A high-strength and high-toughness martensitic precipitation hardened stainless steel forging and a manufacturing method thereof

Abstract

The present invention discloses a high-strength and high-toughness martensitic precipitation hardened stainless steel forging and a manufacturing method thereof. The manufacturing method of the present invention is: re-inspecting the pre-forged raw materials, cutting, forging and heating, and then forging and blanking; after the forging and blanking is completed, the forging blank is returned to the furnace for heat preservation, and after heat preservation, it is taken out of the furnace and put into water for water-air alternating cooling; the stainless steel forging after water-air alternating cooling is subjected to dimensional inspection, and after passing the water-air alternating cooling, it is rough turned; the stainless steel forging after rough turning is subjected to performance heat treatment, and rough turned again to obtain high-strength and high-toughness martensitic precipitation hardened stainless steel forging. The present invention effectively avoids the problem of easy cracking of martensitic precipitation hardened stainless steel forgings by optimizing the raw material components and the preparation process, especially by alternately cooling the forgings after forging and blanking and returning to the furnace for heat preservation with water cooling and air cooling.

Description

Technical Field

[0001] The invention relates to the technical field of manufacturing high alloy steel forgings for aircraft engines and gas turbines, and in particular to a high-strength and high-toughness martensitic precipitation hardened stainless steel forging and a manufacturing method thereof. Background Art

[0002] As the international situation becomes increasingly severe, all countries are focusing on developing science and technology, and the fields of aerospace and gas turbines occupy an important position in the development of science and technology. With the rapid development of the fields of aerospace and gas turbines, higher and higher quality requirements have been put forward for the forgings used in the main structures of aircraft engines and gas turbines, and requirements have also been put forward for mass production of products. Based on the in-depth economic research on the performance of 0Cr17Ni4Cu4Nb (17-4PH), the current problem to be solved is how to mass produce and popularize it in actual industrial production. Due to the high alloy content, 17-4PH has a higher added value than some ordinary alloy steels, and the actual production requires a high yield rate of products. If the yield rate of a material is low, it will not only burden the enterprise, but also directly affect the promotion and application of the material in various fields.

[0003] Although my country has adopted 17-4PH in the fields of aero-engines and gas turbines, there are still many problems in the actual production of 17-4PH, such as the uneven smelting quality of the material, the lack of theoretical research on performance and heat treatment combined with the actual production process, and the lack of industry post-forging heat treatment specifications. Therefore, it is urgent to study the forging and post-forging heat treatment processes of 17-4PH, accumulate sufficient and effective methods of final and final forging temperatures, forging deformation, and post-forging heat treatment, provide data support for 17-4PH materials for my country's aero-engines and gas turbines, prepare for the later batch production, reduce the production difficulties of the material and promote it to other fields.

[0004] 17-4PH is a martensitic precipitation hardening stainless steel, which is a material developed abroad. However, due to its high strength, good toughness, corrosion resistance and weldability, it is widely used in aerospace, nuclear industry, energy, petroleum, chemical industry and other fields. It was later cited in China. The domestic material grade is 0Cr17Ni4Cu4Nb. Due to its good comprehensive mechanical properties, 17-4PH stainless steel is often used in aircraft casings, fasteners, turbine blades, gas turbine casings, mountings, landing gear components, radar lugs, and heat exchange valves for nuclear reactors. However, this material is very difficult to produce in actual production, especially forgings with large wall thickness. On the one hand, it is easy to crack during forging, and on the other hand, it is easy to crack after annealing after forging. This is because the composition of the material determines that its forging temperature range is narrow and the internal organization transformation internal stress is large during annealing after forging. Although this material has been widely used in military industry for decades, there are still many problems in actual production. A lot of research has been done in China on the performance heat treatment of this material, but the performance heat treatment should be carried out only on the premise that qualified products can be forged. Therefore, how to forge thick-walled forgings (here thick-walled forgings refer to forgings with an effective thickness of ≥300mm) and how to perform post-forging preparatory heat treatment to produce qualified blanks in batches and stably are issues that traditional manufacturing companies urgently need to solve. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a high-strength and high-toughness martensitic precipitation hardened stainless steel forging and a manufacturing method thereof. The present invention effectively avoids the problem of easy cracking of martensitic precipitation hardened stainless steel forgings by optimizing the raw material components and the preparation process, especially by alternately cooling the forgings after forging and returning to the furnace for heat preservation with water cooling and air cooling.

