A high-boron martensitic heat-resistant steel and a forging forming method and application thereof

Abstract

The application relates to a high-boron martensitic 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 martensitic heat-resistant steel comprises the following steps: carrying out homogenizing heat treatment on a martensitic heat-resistant steel ingot after smelting, wherein the B content in the martensitic heat-resistant steel ingot is 0.009-0.017 wt.%; carrying out forging heating on the steel ingot after the homogenizing heat treatment; adopting upsetting and WHF method lengthening for two or more times of heating, controlling the initial forging temperature of each time of heating to be 1130-1170 DEG C, controlling the reduction rate of each pass to be 0.001 s ‑1 -0.05 s ‑1 ; carrying out annealing heat treatment and quenching and tempering heat treatment after forging to obtain the high-boron martensitic heat-resistant steel. The obtained high-boron martensitic heat-resistant steel does not generate forging defects, the grain size is uniform and small, and the strength and the endurance performance are excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot working of metal materials, and particularly relates to a high-boron martensitic heat-resistant steel and a forging forming method and application thereof. BACKGROUND

[0002] The steam turbine rotor forging and the large-diameter seamless pipe are the bottleneck problems restricting the development of current ultra-supercritical thermal power units to higher parameters. With the increase of the steam temperature and the steam pressure, the service performance of the martensitic heat-resistant steel for large forgings and large-diameter seamless pipes for ultra-supercritical thermal power units is required to be higher, especially the endurance performance.

[0003] At present, in order to improve the endurance performance of the martensitic heat-resistant steel, a higher B element is added in the alloy composition. However, the B element has a great influence on the hot plasticity of the martensitic heat-resistant steel, the high-B martensitic heat-resistant steel has high crack sensitivity, and the forging crack defects are easily induced in the manufacturing of large forgings, so the forging forming is difficult. In addition, the high-B martensitic heat-resistant steel has serious organizational heredity, and it is difficult to refine the grains, so as to ensure the flaw detection sensitivity and the comprehensive mechanical properties of the forging, the forging state organization needs to be controlled to be uniform and small.

[0004] Therefore, it is urgent to develop a forging forming method for the high-B martensitic heat-resistant steel with high endurance performance, which can be formed without cracking and can obtain a small and uniform organization. SUMMARY

[0005] In view of the above analysis, the present application aims to provide a high-boron martensitic heat-resistant steel and a forging forming method and application thereof, which can be formed without cracks and can obtain a high-boron martensitic heat-resistant steel with high performance and uniform and small organization.

[0006] In one aspect, the present application provides a forging forming method of a high-boron martensitic heat-resistant steel, which comprises the following steps:

[0007] S1: uniformly heat treating the martensitic heat-resistant steel ingot after smelting, and the B content in the martensitic heat-resistant steel ingot is 0.009-0.017wt.%;

[0008] S2: forging heating the steel ingot after the uniform heat treatment;

[0009] S3: adopting the upsetting and WHF method of elongation for two or more heating times, controlling the initial forging temperature of each heating time to be 1140-1160℃, and controlling the reduction rate of each pass to be 0.001s -1 ~0.05s -1 ;

[0010] S4: annealing heat treatment and quenching and tempering heat treatment after forging, to obtain the high-boron martensitic heat-resistant steel.

[0011] Further, in step S1, the homogenization heat treatment is first raised to 250-300 DEG C at a rate of 30-50 DEG C / h, and held for 4-6 h; then raised to 650-700 DEG C at a rate of 40-60 DEG C / h, and held for 7-10 h; finally raised to 1170-1230 DEG C at a rate of 40-60 DEG C / h, and held for 30-50 h; after the holding, the furnace is cooled to 800-1000 DEG C.

[0012] Further, the high-boron martensitic heat-resistant steel comprises, by mass percentage: 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%; and the balance of Fe and inevitable impurities.

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

[0014] Further, in step S3, the upsetting ratio is 2.3-2.7, the WHF method elongation ratio is 2.7-3.2, and the deformation amount of each anvil is 19-25%.

