Heat treatment method for improving transverse performance of martensitic steel

Abstract

The invention relates to the technical field of heat treatment, in particular to a heat treatment method for improving the transverse performance of martensitic steel, which comprises the following steps: carrying out ultrahigh-temperature treatment on a forge piece, namely heating the forge piece to 1100-1130 DEG C and keeping the temperature for a certain time; the forge piece is subjected to standard quenching treatment, and according to the standard quenching treatment, the forge piece subjected to ultra-high temperature treatment is cooled to the standard quenching temperature at the preset speed, subjected to heat preservation for a certain time and then cooled; and the forging is subjected to at least one time of tempering treatment, and the tempering treatment comprises the steps of heating the forging to a certain temperature, keeping the temperature for a certain time and then cooling. According to the heat treatment method provided by the invention, the problems of low transverse plasticity and impact performance of martensitic stainless steel pipe and ring forgings are solved, and the optimization and adjustment of the structure form and performance are realized by adopting ultrahigh-temperature treatment and tempering, so that the transverse plasticity and impact energy indexes of the material meet the standard requirements of GB / T 1220.

Description

Technical Field

[0001] The present invention relates to the field of heat treatment technology, in particular to a heat treatment method for improving the transverse performance of martensitic steel. Background Art

[0002] 14Cr17Ni2 is a classic high-strength martensitic stainless steel. Its outstanding strength, hardness, corrosion resistance, and shock absorption make it widely used in a wide range of industrial applications, including pump and valve shafts, fasteners, turbine blades, medical devices, cutting tools, molds, and military components. According to GB / T 1220, this material requires typical heat treatment: quenching at 950°C to 1050°C with oil cooling and tempering at 275°C to 350°C with air cooling. Mechanical properties must meet the following requirements: room temperature tensile strength ≥ 1080 MPa, elongation ≥ 10%, and Aku ≥ 39 J.

[0003] After heat treatment, the matrix structure of this material is lath martensite. Due to its high chromium (17%) and low nickel (2%) composition, the material's microstructure often contains a certain amount (5% to 20%) of high-temperature ferrite. This high-temperature ferrite cannot be eliminated during hot working and is generally distributed along the forging deformation direction. As a brittle phase, high-temperature ferrite has a certain negative impact on the mechanical properties of the material, and its presence in the structure can reduce strength and toughness.

[0004] Further research found that the distribution morphology of high-temperature ferrite has a great influence on the mechanical properties of the material, especially the transverse plasticity and impact properties. Through the optimization of material composition and the refined control of heat treatment process, the standard process has been able to solve the plasticity and toughness problems of most longitudinal sampling products such as rods and shafts (high-temperature ferrite is distributed longitudinally in strips). However, for tube and ring products, the high-temperature ferrite in the material organization is often distributed in a network. This network distribution of high-temperature ferrite will cause the plasticity and toughness of the material to drop seriously, resulting in the elongation and impact energy after fracture often being only in the single digit. At present, the mechanical performance problems of 14Cr17Ni2 materials for rings and tubes caused by the network distribution of high-temperature ferrite have become a difficult problem that has been difficult to overcome in the industry. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the transverse performance of the current 14Cr17Ni2 steel for rings and tubes, the present invention provides a heat treatment method for improving the transverse performance of martensitic steel, which solves the problem of low transverse plasticity and impact performance of 14Cr17Ni2 martensitic stainless steel tubes and ring forgings. Ultra-high temperature treatment, quenching and tempering processes are used to optimize and adjust the microstructure and performance, so that the transverse plasticity and impact energy indicators of the material meet the standard requirements of GB / T 1220.

[0006] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0007] A heat treatment method for improving the transverse properties of martensitic steel comprises the following steps:

[0008] The forgings are subjected to ultra-high temperature treatment, wherein the ultra-high temperature treatment is to heat the forgings to 1100°C to 1130°C and keep the temperature for a certain period of time;

[0009] Performing standard quenching treatment on the forgings, wherein the standard quenching treatment is to cool the forgings after ultra-high temperature treatment to the standard quenching temperature at a preset rate, keep the temperature for a certain period of time, and then cool;

[0010] The forging is subjected to at least one tempering treatment, wherein the forging is heated to a certain temperature, kept at the temperature for a certain period of time, and then cooled.

