A heat treatment method to improve the transverse properties of martensitic steel

Abstract

This invention relates to the field of heat treatment technology, and in particular to a heat treatment method for improving the transverse properties of martensitic steel, comprising the following steps: subjecting the forging to ultra-high temperature treatment, wherein the ultra-high temperature treatment involves heating the forging to 1100℃ to 1130℃ and holding it at that temperature for a certain time; subjecting the forging to standard quenching treatment, wherein the standard quenching treatment involves cooling the ultra-high temperature treated forging to the standard quenching temperature at a preset rate, holding it at that temperature for a certain time, and then cooling it; and subjecting the forging to at least one tempering treatment, wherein the tempering treatment involves heating the forging to a certain temperature, holding it at that temperature for a certain time, and then cooling it. The heat treatment method provided by this invention solves the problem of low transverse plasticity and impact performance of martensitic stainless steel pipe and ring forgings. By employing ultra-high temperature treatment and tempering, the microstructure and properties are optimized and adjusted, enabling the transverse plasticity and impact energy indicators of the material to meet the requirements of GB / T 1220 standard.

Description

[0001] This application is a divisional application of the invention patent with application number CN202510764641.2, application date June 10, 2025, and invention title "A heat treatment method to improve the transverse properties of martensitic steel". Technical Field

[0002] This invention relates to the field of heat treatment technology, and in particular to a heat treatment method for improving the transverse properties of martensitic steel. Background Technology

[0003] 14Cr17Ni2 is a classic high-strength martensitic stainless steel. Due to its excellent strength, hardness, good corrosion resistance, and vibration damping properties, it is widely used in many industrial fields such as pump and valve shafts, fasteners, turbine blades, medical devices, cutting tools, molds, and military components. According to the GB / T 1220 standard, the typical heat treatment process for this material is quenching: oil cooling at 950℃ to 1050℃; tempering: air cooling at 275℃ to 350℃. The mechanical properties must meet the following requirements: room temperature tensile strength ≥1080MPa, elongation after fracture ≥10%, and Aku ≥39J. After heat treatment, the matrix of this material is lath martensite. Due to its high chromium (17%) and low nickel (2%) composition, a certain amount (5% to 20%) of high-temperature ferrite often exists in the microstructure. This high-temperature ferrite cannot be eliminated during hot working and is generally distributed along the forging deformation direction in the microstructure. As a brittle phase, high-temperature ferrite has a certain negative impact on the mechanical properties of the material, and its presence in the microstructure will cause a decrease in strength and toughness.

[0004] Further research revealed that the distribution morphology of high-temperature ferrite significantly impacts the mechanical properties of materials, particularly transverse plasticity and impact resistance. Through material composition optimization and refined heat treatment processes, standard procedures have been able to resolve the plasticity and toughness issues of most longitudinally sampled products, such as bars and shafts (where high-temperature ferrite is distributed in a strip-like longitudinal pattern). However, for tubular and ring-shaped products, the high-temperature ferrite in the microstructure often exhibits a network distribution. This network distribution severely reduces the material's plasticity and toughness, resulting in elongation at fracture and impact energy often reaching single-digit levels. Currently, the mechanical property problems caused by the network distribution of high-temperature ferrite in ring-shaped and tubular 14Cr17Ni2 materials remain a persistent and difficult challenge for the industry. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the transverse properties of 14Cr17Ni2 steel in ring and pipe forms, this invention provides a heat treatment method to improve the transverse properties of martensitic steel. This method solves the problem of low transverse plasticity and impact performance of 14Cr17Ni2 martensitic stainless steel pipe and ring forgings. The method uses ultra-high temperature treatment, quenching and tempering processes to optimize and adjust the microstructure and properties, so that the transverse plasticity and impact energy of the material meet the requirements of GB / T 1220 standard.

[0006] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions: A heat treatment method for improving the transverse properties of martensitic steel includes the following steps: The forging is subjected to ultra-high temperature treatment, which involves heating the forging to 1100°C to 1130°C and holding it at that temperature for a certain period of time. The forging is subjected to standard quenching treatment, which involves cooling the forging after ultra-high temperature treatment to the standard quenching temperature at a preset rate, holding it at that temperature for a certain time, and then cooling it. The forging is subjected to at least one tempering treatment, wherein the tempering treatment is to heat the forging to a certain temperature and hold it at that temperature for a certain time, and then cool it.

