempering heat treatment is completed, it is taken out of the furnace and cooled to room temperature.

[0015] (9) Finishing: The cylindrical body is finished by using a CNC vertical lathe to obtain a high-strength steel cylindrical body.

[0016] As a preferred option, in the electric arc furnace smelting step, slag is added at the same time as steel material. The slag is lime and fluorite, and the amount of slag added is 3%-6% of the mass of steel material. After controlling the temperature inside the electric arc furnace to be greater than 1500℃, samples are taken for analysis. The decarbonization rate during the oxidation period is ≥0.01% / min. The final C is ≤0.11%, the P at tapping is ≤0.010%, and the tapping temperature is 1650℃~1680℃.

[0017] As a preferred option, in the vacuum degassing step, the temperature of the molten steel before degassing is not lower than 1650℃, and the vacuum time is not lower than 12 minutes; the endpoint of vacuum degassing is that the N content is not higher than 50ppm; after the vacuum treatment is completed, the power is supplied to raise the temperature, and the tapping temperature is 1630℃~1650℃.

[0018] Preferably, in the vacuum casting step, the vacuum degree is ensured to be no higher than 80 Pa, and the casting temperature is 1570℃~1600℃.

[0019] As a preferred option, the slag system used in the electroslag remelting step is calcium fluoride-alumina slag system, with a mass ratio of calcium fluoride to alumina of 7:3. The amount of slag used per ton of steel ingot is 25kg~40kg, and the slag used needs to be fully baked and dried.

[0020] As a preferred option, in the electroslag remelting step, the arc ignition voltage of the electroslag furnace is 35V~55V, the remelting process voltage is 40V~70V, the melting rate is 0.7 t / h~1.7t / h, and the feeding time is not less than 2.5h; argon gas protection is used during the remelting process, and silicon-calcium powder is used for slag surface deoxidation.

[0021] As a preferred option, in the forging process, the single-sided removal rate of the electroslag ingot shall not be less than 3% of the weight of the electroslag ingot, the forging ratio shall not be less than 5.0, the initial forging temperature shall not be higher than 1250℃, and the final forging temperature shall not be lower than 800℃. During the forging process, the dimensions of each part of the forging shall be measured in a timely manner, and attention shall be paid to observing whether there are cracks or defects on the surface of the forging.

[0022] As a preferred embodiment, in the performance heat treatment steps, the furnace loading temperature for quenching heat treatment of the cylindrical body is ≤200℃, the heating rate is ≤100℃ / h, the holding temperature is 880℃~900℃, and the holding time is 2h~8h; the transfer time is not greater than 2.5min, and rapid water cooling is performed, with the initial water temperature not higher than 20℃ and the final water temperature not higher than 35℃; the furnace loading temperature for tempering heat treatment is ≤80℃, the heating rate is ≤100℃ / h, the holding temperature is 610℃~630℃, and the holding time is 4h~12h.

[0023] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0024] 1. This invention proposes a novel forging method for high-strength chromium-nickel-molybdenum-vanadium steel, which can realize the integrated molding of cylindrical bodies made of high-strength chromium-nickel-molybdenum-vanadium steel for underwater pressure equipment without longitudinal seam welding. The final product meets the design requirements, which not only improves the overall performance of underwater pressure equipment and solves the manufacturing problem of cylindrical bodies with large curvature, but also eliminates longitudinal welds and improves manufacturing efficiency.

[0025] 2. The invention employs double vacuum treatment, electroslag remelting, and forging followed by performance heat treatment to ensure excellent metallurgical quality of the cylinder, eliminate longitudinal welds, and ensure that the various performance characteristics of the cylinder meet technical requirements and are uniform and stable. The product is finally delivered in a precision-machined state, which allows for precise control of the cylinder's dimensions and geometric tolerances, facilitating assembly.

[0026] 3. The high-strength steel cylindrical body prepared using the method provided by this invention has the following specifications: outer diameter 300mm~5500mm, height ≤4000mm, wall thickness ≤120mm; its mechanical properties are: yield strength 800MPa~900MPa, elongation after fracture ≥15%, reduction of area ≥50%, and KV2 impact energy at -20℃ ≥80J. Its product specifications and corresponding mechanical properties fully meet the performance requirements of special steel for underwater pressure-resistant equipment. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the high-strength steel cylindrical body of Example 1;

[0029] Figure 2 This is a schematic diagram of the high-strength steel cylindrical body in Example 2. Detailed Implementation

[0030] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0031] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0032] Example 1, such as Figure 1 As shown, a high-strength steel cylindrical body for underwater pressure-resistant equipment and its integrated forging manufacturing method are disclosed. The preparation method is as follows:

[0033] (1) Electric arc furnace smelting: 50t of high-quality steel and ferroalloy materials were fed into the electric arc furnace and 2000kg of slag was added at the same time. The slag was lime and fluorite. Ultra-high power graphite electrodes were used to melt the furnace charge. During the melting process, the temperature inside the electric arc furnace was controlled to be greater than 1500℃. Samples were taken continuously for analysis and oxygen blowing was carried out to assist melting. Then, dephosphorization and decarburization operations were carried out respectively. The steel was roughed and the chemical composition was roughly adjusted: the decarburization rate during the oxidation period was 0.02% / min, the final C content was 0.07%, the P content at tapping was 0.007%, and the tapping temperature was 1660℃.