[0006] The technical solution of the present invention is as follows:

[0007] A high-strength and high-toughness martensitic precipitation hardened stainless steel forging, wherein the stainless steel forging is made of a steel ingot obtained by smelting molten steel as a raw material, and the molten steel comprises the following components in terms of mass percentage:

[0008] C: 0.03-0.06%, Si: 0.45-0.60%, Mn: 0.45-0.60%, P: ≤0.030%, S: ≤0.015%, Cr: 15-17%, Ni: 3.7-4.5%, Cu: 3.0-3.5%, Nb: 0.017-0.03%, and the balance is iron and inevitable impurities.

[0009] A method for manufacturing the high-strength and high-toughness martensitic precipitation hardened stainless steel forging comprises the following steps:

[0010] (1) Re-inspect the pre-forged raw materials, cut them, heat them during forging, and then forge them into blanks;

[0011] (2) After forging, the forging billet is returned to the furnace for heat preservation, and then taken out of the furnace and put into water for alternating water-air cooling;

[0012] (3) After water-air alternating cooling, the stainless steel forgings are inspected for size and rough turned if they pass the test;

[0013] (4) The stainless steel forgings after rough turning are subjected to performance heat treatment and rough turned again to obtain high-strength and high-toughness martensitic precipitation hardened stainless steel forgings.

[0014] Furthermore, in step (1), the forging heating is multi-stage forging heating.

[0015] Furthermore, the multi-stage forging heating is divided into two-stage step forging heating and three-stage step forging heating according to the effective size of the pre-forged raw material; when the effective size of the pre-forged raw material is ≤600mm, two-stage step forging heating is used; when the effective size of the pre-forged raw material is >600mm, three-stage step forging heating is used.

[0016] Furthermore, the two-stage step forging heating is as follows: first, the pre-forging is heated to 850±25°C in the furnace, and the first stage of insulation is performed, and the insulation time is the effective size of the pre-forging multiplied by 0.3min / mm; then, the pre-forging is heated to 1200±25°C in the furnace, and the second stage of insulation is performed, and the insulation time is the effective size of the pre-forging multiplied by (0.4-0.5)min / mm.

[0017] Furthermore, the three-stage forging heating is as follows: first, the pre-forging is heated to 600±25°C with the furnace, and kept warm for 2-3 hours; then, the pre-forging is heated to 850±25°C with the furnace, and a second stage of heat preservation is performed, and the heat preservation time is the effective size of the pre-forging multiplied by 0.3min / mm; then, the pre-forging is heated to 1200±25°C with the furnace, and a third stage of heat preservation is performed, and the heat preservation time is the effective size of the pre-forging multiplied by (0.4-0.5)min / mm.

[0018] Furthermore, in step (1), the initial forging temperature of the forging blank is 1200±25°C, and the final forging temperature is ≥900°C.

[0019] Furthermore, in step (2), the furnace return refers to furnace return before the surface temperature of the forged billet after forging reaches ≥800°C. The furnace return and heat preservation refers to heating the forged billet to 955-1045°C at a rate of ≤150°C / h for heat preservation for 1-2h.

