Heating and heat preservation method of martensite heat-resistant stainless steel forge piece

Abstract

The invention relates to a heating and heat preservation method for a martensite heat-resistant stainless steel forge piece, and belongs to the technical field of alloy forge piece machining. The heating and heat preservation method comprises the steps that whether a steel ingot needs to be preheated or not is judged according to the ingot passing temperature of the martensite heat-resistant stainless steel ingot; when the steel ingot needs to be preheated, low-temperature section heating and heat preservation are conducted on the steel ingot; the steel ingot is subjected to homogenizing heating and heat preservation treatment; forging the steel ingot, and obtaining a forge piece through an upsetting and drawing process; wherein in the upsetting and drawing process of the steel ingot, the steel ingot is subjected to long-time heat preservation treatment. The preheating and homogenizing heating processes before forging are added, firstly, whether the steel ingot is preheated before forging is determined according to the ingot passing temperature of the steel ingot, and the risk that a forge piece cracks due to the fact that the temperature of a cold ingot directly rises to the high temperature can be avoided; and secondly, the steel ingot is subjected to homogenizing heating and heat preservation treatment, meanwhile, long-time heat preservation in the upsetting and drawing process is matched, dendritic segregation can be improved, and the forge piece cracking tendency in the forging period is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of alloy forging processing, in particular to a heating and heat preservation method for a martensitic heat-resistant stainless steel forging. Background Art

[0002] Martensitic heat-resistant stainless steel is now widely used in important gas turbine components such as compressor wheels and rotor shaft heads. However, as a high-alloy steel, martensitic heat-resistant stainless steel will produce severe segregation in its ingots, generating coarse columnar crystals, and cracks are often easily generated along the grain boundaries at the weak links of the primary dendrite grain boundaries. At present, when martensitic stainless steel is forged using the existing forging process, the martensitic stainless steel ingot is usually forged directly, and the heating process during the forging process includes the jaw press fire, the upsetting and drawing fire, and the finished product fire. Each fire adopts a short-time insulation method, and the insulation time of the upsetting and drawing fire is in the range of 10 to 20 hours. After the insulation is completed, the ingot is taken out of the furnace for upsetting and drawing, while the insulation time of the jaw press fire and the finished product fire is shorter. Using the above-mentioned forging process, the ingot is prone to cracking during the forging process, and the uniformity of subsequent performance is also poor. Summary of the invention

[0003] In view of the above analysis, an embodiment of the present invention aims to provide a heating and insulation method for martensitic heat-resistant stainless steel forgings, so as to solve or improve at least one of the problems such as dendrite segregation of martensitic stainless steel ingots, easy cracking during forging process, and poor uniformity of forging performance.

[0004] An embodiment of the present invention provides a method for heating and heat-insulating a martensitic heat-resistant stainless steel forging, comprising:

[0005] According to the ingot temperature of the martensitic heat-resistant stainless steel ingot, determine whether the ingot needs to be preheated;

[0006] When the steel ingot needs to be preheated, the steel ingot is heated and kept warm at a low temperature;

[0007] Conducting uniform heating and heat preservation treatment on the steel ingot;

[0008] The steel ingot is forged and subjected to an upsetting process to obtain a forging; wherein, during the upsetting process of the steel ingot, the forging is subjected to a long-term heat preservation treatment.

[0009] Furthermore, the heating temperature of the homogenization heating and heat-insulating treatment is set to 1150-1200° C., and the heat-insulating time is determined according to the ingot size of the steel ingot.

[0010] Furthermore, when the steel ingot is less than 83t, the insulation time of the steel ingot during the homogenization heating and insulation treatment is greater than or equal to 50h; when the steel ingot is greater than or equal to 83t, the insulation time of the steel ingot during the homogenization heating and insulation treatment is greater than or equal to 60h.

[0011] Furthermore, when the ingot temperature is greater than 600°C, no preheating treatment is required; when the ingot temperature is less than or equal to 600°C, the ingot is preheated, the preheating temperature is 650-700°C, and the holding time is determined according to the ingot temperature.

