High-boron martensite heat-resistant steel and forging forming method and application thereof

Abstract

The invention relates to high-boron martensite heat-resistant steel and a forging forming method and application thereof, and belongs to the technical field of metal material hot working. The forging forming method of the high-boron martensite heat-resistant steel comprises the following steps: carrying out homogenizing heat treatment on a smelted martensite heat-resistant steel ingot, wherein the content of B in the martensite heat-resistant steel ingot is 0.009-0.017 wt.%; forging and heating the steel ingot subjected to the homogenizing heat treatment; upsetting with two or more heating numbers and drawing-out with a WHF method are adopted in forging, the initial forging temperature of each heating number is controlled to be 1130-1170 DEG C, and the reduction rate of each pass is controlled to be 0.001 s <-1 >-0.05 s <-1 >; and annealing heat treatment and quenching and tempering heat treatment are carried out after forging, and the high-boron martensite heat-resistant steel is obtained. The obtained high-boron martensite heat-resistant steel does not generate forging defects, and is uniform and fine in grain size and excellent in strength and durability.

Description

Technical Field

[0001] The invention relates to the technical field of hot processing of metal materials, and in particular to a high-boron martensitic heat-resistant steel and a forging forming method and application thereof. Background Art

[0002] Steam turbine rotor forgings and large-diameter seamless pipes are the "bottleneck" problems that restrict the current ultra-supercritical thermal power units from developing higher parameters. With the increase of steam temperature and steam pressure, ultra-supercritical thermal power units have put forward higher requirements on the service performance of martensitic heat-resistant steel for large forgings and large-diameter seamless pipes, especially the durability performance.

[0003] At present, in order to improve the durability of martensitic heat-resistant steel, a higher B element is added to the alloy composition. However, the B element has a great influence on the thermoplasticity of martensitic heat-resistant steel. High-B martensitic heat-resistant steel has high crack sensitivity, which is easy to induce forging crack defects when manufacturing large forgings, making forging forming difficult. In addition, high-B martensitic heat-resistant steel has serious hereditary structure and difficult grain refinement. In order to ensure the flaw detection sensitivity and comprehensive mechanical properties of forgings, the forged structure needs to be controlled to be uniform and fine.

[0004] Therefore, it is urgent to develop a forging forming method for high-B martensitic heat-resistant steel with high endurance performance that does not crack during forging and can obtain a fine and uniform structure. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a high-boron martensitic heat-resistant steel and a forging forming method and application thereof, wherein no cracks are generated during forming, and high-boron martensitic heat-resistant steel with high performance and uniform and fine structure is obtained.

[0006] In one aspect, the present invention provides a forging method for high-boron martensitic heat-resistant steel, comprising the following steps:

[0007] S1: homogenizing the smelted martensitic heat-resistant steel ingot, wherein the B content in the martensitic heat-resistant steel ingot is 0.009-0.017wt.%;

[0008] S2: Forging and heating the steel ingot after homogenization heat treatment;

[0009] S3: Forging adopts two or more times of upsetting and WHF method drawing, and the initial forging temperature of each fire is controlled to be 1140-1160℃, and the pressing rate of each pass is controlled to be 0.001s -1 ~0.05s -1 ;

[0010] S4: After forging, annealing heat treatment and tempering heat treatment are performed to obtain high-boron martensitic heat-resistant steel.

[0011] Furthermore, in step S1, the homogenization heat treatment is first heated to 250-300°C at a rate of 30-50°C / h, and kept warm for 4-6 hours; then heated to 650-700°C at a rate of 40-60°C / h, and kept warm for 7-10 hours; finally, heated to 1170-1230°C at a rate of 40-60°C / h, and kept warm for 30-50 hours; after the insulation is completed, the furnace is cooled to 800-1000°C.

[0012] Furthermore, the composition of the high-boron martensitic heat-resistant steel, measured by mass percentage, includes: C: 0.06-0.15%; Si: ≤0.50%; Mn: 0.25-0.60%; Cr: 8.0-9.5%; W: ≤3.10%; Mo: ≤1.50%; Co: 1.1-4.0%; V: 0.15-0.30%; Nb: 0.04-0.07%; Cu: ≤1.0%; Zr: ≤0.05%; B: 0.009-0.017%; N: ≤0.02%; the remainder is Fe and unavoidable impurities.