[0015] Further, the high-boron martensitic heat-resistant steel has a grain size grade of 2.0-4.0.

[0016] On the other hand, the present application provides a high-boron martensitic heat-resistant steel prepared by the forging forming method.

[0017] Further, the high-boron martensitic heat-resistant steel has a creep rupture time of greater than 4213 h under the condition of 630 DEG C and 175 MPa.

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

[0019] Further, the high-boron martensitic heat-resistant steel is applied to large shaft forgings and large-diameter seamless pipes, and the diameter of the large shaft forging or the outer diameter of the large-diameter seamless pipe is greater than 150 mm.

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

[0021] 1. The present application provides a forging method of high-B martensitic heat-resistant steel, before forging, homogenization treatment is carried out by using different heating speed, different holding temperature and holding time, by controlling the initial forging temperature, the final forging temperature, the reduction rate and the deformation amount of each pass and other parameters in the forging process, through the mutual cooperation of the above parameters, the problem of forging cracking caused by low plasticity of high-B martensitic heat-resistant steel can be effectively solved, and the excessive grain growth in the forging process is effectively controlled, and the uniformity of the structure is improved.

[0022] 2. In the present application, the content of B element in the martensitic heat-resistant steel is 0.009-0.017% (by weight), and there are also Mn, Cr, W, Mo, Co, V and Zr elements, and the forging forming method provided by the present application 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, the structure is uniform, and the grain size grade is 2.0-4.0 grade.

[0023] 3. By the forming method provided by the present application, the obtained high-boron martensitic heat-resistant steel can be applied to large shaft forgings, after quenching and tempering treatment, the endurance rupture time is greater than 5048h under the condition of 630℃ and 175MPa, 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 application can also be applied to large-diameter seamless pipes, after quenching and tempering treatment, the endurance rupture time is greater than 4213h under the condition of 630℃ and 175MPa, the room temperature tensile strength is above 778MPa, and the room temperature yield strength is above 627MPa.

[0025] In the present application, the above technical solutions can be combined with each other to realize more preferred combination schemes. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification, or will be understood by implementing the present application. The purpose and other advantages of the present application can be realized and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings are included to provide a further understanding of the embodiments, and are not considered as limitations on the present application, and the same reference symbols indicate the same parts throughout the drawings.

[0027] Figure 1 The grain size distribution of Example 1 is shown in the following table:

[0028] Figure 2 The grain size distribution of Comparative Example 1 is shown in the following table:

[0029] Figure 3 The microstructure photo of Example 1 is shown in the following figure:

[0030] Figure 4 Microstructure photograph of Comparative Example 1;

[0031] Figure 5 Macro forging defect of Comparative Example 1. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present application will be described in detail below with reference to the drawings, in which the drawings constitute a part of the present application and are used to explain the principles of the present application together with the embodiments of the present application, but are not used to limit the scope of the present application.

[0033] The steam turbine rotor and large-diameter boiler tube are important components in the ultra-supercritical thermal power unit, and with the increase of the steam temperature and the steam pressure, the service performance of the ultra-supercritical thermal power unit puts forward higher requirements, especially the endurance performance.

[0034] At present, the steam turbine rotor is mainly prepared by using martensitic heat-resistant steel, in order to improve the endurance performance of the martensitic heat-resistant steel, B element is added in the alloy composition. However, the addition of B element can easily induce forging crack defects in the preparation process, and the forging forming is more difficult. In order to improve the forging cracking problem, the content of B element is appropriately reduced, but the endurance performance of the martensitic heat-resistant steel is greatly reduced, which cannot meet the actual demand.

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

[0036] S1: the martensitic heat-resistant steel ingot after smelting is subjected to homogenizing heat treatment, the B content in the martensitic heat-resistant steel ingot is 0.009-0.017wt.%;

[0037] S2: the steel ingot after homogenizing heat treatment is subjected to forging heating;

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

[0039] S4: annealing heat treatment and quenching and tempering heat treatment are carried out after forging, and the high-boron martensitic heat-resistant steel is obtained.