[0012] Furthermore, when the ingot temperature is 550<T≤600℃, the holding time of the preheating treatment is 10≤t<15h; on this basis, the holding time of the preheating treatment increases by 5 to 10h for every 50℃ decrease in the ingot temperature.

[0013] Furthermore, during forging, the steel ingot is subjected to at least one upsetting and drawing process to obtain a forging; wherein, during the upsetting and drawing stages of the steel ingot, the steel ingot is subjected to long-term heating and heat preservation treatments of different temperatures.

[0014] Furthermore, in each upsetting and drawing process, the steel ingot is heated for one upsetting fire and one drawing fire; wherein the holding time of the upsetting fire and the drawing fire is determined according to the ingot size of the steel ingot.

[0015] Furthermore, when the steel ingot is less than or equal to 70t, the holding time of the roughening fire is 35 to 40h; when the steel ingot is greater than 70t, the holding time of the roughening fire is increased by 1 to 2h for every 1t increase in the ingot shape based on 70t.

[0016] Furthermore, when the steel ingot is less than or equal to 70t, the holding time of the drawing fire is 20 to 30h; when the steel ingot is greater than 70t, the holding time of the drawing fire increases by 1 to 2h for every 1t increase in the ingot shape based on 70t.

[0017] Furthermore, after the upsetting and drawing is completed, if the forging is subjected to overall upsetting deformation to produce a finished product, the forging is subjected to heating and insulation treatment before the overall upsetting deformation, the heating temperature is set to 1150-1180° C., and the insulation time is set to be 5-10 hours longer than the insulation time of the drawing fire.

[0018] Compared with the prior art, the heating and heat preservation method of the present invention can achieve at least one of the following beneficial effects:

[0019] 1. Compared with the traditional forging process of martensitic stainless steel forgings, the present invention adds preheating and homogenizing heating processes before forging. First, whether the steel ingot should be preheated before forging is determined according to the ingot passing temperature, and low-temperature heating and heat preservation are performed when necessary, which can avoid the risk of cracking of the forging caused by directly raising the temperature of the cold ingot; secondly, the present invention can improve dendrite segregation and reduce the tendency of forgings to crack during forging by performing homogenizing heating and heat preservation treatment on the martensitic heat-resistant stainless steel ingot before forging.

[0020] 2. Compared with the traditional forging process, the present invention separates the upsetting and drawing fires during the forging process of the steel ingot, and performs different heating and heat preservation in the upsetting and drawing stages respectively, so as to shorten the atomic migration distance through plastic deformation, accelerate atomic diffusion, make the chemical composition of the high-alloy forgings more uniform, further reduce dendrite segregation defects, and ensure good uniformity of subsequent performance.

[0021] 3. The present invention can reduce dendrite segregation defects in forgings by extending the holding time of each fire in the upsetting process, making the grain structure of the forgings more uniform, thereby reducing the cracking tendency of the forgings.

[0022] 4. The present invention aims at large-diameter variable-section forgings. Before the overall upsetting and deformation to produce finished products, the forgings are heated and heat-insulated for a certain period of time. The heat-insulating time should not be too long. The internal atomic migration distance is greatly shortened through the stretching deformation in the previous fire. Combined with the heat-insulating treatment at high temperature this time, the purpose of improving segregation defects can be achieved.

[0023] 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

[0024] 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.

[0025] Figure 1 It is a schematic diagram of the heating treatment process of the steel ingot before forging in Example 1 of the present invention.

[0026] Figure 2 This is a photograph of the steel ingot of Example 1 of the present invention during the forging process.

[0027] Figure 3 This is a photo of the finished forging obtained after forging in Example 1 of the present invention.

[0028] Figure 4 This is a local microstructure photograph of the forging in Example 1 of the present invention.

[0029] Figure 5 This is another local microstructure photograph of the forging in Example 1 of the present invention.

[0030] Figure 6 This is a local microstructure photograph of the forging in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application 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.