[0020] Furthermore, in step (2), the specific method of the water-air alternating cooling is: when the effective size of the forging billet δ≤150mm, the average cooling rate of air cooling and water cooling is controlled to be ≥1.7℃ / S, and the re-warming temperature after 3min of water outlet is measured at the same time. When the re-warming temperature reaches 300℃-350℃, air cooling is performed to room temperature; when the effective size of the forging billet is 150<δ≤300mm, the average cooling rate of air cooling and water cooling is controlled to be ≥0.95℃ / S, and the re-warming temperature after 4min of water outlet is measured at the same time. When the re-warming temperature reaches 250℃-300℃, air cooling is performed to room temperature; when the effective size of the forging billet is >300mm, the average cooling rate of air cooling and water cooling is controlled to be ≥0.7℃ / S, and the re-warming temperature after 5min of water outlet is measured at the same time. When the re-warming temperature reaches 100-150℃, air cooling is performed to room temperature; in the water-air alternating cooling, the water cooling time is greater than the air cooling time. At this time, the air cooling time does not include the time of air cooling to room temperature after reaching the re-warming temperature.

[0021] Furthermore, in step (4), the performance heat treatment includes solution treatment and aging treatment; the temperature of the solution treatment is 1020-1060°C, and water cooling is performed first and then air cooling is performed; the temperature of the forging before aging treatment is lower than 30°C; the performance heat treatment is specifically as follows: heating the forging blank alternately cooled by water and air to 1020-1060°C, keeping it warm for a time equal to the effective size of the forging blank multiplied by 1.3min / mm, then water cooling it to 100-150°C, then air cooling it to room temperature to complete the solution treatment, then heating it to 510-620°C, keeping it warm for a time equal to the effective size of the forging blank multiplied by 2min / mm, and finally air cooling it.

[0022] The effective size in the present invention is the smaller size between the average diameter or side length of the forging and the thickness of the forging. For example, if the diameter of a cylindrical forging is 600 mm and the thickness is 1.5 m, the effective size of the forging is 600 mm.

[0023] Since AC3 of 17-4PH material is 704℃, M s =132℃,M f =35℃, which is different from the actual composition of the material. After the forging is solid-solutionized, when the forging temperature is ≥30℃, the temperature of the core of the forging will be slightly higher, and the core has not yet completely transformed into martensite. The present invention controls the temperature before aging to be lower than the martensite transformation termination point M f , achieving complete transformation of martensite.

[0024] Since 17-4PH is a precipitation hardening stainless steel, the present invention adopts water-air alternating cooling instead of annealing process after the forging billet is returned to the furnace for heat preservation, and austenite is transformed into martensite at a faster cooling rate. The present invention investigates that different cooling rates when entering water after forging have a great influence on its effect. The faster the cooling rate after forging, the more effective it is, and the more austenite is transformed into martensite; the slower the cooling rate after forging, the worse the effect, the less austenite is transformed into martensite, and there is a lot of residual austenite.

[0025] The ingot is originally a cast structure, which is changed to a forged structure after forging. Without heat treatment, the structure of the forging is uneven, and the thermal stress and structural stress are very large. At this time, if the conventional annealing process is used, it is equivalent to an aging treatment for the material, and the strengthening phases such as ε-Cu and NbC are dispersed and precipitated. Although the strength and internal stress of the forging can be improved, insufficient annealing and improper control are particularly prone to cracking of the forging after forging. The present invention adopts water-air alternating cooling after the forging billet is returned to the furnace for heat preservation, and the cooling rate is accelerated. Some alloy phases have no time to precipitate, and the internal stress of the forging is small, so the forging is not easy to crack. In actual production, the forging has different effective thicknesses, and the cooling rate of the product surface is inconsistent with the cooling rate of the core. The greater the wall thickness, the greater the difference between the cooling rate of the core and the surface, and the smaller the wall thickness, the smaller the cooling rate of the core and the surface. In order to reduce the temperature difference between the surface and the core of the forging, and reduce the structural transformation stress and thermal stress, the present invention adopts water-air alternating cooling.

[0026] The beneficial technical effects of the present invention are:

[0027] The present invention adopts water-air alternating cooling after forging instead of annealing after forging, thus avoiding product cracking and failure due to complicated annealing process, improving the turnover rate of heat treatment furnace, shortening product manufacturing cycle and reducing production cost. The temperature of forgings before aging treatment of the present invention is lower than 30°C, achieving complete transformation of martensite.