[0007] According to one aspect of the invention, the preset rate is 50°C to 150°C / h.

[0008] According to one aspect of the present invention, the ultra-high temperature treatment holding time is 1 to 2 min / mm.

[0009] According to one aspect of the invention, the standard quenching temperature is 950°C to 1050°C, and the standard quenching holding time is 0.5 to 1.5 min / mm.

[0010] According to one aspect of the invention, the tempering temperature is 275°C to 350°C, and the tempering holding time is 1.5 to 2.5 min / mm.

[0011] According to one aspect of the invention, the forging is further subjected to a high-temperature tempering pretreatment before undergoing ultra-high temperature treatment, wherein the high-temperature tempering involves heating the forging to a certain temperature and holding it at that temperature for a certain time, followed by cooling.

[0012] According to one aspect of the present invention, the high-temperature tempering temperature is 680°C to 700°C, and the high-temperature tempering holding time is ≥4 hours.

[0013] According to one aspect of the present invention, after the standard quenching treatment and heat preservation are completed, the temperature is oil-cooled to below 50°C.

[0014] According to one aspect of the present invention, the number of tempering treatments is set according to the thickness of the forging. If the heat-treated thickness of the forging is ≤300mm, the number of tempering treatments is 2 times; if the heat-treated thickness of the forging is ≥300mm, the number of tempering treatments is 3 times.

[0015] According to one aspect of the invention, the forging after heat treatment is sampled and subjected to mechanical property tests.

[0016] The advantages of this invention are as follows: High-temperature tempering eliminates residual stress generated during forging, reducing the risk of deformation and cracking during subsequent ultra-high temperature treatment. Simultaneously, high-temperature tempering promotes uniform precipitation and initial spheroidization of carbides in the original microstructure, optimizing the matrix microstructure and creating favorable conditions for the full diffusion of high-temperature ferrite in the subsequent ultra-high temperature treatment process. This more efficiently transforms network ferrite into a uniform granular distribution, further enhancing the improvement effect of ultra-high temperature treatment on the transverse plasticity and toughness of the material, and ensuring the uniformity and stability of the mechanical properties of the forging after final heat treatment. Ultra-high temperature treatment promotes the full diffusion of high-temperature ferrite in the forging, improves the distribution morphology of network ferrite, and results in a uniform granular distribution of high-temperature ferrite, effectively cutting off the cutting effect of ferrite on the matrix. Granular high-temperature ferrite can reduce stress concentration and improve the transverse properties of materials. Multiple tempering processes reduce the content of retained austenite, resulting in a uniform tempered martensite and dispersed granular high-temperature ferrite microstructure. This reduces material anisotropy and improves transverse mechanical properties, enabling transversely sampled forgings such as pipes and rings to achieve performance levels comparable to bar and shaft forgings. This invention provides a heat treatment method to improve the transverse properties of martensitic steel, solving the problem of low transverse plasticity and impact resistance in 14Cr17Ni2 martensitic stainless steel pipe and ring forgings. Ultra-high temperature treatment and tempering optimize and adjust the microstructure and properties, ensuring that the material's transverse plasticity and impact resistance meet the requirements of GB / T 1220. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The table shows the longitudinal and transverse properties obtained using conventional heat treatment processes; Figure 2 Typical microstructure diagrams of bar and shaft forgings (high-temperature ferrite is longitudinally distributed); Figure 3 Typical microstructure diagram of pipe and ring forgings (high-temperature ferrite is distributed in a network). Figure 4 This is a process flow diagram of a heat treatment method for improving the transverse properties of martensitic steel according to the present invention. Figure 5 This is a process curve diagram of the pretreatment of forgings in a heat treatment method for improving the transverse properties of martensitic steel according to the present invention. Figure 6 This is a process curve diagram of ultra-high temperature treatment and standard quenching treatment in the heat treatment method for improving the transverse properties of martensitic steel according to the present invention. Figure 7 This is a process curve diagram of a single tempering treatment in a heat treatment method for improving the transverse properties of martensitic steel according to the present invention. Figure 8 This is a schematic diagram of the pipe-type forging in Embodiment 3 of the present invention; Figure 9 This is a process curve diagram of the ultra-high temperature treatment and standard quenching treatment in Embodiment 3 of the present invention; Figure 10 This is a process curve diagram of the two tempering processes in Embodiment 3 of the present invention; Figure 11 This is a schematic diagram of the ring-shaped forging in Embodiment 4 of the present invention; Figure 12 This is a process curve diagram of the ultra-high temperature treatment and standard quenching treatment in Example 4 of the present invention; Figure 13 This is a process curve diagram of the two tempering processes in Embodiment 4 of the present invention; Figure 14 This is a microstructure diagram of the forging after heat treatment in Example 3 of the present invention; Figure 15 This is a microstructure diagram of the forging after heat treatment in Example 4 of the present invention; Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In existing technologies, forgings subjected to conventional heat treatment processes are subjected to performance testing, and the performance test results are as follows: Figure 1 As shown, the forging has a transverse tensile strength of 1201 MPa, an elongation after fracture of 6.5%, and an average impact energy of 28 J. The transverse high impact energy is lower than the standard requirement. Figure 2The figure shows a typical microstructure of bar and shaft forgings. As can be seen from the figure, the high-temperature ferrite is distributed longitudinally. Figure 3 The image shows a typical microstructure of pipe and ring forgings. As can be seen from the image, the high-temperature ferrite is distributed in a network pattern.