[0013] Further, in step S2, the temperature is heated to 1130-1170°C at a rate of 80-100°C / h, and the holding time is not less than 1h / 100mm.

[0014] Further, in step S3, the upsetting ratio is 2.3-2.7, the forging ratio during WHF drawing is 2.7-3.2, and the amount of compression deformation per anvil is 19-25%.

[0015] Furthermore, the grain size grade of the high-boron martensitic heat-resistant steel is 2.0-4.0.

[0016] On the other hand, the present invention provides a high-boron martensitic heat-resistant steel, which is produced by the forging forming method of the present invention.

[0017] Furthermore, the high-boron martensitic heat-resistant steel has a sustained fracture time of more than 4213 h at 630° C. and 175 MPa.

[0018] Furthermore, the high-boron martensitic heat-resistant steel has a room temperature tensile strength of more than 778 MPa and a room temperature yield strength of more than 627 MPa.

[0019] Furthermore, a high-boron martensitic heat-resistant steel is used in large shaft forgings and large-diameter seamless pipes, wherein the diameter of the large shaft forgings or the outer diameter of the large-diameter seamless pipes is greater than 150 mm.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. The present invention provides a forging method for a high-B martensitic heat-resistant steel. Before forging, different heating rates, different holding temperatures and holding times are used for homogenization treatment. During the forging process, the initial forging temperature, the final forging temperature, the reduction rate of each pass, the deformation amount and other parameters are controlled. Through the mutual coordination of the above parameters, the forging cracking problem caused by the low plasticity of the high-B martensitic heat-resistant steel can be effectively solved. At the same time, the excessive growth of grains during the forging process is effectively controlled, and the uniformity of the organization is improved.

[0022] 2. The B element content in the martensitic heat-resistant steel of the present invention is 0.009-0.017% (weight), and it also contains elements such as Mn, Cr, W, Mo, Co, V and Zr. Combined with the forging forming method provided by the present invention, it can not only ensure the durability of the martensitic heat-resistant steel, but also ensure the comprehensive mechanical properties of the martensitic heat-resistant steel, uniform organization, and a grain size grade of 2.0-4.0.

[0023] 3. Through the forming method provided by the present invention, the obtained high-boron martensitic heat-resistant steel can be applied to large shaft forgings. After quenching and tempering treatment, at 630°C and 175MPa, the sustained fracture time is greater than 5048h; the room temperature tensile strength is above 855MPa, and the room temperature yield strength is above 728MPa.

[0024] 4. The high-boron martensitic heat-resistant steel prepared by the present invention can also be applied to large-diameter seamless pipes. After quenching and tempering, the sustained fracture time is greater than 4213h at 630°C and 175MPa; the room temperature tensile strength is above 778MPa, and the room temperature yield strength is above 627MPa.

[0025] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0027] Figure 1 The grain size distribution of Example 1;

[0028] Figure 2 The grain size distribution of Comparative Example 1;

[0029] Figure 3 This is a microstructure photo of Example 1;

[0030] Figure 4 This is a microstructure photo of Comparative Example 1;

[0031] Figure 5 This is the macro forging defect of comparative example 1. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0033] Steam turbine rotors and large-diameter boiler tubes are important components in ultra-supercritical thermal power units. With the increase of steam temperature and steam pressure, ultra-supercritical thermal power units have higher requirements on their service performance, especially endurance performance.

[0034] At present, steam turbine rotors are mainly made of martensitic heat-resistant steel. In order to improve the durability of martensitic heat-resistant steel, element B is added to the alloy composition. However, the addition of element B will easily induce forging crack defects during the preparation process, making forging difficult. In order to improve the forging cracking problem, the content of element B was appropriately reduced, but this led to a significant decrease in the durability of martensitic heat-resistant steel, which could not meet actual needs.

[0035] Therefore, the present invention provides a forging method for high-boron martensitic heat-resistant steel, comprising the following steps:

[0036] S1: homogenizing the smelted martensitic heat-resistant steel ingot, wherein the B content in the martensitic heat-resistant steel ingot is 0.009-0.017wt.%;

[0037] S2: Forging and heating the steel ingot after homogenization heat treatment;

[0038] S3: Forging adopts two or more times of upsetting and WHF method drawing, and the initial forging temperature of each fire is controlled to be 1130-1170℃, and the pressing rate of each pass is controlled to be 0.001s -1 ~0.05s -1 ;

[0039] S4: After forging, annealing heat treatment and tempering heat treatment are performed to obtain high-boron martensitic heat-resistant steel.