[0028] The invention improves the first-time qualified rate through internal component control and performance heat treatment, is easy to control on-site in the workshop, avoids energy waste caused by rework and repair, shortens the production cycle and manufacturing cost, and solves the problem that forgings produced by using 17-4PH martensitic precipitation hardening stainless steel are prone to post-forging cracking and thus causing product failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a process flow chart of the present invention.

[0030] Figure 2 This is a process diagram for preparing heat treatment after forging according to the present invention.

[0031] Figure 3 It is a two-stage forging heating process.

[0032] Figure 4It is a three-stage forging heating process. DETAILED DESCRIPTION

[0033] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0034] Example 1

[0035] The high-strength and high-toughness martensitic precipitation-hardened stainless steel forgings are made of steel ingots obtained by smelting molten steel as raw materials. The molten steel includes the following components by mass percentage: C: 0.03%, Si: 0.49%, Mn: 0.46%, P: 0.029%, S: 0.001%, Cr: 15.50%, Ni: 3.84%, Cu: 3.25%, Nb: 0.021%, and the balance is iron and inevitable impurities.

[0036] The preparation method of high-strength and high-toughness martensitic precipitation hardened stainless steel forgings is as follows:

[0037] (1) The pre-forged forgings (raw materials) are re-inspected, unloaded, forged and heated, and then forged into blanks; the effective size of the forging is 485 mm, which is less than 600 mm, so two-stage step forging heating is adopted; the specific method is: firstly, the forging is heated to 850°C with the furnace, and the first stage of heat preservation is carried out, and the heat preservation time is 145.5 min, which is the effective size of the forging multiplied by 0.3 min / mm; then, the forging is heated to 1200°C with the furnace, and the second stage of heat preservation is carried out, and the heat preservation time is 194 min, which is the effective size of the forging multiplied by (0.4) min / mm; the initial forging temperature of the forging blank is 1200°C, and the final forging temperature is ≥900°C.

[0038] (2) After forging, the forging billet is returned to the furnace before the surface temperature of the forging billet is ≥800°C, and the temperature is raised to 980°C at a rate of ≤150°C / h for insulation for 1h. After insulation, the forging billet is taken out of the furnace and put into water for alternating water-air cooling;

[0039] (3) After water-air alternating cooling, the stainless steel forgings are inspected for size and rough turned if they pass the test;

[0040] The specific method of the water-air alternating cooling is: because the effective size of the forging billet is greater than 300mm, the following process is adopted: the forging billet after insulation is put into water for water cooling for a certain period of time, and then taken out for air cooling, the time of each water cooling is greater than the air cooling time, and the average cooling rate of air cooling and water cooling is controlled to be ≥0.7℃ / S. During air cooling, the return temperature is measured 5 minutes after the water is taken out. When the return temperature reaches 120℃, no more water is put in and air cooling is performed to room temperature.

[0041] (4) The forging blank that has been alternately cooled in water and air is rough turned, and then subjected to a performance heat treatment, and rough turned again to obtain a high-strength and high-toughness martensitic precipitation hardened stainless steel forging; the performance heat treatment includes a solution treatment and an aging treatment; the conditions of the performance heat treatment are shown in Table 1; the temperature of the forging before the aging treatment is lower than 30°C.

[0042] Embodiment 2-8

[0043] Example 2 is the same as Example 1, except for the conditions of furnace insulation, water-air alternating cooling and performance heat treatment process. The specific differences between the embodiments are shown in Table 1.

[0044] Table 1 Process parameters of reheating, water-cooling and heat treatment of Examples 1-8

[0045]

[0046] Example 9

[0047] The high-strength and high-toughness martensitic precipitation hardened stainless steel forgings are made from steel ingots obtained by smelting molten steel. The molten steel includes the following components by mass percentage:

[0048] C: 0.05%, Mn: 0.52%, P: 0.024%, S: 0.004%, Si: 0.50%, Cr: 16.70%, Ni: 3.85%, Cu: 3.14%, Nb: 0.030%, and the balance is iron and inevitable impurities.