[0032] An embodiment of the present invention provides a method for heating and heat-insulating a martensitic heat-resistant stainless steel forging, comprising:

[0033] According to the ingot temperature of the martensitic heat-resistant stainless steel ingot, determine whether the ingot needs to be preheated;

[0034] When the steel ingot needs to be preheated, the steel ingot is heated and kept warm at a low temperature;

[0035] Conducting homogenized heating and heat preservation treatment on martensitic heat-resistant stainless steel ingots;

[0036] The steel ingot is forged and subjected to an upsetting process to obtain a forging; wherein, during the upsetting process of the steel ingot, the forging is subjected to a long-term heat preservation treatment.

[0037] Compared with the traditional forging process, the embodiment of the present invention adds preheating treatment and homogenization treatment steps to the martensitic heat-resistant stainless steel ingot before forging. First, preheating the ingot can avoid the ingot cracking caused by directly heating the cold ingot with a low ingot temperature; secondly, homogenizing heating and heat preservation treatment before forging can reduce the dendrite segregation defects of the forging, refine and homogenize the grain structure, so as to reduce the cracking tendency of the forging during the subsequent forging process.

[0038] In the embodiment of the present invention, before the homogenization heating and heat preservation treatment before forging, it is judged whether the steel ingot needs to be preheated according to the ingot passing temperature; and when the steel ingot needs to be preheated, the steel ingot is heated and kept at a low temperature to avoid the cold ingot being directly heated to the homogenization heating temperature, which may cause cracking of the forging. The ingot passing temperature refers to the temperature of the surface of the steel ingot.

[0039] In some embodiments, when the ingot temperature is less than or equal to 600°C, the ingot is preheated; when the ingot temperature is greater than 600°C, no preheating is required. When the ingot temperature is greater than 600°C, directly heating to the homogenization heating temperature will not cause the ingot to crack due to the large temperature difference.

[0040] In some embodiments, during the preheating treatment, the preheating temperature is 650-700°C, that is, the low temperature stage heating and heat preservation is carried out at 650-700°C. If the preheating temperature is too high, the temperature difference between the forging surface temperature and the furnace temperature is too large, which makes the forging easy to crack; if the preheating temperature is too low, the preheating effect is not achieved, and the temperature difference of the forging is too large during the subsequent heating to the homogenization stage, which is also very likely to cause cracking.

[0041] In some embodiments, the surface temperature of the steel ingot can be measured, and the holding time during the preheating treatment can be determined according to the ingot temperature. The lower the ingot temperature, the longer the holding time. Specifically, when the ingot temperature is 550<T≤600℃, the holding time of the preheating treatment is 10≤t<15h; on this basis, the holding time of the preheating treatment increases by 5 to 10h for every 50℃ decrease in the ingot temperature.

[0042] Exemplarily, when the ingot temperature is greater than 600° C., the ingot is directly heated to the homogenization heating temperature without preheating.

[0043] When the ingot temperature is 550<T≤600℃, the holding time of preheating treatment is 10≤t<15h;

[0044] When the ingot temperature is 500<T≤550℃, the holding time of preheating treatment is 15≤t<20h;

[0045] When the ingot temperature is 450<T≤500℃, the holding time of preheating treatment is 20≤t<30h; and so on.

[0046] In the embodiment of the present invention, if the holding time of the steel ingot with low ingot temperature is too short, the core of the steel ingot may not be fully preheated, and there is bound to be a temperature difference between the core and the surface, and the resulting temperature stress will cause the steel ingot to crack; if the holding time is too long, it will lead to energy waste. The present invention sets different preheating and holding times for steel ingots with different ingot temperature ranges to ensure that the core of the steel ingots with different ingot temperature ranges can be fully preheated while avoiding excessive energy consumption.

[0047] In some embodiments, when the steel ingot is subjected to homogenization heating and heat preservation treatment before forging, the heating temperature is set to 1150°C to 1200°C. Homogenization heating of the steel ingot within this temperature range can ensure that the harmful phases precipitated along the grain boundaries in the steel ingot can be fully melted back without producing high-temperature ferrite, and is beneficial to the atomic diffusion inside the forging. Preferably, the heating temperature is 1180±10°C. It should be noted that 1180±10°C means that the allowable fluctuation range of the actual heating temperature can be within ±10°C.