[0040] Compared with the prior art, the present invention provides a forging method for high B martensitic heat-resistant steel, which uses different heating rates, different holding temperatures and holding times for homogenization before forging, and controls the parameters such as the initial forging temperature, the final forging temperature, the reduction rate of each pass, and the deformation amount during the forging process. Through the mutual coordination of the above parameters, the forging cracking problem caused by the low plasticity of high B martensitic heat-resistant steel can be effectively solved, and at the same time, the excessive growth of grains during the forging process is effectively controlled, thereby improving the uniformity of the organization.

[0041] In addition, the B content in the martensitic heat-resistant steel ingot is 0.009-0.017wt.%, which can ensure the high-temperature durability and room-temperature strength of the obtained martensitic heat-resistant steel. The forming method provided by the present invention can not only ensure the performance of the martensitic heat-resistant steel, but also will not cause cracking problems during the forging process.

[0042] Specifically, in step S1, the components of the high boron martensitic heat-resistant steel, measured by mass percentage, include: C: 0.06-0.15%; Si: ≤0.50%; Mn: 0.25-0.60%; Cr: 8.0-9.5%; W: ≤3.10%; Mo: ≤1.50%; Co: 1.1-4.0%; V: 0.15-0.30%; Nb: 0.04-0.07%; Cu: ≤1.0%; Zr: ≤0.05%; B: 0.009-0.017%; N: ≤0.02%; the remainder is Fe and unavoidable impurities.

[0043] It should be noted that the martensitic heat-resistant steel ingot is melted using existing smelting technology and can be melted in a vacuum induction furnace or an electric furnace. The ingot obtained by casting can also be subjected to secondary smelting by protective atmosphere electroslag remelting to ensure that the composition ratio meets the requirements.

[0044] Cu has a low solid solubility in martensite and can form a dispersed nano copper-rich phase, thereby pinning the grain boundaries, hindering the interface migration of lath martensite, and improving the stability of the organization. When the Cu content is too high, the high-temperature plasticity of the material will be seriously reduced, affecting the hot workability of large forgings, so the Cu content is controlled below 1.0%. Mn is an austenite-forming element and can inhibit the formation of high-temperature delta ferrite. At the same time, Mn can stabilize the S element, avoid the formation of low-melting-point sulfides, and improve the hot working properties of the material. Zr carbonitrides are extremely stable, and adding Zr elements can significantly reduce the tendency of grain growth during heating. In the high-temperature austenite region, Zr-containing carbonitrides can inhibit the growth of austenite grains.

[0045] Specifically, in step S1, the homogenization heat treatment is first heated to 250-300°C at a rate of 30-50°C / h, and kept warm for 4-6 hours; then heated to 650-700°C at a rate of 40-60°C / h, and kept warm for 7-10 hours; finally, heated to 1170-1230°C at a rate of 40-60°C / h, and kept warm for 30-50 hours; after the insulation is completed, the furnace is cooled to 800-1000°C.

[0046] It should be noted that the thermal stress can be fully reduced by performing step-type heating according to the above steps. The temperature is raised to 250-300℃ at a rate of 30-50℃ / h, reaching the first temperature range with the largest temperature difference between the surface and the core. At this time, the core temperature is lower than 100℃, and the heat-resistant steel billet is still in a cold and hard state. It is easy to generate stress due to the huge temperature difference, resulting in internal cracks. By keeping warm for 4-6 hours, the surface and core temperatures can be made uniform, and the thermal stress can be fully reduced. Then continue to heat up to 650-700℃ at a rate of 40-60℃ / h, at which time the second temperature range with the largest temperature difference is reached, and the core temperature is lower than 350℃. Keep warm for 7-10 hours and keep warm for 3-5 hours to reduce the temperature difference between the surface and the core, and prevent cracks caused by excessive thermal stress. Finally, the temperature is raised to 1170-1230℃ at a rate of 40-60℃ / h. This temperature range can avoid overheating and overheating. The temperature is kept for 30-50h, which can effectively eliminate dendrites, and no δ ferrite is formed. At the same time, there is no harmful phase such as M3B2, and the homogenization effect is good. After the homogenization and heat preservation is completed, the furnace is cooled to 800-1000℃ to prevent the temperature difference between the core and the surface of the heat-resistant steel billet from being too fast due to the cooling rate, resulting in thermal stress and cracks.