[0011] According to one aspect of the present invention, the preset rate is 50°C to 150°C / h.

[0012] According to one aspect of the present invention, the ultra-high temperature treatment holding time is 1 to 2 min / mm.

[0013] According to one aspect of the present 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.

[0014] According to one aspect of the present invention, the tempering treatment temperature is 275° C. to 350° C., and the tempering treatment holding time is 1.5 to 2.5 min / mm.

[0015] According to one aspect of the present invention, the forging is further subjected to high temperature tempering pretreatment before the ultra-high temperature treatment. The high temperature tempering is to heat the forging to a certain temperature, keep the temperature for a certain time, and then cool it.

[0016] 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.

[0017] According to one aspect of the present invention, the standard quenching treatment is oil-cooled to below 50° C. after the heat preservation is completed.

[0018] 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 ≤300 mm, the number of tempering treatments is 2 times; if the heat-treated thickness of the forging is ≥300 mm, the number of tempering treatments is 3 times.

[0019] According to one aspect of the present invention, the method further comprises sampling the forging after heat treatment and performing a mechanical property test.

[0020] The advantages of the present invention are as follows: the residual stress generated during the forging process of the forging is eliminated through high-temperature tempering treatment, reducing the risk of deformation and cracking during subsequent ultra-high temperature treatment; at the same time, the high-temperature tempering treatment promotes the uniform precipitation and initial spheroidization of carbides in the original structure, optimizes the matrix structure state, and creates favorable conditions for the full diffusion of high-temperature ferrite in the subsequent ultra-high temperature treatment process, thereby more efficiently transforming the network ferrite into a uniform granular distribution, further enhancing the improvement effect of ultra-high temperature treatment on the transverse plastic toughness of the material, and ensuring the uniformity and stability of the mechanical properties of the forging after the final heat treatment. Ultra-high temperature treatment can promote the full diffusion of high-temperature ferrite in the forging, improve the distribution morphology of the network ferrite, make the high-temperature ferrite uniformly distributed in a granular form, and effectively cut off the ferrite's cutting effect on the matrix. Granular high-temperature ferrite reduces stress concentration and improves the material's transverse properties. Multiple tempering processes reduce the amount of retained austenite, resulting in a uniform structure of tempered martensite and dispersed granular high-temperature ferrite. This reduces material anisotropy and improves the material's transverse mechanical properties, bringing the performance of transversely sampled forgings like tubes and rings to the same level as rods and shafts. The present invention provides a heat treatment method for improving the transverse properties of martensitic steel, resolving the issue of low transverse plasticity and impact performance in 14Cr17Ni2 martensitic stainless steel tubes and rings. Ultra-high temperature treatment and tempering are employed to optimize and adjust the microstructure and properties, ensuring that the material's transverse plasticity and impact energy meet the requirements of GB / T 1220. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 The longitudinal and transverse performance tables are shown for conventional heat treatment processes;

[0023] Figure 2 This is a typical microstructure diagram of rod and shaft forgings (high-temperature ferrite is distributed longitudinally);

[0024] Figure 3 This is a typical microstructure diagram of tube and ring forgings (high temperature ferrite is distributed in a network pattern);

[0025] Figure 4 This is a process flow chart of a heat treatment method for improving the transverse properties of martensitic steel according to the present invention;

[0026] Figure 5This is a process curve diagram for pre-treating forgings in a heat treatment method for improving the transverse properties of martensitic steel according to the present invention;

[0027] Figure 6 This is a process curve diagram of ultra-high temperature treatment and standard quenching treatment in a heat treatment method for improving the transverse properties of martensitic steel according to the present invention;

[0028] 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;

[0029] Figure 8 This is a schematic structural diagram of a pipe forging in Example 3 of the present invention;

[0030] Figure 9 This is a process curve diagram of the ultra-high temperature treatment and standard quenching treatment in Example 3 of the present invention;

[0031] Figure 10 This is a process curve diagram of the double tempering treatment in Example 3 of the present invention;