[0021] Example 1: like Figure 4 , Figure 6 and Figure 7 As shown, a heat treatment method for improving the transverse properties of martensitic steel is presented. This heat treatment method is generally applicable to forgings of martensitic stainless steel such as rings and pipes, and is particularly suitable for 14Cr17Ni2 stainless steel. It includes the following steps: S1: Ultra-high temperature treatment of forgings: The forgings are subjected to ultra-high temperature treatment by heating them in a furnace to 1100℃ to 1130℃ and holding them at that temperature for a certain period of time. The holding time is implemented according to the principle of 1 to 2 min / mm based on the effective thickness of the heat treatment.

[0022] The main purpose of ultra-high temperature treatment is to allow the high-temperature ferrite in the material to diffuse fully through ultra-high temperature treatment above 1100℃, improve the distribution morphology of network ferrite, and make the high-temperature ferrite have a uniform granular distribution morphology.

[0023] S2: Standard quenching treatment is performed on the forgings. The forgings undergo standard quenching treatment, which involves cooling the ultra-high temperature forgings to the standard quenching temperature at a preset rate, holding them at that temperature for a certain time, and then rapidly oil-cooling them. The preset rate is 50°C to 150°C / h, the standard quenching temperature is 950°C to 1050°C, and the holding time is 0.5 to 1.5 min / mm. Specifically, after the ultra-high temperature treatment, the forgings are cooled to the standard quenching temperature of 950°C to 1050°C at a rate of 50°C to 150°C / h, held at that temperature for a certain time at a rate of 0.5 to 1.5 min / mm, and then oil-cooled. After the standard quenching treatment, the forgings are oil-cooled to below 50°C.

[0024] After the ultra-high temperature treatment is completed, the temperature is lowered to the standard quenching temperature. This is to prevent excessive thermal stress from direct quenching at ultra-high temperature, which could increase the risk of workpiece cracking, and to prevent excessively high quenching temperature from causing increased hardness after tempering, which could reduce the material's plasticity and toughness.

[0025] S3: The forging shall be tempered at least once; Forgings that have undergone standard quenching are subjected to at least one tempering treatment, i.e., multiple repeated tempering treatments. The tempering treatment involves heating the forging to a certain temperature and holding it at that temperature for a certain time, followed by air cooling. The tempering temperature is between 275℃ and 350℃, and the holding time is 1.5 to 2.5 min / mm. Specifically, the forging is heated to 275℃ to 350℃, and the holding time is implemented according to the effective thickness of the workpiece at 1.5 to 2.5 min / mm. After holding, it is removed from the furnace and air-cooled. Multiple tempering processes are repeated according to this procedure. After high-temperature quenching, a small amount of austenite may remain in the material. By implementing a multiple tempering process, the content of retained austenite can be effectively reduced, thereby improving the plasticity and toughness of the material.