[0047] Specifically, in step S2, the heat-resistant steel billet cooled to 800-1000°C in step S1 is heated to 1130-1170°C at a rate of 80-100°C / h, and the holding time is not less than 1h / 100mm.

[0048] It should be noted that rapid heating to 1130-1170℃ at 80-100℃ / h can shorten the heating time, inhibit the grain growth of heat-resistant steel billets at high temperatures, reduce energy consumption, and improve production efficiency. The heat-resistant steel billet is kept at 1130-1170℃ for no less than 1h / 100mm, which can fully ensure the uniformity of the billet temperature and structure before forging.

[0049] Specifically, the initial forging temperature of each fire is 1130-1170°C, and the pressing rate of each pass is 0.001s -1 ~0.05s -1 .

[0050] It should be noted that, in the forging process of the present invention, the initial forging temperature is controlled at 1130-1170°C, which can avoid the B element from segregating at the grain boundary when the temperature is too high, making the grain boundary prone to cracking due to stress during deformation, thereby improving the plasticity of high B martensitic heat-resistant steel, reducing the risk of forging cracking of high B martensitic heat-resistant steel, and avoiding excessive grain growth control.

[0051] In the forging process of the present invention, the final forging temperature is controlled to be not less than 950° C., so as to ensure that the recrystallization process of the high-B martensitic heat-resistant steel is fully carried out and avoid work hardening.

[0052] Specifically, when the surface temperature of the forging or billet is lower than 950°C during the forging process, the forging is stopped and it needs to be reheated to 1130-1170°C and kept warm for 3.5 hours before being taken out of the furnace for forging.

[0053] It should be noted that the present invention controls the pressing rate of each pass to be 0.001s during the forging process. -1 ~0.05s -1 When the deformation rate is too high, the B element diffuses rapidly to the grain boundaries, causing non-equilibrium segregation at the grain boundaries, resulting in a decrease in the plasticity of high-B martensitic heat-resistant steel; when the deformation rate is too low, the grains after dynamic recrystallization have sufficient time to grow, which also leads to a decrease in plasticity and increases the risk of forging cracking.

[0054] Preferably, the initial forging temperature of each fire is 1140-1160°C, and the pressing rate of each pass is 0.005s -1 ~0.05s -1 .

[0055] More preferably, the initial forging temperature of each fire is 1150°C, and the reduction rate of each pass is 0.005s -1 .

[0056] Specifically, in step S3, the upsetting ratio during upsetting is 2.3-2.7, the forging ratio during WHF drawing is 2.7-3.2, and the amount of compression deformation per anvil is 19-25%.

[0057] It should be noted that forging uses upsetting and WHF method drawing with more than two fires. The upsetting ratio during upsetting is 2.3-2.7, which can ensure that the cross section of the heat-resistant steel ingot after upsetting meets the large drawing ratio drawing in the next fire; the forging ratio during WHF method drawing is 2.7-3.2, which can meet the multi-pass deformation of each anvil to reach 19-25%, and then fully press the internal casting defects, break the cast structure, refine the grains, and improve the uniformity of the forging structure. When the forging ratio is too small, the defects inside the heat-resistant steel ingot will be enlarged, and the loose structure and hole defects inside the heat-resistant steel ingot cannot be effectively forged; when the forging ratio is too large, the excessive deformation will also cause stress concentration inside the heat-resistant steel ingot, affecting the performance of the forging, and even forming obvious fiber structure, resulting in anisotropy of performance.

[0058] Preferably, in step S3, the upsetting ratio during upsetting is 2.3, the forging ratio during WHF drawing is 2.7, and the amount of compression deformation per anvil is 20%.

[0059] Specifically, in step S4, the forged steel ingot is transferred to a holding furnace at 715-745°C for annealing after forging, and the holding time is 150-400 hours.