[0032] Figure 11 Schematic diagram of the structure of the ring forging in Example 4 of the present invention;

[0033] 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;

[0034] Figure 13 This is a process curve diagram of the double tempering treatment in Example 4 of the present invention;

[0035] Figure 14 This is a microstructure diagram of the forging after heat treatment according to Example 3 of the present invention;

[0036] Figure 15 This is a microstructure diagram of the forging after heat treatment according to Example 4 of the present invention; DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] In the prior art, the performance test of forgings using conventional heat treatment process is carried out, and the performance test results are as follows: Figure 1As shown, the transverse tensile strength of the forging is 1201MPa, the elongation after fracture is 6.5%, the average impact energy is 28J, and the transverse high impact energy is lower than the standard requirement. Figure 2 The figure shows a typical microstructure of rod and shaft forgings. It can be seen from the figure that high-temperature ferrite is distributed longitudinally; Figure 3 The figure shows a typical microstructure diagram of tube and ring forgings. It can be seen from the figure that the high-temperature ferrite is distributed in a network shape.

[0039] Example 1:

[0040] like Figure 4 、 Figure 6 and Figure 7 As shown, a heat treatment method for improving the transverse properties of martensitic steel is generally applicable to martensitic stainless steel forgings such as rings and tubes, and is particularly suitable for 14Cr17Ni2 stainless steel. It includes the following steps:

[0041] S1: Ultra-high temperature treatment of forgings:

[0042] The forgings are subjected to ultra-high temperature treatment, heating the forgings to 1100°C to 1130°C in a furnace and holding the temperature for a certain period of time. The holding time is implemented in principle of 1 to 2 minutes / mm according to the effective thickness of the heat treatment.

[0043] The main purpose of ultra-high temperature treatment is to fully diffuse the high-temperature ferrite in the material through ultra-high temperature treatment above 1100°C, improve the distribution of the network ferrite, and make the high-temperature ferrite uniformly distributed in a granular form.

[0044] S2: Standard quenching treatment of forgings:

[0045] The forgings are subjected to a standard quenching treatment, which involves cooling the ultra-high temperature treated forgings to a standard quenching temperature at a preset rate, holding the temperature for a certain period, and then rapidly oil cooling. 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. This means that after the ultra-high temperature treatment, the forgings are cooled at a rate of 50°C to 150°C / h to a standard quenching temperature of 950°C to 1050°C, held at the temperature for a certain period at a rate of 0.5 to 1.5 min / mm, and then removed from the furnace and oil cooled. After the standard quenching treatment is completed, the forgings are oil cooled to below 50°C.

[0046] After the ultra-high temperature treatment, the temperature is lowered to the conventional quenching temperature specified in the standard. On the one hand, this prevents the thermal stress of ultra-high temperature direct quenching from being too large, which increases the risk of cracking in the workpiece. On the other hand, it prevents the quenching temperature from being too high, which causes the hardness to increase after tempering and reduces the plastic toughness of the material.

[0047] S3: Temper the forging at least once;

[0048] Forgings that have undergone standard quenching are subjected to at least one tempering treatment, i.e., repeated tempering treatments. The tempering treatment involves heating the forging to a certain temperature, holding it for a certain period of time, and then air-cooling it. The tempering temperature is 275°C to 350°C, and the tempering time is 1.5 to 2.5 min / mm. Specifically, the forging is heated to 275°C to 350°C for a holding time of 1.5 to 2.5 min / mm depending on the effective thickness of the workpiece. After holding, the forging is removed from the furnace and air-cooled. This tempering process is repeated multiple times. After high-temperature quenching, a small amount of austenite may remain in the material. By implementing multiple tempering treatments, the content of retained austenite can be effectively reduced, thereby improving the plasticity and toughness of the material.

[0049] The number of tempering treatments is mainly determined by the size of the forging. Preferably, two tempering treatments are used for heat treatment thickness ≤ 300 mm, and three tempering treatments are used for heat treatment thickness above 300 mm.

[0050] S4: Take samples of forgings and conduct performance tests:

[0051] The heat-treated forgings are sampled and subjected to performance tests, including but not limited to mechanical property tests, grain size tests, etc. The mechanical property tests include but are not limited to tensile tests, impact tests, hardness tests, etc.