[0026] The number of tempering treatments is mainly determined by the size of the forging. Preferably, two tempering treatments are used for heat treatment thickness ≤ 300mm, and three tempering treatments are used for heat treatment thickness ≥ 300mm.

[0027] S4: Take samples of the forgings and conduct performance tests: Samples of the heat-treated forgings are taken and subjected to performance tests, including but not limited to mechanical property tests and grain size tests. The mechanical property tests include, but are not limited to, tensile tests, impact tests, and hardness tests.

[0028] The advantages of this embodiment are: Ultra-high temperature treatment promotes the full diffusion of high-temperature ferrite in forgings, improves the distribution morphology of network ferrite, and results in a uniform granular distribution of high-temperature ferrite, effectively cutting off the cutting effect of ferrite on the matrix. Granular high-temperature ferrite reduces stress concentration and improves the transverse properties of the material. This embodiment effectively solves the problem of decreased transverse plasticity and toughness caused by network high-temperature ferrite in 14Cr17Ni2 forgings such as rings and tubes through a combination of ultra-high temperature treatment, standard quenching, and multiple tempering. Ultra-high temperature treatment transforms network ferrite into a uniform granular distribution. Combined with stepped cooling to the standard quenching temperature, it reduces the risk of cracking while avoiding excessive hardness. Multiple tempering reduces the content of retained austenite, resulting in a uniform tempered martensite and dispersed granular high-temperature ferrite structure, reducing material anisotropy and improving the transverse mechanical properties of the material. This allows the transversely sampled forgings such as tubes and rings to achieve the same performance level as bar and shaft forgings. This process not only has low production costs, but also significantly improves the uniformity and stability of the material's transverse properties, making it very suitable for application in key areas such as high-pressure pipelines and military components, and has significant industrial application value.

[0029] Example 2: like Figure 4 , Figure 5 , Figure 6 and Figure 7As shown, a heat treatment method for improving the transverse properties of martensitic steel is described. This heat treatment method is generally applicable to ring and tubular forgings of 14Cr17Ni2 and includes the following steps: S1: Pre-treatment of forgings: The forgings undergo pretreatment, specifically high-temperature tempering. This high-temperature tempering involves heating the forgings to a specific temperature and holding them at that temperature for a certain time, followed by air cooling. Specifically, the material is tempered at 680°C to 700°C after forging and before molding, and held at that temperature for at least 4 hours, followed by air cooling. The main purpose of this high-temperature tempering is to reduce hardness, improve machinability, eliminate forging stress, and prevent cracking during subsequent processing.

[0030] S2: The forgings undergo ultra-high temperature quenching treatment. The forgings are subjected to ultra-high temperature quenching treatment by heating them in a furnace to 1100℃ to 1130℃ and holding them at that temperature for a certain period of time. The holding time is implemented according to the principle of 1 to 2 min / mm based on the effective thickness of the heat treatment.

[0031] The main purpose of using ultra-high temperature quenching is to allow the high-temperature ferrite in the material to diffuse fully through ultra-high temperature treatment above 1100℃, improve the distribution morphology of network ferrite, and make the high-temperature ferrite have a uniform granular distribution morphology.

[0032] S3: Standard quenching treatment for forgings: The forgings undergo standard quenching treatment, which involves cooling the ultra-high temperature quenched forgings to the standard quenching temperature at a preset rate, holding them at that temperature for a certain time, and then rapidly oil-cooling them. The preset rate is 50°C to 150°C / h, the standard quenching temperature is 950°C to 1050°C, and the holding time is 0.5 to 1.5 min / mm. Specifically, after the ultra-high temperature treatment, the forgings are cooled to the standard quenching temperature of 950°C to 1050°C at a rate of 50°C to 150°C / h, held at that temperature for a certain time at a rate of 0.5 to 1.5 min / mm, and then oil-cooled. After the standard quenching treatment, the forgings are oil-cooled to below 50°C.

[0033] After the ultra-high temperature treatment is completed, the temperature is lowered to the standard quenching temperature. This is to prevent excessive thermal stress from direct quenching at ultra-high temperature, which could increase the risk of workpiece cracking, and to prevent excessively high quenching temperature from causing increased hardness after tempering, which could reduce the material's plasticity and toughness.