[0040] Compared with the prior art, the present application provides a forging method of high-B martensitic heat-resistant steel, which adopts different heating speeds, different holding temperatures and holding times for homogenization treatment before forging, and controls the initial forging temperature, the final forging temperature, the reduction rate and the deformation amount of each pass and other parameters during the forging process. Through the mutual cooperation of the above parameters, the problem of forging cracking caused by low plasticity of high-B martensitic heat-resistant steel can be effectively solved, and the excessive grain growth during the forging process can be effectively controlled, and the uniformity of the structure is improved.

[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. By using the forming method provided by the present application, the performance of the martensitic heat-resistant steel can be ensured, and the cracking problem during the forging process can be avoided.

[0042] Specifically, in step S1, the high-boron martensitic heat-resistant steel composition comprises, by mass percentage: 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%; and the balance of Fe and unavoidable impurities.

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

[0044] Cu has a low solid solubility in martensite and can form a dispersedly distributed nanometer copper-rich phase, thereby pinning the grain boundary, hindering the migration of the lath martensite interface, and improving the organizational stability. When the Cu content is too high, the high-temperature plasticity of the material will be seriously reduced, and the hot workability of the large forging will be affected, so the Cu element content is controlled to be less than 1.0%. Mn is an austenite forming element and can inhibit the formation of high-temperature δ-ferrite. At the same time, Mn can stabilize S element and avoid the formation of low-melting-point sulfides, thereby improving the hot workability of the material. The carbonitride of Zr is extremely stable, and the addition of Zr element can significantly reduce the tendency of grain growth during heating. In the high-temperature austenite region, the carbonitride containing Zr can inhibit the growth of austenite grains.

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

[0046] It should be noted that the step-type heating according to the above steps can sufficiently reduce thermal stress. The temperature is raised to 250-300°C at a rate of 30-50°C / h to reach the first temperature interval with the largest temperature difference between the surface and the core, at which time the core temperature is lower than 100°C, and the heat-resistant steel blank is still in a cold-hard state, which is prone to cause internal cracks due to the huge temperature difference. By holding for 4-6h, the temperature of the surface and the core can be made uniform, and the thermal stress can be sufficiently reduced. Subsequently, the temperature is raised to 650-700°C at a rate of 40-60°C / h, at which time the second temperature interval with the largest temperature difference is reached, and the core temperature is lower than 350°C. Holding for 7-10h can reduce the temperature difference between the surface and the core, and prevent cracks from being caused by excessive thermal stress. Finally, the temperature is raised to 1170-1230°C at a rate of 40-60°C / h, which can avoid overburning and overheating. Holding for 30-50h can effectively eliminate the dendrites, and no δ ferrite is formed, and there is no harmful phase such as M3B2, and the homogenization effect is good. After the homogenization holding is completed, the furnace is cooled to 800-1000°C, which can prevent the cold speed from being too fast to cause a large temperature difference between the core and the surface of the heat-resistant steel blank, and generate thermal stress to cause cracks.

[0047] Specifically, in step S2, the heat-resistant steel blank 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 the rapid heating to 1130-1170°C at a rate of 80-100°C / h can shorten the heating time, inhibit the grain growth of the heat-resistant steel blank at high temperature, and reduce energy consumption and improve production efficiency. The holding time of the heat-resistant steel blank at 1130-1170°C is not less than 1h / 100mm, which can sufficiently ensure the uniformity of the temperature and the structure before forging.

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

[0050] It should be noted that the forging process of the present application controls the initial forging temperature to be 1130-1170 DEG C, which can avoid the segregation of B element at the grain boundary when the temperature is too high, so that the grain boundary is easy to crack under stress during deformation, thereby improving the plasticity of high-B martensitic heat-resistant steel, reducing the risk of high-B martensitic heat-resistant steel forging cracking, and avoiding excessive grain growth control.

[0051] The final forging temperature in the forging process of the present application is not less than 950 DEG C, which ensures that the recrystallization process of high-B martensitic heat-resistant steel is fully carried out, and avoids work hardening.