[0060] It should be noted that the present invention provides a forging forming method for preventing cracking of large forgings and large-diameter seamless pipes for high-B martensitic heat-resistant steel, which solves the forging cracking problem caused by the low plasticity of high-B martensitic heat-resistant steel; at the same time, it effectively controls the excessive grain growth during the forging process, improves the uniformity of the overall cross-sectional structure and grain size of large forgings, and opens up a path for the application of high-B martensitic heat-resistant steel.

[0061] Specifically, the grain size grade of the high-boron martensitic heat-resistant steel is 2.0-4.0.

[0062] Specifically, the application of high-boron martensitic heat-resistant steel in large shaft forgings and large-diameter seamless pipes is characterized in that the diameter of the large shaft forgings or the outer diameter of the large-diameter seamless pipe is greater than 150 mm.

[0063] The high-boron martensitic heat-resistant steel obtained by the present invention can be used for preparing large shaft forgings. In order to ensure the performance of the large shaft forgings, tempering treatment is required, and the tempering heat treatment is as follows: the quenching temperature is 1070-1130 DEG C, the holding time is not less than 1h / 100mm, the cooling form is oil cooling, air cooling or controlled speed cooling, and the cooling rate of the controlled speed cooling is 80-150 DEG C / h; the first tempering temperature is 550-590 DEG C, the holding time is not less than 1h / 100mm, the cooling form is air cooling or controlled speed cooling, and the cooling rate of the controlled speed cooling is 30-60 DEG C / h; the second tempering temperature is 680-740 DEG C, the holding time is not less than 1h / 100mm, the cooling form is air cooling or controlled speed cooling, and the cooling rate of the controlled speed cooling is 30-60 DEG C / h.

[0064] After quenching and tempering treatment, the sustained fracture time of large shaft forgings at 630℃ and 175MPa is greater than 5048h; the room temperature tensile strength is above 855MPa, and the room temperature yield strength is above 728MPa.

[0065] The high-boron martensitic heat-resistant steel obtained by the present invention can also be used to prepare large-diameter seamless pipes. In order to ensure the performance of large-diameter seamless pipes, tempering heat treatment is also required, specifically: the normalizing temperature is 1070-1130°C, the holding time is not less than 1h / 100mm, and the cooling form is air cooling; the tempering temperature is 760-800°C, the holding time is not less than 1h / 100mm, and the cooling form is air cooling.

[0066] After quenching and tempering treatment, the large-diameter seamless pipe has a sustained rupture time of more than 4213h at 630℃ and 175MPa; the room temperature tensile strength is above 778MPa, and the room temperature yield strength is above 627MPa.

[0067] In order to describe the present invention more clearly, the following examples and comparative examples are provided to further illustrate the present invention. The preparation and composition of the martensitic heat-resistant steel ingot are shown in the preparation example.

[0068] Preparation Example 1

[0069] The martensitic heat-resistant steel ingot is prepared by vacuum induction melting and protective atmosphere electroslag remelting, and its chemical composition is: C is 0.12%; Si is 0.08%; Mn is 0.51%; Cr is 9.01%; W is 2.10%; Mo is 0.48%; Co is 2.95%; V is 0.20%; Nb is 0.05%; Cu is 0.05%; Zr is 0.01%; B is 0.014%; N is 0.008%; and the balance is Fe.

[0070] Preparation Example 2

[0071] The difference between Preparation Example 2 and Preparation Example 1 is that the chemical composition is different. Preparation Example 2 is C: 0.14%; Si: 0.09%; Mn: 0.35%; Cr: 9.41%; W: 0.01%; Mo: 1.49%; Co: 1.3%; V: 0.17%; Nb: 0.04%; Cu: 0.05%; Zr: 0.001%; ​​B: 0.010%; N: 0.020%; and the balance is Fe.

[0072] Preparation Example 3

[0073] The difference between Preparation Example 3 and Preparation Example 1 is that the chemical composition is different. Preparation Example 3 is C: 0.08%; Si is 0.35%; Mn is 0.55%; Cr is 8.81%; W is 2.89%; Mo is 0.01%; Co is 3.20%; V is 0.23%; Nb is 0.06%; Cu is 0.83%; Zr is 0.008%; B is 0.016%; N is 0.006%; and the balance is Fe.