[0052] Advantages of this embodiment: Ultra-high temperature treatment promotes the full diffusion of high-temperature ferrite in forgings, improves the distribution of reticular ferrite, and achieves a uniform granular distribution of high-temperature ferrite, effectively eliminating the ferrite's ability to fracture the matrix. Granular high-temperature ferrite reduces stress concentration and improves the material's transverse properties. This embodiment effectively addresses the problem of reduced transverse plasticity and toughness caused by reticular high-temperature ferrite in 14Cr17Ni2 forgings, such as rings and tubes, through a combined process of ultra-high temperature treatment, standard quenching, and multiple tempering. Ultra-high temperature treatment transforms the reticular ferrite into a uniform granular distribution. Combined with stepwise cooling to the standard quenching temperature, this reduces the risk of cracking while preventing excessive hardness. Multiple tempering reduces the retained austenite content, resulting in a uniform tempered martensite and a dispersed granular high-temperature ferrite structure. This reduces material anisotropy and improves the material's transverse mechanical properties, bringing the performance of transversely sampled forgings, such as tubes and rings, to the same level as rods and shafts. This process not only has low production costs, but also significantly improves the uniformity and stability of the material's lateral performance. It is very suitable for application in key areas such as high-pressure pipelines and military components, and has significant industrial application value.

[0053] Example 2:

[0054] like Figure 4 、 Figure 5 、 Figure 6 and Figure 7 As shown, a heat treatment method for improving the transverse properties of martensitic steel is generally applicable to 14Cr17Ni2 forgings such as rings and tubes, and includes the following steps:

[0055] S1: Pretreatment of forgings:

[0056] Forgings undergo pretreatment with high-temperature tempering, which involves heating the forgings to a specific temperature, holding the temperature for a specified period, and then air-cooling them. This involves heating the material to 680°C to 700°C and holding it for at least four hours before air-cooling. The primary purpose of high-temperature tempering is to reduce hardness, improve workability, and eliminate forging stresses to prevent cracking during subsequent processing.

[0057] S2: Ultra-high temperature quenching treatment of forgings:

[0058] The forgings are subjected to ultra-high temperature quenching treatment, heating the forgings to 1100°C to 1130°C in a furnace and holding the temperature for a certain period of time. The holding time is implemented in principle of 1 to 2 minutes / mm according to the effective thickness of the heat treatment.

[0059] The main purpose of ultra-high temperature quenching treatment is to fully diffuse the high temperature ferrite in the material through ultra-high temperature treatment above 1100°C, improve the distribution of the network ferrite, and make the high temperature ferrite uniformly distributed in a granular form.

[0060] S3: Standard quenching treatment of forgings:

[0061] The forgings are subjected to a standard quenching treatment, which involves cooling the forgings after ultra-high temperature quenching at a preset rate to the standard quenching temperature, holding the temperature for a certain period, and then rapidly oil cooling. 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. That is, after the ultra-high temperature treatment, the forgings are cooled at a rate of 50°C to 150°C / h to the standard quenching temperature of 950°C to 1050°C, held at the temperature for a certain period of 0.5 to 1.5 min / mm, and then removed from the furnace and oil cooled. After the standard quenching treatment is completed, the temperature is oil cooled to below 50°C.

[0062] After the ultra-high temperature treatment, the temperature is lowered to the conventional quenching temperature specified in the standard. On the one hand, this prevents the thermal stress of ultra-high temperature direct quenching from being too large, which increases the risk of cracking in the workpiece. On the other hand, it prevents the quenching temperature from being too high, which causes the hardness to increase after tempering and reduces the plastic toughness of the material.

