Martensitic heat-resistant steel forging and forging method thereof

Abstract

The invention discloses a martensitic heat-resistant steel forging and a forging method thereof, and belongs to the technical field of forging manufacturing. The martensitic heat-resistant steel forging of the invention uses a steel ingot obtained by smelting molten steel as a raw material, and the molten steel includes the following components by weight percentage: C0.13-0.17%, Si<0.50%, Mn<0.50%, P<0.030%, S<0.015%, Cr11.00-12.00%, Ni1.80-2.10%, Mo1.10-1.65%, V0.20-0.30%, Nb0.20-0.30%, W0.70-1.00%, N0.02-0.08%, and the balance is Fe and unavoidable impurities. The invention solves the mixed crystal phenomenon caused by grain inheritance in existing martensitic heat-resistant steel forgings by improving the raw material ratio and forging process. The prepared forgings have fine grains and excellent structural uniformity, ensuring high strength while avoiding cracking of the forgings.

Description

Technical Field

[0001] The invention relates to the technical field of forging manufacturing, and in particular to a martensitic heat-resistant steel forging and a forging method thereof. Background Art

[0002] 1Cr12Ni2WMoVNbN forgings are mainly used in the fields of gas turbines and aircraft engines, and are widely used in power turbine outer casings, gas turbine support rings, covers, etc. The material has good thermal strength and good comprehensive mechanical properties at high temperatures. It is suitable for working in high temperature environments below 650°C and is often used in key equipment structures and components of aircraft engines and gas turbines. In recent years, my country has made great progress in the field of aviation, which is inseparable from the research and development of basic materials. With the development of the aviation industry, higher requirements have been placed on materials. 1Cr12Ni2WMoVNbN is a modified version of Cr13. It is a new type of steel in my country and requires in-depth research, especially forgings made of this material in terms of high strength and toughness, uniform structure, and fine grain size.

[0003] 1Cr12Ni2WMoVNbN belongs to martensitic heat-resistant steel, commonly known as GX-8 in the industry. High Cr increases the strength of the material, Ni increases the hardenability of the material, Mo and W increase the solid solution strengthening effect of the material, and the carbides formed by V and C increase the precipitation strengthening effect of the material. Due to the high content of alloy components in this material, it is very difficult to smelt, which is manifested in the frequent presence of central cracks in the ingot, resulting in frequent cracking of the billet head during subsequent forging and blanking. However, the acceptance values ​​of grain size, strength and impact value for aviation forgings are relatively high. Therefore, sufficient "casting to forging" breaks the as-cast structure, and at the same time, the blanking temperature and the amount of deformation are controlled to achieve matrix grain refinement, which increases the difficulty of actual production. On the other hand, due to the types of alloy elements in this material, the material has grain heredity, which requires post-forging heat treatment to eliminate grain heredity and refine the grains, so as to prepare the organization for subsequent performance heat treatment. In addition, due to the high hardenability of the material, the cooling rate, liquid outlet temperature, and matrix temperature of the forgings before tempering should be controlled during the subsequent heat treatment. Too fast quenching cooling rate and low liquid outlet temperature during quenching can easily cause the forgings to crack during quenching. Too slow quenching cooling rate and too high liquid outlet temperature will reduce the impact value of the forgings, resulting in failure to meet the acceptance value of the forgings; the matrix temperature of the forgings before tempering is too high, the structure has not been completely transformed, and there will be more residual austenite. The matrix temperature of the forgings before tempering is too low. Due to the complex structure of the forgings, it is easy to crack under the dual effects of thermal stress and organizational stress, resulting in product failure. In addition, due to the high content and variety of alloy elements in the material, the material has temper brittleness. Therefore, under the premise of ensuring strength, in order to meet the high impact value of the forgings, it is necessary to avoid tempering in the temper brittleness range of the material. Therefore, when manufacturing high-performance 1Cr12Ni2WMoVNbN forgings for aviation, in engineering applications, it is necessary to comprehensively combine the material properties to formulate a matching hot working process.