[0034] (2) Steel ladle refining furnace (LF furnace) refining: slag removal is carried out when molten steel is poured into the LF furnace. During the steel pouring process, ferromanganese, ferrosilicon, aluminum ingots, etc. are added for reduction operation. After steel pouring, power is supplied to raise the temperature and slag-forming materials and ferroalloys are added. Aluminum powder or silicon-calcium powder is used for slag deoxidation. After the slag deoxidation state is good, samples are taken for analysis and the composition is fine-tuned. After the slag turns white, has good reducibility, reaches the process requirements and the composition is uniform, samples are taken for full analysis. According to the sampling analysis results, alloys are added to the specification limit. After all alloys are added, power is supplied for more than 8 minutes, the electrodes are raised, Ar gas is introduced and the power is stopped and strong stirring is performed for more than 1 minute. Second samples are taken for full analysis, and the composition ratio is fine-tuned according to the composition.

[0035] (3) Vacuum degassing: After the composition of the molten steel meets the above process requirements, the molten steel is sent to the vacuum degassing furnace for degassing. Argon gas is introduced to ensure that the vacuum degree is not higher than 80Pa and that the temperature of the molten steel before degassing is not lower than 1650℃. The vacuum time is 17min. The endpoint of vacuum degassing: N content is 39ppm.

[0036] (4) Vacuum casting: A vacuum casting system is used. Before casting, the ingot plate, refractory materials, etc. are dried and the molten steel is diverted from the bottom of the molten steel. There is a permeable brick at the bottom of the LF furnace. Argon gas is blown into the ladle to stir the molten steel. The molten steel in the LF furnace is at the bottom and the slag is at the top. Under normal circumstances, the slag covers the molten steel to prevent the molten steel from contacting the air and causing oxidation. When blowing in argon gas, attention should be paid to controlling the flow rate. It should not only stir the molten steel, but also avoid blowing the slag on the surface. During the casting process, the flow rate of bottom blowing argon gas should be controlled so that the surface of the molten steel is not exposed and the vacuum degree is not higher than 80 Pa. The temperature during casting is 1590℃.

[0037] (5) Electroslag remelting: Electroslag remelting is carried out in an electroslag furnace. The selected slag system is calcium fluoride-alumina slag system with a mass ratio of calcium fluoride to alumina of 7:3. The amount of slag added is 1700 kg. The slag material needs to be fully baked and dried. The arc starting voltage of the electroslag furnace is 45V, the remelting process voltage is 60V, the melting rate is 1.3t / h, and the feeding time is 3h. Argon gas protection is used during the remelting process, and silicon calcium powder is used to deoxidize the slag surface to obtain electroslag ingots.

[0038] (6) Forging and forming: Free forging is carried out using a forging press, with a single-sided removal rate of 4% for the electroslag ingot; the forging ratio is 6.3; the initial forging temperature is 1010℃ and the final forging temperature is 850℃ to obtain the forging billet;

[0039] (7) Rough machining: The forging billet is rough machined using a CNC vertical lathe to obtain a cylindrical body;

[0040] (8) Performance heat treatment: The cylindrical body performance heat treatment is completed by resistance heat treatment furnace and water tank. The process is quenching and tempering. The furnace loading temperature for quenching heat treatment is 185℃, the heating rate is 80℃ / h, the holding temperature is 890℃, and the holding time is 4h. After the quenching heat treatment holding is completed, the body is quickly transferred to the water tank for rapid water cooling. The transfer time is 2min. The initial water temperature for water cooling is not higher than 20℃, and the final water temperature is not higher than 35℃. The furnace loading temperature for tempering heat treatment is 75℃, the heating rate is 80℃ / h, the holding temperature is 615℃, and the holding time is 9h. After the tempering heat treatment holding is completed, the body is taken out of the furnace and cooled to room temperature.

[0041] (9) Finishing: The cylindrical body is finished by using a CNC vertical lathe to obtain a high-strength steel cylindrical body with an outer diameter of 2500mm, a height of 3000mm, and a wall thickness of 80mm.

[0042] Mechanical properties of the high-strength steel cylindrical body of Example 1 were tested. Its yield strength was 824 MPa, elongation after fracture was 18%, reduction of area was 53%, and the KV2 impact energy at -20℃ was 185 J.