[0034] S4: The forging shall be tempered at least once; Forgings that have undergone standard quenching are subjected to at least one tempering treatment, i.e., multiple repeated tempering treatments. The tempering treatment involves heating the forging to a certain temperature and holding it at that temperature for a certain time, followed by air cooling. The tempering temperature is between 275℃ and 350℃, and the holding time is implemented at 1.5 to 2.5 min / mm based on the effective thickness of the forging. Specifically, the forging is heated to 275℃ to 350℃, held for 1.5 to 2.5 min / mm based on the effective thickness of the workpiece, and then air-cooled after the holding period. Multiple tempering processes are repeated in this manner. After high-temperature quenching, a small amount of austenite may remain in the material. By implementing a multiple tempering process, the content of retained austenite can be effectively reduced, thereby improving the plasticity and toughness of the material.

[0035] The number of tempering treatments is mainly determined by the size of the forging. Preferably, two tempering treatments are used for heat treatment thickness ≤ 300mm, and three tempering treatments are used for heat treatment thickness ≥ 300mm.

[0036] S5: Take samples of the forgings and conduct performance tests: Samples of the heat-treated forgings are taken and subjected to performance tests, including but not limited to mechanical property tests and grain size tests. The mechanical property tests include, but are not limited to, tensile tests, impact tests, and hardness tests.

[0037] The advantages of this embodiment are: high-temperature tempering eliminates residual stress generated during forging, reducing the risk of deformation and cracking during subsequent ultra-high temperature quenching; at the same time, high-temperature tempering promotes uniform precipitation and initial spheroidization of carbides in the original microstructure, optimizes the matrix microstructure, and creates favorable conditions for the full diffusion of high-temperature ferrite in the subsequent ultra-high temperature quenching process, thereby more efficiently transforming network ferrite into a uniform granular distribution, further improving the effect of ultra-high temperature quenching on the transverse plasticity and toughness of the material, and ensuring the uniformity and stability of the mechanical properties of the forging after the final heat treatment.

[0038] Example 3: like Figure 8 , Figure 9 , Figure 10 and Figure 14 As shown, a heat treatment method for improving the transverse properties of martensitic steel is described in this embodiment. A nozzle forging is used. The nozzle section of the forging has an outer diameter of 320 mm, an inner diameter of 155 mm, and a length of 417 mm. The nozzle end of the forging has an outer diameter of 420 mm, an inner diameter of 155 mm, and a length of 68 mm. Figure 8 As shown, the effective thickness after heat treatment is 82.5 mm, and the forging material is 14Cr17Ni2 stainless steel. The heat treatment method includes the following steps: S1: Pre-treatment of forgings; The forgings are pretreated by high-temperature tempering. The forgings are tempered at high temperature after forging and before molding. The forgings are heated to 680°C to 700°C and held at that temperature for 5 hours before being air-cooled.

[0039] S2: Forgings are subjected to ultra-high temperature treatment; like Figure 9 As shown, the forging is subjected to ultra-high temperature treatment by heating it in the furnace to 1120℃±10℃ and holding it for 2 hours.

[0040] S3: Perform standard quenching treatment on the forgings; like Figure 9 As shown, the forging is subjected to standard quenching treatment, which involves cooling the forging after ultra-high temperature treatment to 1040℃±10℃ at a rate of 80℃ / h, holding it at that temperature for 1.5h, and then removing it from the furnace and immersing it in oil to cool it to below 50℃.

[0041] S4: The forging shall be tempered at least once; S41: Perform the first tempering treatment on the forgings after standard quenching; The forgings that have undergone standard quenching are heated to 320℃±10℃, held at that temperature for 3 hours, and then air-cooled to room temperature.

[0042] S42: Perform a second tempering treatment on the forgings after the first tempering treatment: After the forgings underwent the first tempering treatment, they were cooled to room temperature and then reheated to 320℃±10℃. After holding at this temperature for 3 hours, they were removed from the furnace and air-cooled to room temperature.

[0043] S5: Take samples of the forgings and conduct performance tests: Samples of the heat-treated forgings were taken and subjected to performance tests, including but not limited to mechanical property tests and grain size tests. The mechanical property tests included, but were not limited to, tensile tests, impact tests, and hardness tests. The performance test results of the forgings are shown in the table below:

[0044] Microstructure images of the heat-treated forgings obtained by metallographic microscopy are shown below. Figure 14 As shown in the figure, the scale bar is 100 micrometers.