[0063] S4: Temper the forgings at least once;

[0064] Forgings that have undergone standard quenching are subjected to at least one tempering treatment, i.e., repeated tempering treatments. The tempering treatment involves heating the forging to a certain temperature, holding it for a certain period of time, and then air-cooling it. The tempering temperature is 275°C to 350°C, and the tempering holding time is 1.5 to 2.5 min / mm depending on the effective thickness of the forging. That is, the forging workpiece is heated to 275°C to 350°C, and the holding time is 1.5 to 2.5 min / mm depending on the effective thickness of the workpiece. After holding, it is removed from the furnace and air-cooled; multiple tempering processes are repeated according to this process. After high-temperature quenching, a small amount of austenite may remain in the material. By implementing multiple tempering treatment processes, the content of retained austenite can be effectively reduced, thereby improving the plasticity and toughness of the material.

[0065] The number of tempering treatments is mainly determined by the size of the forging. Preferably, two tempering treatments are used for heat treatment thickness ≤ 300 mm, and three tempering treatments are used for heat treatment thickness above 300 mm.

[0066] S5: Take samples of forgings and conduct performance tests:

[0067] The heat-treated forgings are sampled and subjected to performance tests, including but not limited to mechanical property tests, grain size tests, etc. The mechanical property tests include but are not limited to tensile tests, impact tests, hardness tests, etc.

[0068] The advantages of this embodiment are as follows: the residual stress generated during the forging process of the forging is eliminated through high-temperature tempering treatment, thereby reducing the risk of deformation and cracking during subsequent ultra-high temperature quenching; at the same time, the high-temperature tempering treatment promotes the uniform precipitation and initial spheroidization of carbides in the original structure, optimizes the matrix structure state, and creates favorable conditions for the sufficient diffusion of high-temperature ferrite in the subsequent ultra-high temperature quenching process, thereby more efficiently transforming the network ferrite into a uniform granular distribution, further enhancing the improvement effect of ultra-high temperature quenching treatment on the transverse plastic toughness of the material, and ensuring the uniformity and stability of the mechanical properties of the forging after the final heat treatment.

[0069] Example 3:

[0070] 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 used. In this embodiment, a pipe forging is used. The pipe section of the pipe forging has an outer diameter of 320 mm, an inner diameter of 155 mm, and a length of 417 mm. The pipe end of the pipe 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 of the heat treatment is 82.5mm, and the forging material is 14Cr17Ni2 stainless steel. The heat treatment method includes the following steps:

[0071] S1: Pre-treating forgings;

[0072] The forgings are pretreated by high-temperature tempering. The forgings are subjected to high-temperature tempering after forging and before modulation. The forgings are heated to 680° C. to 700° C., kept at this temperature for 5 hours, and then air-cooled.

[0073] S2: Ultra-high temperature treatment of forgings;

[0074] like Figure 9 As shown, the forgings are subjected to ultra-high temperature treatment, and the forgings are heated to 1120℃±10℃ with the furnace and kept warm for 2 hours.

[0075] S3: Perform standard quenching treatment on forgings;

[0076] like Figure 9 As shown, the forgings are subjected to standard quenching treatment, wherein the standard quenching treatment is to cool the forgings after ultra-high temperature treatment and insulation to 1040°C ± 10°C at a rate of 80°C / h, and then take them out of the furnace and cool them to below 50°C after insulation for 1.5 hours.

[0077] S4: Temper the forgings at least once;

[0078] S41: Perform the first tempering treatment on the forgings after standard quenching treatment;

[0079] Heat the standard quenched forgings to 320℃±10℃, keep them warm for 3h, then take them out of the furnace and air cool them to room temperature.

[0080] S42: Perform the second tempering treatment on the forging after the first tempering treatment:

[0081] After the first tempering treatment, the forgings are cooled to room temperature and then reheated to 320℃±10℃. After keeping the temperature for 3 hours, they are taken out of the furnace and air-cooled to room temperature.

[0082] S5: Take samples of forgings and conduct performance tests:

[0083] After heat treatment, samples of forgings were taken and subjected to performance tests, including but not limited to mechanical performance tests and grain size tests. Mechanical performance tests include but are not limited to tensile tests, impact tests, hardness tests, etc. The performance test results of forgings are shown in the following table:

[0084]

[0085] The microstructure image of the forging after heat treatment obtained by metallographic microscope is as follows: Figure 14 As shown, the scale bar in the figure is 100 microns.