[0048] In some embodiments, the holding time during the homogenization heating and holding treatment can be determined according to the size of the ingot to be suitable for ingots of different shapes, ensuring that the core of the large ingot can be fully heated and kept warm, and ensuring the uniformity of the surface and core of the ingot.

[0049] Among them, when the steel ingot is less than 83t, the insulation time of the steel ingot during the homogenization heating and insulation treatment is greater than or equal to 50h; preferably, the insulation time is 50-60h to avoid energy waste. When the steel ingot is greater than or equal to 83t, the insulation time of the steel ingot during the homogenization heating and insulation treatment is greater than or equal to 60h, preferably, the insulation time is 60-70h to avoid energy waste.

[0050] The embodiments of the present invention can improve the dendrite segregation of the steel ingot and reduce the cracking tendency of the forging during forging by performing a long-term homogenization heating and heat preservation treatment on the steel ingot, which is the key to ensuring a good start in the forging stage.

[0051] During the forging process, the steel ingot is subjected to at least one upsetting and drawing (i.e., at least one upsetting and drawing) to obtain a forging. In some embodiments, the steel ingot is subjected to long-term heating and heat preservation treatments of different fire times during the upsetting and drawing stages of the steel ingot.

[0052] In the traditional forging process, one upsetting and drawing process is one heat, that is, the steel ingot is heated once and then upsetting and drawing process is performed once. In contrast, in order to ensure that the alloy in the martensitic heat-resistant stainless steel can fully diffuse atoms, the embodiment of the present invention separates the upsetting and drawing processes, shortens the distance of atomic migration by plastic deformation, accelerates atomic diffusion, makes the chemical composition of the high-alloy forging more uniform, and can significantly reduce the degree of alloy segregation.

[0053] In some embodiments, the heating temperature of each fire in the forging process can be set to 1150-1200°C; preferably, the heating temperature is 1180±10°C. The higher the heating temperature of each fire, the greater the atomic vibration energy, which is more conducive to the atomic diffusion inside the steel ingot, and the easier it is for the steel ingot to deform; however, when the heating temperature is too high, not only is the steel ingot prone to overheating and overburning, but the steel ingot is also prone to precipitating high-temperature ferrite in the high-temperature range. Usually, high-temperature ferrite is easily transformed into a brittle phase, which reduces the toughness of the material and causes brittle failure.

[0054] In some embodiments, the heating times of the steel ingot in the upsetting process are determined according to the upsetting times. Specifically, in the upsetting process, the upsetting times = the upsetting times, and the drawing times = the upsetting times, that is, the steel ingot needs to be heated for one upsetting time and one drawing time in each upsetting and drawing process.

[0055] In some embodiments, the holding time of each upsetting fire and / or drawing fire can be determined according to the ingot size of the steel ingot. When the ingot is large, the steel ingot needs to be heated and kept warm for a longer time to ensure that the core of the steel ingot is fully heated. In addition, the pressure during the forging process can also be considered when determining the holding time. When the ingot is large or the pressure required during the forging process is high, the steel ingot needs to be heated and kept warm for a longer time.

[0056] Among them, when the steel ingot is less than or equal to 70t, the holding time of the roughening fire is 35-40h. When the steel ingot is greater than 70t, the holding time of the roughening fire increases by 1-2h for every 1t increase in the ingot shape m on the basis of 70t, that is, the holding time is (35-40)+(1-2)×(m-70)h.

[0057] When the steel ingot is less than or equal to 70t, the holding time of the drawing fire is 20 to 30h; when the steel ingot is greater than 70t, the holding time of the drawing fire increases by 1 to 2h for every 1t increase in the ingot shape on the basis of 70t, that is, the holding time is (20 to 30) + (1 to 2) × (m-70)h.