[0004] 1Cr12Ni2WMoVNbN generally adopts the "electric furnace + electroslag remelting" smelting process, and also adopts the "vacuum induction + electroslag remelting" smelting process. 1Cr12Ni2WMoVNbN raw materials are medium-to-high-end materials among general materials, and the added value of forgings produced by them is relatively high, but the production cost of such forgings is high, difficult, and the cycle is long. At present, the research on 1Cr12Ni2WMoVNbN materials basically includes the influence of composition, performance, and heat treatment on the organization and performance of forgings. Most of the data are from the mechanism analysis of small laboratory specimens. In engineering applications, aviation forgings have many practical problems in the control of forging and heat treatment due to their complex structure, large product specifications, and heavy forgings, such as the control of the original grain size of the forgings, the heat treatment transportation time, and the uneven temperature of the billet caused by large equipment. 1Cr12Ni2WMoVNbN forgings for aviation not only require high strength and toughness, but also have high requirements for grain size. In actual acceptance, coarse grains or uneven grains often lead to product scrapping, causing great losses.

[0005] Therefore, how to prepare 1Cr12Ni2WMoVNbN forgings with high strength, high toughness, uniform structure and fine grain size and avoid internal cracking of the forgings is an urgent problem to be solved in this field. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a martensitic heat-resistant steel forging and a forging method thereof. The present invention solves the mixed crystal phenomenon caused by grain inheritance in the existing martensitic heat-resistant steel forgings by improving the raw material ratio and forging process. The prepared forgings have fine grains and excellent structural uniformity, ensuring high strength while avoiding cracking of the forgings.

[0007] The technical solution of the present invention is as follows:

[0008] The first aspect of the present invention provides a martensitic heat-resistant steel forging, which is made of a steel ingot obtained by smelting molten steel. The molten steel comprises the following components by weight percentage: C 0.13-0.17%, Si < 0.50%, Mn < 0.50%, P < 0.030%, S < 0.015%, Cr 11.00-12.00%, Ni 1.80-2.10%, Mo 1.10-1.65%, V 0.20-0.30%, Nb 0.20-0.30%, W 0.70-1.00%, N 0.02-0.08%, and the remainder is Fe and unavoidable impurities.

[0009] A second aspect of the present invention provides a method for preparing the martensitic heat-resistant steel forging according to the first aspect, the method comprising the following steps:

[0010] S1: smelting and forging the above raw materials to obtain ingots;

[0011] S2: heating the ingot, forging and blanking to obtain the blank;

[0012] S3: Put the billet into the furnace for cooling along with the furnace, and then carry out normalizing, waiting and fine grain heat treatment;

[0013] S4: The blank processed in step S3 is subjected to rough turning and flaw detection, and then subjected to performance heat treatment, and cooled to obtain a martensitic heat-resistant steel forging.

[0014] Preferably, in step S2, the ingot heating includes two-stage step heating and / or three-stage step heating;

[0015] When the weight of the ingot is ≤4T, and / or the cross-sectional size of the ingot is ≤650mm, two-stage step heating is adopted;

[0016] When the weight of the ingot is greater than 4T, and / or the cross-sectional size of the ingot is greater than 650mm, three-stage step heating is adopted;

[0017] Preferably, the two-stage step heating method is: the temperature of the first forging step is 600-700°C, and the insulation time is 2-4h; the temperature of the second step is 800-900°C, and the insulation time is ≥0.3min / mm multiplied by the effective thickness of the ingot, and the unit of the effective thickness of the ingot is mm;

[0018] Preferably, the three-stage step heating method is: the temperature of the first forging step is 650°C, and the insulation time is 2-4h; the temperature of the second step is 850°C, and the insulation time is 0.3min / mm×the effective thickness of the ingot; the temperature of the third step is 1150-1180°C, and the insulation time is 0.4-0.5min / mm multiplied by the effective thickness of the ingot; wherein the unit of the effective thickness of the ingot is mm.

[0019] Preferably, in step S2, the forging process comprises: heating the ingot, taking it out of the furnace, and removing the chill layer on the surface of the ingot; and then performing two upsetting and two drawing to obtain a forged billet;

[0020] The deformation of each upsetting of the two upsetting and two drawing is ≥40%, the deformation of each drawing is ≥40%, and the total forging ratio is ≥7;

[0021] The initial forging temperature of the forging blank is Final forging temperature ≥850℃.

[0022] Preferably, in step S2, when the blank is a ring forging, the forging process further includes punching, and / or horse frame reaming, and / or ring rolling;

[0023] Among them, when the wall thickness ratio before and after ring rolling is less than 2, punching is performed after forging, and the blank is formed by ring rolling; when the wall thickness ratio before and after ring rolling is ≥2, punching and horse frame expansion are performed after forging, and finally the blank is formed by ring rolling;

[0024] In step S2, when the blank is a shaft forging and / or a disc forging, the blank is directly obtained after upsetting and drawing of the forging blank, and the deformation amount of the last fire is ≥25%.