[0086] The advantages of this embodiment include the use of a combined process of "high-temperature tempering pretreatment, ultra-high-temperature treatment, standard quenching, and double tempering" for pipe forgings. The high-temperature tempering pretreatment fully eliminates forging residual stresses and promotes the initial spheroidization of the original network ferrite, laying the foundation for subsequent microstructure optimization. The ultra-high-temperature treatment fully diffuses the ferrite and transforms it into a uniform granular distribution. Combined with the standard quenching treatment, this reduces thermal stress and cracking while ensuring a reasonable hardness of the martensite matrix. The double tempering effectively eliminates quenching stress, reduces retained austenite, and further improves plasticity and toughness. Measured data show that the forgings achieve a transverse tensile strength of 1232 to 1245 MPa, an elongation after fracture of 12.0% to 12.5%, and an average impact energy of over 45 J, all far exceeding standard requirements. Furthermore, the ferrite in the microstructure is uniformly distributed. This demonstrates that this process can precisely control the microstructure of medium-thick 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.

[0087] Example 4:

[0088] 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 used. In this embodiment, a ring forging is used, and the ring forging has an outer diameter of 535 mm, an inner diameter of 450 mm, and a length of 245. Figure 11 As shown, the effective thickness of the heat treatment is 42.5 mm, and the heat treatment method includes the following steps:

[0089] S1: Pretreatment of forgings:

[0090] The forgings are pretreated by high-temperature tempering. The forgings are subjected to high-temperature tempering after forging and before modulation. The forgings are heated to 690°C ± 10°C and kept at this temperature for 4 hours before being taken out of the furnace and air-cooled.

[0091] S2: Ultra-high temperature treatment of forgings:

[0092] like Figure 12 As shown, the forgings are subjected to ultra-high temperature treatment, and the forgings are heated to 1120℃±10℃ with the furnace and kept warm for 1.5 hours.

[0093] S3: Standard quenching treatment of forgings:

[0094] like Figure 12 As shown, the forgings are subjected to standard quenching treatment, wherein the standard quenching treatment is to cool the forgings after ultra-high temperature treatment to 1000°C ± 10°C at a rate of 100°C / h, and then take them out of the furnace and cool them to below 50°C after being kept at this temperature for 1 hour and then immersed in oil.

[0095] S4: Temper the forgings at least once;

[0096] S41: First tempering treatment of forgings after standard quenching treatment:

[0097] Heat the standard quenched forgings to 290℃±10℃, keep them at this temperature for 2 hours, then take them out of the furnace and air-cool them to room temperature.

[0098] S42: Perform the second tempering treatment on the forging after the first tempering treatment:

[0099] After the first tempering treatment, the forging is cooled to room temperature and then reheated to 290℃±10℃. After keeping the temperature for 2 hours, it is taken out of the furnace and air-cooled to room temperature.

[0100] S5: Take samples of forgings and conduct performance tests:

[0101] After heat treatment, samples of forgings were taken and subjected to performance tests, including but not limited to mechanical performance tests and grain size tests. Mechanical performance tests include but are not limited to tensile tests, impact tests, hardness tests, etc. The performance test results of forgings are shown in the following table:

[0102]

[0103] The microstructure image of the forging after heat treatment obtained by metallographic microscope is as follows: Figure 15 As shown, the scale bar in the figure is 100 microns.

[0104] The advantages of this embodiment include the use of a combined process of "high-temperature tempering pretreatment, ultra-high-temperature treatment, standard quenching, and double tempering" for ring forgings. The high-temperature tempering pretreatment fully eliminates forging residual stresses and promotes the initial spheroidization of the original network ferrite, laying the foundation for subsequent microstructure optimization. The ultra-high-temperature treatment fully diffuses the ferrite and transforms it into a uniform granular distribution. Combined with the standard quenching treatment, this reduces thermal stress and cracking while ensuring a reasonable hardness of the martensite matrix. The double tempering effectively eliminates quenching stress, reduces retained austenite, and further improves plasticity and toughness. Measured data show that the forgings achieve a transverse tensile strength of 1214 to 1235 MPa, an elongation after fracture of 13.5% to 14.0%, and an average impact energy of over 50 J, all far exceeding standard requirements. Furthermore, the ferrite in the microstructure exhibits a uniform granular distribution. This demonstrates that this process can precisely control the microstructure of medium-thick 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.