[0074] Example 1

[0075] A forging method for high-boron martensitic heat-resistant steel comprises the following steps:

[0076] S1: subjecting the martensitic heat-resistant steel ingot obtained in Preparation Example 1 to homogenization heat treatment,

[0077] Raise the temperature to 280℃ at a rate of 40℃ / h and keep it for 5h; continue to raise the temperature to 680℃ at a rate of 50℃ / h and keep it for 8h; continue to raise the temperature to 1200℃ at a rate of 50℃ / h and keep it for 45h; after the end of the insulation, cool the furnace to 900℃;

[0078] S2: The steel ingot after homogenization heat treatment is heated for forging; starting from 900°C to 1150°C at a rate of 90°C / h, and kept at this temperature for 9h;

[0079] S3: Forging adopts two or more times of upsetting and WHF method drawing, and the initial forging temperature of each fire is controlled to be 1150℃, and the pressing rate of each pass is controlled to be 0.005s -1 ; The upsetting ratio during upsetting is 2.3, the forging ratio during WHF drawing is 2.7, the reduction deformation per anvil is 20%, and the final forging temperature is 955℃;

[0080] S4: After forging, annealing heat treatment is performed at a temperature of 730° C. and a holding time of 250 h to obtain high-boron martensitic heat-resistant steel.

[0081] The high B martensitic heat-resistant steel obtained in this embodiment is applied to large shaft forgings, and the tempering heat treatment is as follows: the quenching temperature is 1100°C, kept warm for 5 hours, and cooled to room temperature at a cooling rate of 100°C / h; the first tempering temperature is 570°C, kept warm for 8 hours, and cooled to room temperature at a cooling rate of 50°C / h; the second tempering temperature is 700°C, kept warm for 8 hours, and cooled to room temperature at a cooling rate of 50°C / h.

[0082] Examples 2-5, Comparative Examples 1-5

[0083] The preparation processes of Examples 2-5 and Comparative Examples 1-5 are substantially the same as those of Example 1, except for the differences shown in Table 1.

[0084] Example 6-7, Comparative Example 6-7

[0085] The preparation process of Example 6-7 and Comparative Example 6-7 is substantially the same as that of Example 3, and the differences are shown in Table 1. In addition, both Example 6-7 and Comparative Example 6-7 are applied to large-diameter boiler tubes, and need to be subjected to tempering heat treatment after step S4, specifically: normalizing temperature is 1100°C, heat preservation for 5 hours, and air cooling to room temperature; tempering temperature is 780°C, heat preservation for 8 hours, and air cooling to room temperature.

[0086] Table 1 Forging process parameters of Examples 1-7 and Comparative Examples 1-7

[0087]

[0088] Example 8

[0089] The preparation process of Example 8 is substantially the same as that of Example 1, except that in Example 8, the temperature is increased to 280°C at a rate of 33°C / h and kept at this temperature for 4 hours; the temperature is further increased to 660°C at a rate of 43°C / h and kept at this temperature for 7 hours; the temperature is further increased to 1180°C at a rate of 50°C / h and kept at this temperature for 47 hours; after the insulation is completed, the furnace is cooled to 850°C.

[0090] Example 9

[0091] The preparation process of Example 9 is substantially the same as that of Example 1, except that in Example 9, the temperature is increased to 280°C at a rate of 48°C / h and kept at this temperature for 6 hours; the temperature is then increased to 695°C at a rate of 57°C / h and kept at this temperature for 10 hours; the temperature is then increased to 1230°C at a rate of 50°C / h and kept at this temperature for 35 hours; after the insulation is completed, the furnace is cooled to 960°C.

[0092] Comparative Example 8

[0093] The preparation process of Comparative Example 8 is substantially the same as that of Example 1, except that in Comparative Example 8, C is 0.12%; Si is 0.09%; Mn is 0.54%; Cr is 9.06%; W is 2.11%; Mo is 0.49%; Co is 2.97%; V is 0.21%; Nb is 0.05%; Cu is 1.4%; Zr is 0.09%; B is 0.014%; N is 0.008%; and the balance is Fe.

[0094] Performance Testing

[0095] The above-mentioned Examples 1-9 and Comparative Examples 1-8 were subjected to performance testing after tempering heat treatment, mainly including durability, strength, etc., as well as microstructure observation and macroscopic testing. The test results are shown in Tables 2 and 3.