[0058] The present invention is beneficial to improving the segregation problem of martensitic heat-resistant stainless steel by extending the holding time of upsetting and drawing fire during the forging process, reducing its cracking tendency during the forging process, ensuring that the forging process can proceed smoothly, and is of great significance for reducing the forging allowance and machining removal amount and reducing the forging cost.

[0059] In some embodiments, after the upsetting is completed and before the finished product is produced, the forging is heated and kept warm so as to facilitate shaping of the forging to obtain a finished product of the desired shape and size. The heating temperature is set to 1150-1180°C; preferably, the heating temperature is 1180±10°C. Furthermore, the holding time can be determined according to the forging process of the martensitic heat-resistant stainless steel forging.

[0060] If the finished product is produced after drawing, that is, the subsequent fire after drawing is the fire of drawing the finished product, the shaft deformation of the forging at this stage is small, there is no forging ratio or the forging ratio is small. In order to ensure that the flaw detection limit sensitivity of the forging after the finished product meets the standard requirements, short-term heating and heat preservation are carried out before the finished product is produced, instead of long-term heating and heat preservation, so as to prevent coarse grains caused by long-term heat preservation.

[0061] Among them, the holding time of short-time heating and heat preservation can be determined according to the ingot size or cross-sectional size of the forging. For example, according to the ingot type, when the ingot type is 18-24t, the holding time is 7 hours; when the ingot type is 25-32t, the holding time is 7.5 hours; when the ingot type is 33-40t, the holding time is 11 hours. According to the cross-section, when the cross-sectional size r of the forging is 1000≤r<1230mm, the holding time is 7 hours; when the cross-sectional size is 1230≤r<1400mm, the holding time is 7.5 hours; when the cross-sectional size is 1400≤r<1600mm, the holding time is 11 hours.

[0062] If there is a large deformation in the forging after drawing, that is, the subsequent fire after drawing is not the fire to produce the finished product, the forging needs to be subjected to overall upsetting deformation before the finished product. For example, for large-diameter variable-section forgings, after the upsetting is completed, drawing and upsetting are carried out in sequence. At this time, the forging ratio of the forging is relatively large, and the forging can be heated and heat-insulated for a certain period of time before the overall upsetting deformation. This insulation time should not be too long, and is generally longer than the insulation time of the drawing fire to produce the finished product. The deformation of the previous drawing fire greatly shortens the atomic migration distance in the martensitic heat-resistant stainless steel, and the insulation treatment at high temperature in this stage is combined to achieve the purpose of improving segregation defects.

[0063] Among them, the holding time of the upsetting fire can be set to be 5 to 10 hours longer than the holding time of the drawing fire. Specifically, when the steel ingot is less than or equal to 70 tons, the holding time of the forging is 30 to 35 hours; when the steel ingot is greater than 70 tons, the holding time of the forging is (30 to 35) + (1 to 2) × (m-70) hours.

[0064] It should be noted that the holding time of the upsetting fire is shorter than that of the previous upsetting fire. Since there is a drawing process with a large forging ratio after the upsetting fire, even if the long-term holding time of the upsetting fire causes coarse grains in the martensitic heat-resistant stainless steel, it can be refined through the subsequent drawing process; while there is no large deformation of the drawing process after the upsetting fire, the grains cannot be refined. If a long-term holding time is performed before the upsetting deformation, the grain directionality will be obvious during the upsetting, and there is a risk of failure in the flaw detection. Therefore, the present invention adopts a shorter holding time in the upsetting fire than the upsetting fire to ensure that the forging can be upset and deformed.

[0065] In addition, in some embodiments, for non-center compaction fires other than the finished product fire, for example, the jaw pressing process of the first fire and the unloading process before the finished product fire, the process insulation time can also be extended. Although the core of the forging has little or no deformation in the above processes, the effect of improving segregation is poor compared to the large deformation of the compaction process (upsetting, drawing, etc.), it can also improve the dendrite segregation problem to a certain extent.

[0066] The holding time can be 5 to 10 hours, and the specific time can be controlled according to the cross-sectional size of the forging or the size of the ingot. For example, the forging process of the forging is jaw pressing, one or two upsettings, drawing and blanking, and upsetting the finished product. For the jaw pressing fire and / or drawing and blanking fire, the holding time can be set to 5 to 10 hours.