[0105] The advantages of the present invention are as follows: the residual stress generated during the forging process of the forging is eliminated through high-temperature tempering treatment, reducing the risk of deformation and cracking during subsequent ultra-high temperature treatment; at the same time, the high-temperature tempering treatment promotes the uniform precipitation of carbides in the original structure and preliminary spheroidization optimization, and the matrix structure state, creating favorable conditions for the full diffusion of high-temperature ferrite in the subsequent ultra-high temperature treatment process, thereby more efficiently transforming the network ferrite into a uniform granular distribution, further enhancing the effect of ultra-high temperature treatment on the improvement of the transverse plastic toughness of the material, and ensuring the uniformity and stability of the mechanical properties of the forging after the final heat treatment. Ultra-high temperature treatment can promote the full diffusion of high-temperature ferrite in the forging, improve the distribution morphology of the network ferrite, make the high-temperature ferrite uniformly distributed in a granular form, and effectively cut off the ferrite's cutting effect on the matrix. Granular high-temperature ferrite reduces stress concentration and improves the material's transverse properties. Multiple tempering processes reduce the amount of retained austenite, resulting in a uniform structure of tempered martensite and dispersed granular high-temperature ferrite. This reduces material anisotropy and improves the material's transverse mechanical properties, bringing the performance of transversely sampled forgings like tubes and rings to the same level as rods and shafts. The present invention provides a heat treatment method for improving the transverse properties of martensitic steel, resolving the issue of low transverse plasticity and impact performance in 14Cr17Ni2 martensitic stainless steel tubes and rings. Ultra-high temperature treatment and tempering are employed to optimize and adjust the microstructure and properties, ensuring that the material's transverse plasticity and impact energy meet the requirements of GB / T 1220.

[0106] 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 changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A heat treatment method for improving the transverse properties of martensitic steel, characterized in that: The following steps are involved: The forgings are subjected to ultra-high temperature treatment, wherein the ultra-high temperature treatment is to heat the forgings to 1100°C to 1130°C and keep the temperature for a certain period of time; Performing standard quenching treatment on the forgings, wherein the standard quenching treatment is to cool the forgings after ultra-high temperature treatment to the standard quenching temperature at a preset rate, keep the temperature for a certain period of time, and then cool; The forging is subjected to at least one tempering treatment, wherein the forging is heated to a certain temperature, kept at the temperature for a certain period of time, and then cooled.

2. The heat treatment method for improving the transverse properties of martensitic steel according to claim 1, characterized in that: The preset rate is 50°C to 150°C / h.

3. The heat treatment method for improving the transverse properties of martensitic steel according to claim 1, characterized in that: The ultra-high temperature treatment holding time is 1 to 2 min / mm.

4. The heat treatment method for improving the transverse properties of martensitic steel according to claim 1, characterized in that: The standard quenching temperature is 950° C. to 1050° C., and the standard quenching holding time is 0.5 to 1.5 min / mm.

5. The heat treatment method for improving the transverse properties of martensitic steel according to claim 1, characterized in that: The tempering treatment temperature is 275° C. to 350° C., and the tempering treatment holding time is 1.5 to 2.5 min / mm.

6. The heat treatment method for improving the transverse properties of martensitic steel according to claim 1, characterized in that: The method also includes performing high-temperature tempering pretreatment on the forging before the ultra-high temperature treatment, wherein the high-temperature tempering is to heat the forging to a certain temperature, keep the temperature for a certain time, and then cool it.

7. The heat treatment method for improving the transverse properties of martensitic steel according to claim 6, characterized in that: The high temperature tempering temperature is 680° C. to 700° C., and the high temperature tempering holding time is ≥4 hours.

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

9. The heat treatment method for improving the transverse properties of martensitic steel according to claim 1, characterized in that: 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.

10. The heat treatment method for improving the transverse properties of martensitic steel according to any one of claims 1 to 9, characterized in that: It also includes sampling the forgings after heat treatment and conducting mechanical property tests.

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