[0049] The preparation method of high-strength and high-toughness martensitic precipitation hardened stainless steel forgings is as follows:

[0050] (1) The pre-forged forgings are re-inspected, cut, and forged and heated. The effective size of the forgings is 645 mm, which is larger than 600 mm. Therefore, three-stage step forging heating is adopted. The specific method is as follows: first, the forgings are heated to 600°C with the furnace and kept warm for 3 hours. Then, the forgings are heated to 850°C with the furnace and kept warm for the second stage. The holding time is the effective size of the forging × 0.3 min / mm, that is, 258 min. Then, the forgings are heated to 1200°C with the furnace and kept warm for the third stage. The holding time is the effective size of the forging × (0.4) min / mm, that is, 258 min.

[0051] (2) After forging, the forging billet is returned to the furnace before the surface temperature of the forging billet is ≥800°C, and the temperature is raised to 980°C at a rate of 150°C / h for insulation for 1 hour. After insulation, the forging billet is taken out of the furnace and put into water for alternating water-air cooling;

[0052] (3) After water-air alternating cooling, the stainless steel forgings are inspected for size and rough turned if they pass the test;

[0053] The specific method of water-air alternating cooling is: because the effective size of the forging billet is greater than 300mm, the following process is adopted: the forging billet after heat preservation is put into water for water cooling for a certain period of time, and then taken out for air cooling, the water cooling time each time is greater than the air cooling time, and the average cooling rate of air cooling and water cooling is controlled to be ≥0.7℃ / S. During air cooling, the return temperature is measured 5 minutes after the water is taken out. When the return temperature reaches 150℃, no more water is put in, and air cooling is performed to room temperature. ;

[0054] (4) rough turning the forging blank after water-air alternating cooling, then performing a performance heat treatment, and rough turning again to obtain a high-strength and high-toughness martensitic precipitation hardened stainless steel forging; the performance heat treatment includes a solution treatment and an aging treatment; the heating temperature of the solution treatment is 1040° C., the holding time and the cooling method are the same as those in Example 1, the heating temperature of the aging treatment is 540° C., the holding time and the cooling method are the same as those in Example 1; the temperature of the forging before the aging treatment is lower than 30° C.

[0055] Example 10

[0056] The high-strength and high-toughness martensitic precipitation hardened stainless steel forgings are made from steel ingots obtained by smelting molten steel. The molten steel includes the following components by mass percentage:

[0057] C: 0.06%, Si: 0.60%, Mn: 0.60%, P: 0.024%, S: 0.004%, Cr: 17%, Ni: 4.5%, Cu: 3.5%, Nb: 0.017%, and the balance is iron and inevitable impurities.

[0058] The preparation method of high-strength and high-toughness martensitic precipitation hardened stainless steel forgings is as follows:

[0059] (1) The pre-forged forgings are re-inspected, blanked, and forged and heated. The effective size of the forgings is 250 mm, which is less than 600 mm. Therefore, two-stage step forging heating is adopted. The specific method is as follows: the forgings are first heated to 850°C with the furnace, and the first stage of heat preservation is carried out. The heat preservation time is 75 minutes, which is equal to the effective size of the forging multiplied by 0.3 min / mm; then the forgings are heated to 1200°C with the furnace, and the second stage of heat preservation is carried out. The heat preservation time is 125 minutes, which is equal to the effective size of the forging multiplied by (0.5) min / mm; the initial forging temperature of the forging is 1200±°C, and the final forging temperature is ≥900°C.