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

[0053] It should be noted that the reduction rate of each pass in the forging process of the present application is 0.001 s -1 -0.05 s -1 When the deformation rate is too high, B element quickly diffuses to the grain boundary, resulting in non-equilibrium segregation at the grain boundary, which leads to the reduction of 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 the reduction of plasticity and increases the risk of forging cracking.

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

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

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

[0057] It should be noted that the forging adopts two or more times of upsetting and WHF stretching, 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 stretching ratio of the next fire; the forging ratio during WHF stretching is 2.7-3.2, which can meet the deformation amount of 19-25% of each anvil in multiple passes, thereby fully pressing the internal casting defects, breaking the as-cast structure, refining the grains, and improving the uniformity of the forging structure. When the forging ratio is too small, the internal defects of the heat-resistant steel ingot will be enlarged, and the loose structure and cavity defects in the heat-resistant steel ingot cannot be effectively forged; when the forging ratio is too large, the large deformation will also cause stress concentration in the heat-resistant steel ingot, affecting the performance of the forging, and even forming obvious fiber structure, causing performance anisotropy.

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

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

[0060] It should be noted that the present application provides a large forging and large-diameter seamless pipe anti-cracking forging forming method for high-B martensitic heat-resistant steel, solves the problem of forging cracking caused by low plasticity of high-B martensitic heat-resistant steel, effectively controls the excessive grain growth during forging, improves the uniformity of the overall cross-section structure and grain size of the large forging, and opens up a way 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 forging or the outer diameter of the large-diameter seamless pipe is greater than 150 mm.

[0063] In order to ensure the performance of the large shaft forging, quenching and tempering treatment is required, and the quenching and tempering heat treatment is as follows: the quenching temperature is 1070-1130 DEG C, the holding time is not less than 1 h / 100 mm, the cooling form is oil cooling, air cooling or controlled cooling, the cooling rate of the controlled cooling is 80-150 DEG C / h; the first tempering temperature is 550-590 DEG C, the holding time is not less than 1 h / 100 mm, the cooling form is air cooling or controlled cooling, the cooling rate of the controlled cooling is 30-60 DEG C / h; the second tempering temperature is 680-740 DEG C, the holding time is not less than 1 h / 100 mm, the cooling form is air cooling or controlled cooling, and the cooling rate of the controlled cooling is 30-60 DEG C / h.

[0064] After the quenching and tempering treatment, the large shaft forging has a creep rupture time of greater than 5048 h at 630 DEG C and 175 MPa, a room temperature tensile strength of greater than 855 MPa, and a room temperature yield strength of greater than 728 MPa.

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

[0066] After the tempering treatment, the large-diameter seamless pipe has a rupture time of greater than 4213 h at 630 DEG C and 175 MPa, a tensile strength at room temperature of greater than 778 MPa, and a yield strength at room temperature of greater than 627 MPa.

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

[0068] Preparation Example 1

[0069] A martensitic heat-resistant steel ingot is prepared by vacuum induction melting and protective atmosphere electroslag remelting, and has the following chemical composition: 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] Preparation Example 2 is different from Preparation Example 1 in that the chemical composition is different, and Preparation Example 2 has the following chemical composition: C is 0.14%; Si is 0.09%; Mn is 0.35%; Cr is 9.41%; W is 0.01%; Mo is 1.49%; Co is 1.3%; V is 0.17%; Nb is 0.04%; Cu is 0.05%; Zr is 0.001%; B is 0.010%; N is 0.020%; and the balance is Fe.