[0096] Table 2 Performance test results

[0097]

[0098]

[0099] Table 3 Microscopic test results

[0100]

[0101] In combination with Examples 1-9 and Comparative Examples 1-8 and Tables 2 and 3, it can be seen that when the forming method provided by Examples 1-9 of the present invention is used for preparation, the obtained high-boron martensitic heat-resistant steel has high durability and strength. When the obtained high-boron martensitic heat-resistant steel is applied to large shaft forgings, after quenching and tempering, at 630°C and 175MPa, the durable fracture time is greater than 5048h; the room temperature tensile strength is above 855MPa, and the room temperature yield strength is above 728MPa. When the obtained high-boron martensitic heat-resistant steel is applied to large-diameter seamless pipes, after quenching and tempering, at 630°C and 175MPa, the durable fracture time is greater than 4213h; the room temperature tensile strength is above 778MPa, and the room temperature yield strength is above 627MPa.

[0102] Combined with Example 1 and Comparative Example 1 Figure 1-5 It can be seen that when the forming method provided in Example 1 of the present invention is used to prepare high-boron martensitic heat-resistant steel, no cracks will occur, and the grain size is relatively uniform at the level of 2.0-3.0.

[0103] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A forging method for high-boron martensitic heat-resistant steel, characterized in that: The following steps are involved: S1: homogenizing the smelted martensitic heat-resistant steel ingot, wherein the B content in the martensitic heat-resistant steel ingot is 0.009-0.017wt.%; S2: Forging and heating the steel ingot after homogenization heat treatment; S3: Forging adopts two or more times of upsetting and WHF method drawing, and the initial forging temperature of each fire is controlled to be 1130-1170℃, and the pressing rate of each pass is controlled to be 0.001s -1 ~0.05s -1 ; S4: After forging, annealing heat treatment and tempering heat treatment are performed to obtain high-boron martensitic heat-resistant steel.

2. The forging method of high-boron martensitic heat-resistant steel according to claim 1, characterized in that: In step S1, the homogenization heat treatment is first heated to 250-300°C at a rate of 30-50°C / h and kept warm for 4-6 hours; then heated to 650-700°C at a rate of 40-60°C / h and kept warm for 7-10 hours; finally heated to 1170-1230°C at a rate of 40-60°C / h and kept warm for 30-50 hours; after the insulation is completed, the furnace is cooled to 800-1000°C.

3. The forging method of high-boron martensitic heat-resistant steel according to claim 1, characterized in that: The high-boron martensitic heat-resistant steel comprises, by mass percentage, the following components: C: 0.06-0.15%; Si: ≤0.50%; Mn: 0.25-0.60%; Cr: 8.0-9.5%; W: ≤3.10%; Mo: ≤1.50%; Co: 1.1-4.0%; V: 0.15-0.30%; Nb: 0.04-0.07%; Cu: ≤1.0%; Zr: ≤0.05%; B: 0.009-0.017%; N: ≤0.02%; the remainder is Fe and unavoidable impurities.

4. The forging method of high-boron martensitic heat-resistant steel according to claim 1, characterized in that: In step S2, heating is performed to 1130-1170°C at a rate of 80-100°C / h, and the heat preservation time is not less than 1h / 100mm.

5. The forging method of high-boron martensitic heat-resistant steel according to claim 1, characterized in that: In step S3, the upsetting ratio is 2.3-2.7, the forging ratio during WHF drawing is 2.7-3.2, and the amount of deformation per anvil is 19-25%.

6. The forging method of high-boron martensitic heat-resistant steel according to claim 1, characterized in that: The grain size grade of the high-boron martensitic heat-resistant steel is 2.0-4.

0.

7. A high-boron martensitic heat-resistant steel, characterized in that: It is produced by the forging method according to any one of claims 1 to 6.

8. The high-boron martensitic heat-resistant steel according to claim 7, characterized in that: The high-boron martensitic heat-resistant steel has a sustained fracture time of more than 4213 hours at 630° C. and 175 MPa.

9. The high-boron martensitic heat-resistant steel according to claim 7, characterized in that: The high-boron martensitic heat-resistant steel has a room temperature tensile strength of more than 778 MPa and a room temperature yield strength of more than 627 MPa.

10. Application of the high-boron martensitic heat-resistant steel according to any one of claims 7 to 9 in large shaft forgings and large-diameter seamless pipes, characterized in that: The diameter of the large shaft forging or the outer diameter of the large-diameter seamless pipe is greater than 150 mm.

Images