[0060] (2) After forging, the forging billet is returned to the furnace before the surface temperature of the forging billet is ≥800°C, and the temperature is raised to 980°C at a rate of 150°C / h for insulation for 1 hour. After insulation, the forging billet is taken out of the furnace and put into water for alternating water-air cooling;

[0061] (3) After water-air alternating cooling, the stainless steel forgings are inspected for size and rough turned if they pass the test;

[0062] The specific method of the water-air alternating cooling is: because the effective size of the forging billet is 150<δ≤300mm, the following process is adopted: the forging billet after insulation is put into water for water cooling for a certain period of time, and then taken out for air cooling, the time of each water cooling is greater than the air cooling time, and the average cooling rate of air cooling and water cooling is controlled to be ≥0.95℃ / S. At the same time, the return temperature is measured 4 minutes after the water is discharged. When the return temperature reaches 300℃, it is air cooled to room temperature.

[0063] (4) rough turning the forging blank after water-air alternating cooling, then performing a performance heat treatment, and rough turning again to obtain a high-strength and high-toughness martensitic precipitation hardened stainless steel forging; the performance heat treatment includes a solution treatment and an aging treatment; the heating temperature of the solution treatment is 1040° C., the holding time and the cooling method are the same as those in Example 1, the heating temperature of the aging treatment is 540° C., the holding time and the cooling method are the same as those in Example 1; the temperature of the forging before the aging treatment is lower than 30° C.

[0064] Comparative Example 1

[0065] The same as Example 1, but as shown in Table 1, water-air alternating cooling was not used, but air cooling to room temperature after returning to the furnace for heat preservation was used. The forging cracked on the second day. The qualified parts of the flaw detection were selected for sampling and physical and chemical testing.

[0066] Comparative Example 2

[0067] The same as Example 1, as shown in Table 2, the difference is that in the water-air alternating cooling, the average cooling rate is 0.4°C / S, and the air cooling time is relatively long.

[0068] Comparative Example 3

[0069] Same as Example 1, except that, as shown in Table 2, water-air alternating cooling is used after reheating and water cooling is used until the forging temperature reaches 150° C. The surface cracks of the forging extend. The qualified parts of the flaw detection are selected for sampling and physical and chemical testing.

[0070] Table 2 Process parameters of reheating, water cooling and performance heat treatment in comparative examples

[0071]

[0072] Test example:

[0073] The tensile strength, yield strength and other properties of the forgings prepared in the examples and comparative examples were measured. Specifically, the tensile strength, yield strength, elongation and shrinkage were measured using a universal testing machine according to GB / T228; the impact energy was measured using an impact testing machine according to GB / T229; and the hardness was measured using a Brinell hardness tester. The test results are shown in Table 3.

[0074] Table 3 Performance tests of embodiments and comparative examples

[0075]

[0076]

[0077] As can be seen from Table 3, after forging, water cooling and air cooling are alternately used for preliminary heat treatment, and then solution and aging treatment are performed. There is no cracking in the forgings, and the final technical requirements of the products can be met. This shows that entering water after forging does not affect the performance, does not cause cracking in the forgings, avoids the cracking caused by traditional post-forging annealing, and can achieve better coordination with performance heat treatment. At the same time, it can be seen from the comparative examples that after the speed of water-air alternating cooling is changed, although the prepared forgings have no cracks, the strength and plasticity of the forgings are reduced. When only air cooling is used, the cooling rate is slow and the generation efficiency is low. The forgings will crack due to large stress generated by the organizational transformation. When only water cooling is used, due to the fast cooling rate of the forgings and the presence of microcracks on the surface of the forgings, the cracks in the forgings will further extend under the combined action of thermal stress and organizational transformation stress, causing the forgings to crack. Therefore, the present invention proposes water-air alternating cooling with a specific cooling rate to avoid cracking of the forgings while improving the strength and toughness of the forgings.