[0045] The advantages of this embodiment are as follows: For the nozzle forging, a combined process of "high-temperature tempering pretreatment, ultra-high temperature treatment, standard quenching, and double tempering" is adopted. The high-temperature tempering pretreatment effectively eliminates residual forging stress and promotes the initial spheroidization of the original network ferrite, laying the foundation for subsequent microstructure optimization. The ultra-high temperature treatment allows the ferrite to fully diffuse and transform into a uniform granular distribution. Combined with standard quenching, this reduces thermal stress to prevent cracking and ensures reasonable hardness of the martensitic matrix. The double tempering effectively eliminates quenching stress, reduces residual austenite, and further improves ductility and toughness. Actual measurement data shows that the transverse tensile strength of the forging reaches 1232 to 1245 MPa, the elongation after fracture is 12.0% to 12.5%, and the average impact energy is over 45 J, all far exceeding standard requirements. Furthermore, the ferrite in the microstructure exhibits a uniform granular distribution, proving that this process can precisely control the microstructure of medium-thickness ring forgings, significantly improving the uniformity and stability of transverse properties. The process parameters are highly reproducible, providing an efficient and feasible solution for the heat treatment of similar complex structural parts.

[0046] Example 4: like Figure 11 , Figure 12 , Figure 13 and Figure 15 As shown, a heat treatment method for improving the transverse properties of martensitic steel is described in this embodiment. A ring forging is used, with an outer diameter of 535 mm, an inner diameter of 450 mm, and a length of 245 mm. Figure 11 As shown, the effective thickness after heat treatment is 42.5 mm, and the heat treatment method includes the following steps: S1: Pre-treatment of forgings: The forgings are pretreated by high-temperature tempering. After forging and before molding, the forgings are tempered at high temperature. The forgings are heated to 690℃±10℃ and held at that temperature for 4 hours before being removed from the furnace and air-cooled.

[0047] S2: Ultra-high temperature treatment of forgings: like Figure 12 As shown, the forging is subjected to ultra-high temperature treatment by heating it in the furnace to 1120℃±10℃ and holding it for 1.5 hours.

[0048] S3: Standard quenching treatment for forgings: like Figure 12 As shown, the forging is subjected to standard quenching treatment, which involves cooling the forging after ultra-high temperature treatment to 1000℃±10℃ at a rate of 100℃ / h, holding it at that temperature for 1 hour, and then removing it from the furnace and immersing it in oil to cool it to below 50℃.

[0049] S4: The forging shall be tempered at least once; S41: Perform the first tempering treatment on forgings that have undergone standard quenching: The forgings that have undergone standard quenching are heated to 290℃±10℃, held at that temperature for 2 hours, and then air-cooled to room temperature.

[0050] S42: Perform a second tempering treatment on the forgings after the first tempering treatment: After the forgings were cooled to room temperature after the first tempering treatment, they were reheated to 290℃±10℃, held at that temperature for 2 hours, and then air-cooled to room temperature.

[0051] S5: Take samples of the forgings and conduct performance tests: Samples of the heat-treated forgings were taken and subjected to performance tests, including but not limited to mechanical property tests and grain size tests. The mechanical property tests included, but were not limited to, tensile tests, impact tests, and hardness tests. The performance test results of the forgings are shown in the table below:

[0052] Microstructure images of the heat-treated forgings obtained by metallographic microscopy are shown below. Figure 15 As shown in the figure, the scale bar is 100 micrometers.

[0053] The advantages of this embodiment are as follows: For ring forgings, a combined process of "high-temperature tempering pretreatment, ultra-high temperature treatment, standard quenching, and double tempering" is employed. The high-temperature tempering pretreatment effectively eliminates residual forging stress and promotes the initial spheroidization of the original network ferrite, laying the foundation for subsequent microstructure optimization. The ultra-high temperature treatment allows the ferrite to fully diffuse and transform into a uniform granular distribution. Combined with standard quenching, this reduces thermal stress to prevent cracking and ensures reasonable hardness of the martensitic matrix. The double tempering effectively eliminates quenching stress, reduces residual austenite, and further improves ductility and toughness. Actual measurement data shows that the transverse tensile strength of the forgings reaches 1214 to 1235 MPa, the elongation after fracture is 13.5% to 14.0%, and the average impact energy is over 50 J, all far exceeding standard requirements. Furthermore, the ferrite in the microstructure exhibits a uniform granular distribution, proving that this process can precisely control the microstructure of medium-thickness ring forgings, significantly improving the uniformity and stability of transverse properties. The process parameters are highly reproducible, providing an efficient and feasible solution for the heat treatment of similar complex structural parts.