[0043] Example 2, as Figure 2 As shown, a high-strength steel cylindrical body for underwater pressure-resistant equipment and its integrated forging manufacturing method are disclosed. The preparation method is as follows:

[0044] (1) Electric arc furnace smelting: 60t of high-quality steel and ferroalloy materials were fed into the electric arc furnace and 3000kg of slag was added at the same time. The slag was lime and fluorite. Ultra-high power graphite electrodes were used to melt the furnace charge. During the melting process, the temperature inside the electric arc furnace was controlled to be greater than 1500℃. Samples were taken continuously for analysis and oxygen blowing was carried out to assist melting. Then, dephosphorization and decarburization operations were carried out respectively. The steel was roughed and the chemical composition was roughly adjusted: the decarburization rate during the oxidation period was 0.03% / min, the final C content was 0.08%, the P content at tapping was 0.007%, and the tapping temperature was 1680℃.

[0045] (2) Steel ladle refining furnace (LF furnace) refining: slag removal is carried out when molten steel is poured into the LF furnace. During the steel pouring process, ferromanganese, ferrosilicon, aluminum ingots, etc. are added for reduction operation. After steel pouring, power is supplied to raise the temperature and slag-forming materials and ferroalloys are added. Aluminum powder or silicon-calcium powder is used for slag deoxidation. After the slag deoxidation state is good, samples are taken for analysis and the composition is fine-tuned. After the slag turns white, has good reducibility, reaches the process requirements and the composition is uniform, samples are taken for full analysis. According to the sampling analysis results, alloys are added to the specification limit. After all alloys are added, power is supplied for more than 8 minutes, the electrodes are raised, Ar gas is introduced and the power is stopped and strong stirring is performed for more than 1 minute. Second samples are taken for full analysis, and the composition ratio is fine-tuned according to the composition.

[0046] (3) Vacuum degassing: After the composition of the molten steel meets the above process requirements, the molten steel is sent to the vacuum degassing furnace for degassing. Argon gas is introduced to ensure that the vacuum degree is not higher than 80Pa and that the temperature of the molten steel before degassing is not lower than 1650℃. The vacuum time is 15min. The endpoint of vacuum degassing: N content is 44ppm.

[0047] (4) Vacuum casting: A vacuum casting system is used. Before casting, the ingot plate, refractory materials, etc. are dried and the molten steel is diverted from the outlet. During the casting process, the vacuum degree is ensured to be no higher than 80Pa. The argon flow rate is controlled so that the surface of the molten steel is not exposed. The temperature during casting is 1585℃.

[0048] (5) Electroslag remelting: Electroslag remelting is carried out in an electroslag furnace. The selected slag system is calcium fluoride-alumina slag system with a mass ratio of calcium fluoride to alumina of 7:3. The amount of slag added is 1800 kg. The slag material needs to be fully baked and dried. The arc starting voltage of the electroslag furnace is 45V, the remelting process voltage is 55V, the melting rate is 1.1t / h, and the feeding time is 3.5h. Argon gas protection is used during the remelting process, and silicon calcium powder is used to deoxidize the slag surface to obtain electroslag ingots.

[0049] (6) Forging and forming: Free forging is carried out using a forging press, with a single-sided removal rate of 4% for the electroslag ingot; the forging ratio is 5.5; the initial forging temperature is 1200℃ and the final forging temperature is 880℃ to obtain the forging billet;

[0050] (7) Rough machining: The forging billet is rough machined using a CNC vertical lathe to obtain a cylindrical body;

[0051] (8) Performance heat treatment: The cylindrical body performance heat treatment is completed by resistance heat treatment furnace and water tank. The process is quenching and tempering. The furnace loading temperature for quenching heat treatment is 195℃, the heating rate is 60℃ / h, the holding temperature is 895℃, and the holding time is 8h. After the holding time of quenching heat treatment, the body is quickly transferred to the water tank for water cooling. The transfer time is 2.5min. The initial water temperature for water cooling is not higher than 20℃, and the final water temperature is not higher than 35℃. The furnace loading temperature for tempering heat treatment is 80℃, the heating rate is 80℃ / h, the holding temperature is 625℃, and the holding time is 11h. After the holding time of tempering heat treatment, the body is taken out of the furnace and cooled to room temperature.

[0052] (9) Finishing: The cylindrical body is finished by using a CNC vertical lathe to obtain a high-strength steel cylindrical body with an outer diameter of 5000mm, a height of 3000mm, and a wall thickness of 100mm.