[0067] The present invention can improve dendrite segregation, reduce forging segregation defects and forging cracking tendency by performing homogenization heating and heat preservation treatment on the steel ingot before forging and extending the heat preservation time of other fires except the finished product fire, thereby ensuring the uniformity of forging performance. It should be noted that the heating and heat preservation method of the present invention is applicable to any martensitic heat-resistant stainless steel forging to improve its dendrite segregation defect and reduce the tendency of forging cracking caused by segregation defects.

[0068] The heating and heat preservation method of the martensitic heat-resistant stainless steel forging of the present invention is further described below with reference to specific embodiments.

[0069] Example 1

[0070] For a batch of gas turbine forgings, the steel ingot used is a 20t ingot, and its material composition, by mass percentage, includes: 0.15% C, ≤0.12% Si, 0.4% Mn, ≤0.01% P, ≤0.005% S, 10.6% Cr, 0.7% Ni, 0.9% Mo, 0.25% V, ≤0.01% Al, ≤1.0% W, 0.06% Nb, 0.03% N, and the rest is Fe.

[0071] (1) The steel ingot is subjected to a heating treatment before forging.

[0072] First, measure the surface temperature of the steel ingot (i.e. the ingot temperature) and perform preheating according to the ingot temperature. Figure 1 As shown, the preheating treatment temperature is 650±10℃; when the ingot temperature is greater than 600℃, no preheating treatment is performed; when the ingot temperature is 550<T≤600℃, preheat at 650±10℃ for 10h; when the ingot temperature is 500<T≤550℃, preheat at 650±10℃ for 15h; when the ingot temperature is 450<T≤500℃, preheat at 650±10℃ for 20h.

[0073] After the preheating treatment is completed, the steel ingot is subjected to homogenization heating and heat preservation treatment. Figure 1 As shown, after the preheating and insulation is completed, the heating temperature is increased to the uniform heating temperature of 1180±10℃ and kept warm for 50h.

[0074] (2) Forging the steel ingot.

[0075] The steel ingot is subjected to two upsetting and drawing processes in the compaction process. Specifically, the forging process is: jaw pressing, upsetting, KD drawing, upsetting, KD drawing, and drawing out the finished product.

[0076] Among them, in the jaw pressing process, the heating temperature is 1180±10℃, and the holding time is 5h; in the two upsetting processes, the heating temperature is 1180±10℃, and the holding time is 35h; in the two KD drawing processes, the heating temperature is 1180±10℃, and the holding time is 20h; in the drawing process to produce finished products, the heating temperature is 1180±10℃, and the holding time is 7h.

[0077] like Figure 2 and Figure 3 As shown in the figure, there was no serious cracking problem in the forgings during the forging process, and the entire forging process was relatively smooth.

[0078] The local structure of forgings is as follows Figure 4 As shown in the figure, there is no obvious segregation zone in the forging grain structure, and the grain structure is well uniform. In addition, at the forging temperature of 1180℃, the harmful phase in the martensitic stainless steel can be fully dissolved back, such as Figure 5 As shown, the tendency of forgings to crack is reduced.

[0079] The yield strength and impact toughness of different positions of the forgings were analyzed, and the results of the performance analysis are shown in Table 1. According to Table 1, the yield strength and impact toughness of different positions of the forgings are slightly different, the yield strength Rp0.2 is 812-825Mpa, and the impact toughness Kv2 is 36-45J, indicating that the performance of the forgings has good uniformity.