[0054] The advantages of this invention are as follows: High-temperature tempering eliminates residual stress generated during forging, reducing the risk of deformation and cracking during subsequent ultra-high temperature treatment. Simultaneously, high-temperature tempering promotes uniform precipitation and initial spheroidization optimization of carbides in the original microstructure, improving the matrix microstructure and creating favorable conditions for the full diffusion of high-temperature ferrite in the subsequent ultra-high temperature treatment process. This more efficiently transforms network ferrite into a uniform granular distribution, further enhancing the improvement effect of ultra-high temperature treatment on the transverse plasticity and toughness of the material, and ensuring the uniformity and stability of the mechanical properties of the forging after final heat treatment. Ultra-high temperature treatment promotes the full diffusion of high-temperature ferrite in the forging, improves the distribution morphology of network ferrite, and results in a uniform granular distribution of high-temperature ferrite, effectively cutting off the cutting effect of ferrite on the matrix. Granular high-temperature ferrite can reduce stress concentration and improve the transverse properties of materials. Multiple tempering processes reduce the content of retained austenite, resulting in a uniform tempered martensite and dispersed granular high-temperature ferrite microstructure. This reduces material anisotropy and improves transverse mechanical properties, enabling transversely sampled forgings such as pipes and rings to achieve performance levels comparable to bar and shaft forgings. This invention provides a heat treatment method to improve the transverse properties of martensitic steel, solving the problem of low transverse plasticity and impact resistance in 14Cr17Ni2 martensitic stainless steel pipe and ring forgings. Ultra-high temperature treatment and tempering optimize and adjust the microstructure and properties, ensuring that the material's transverse plasticity and impact resistance meet the requirements of GB / T 1220.

[0055] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A heat treatment method for improving the transverse properties of martensitic steel, characterized in that, Includes the following steps: The forgings are subjected to high-temperature tempering pretreatment, wherein the high-temperature tempering is to heat the forgings to a certain temperature and hold them at that temperature for a certain time, and then cool them. The forging is subjected to ultra-high temperature treatment, wherein the ultra-high temperature treatment is to heat the forging to 1100℃ to 1130℃ and hold it at that temperature for a certain period of time, wherein the holding time of the ultra-high temperature treatment is 1 to 2 min / mm. The forging is subjected to standard quenching treatment, which involves cooling the forging after ultra-high temperature treatment to the standard quenching temperature at a preset rate, holding it at that temperature for a certain time, and then cooling it. The standard quenching temperature is 950℃ to 1050℃, the preset rate is 50℃ to 150℃ / h, and the standard quenching holding time is 0.5 to 1.5min / mm. The forging is subjected to more than one tempering treatment. The number of tempering treatments is set according to the thickness of the forging. If the heat-treated thickness of the forging is ≤300mm, the number of tempering treatments is 2. If the heat-treated thickness of the forging is >300mm, the number of tempering treatments is 3. The tempering treatment involves heating the forging to a certain temperature and holding it at that temperature for a certain time, followed by cooling. The tempering temperature is 275℃ to 350℃, and the holding time is 1.5 to 2.5 min / mm. The forging is a nozzle forging or a ring forging.

2. The heat treatment method for improving the transverse properties of martensitic steel according to claim 1, characterized in that, The high-temperature tempering temperature is 680℃ to 700℃, and the high-temperature tempering holding time is ≥4 hours.

3. The heat treatment method for improving the transverse properties of martensitic steel according to claim 1, characterized in that, After the standard quenching and heat preservation treatment is completed, the temperature is cooled to below 50°C by oil.

4. The heat treatment method for improving the transverse properties of martensitic steel according to any one of claims 1 to 3, characterized in that, It also includes sampling the heat-treated forgings and conducting mechanical property tests.

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