[0053] Mechanical properties of the high-strength steel cylindrical body of Example 2 were tested. Its yield strength was 870 MPa, elongation after fracture was 16%, reduction of area was 55%, and the KV2 impact energy at -20℃ was 155 J.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method of integrally forging a high-strength steel cylindrical shell for underwater pressure equipment, characterized by, Specifically, the following steps are included: (1) Electric arc furnace smelting: High-quality steel materials and ferroalloys are selected and fed into the electric arc furnace. Ultra-high power graphite electrodes are used to melt the furnace materials. Oxygen blowing is carried out to assist melting during the melting process. Then, dephosphorization and decarburization operations are carried out respectively to perform rough steelmaking and rough adjustment of chemical composition. (2) Steel ladle refining furnace (LF furnace): When the molten steel is poured into the LF furnace, slag is removed. During the steel pouring process, ferromanganese, ferrosilicon and aluminum ingots are added for reduction. After steel pouring, the power is supplied to raise the temperature and slag-forming materials and ferroalloys are added. Aluminum powder or silicon-calcium powder is used for slag deoxidation. After the slag deoxidation state is good, samples are taken for analysis and the composition is fine-tuned. (3) Vacuum degassing: A vacuum degassing furnace is used to degas the molten steel. Argon gas is introduced to ensure that the vacuum degree does not exceed 80 Pa. After the vacuum treatment is completed, the power is supplied to raise the temperature. (4) Vacuum casting: A vacuum casting system is used. Before casting, the ingot plate and refractory are dried, and the molten steel is diverted from the outlet. During the casting process, the argon flow rate is controlled to prevent the molten steel surface from being exposed. Casting is then carried out to obtain the steel ingot. (5) Electroslag remelting: The steel ingot is electroslag remelted in an electroslag furnace to obtain electroslag ingots; (6) Forging: The electroslag ingot is transferred to a forging press for free forging to obtain a forging billet; (7) Rough machining: The forging billet is rough machined using a CNC vertical lathe to obtain a cylindrical body; (8) Performance heat treatment: The cylindrical body performance heat treatment is completed by using a high-precision resistance heat treatment furnace and water tank; the performance heat treatment process is quenching and tempering; after the quenching heat treatment is completed, it is transferred to the water tank, and the transfer time is no more than 2.5 min, followed by rapid water cooling; then tempering heat treatment is performed, and after the tempering heat treatment is completed, it is taken out of the furnace and cooled to room temperature. (9) Finishing: The cylindrical body is finished using a CNC vertical lathe to obtain a high-strength steel cylindrical body; In the electric arc furnace smelting process, slag is added simultaneously with steel material. The slag consists of lime and fluorite, and the amount of slag added is 3%-6% of the mass of the steel material. After controlling the temperature inside the electric arc furnace to be greater than 1500℃, samples are taken for analysis. The carbon removal rate during the oxidation period is ≥0.01% / min. The final carbon content is ≤0.11%, the tapping P is ≤0.010%, and the tapping temperature is 1650℃~1680℃. During the vacuum degassing step, ensure that the temperature of the molten steel before degassing is not lower than 1650℃ and the vacuum time is not lower than 12min; the endpoint of vacuum degassing is that the N content is not higher than 50ppm; after the vacuum treatment is completed, power is supplied to raise the temperature, and the tapping temperature is 1630℃~1650℃. During the vacuum casting process, ensure that the vacuum level does not exceed 80 Pa and the casting temperature is 1570℃~1600℃.

2. The method of claim 1, wherein the method further comprises: In the electroslag remelting process, the selected slag system is calcium fluoride-alumina slag system, with a mass ratio of calcium fluoride to alumina of 7:

3. The amount of slag used per ton of steel ingot is 25kg~40kg, and the slag used must be fully baked and dried. ​ 3. The method of claim 1, wherein the method further comprises: In the electroslag remelting step, the arc ignition voltage of the electroslag furnace is 35V~55V, the remelting process voltage is 40V~70V, the melting rate is 0.7t / h~1.7t / h, and the feeding time is not less than 2.5h. ​ 4. The integrated forging method for a high-strength steel cylindrical body for underwater pressure-resistant equipment according to claim 1, characterized in that, During the forging process, the single-sided removal rate of the electroslag ingot shall not be less than 3% of the weight of the electroslag ingot, the forging ratio shall not be less than 5.0, the initial forging temperature shall not be higher than 1250℃, and the final forging temperature shall not be lower than 800℃.

5. The integrated forging method for a high-strength steel cylindrical body for underwater pressure-resistant equipment according to claim 1, characterized in that, In the performance heat treatment steps, the furnace loading temperature for quenching heat treatment of cylindrical bodies is ≤200℃, the heating rate is ≤100℃ / h, the holding temperature is 880℃~900℃, and the holding time is 2h~8h; the transfer time is no more than 2.5min, and rapid water cooling is performed, with the initial water temperature not exceeding 20℃ and the final water temperature not exceeding 35℃; the furnace loading temperature for tempering heat treatment is ≤80℃, the heating rate is ≤100℃ / h, the holding temperature is 610℃~630℃, and the holding time is 4h~12h.

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