[0080] Table 1 Analysis results of yield strength and impact toughness at different positions of forgings in Example 1

[0081] Serial number Sampling location Strength Rp0.2 / MPa Impact Kv2 / J 1 Roulette wheel outer edge - 0° 823 37 2 Roulette outer edge - 90° 816 42 3 Roulette wheel outer edge - 180° 813 43 4 Roulette outer edge - 270° 825 36 5 Wheel end face 2 / 3R-0° 819 40 6 Wheel end face 2 / 3R-90° 814 43 7 Wheel end face 2 / 3R-180° 812 45 8 Wheel end face 2 / 3R-270° 823 38

[0082] Comparative Example 1

[0083] This comparative example adopts the traditional forging process, and the difference from Example 1 is that: this comparative example does not perform preheating treatment and homogenization heating and heat preservation treatment on the steel ingot; during the forging process, the upsetting and drawing fires are not separated in the upsetting and drawing stage, and the heat preservation time is short.

[0084] Specifically, the forging process of the forging is: pressing the jaws, upsetting-KD drawing, upsetting-KD drawing, and drawing the finished product. In the upsetting-KD drawing process, after one heating, upsetting and KD drawing are performed once, the heating temperature is 1180±10℃, and the holding time is 10h.

[0085] The microstructure of the forging in this comparative example is as follows Figure 6 As shown, obvious segregation bands can be seen and the grain structure is uneven.

[0086] 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 method for heating and heat preservation of martensitic heat-resistant stainless steel forgings, characterized in that: include: According to the ingot passing temperature of the martensitic heat-resistant stainless steel ingot, judging whether the ingot needs to be preheated; When the steel ingot needs to be preheated, the steel ingot is heated and kept warm at a low temperature; Performing homogenizing heating and heat preservation treatment on the steel ingot; The steel ingot is forged and subjected to an upsetting process to obtain a forging; wherein, during the upsetting process of the steel ingot, the steel ingot is subjected to a long-term heat preservation treatment.

2. The method according to claim 1, characterized in that The heating temperature of the homogenization heating and heat-insulating treatment is set to 1150-1200° C., and the heat-insulating time is determined according to the ingot size of the steel ingot.

3. The method according to claim 2, characterized in that When the steel ingot is less than 83t, the holding time of the steel ingot during homogenization heating and holding treatment is greater than or equal to 50h; When the weight of the steel ingot is greater than or equal to 83t, the insulation time of the steel ingot during homogenization heating and insulation treatment is greater than or equal to 60h.

4. The method according to claim 1, characterized in that When the ingot temperature is greater than 600°C, the preheating treatment is not required; When the ingot temperature is less than or equal to 600° C., the ingot is subjected to the preheating treatment, the preheating temperature is 650-700° C., and the holding time is determined according to the ingot temperature.

5. The method according to claim 4, characterized in that When the ingot temperature is 550<T≤600℃, the preheating time is 10≤t<15h. On this basis, the preheating time increases by 5 to 10h for every 50℃ decrease in the ingot temperature.

6. The method according to claim 1, characterized in that In the upsetting and drawing process, the steel ingot is subjected to at least one upsetting and drawing to obtain the forging; wherein, in the upsetting and drawing stages of the steel ingot, the steel ingot is subjected to long-term heating and heat preservation treatment of different temperatures.

7. The method according to claim 6, characterized in that In each upsetting and drawing process, the steel ingot is heated through an upsetting fire and a drawing fire; The holding time of the upsetting fire and the drawing fire is determined according to the ingot size of the steel ingot.

8. The method according to claim 7, characterized in that When the ingot is less than or equal to 70t, the holding time of the upsetting fire is 35 to 40h; When the steel ingot is larger than 70 tons, the holding time of the upsetting fire is increased by 1 to 2 hours for every 1 ton increase in the ingot shape based on 70 tons.

9. The method according to claim 7, characterized in that: When the steel ingot is less than or equal to 70t, the holding time of the drawing fire is 20 to 30h; When the steel ingot is larger than 70t, the holding time of the drawing fire increases by 1 to 2h for every 1t increase in the ingot shape based on 70t.

10. The method according to claim 1, characterized in that After the upsetting and drawing, if the forging is subjected to overall upsetting deformation to produce a finished product, the forging is heated and heat-insulated before the overall upsetting deformation, the heating temperature is set to 1150-1180° C., and the insulation time is set to be 5-10 hours longer than the insulation time of the drawing and drawing process.

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