[0072] Preparation Example 3

[0073] Preparation Example 3 is different from Preparation Example 1 in that the chemical composition is different, and Preparation Example 3 has the following chemical composition: C is 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 forming method of a high-boron martensitic heat-resistant steel, comprising the following steps:

[0076] S1: uniformly heat treating the martensitic heat-resistant steel ingot obtained in Preparation Example 1,

[0077] Ramp up at a rate of 40°C / h to 280°C, hold for 5h; continue to ramp up at a rate of 50°C / h to 680°C, hold for 8h; continue to ramp up at a rate of 50°C / h to 1200°C, hold for 45h; after the holding, cool the furnace to 900°C;

[0078] S2: the steel ingot after homogenization heat treatment is forged and heated; start heating at 900°C at a rate of 90°C / h to 1150°C, hold for 9h;

[0079] S3: the forging adopts upsetting and WHF method elongation for more than two times, the initial forging temperature of each time is controlled to be 1150°C, the reduction rate of each pass is controlled to be 0.005s -1 ; the upsetting ratio during upsetting is 2.3, the forging ratio during WHF method elongation is 2.7, the deformation amount of each anvil reduction is 20%, and the final forging temperature is 955°C;

[0080] S4: after forging, annealing heat treatment is carried out, the temperature of the annealing heat treatment is 730°C, the holding time is 250h, and the high-B martensitic heat-resistant steel is obtained.

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

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

[0083] Examples 2-5, Comparative Examples 1-5 and the preparation process of Example 1 are basically the same, and the differences are shown in Table 1.

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

[0085] Examples 6-7, Comparative Examples 6-7 and the preparation process of Example 3 are basically the same, and the differences are shown in Table 1. In addition, Examples 6-7 and Comparative Examples 6-7 are both applied to large-diameter boiler pipes, and need to be subjected to quenching and tempering heat treatment after the S4 step, specifically: the normalizing temperature is 1100°C, the holding time is 5h, and the temperature is air-cooled to room temperature; the tempering temperature is 780°C, the holding time is 8h, and the temperature is air-cooled to room temperature.

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

[0087]

[0088] Example 8

[0089] Example 8 was prepared in substantially the same manner as Example 1, except that in Example 8 the temperature was increased at a rate of 33°C / h to 280°C, held for 4h; continued to increase at a rate of 43°C / h to 660°C, held for 7h; continued to increase at a rate of 50°C / h to 1180°C, held for 47h; after the holding period, the furnace was cooled to 850°C.

[0090] Example 9

[0091] Example 9 was prepared in substantially the same manner as Example 1, except that in Example 9 the temperature was increased at a rate of 48°C / h to 280°C, held for 6h; continued to increase at a rate of 57°C / h to 695°C, held for 10h; continued to increase at a rate of 50°C / h to 1230°C, held for 35h; after the holding period, the furnace was cooled to 960°C.

[0092] Comparative Example 8

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

[0094] Performance Testing

[0095] The above Examples 1-9 and Comparative Examples 1-8 were tested for performance after the quenching and tempering heat treatment, including mainly the endurance performance, strength, and microstructure observation and macroscopic testing. The results are shown in Tables 2 and 3.

[0096] Table 2 Performance Testing Results

[0097]

[0098]

[0099] Table 3 Microscopic Testing Results

[0100]

[0101] In combination with Examples 1-9 and Comparative Examples 1-8, and in combination with Table 2 and Table 3, it can be seen that when the high-boron martensitic heat-resistant steel is prepared by using the forming method provided in Examples 1-9 of the present application, the high-boron martensitic heat-resistant steel has higher endurance and strength, and when the high-boron martensitic heat-resistant steel is applied to a large shaft forging, after quenching and tempering treatment, the endurance rupture time is greater than 5048 h at 630℃ and 175 MPa; the tensile strength at room temperature is greater than 855 MPa, and the yield strength at room temperature is greater than 728 MPa. When the high-boron martensitic heat-resistant steel is applied to a large-diameter seamless pipe, after quenching and tempering treatment, the endurance rupture time is greater than 4213 h at 630℃ and 175 MPa; the tensile strength at room temperature is greater than 778 MPa, and the yield strength at room temperature is greater than 627 MPa.

[0102] In combination with Example 1 and Comparative Example 1, and in combination with Figures 1-5 It can be seen that when the high-boron martensitic heat-resistant steel is prepared by using the forming method provided in Example 1 of the present application, no cracks are generated, and the grain size is relatively uniform at 2.0-3.0 levels.