[0078] The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A high-strength and high-toughness martensitic precipitation-hardened stainless steel forging, characterized in that: The stainless steel forging is made of a steel ingot obtained by smelting molten steel. The molten steel comprises the following components by mass percentage: C: 0.03-0.06%, Si: 0.45-0.60%, Mn: 0.45-0.60%, P: ≤0.030%, S: ≤0.015%, Cr: 15-17%, Ni: 3.7-4.5%, Cu: 3.0-3.5%, Nb: 0.017-0.03%, and the balance is iron and unavoidable impurities; The manufacturing method of the high-strength and high-toughness martensitic precipitation hardened stainless steel forging is as follows: (1) Re-inspect the pre-forged raw materials, cut them, heat them during forging, and then forge them into blanks; (2) After forging, the forging billet is returned to the furnace for heat preservation, and then taken out of the furnace and put into water for alternating water-air cooling; (3) After water-air alternating cooling, the stainless steel forgings are inspected for size and rough turned if they pass the test; (4) The stainless steel forgings after rough turning are subjected to performance heat treatment, and rough turning is performed again to obtain high-strength and high-toughness martensitic precipitation hardened stainless steel forgings; In step (2), the furnace return refers to furnace return before the surface temperature of the forging billet after forging reaches ≥800°C; the holding temperature is 955-1045°C and the time is 1-2h; In step (2), the specific method of the water-air alternating cooling is: when the effective size of the forging billet is δ≤150mm, the average cooling rate of air cooling and water cooling is controlled to be ≥1.7℃ / S, and the re-warming temperature after 3min of water discharge is measured at the same time. When the re-warming temperature reaches 300℃-350℃, air cooling is performed to room temperature; when the effective size of the forging billet is 150<δ≤300mm, the average cooling rate of air cooling and water cooling is controlled to be ≥0.95℃ / S, and the re-warming temperature after 4min of water discharge is measured at the same time. When the re-warming temperature reaches 250℃-300℃, air cooling is performed to room temperature; when the effective size of the forging billet is δ>300mm, the average cooling rate of air cooling and water cooling is controlled to be ≥0.7℃ / S, and the re-warming temperature after 5min of water discharge is measured at the same time. When the re-warming temperature reaches 100-150℃, air cooling is performed to room temperature; In step (4), the performance heat treatment includes solution treatment and aging treatment; the solution temperature is 1020-1060°C, and water cooling or air cooling is adopted; the temperature of the forging before aging treatment is lower than 30°C.

2. The high-strength and high-toughness martensitic precipitation hardened stainless steel forging according to claim 1, characterized in that: In step (1), the forging heating is multi-stage forging heating.

3. The high-strength and high-toughness martensitic precipitation hardened stainless steel forging according to claim 2, characterized in that: The multi-stage forging heating is divided into two-stage step forging heating and three-stage step forging heating according to the effective size of the pre-forged raw material; when the effective size of the pre-forged raw material is ≤600mm, two-stage step forging heating is used; when the effective size of the pre-forged raw material is >600mm, three-stage step forging heating is used.

4. The high-strength and high-toughness martensitic precipitation hardened stainless steel forging according to claim 3, characterized in that: The two-stage step forging heating is as follows: first, the pre-forged raw material is heated to 850±25°C with the furnace, and the first stage of insulation is carried out, and the insulation time is the effective size of the pre-forged raw material multiplied by 0.3min / mm; then, it is heated to 1200±25°C with the furnace, and the second stage of insulation is carried out, and the insulation time is the effective size of the pre-forged raw material multiplied by (0.4-0.5)min / mm.

5. The high-strength and high-toughness martensitic precipitation hardened stainless steel forging according to claim 3, characterized in that: The three-stage forging heating is: First, heat the pre-forged raw material to 600±25℃ at ≤70℃ / h and keep it warm for 2-3h. Then, heat the pre-forged raw material to 850±25℃ at ≤90℃ / h for the second heat preservation. The heat preservation time is the effective size of the pre-forged raw material multiplied by 0.3min / mm. Then, heat it to 1200±25℃ at ≤120℃ / h for the third heat preservation. The heat preservation time is the effective size of the pre-forged raw material multiplied by (0.4-0.5)min / mm.

6. The high-strength and high-toughness martensitic precipitation hardened stainless steel forging according to claim 1, characterized in that: In step (1), the initial forging temperature of the forging blank is 1200±25°C, and the final forging temperature is ≥900°C.

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