[0103] The above description is merely preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions easily thought of by those skilled in the art within the technical scope disclosed by the present application should be encompassed within the protection scope of the present application.

Claims

1. A forging forming method of a high-boron martensitic heat-resistant steel, characterized by, The method comprises the following steps: S1: homogenizing heat treatment is performed on the smelted martensitic heat-resistant steel ingot, and the B content in the martensitic heat-resistant steel ingot is 0.009-0.017 wt.%; The homogenizing heat treatment is first heated at a rate of 30-50 ℃ / h to 250-300 ℃, and then kept for 4-6 h; then heated at a rate of 40-60 ℃ / h to 650-700 ℃, and then kept for 7-10 h; finally heated at a rate of 40-60 ℃ / h to 1170-1230 ℃, and then kept for 30-50 h; after the keeping, the furnace is cooled to 800-1000 ℃; S2: the steel ingot after the homogenizing heat treatment is heated for forging; S3: the forging adopts upsetting and WHF method elongation for two or more times, the initial forging temperature of each time is controlled to be 1130-1170℃, and the reduction rate of each pass is controlled to be 0.001s -1 0.05s -1 ; wherein the upsetting ratio is 2.3-2.7, the forging ratio during the WHF method elongation is 2.7-3.2, and the reduction deformation amount of each anvil is 19-25%. S4: annealing heat treatment and quenching and tempering heat treatment are performed after forging, so that the high-boron martensitic heat-resistant steel is obtained; The high-boron martensitic heat-resistant steel comprises, by mass percent: 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%; and the balance of Fe and inevitable impurities.

2. The method of claim 1, wherein the high boron maraging steel is forged into a shape. In step S1, the homogenizing heat treatment is first heated at a rate of 40-50 ℃ / h to 280-300 ℃, and then kept for 5-6 h; then heated at a rate of 50-60 ℃ / h to 680-700 ℃, and then kept for 8-10 h; finally heated at a rate of 50-60 ℃ / h to 1200-1230 ℃, and then kept for 45-50 h; after the keeping, the furnace is cooled to 900-1000 ℃.

3. The method of claim 1, wherein the high boron maraging steel is forged into a shape. The high-boron martensitic heat-resistant steel comprises, by mass percent: C: 0.08-0.15%; Si: ≤0.50%; Mn: 0.25-0.55%; Cr: 8.81-9.5%; W: ≤3.10%; Mo: ≤1.50%; Co: 1.1-3.2%; V: 0.23-0.30%; Nb: 0.04-0.06%; Cu: ≤1.0%; Zr: ≤0.05%; B: 0.009-0.016%; N: ≤0.02%; and the balance of Fe and inevitable impurities.

4. The method of claim 1, wherein the high boron maraging steel is forged into a shape. In step S2, heating is performed at a rate of 80-100 ℃ / h to 1130-1170 ℃, and the keeping time is not less than 1 h / 100 mm.

5. The method of claim 1, wherein the high boron maraging steel is forged into a shape. In step S3, the upsetting ratio is 2.3, the forging ratio in the WHF method is 2.7, and the deformation amount of each anvil is 20-25%.

6. The method of claim 1, wherein the wrought forming of the high boron maraging steel is performed at a temperature of 800°C to 950°C. The grain size grade of the high-boron martensitic heat-resistant steel is 2.0-4.

0.

7. A high boron maraging heat resistant steel, characterized in that, The high-boron martensitic heat-resistant steel is obtained by the forging forming method in any one of claims 1-6.

8. The high boron maraging steel heat-resistant steel according to claim 7, characterized in that, The high-boron martensitic heat-resistant steel has a creep rupture time of greater than 4213 h under the condition of 630 ℃ and 175 MPa.

9. The high boron maraging steel heat resistant steel of claim 7, wherein, The high-boron martensitic heat-resistant steel has a room-temperature tensile strength of greater than 778 MPa and a room-temperature yield strength of greater than 627 MPa.

10. Use 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.

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