[0025] Preferably, in step S3, the furnace cooling is to place the blank in a heat treatment furnace or a forging furnace for furnace cooling;

[0026] And / or, the furnace temperature during furnace cooling is ≤850°C; and / or, before normalizing, the surface temperature of the billet is 400-500°C.

[0027] Preferably, in step S3, the normalizing process comprises: heating the blank to 1130±10°C at a rate of ≤120°C / h, keeping the temperature, and air cooling after leaving the furnace;

[0028] Preferably, the holding time is ≥90 min+effective heat treatment thickness of the forging blank multiplied by 0.7-1.2 min / mm, wherein the unit of the effective heat treatment thickness of the forging blank is mm;

[0029] Preferably, the air cooling after leaving the furnace refers to air cooling until the surface temperature of the blank is 150±50°C;

[0030] The waiting time is 2-3 hours.

[0031] Preferably, in step S3, the specific process of the fine grain heat treatment includes: heating to a temperature of ≤130°C / h First insulation: Turn off the power and cool the furnace until the surface temperature of the forging blank is Carry out the second heat preservation; after the power is turned off and the furnace is cooled again, it is taken out of the furnace and air-cooled to room temperature;

[0032] Preferably, the first heat preservation time is the effective heat treatment thickness of the blank multiplied by (1.5-3) min / mm;

[0033] Preferably, the second heat preservation time is the effective heat treatment thickness of the blank multiplied by (2.0-3) min / mm;

[0034] Preferably, when the effective heat treatment thickness of the forging blank is ≥500mm, the second power-off furnace cooling refers to furnace cooling until the surface temperature of the blank is ≤200°C; when the effective heat treatment thickness of the forging blank is <500mm, the second power-off furnace cooling refers to furnace cooling until the surface temperature of the blank is ≤400°C.

[0035] Before the fine grain heat treatment, the temperature of the heat treatment furnace is ≤200°C.

[0036] Preferably, in step S4, the performance heat treatment includes quenching, annealing, and tempering.

[0037] Preferably, the quenching process is to heat up to 1120±10°C at a rate of ≤90°C / h, keep warm for (0.7-1.2min)*effective heat treatment thickness of forging blank+90min, and cool out of the furnace;

[0038] Preferably, the process of cooling after being taken out of the furnace comprises: firstly, cooling the forging blank by repeated alternation of liquid cooling and air cooling until the surface temperature of the forging blank is 200-250°C, and then cooling the forging blank by air until the surface temperature of the forging blank is 100-150°C;

[0039] The time for waiting for material is 1-2h;

[0040] The tempering process includes: heating to 680±10°C at a speed of ≤80°C / h, keeping warm for (1.2-1.5)*effective thickness of forging blank+120min, then water cooling to 300-350°C, and air cooling to room temperature after being taken out of the furnace.

[0041] The beneficial technical effects of the present invention are:

[0042] The present invention improves the raw material ratio, forging process and heat treatment process, avoids tempering in the temper brittleness range of the material, solves the mixed crystal problem (grain size difference exceeds 3 levels) caused by grain inheritance of existing martensitic heat-resistant steel forgings, and prepares forgings with fine grains and excellent structural uniformity, ensuring high strength and high impact energy while avoiding forging cracking.

[0043] The present invention further refines the grains and eliminates grain heredity by optimizing process parameters such as fine grain heat treatment parameters and performance heat treatment parameters, thereby improving the strength of forgings while avoiding quenching cracks caused by too fast quenching cooling rate, improving the first-time qualified rate of products, avoiding energy waste caused by rework, shortening the production cycle, and reducing manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the process flow of the present invention.

[0045] Figure 2 This is a normal annealing process diagram.

[0046] Figure 3 This is a diagram of fine grain heat treatment in some embodiments of the present invention.

[0047] Figure 4 This is a performance heat treatment diagram for some embodiments of the present invention.

[0048] Figure 5 This is a diagram of stress relief annealing in some embodiments of the present invention.

[0049] Figure 6 The metallographic structure diagrams of the forgings of the embodiments of the present invention and the comparative examples are shown in FIG.

[0050] In the figure: a, metallographic structure diagram of the forging of Example 3 at a magnification of 100 times; b, metallographic structure diagram of the forging of Example 3 at a magnification of 200 times; c, metallographic structure diagram of the forging of Comparative Example 2 at a magnification of 100 times; d, metallographic structure diagram of the forging of Comparative Example 2 at a magnification of 200 times. DETAILED DESCRIPTION

[0051] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0052] The first aspect of the present invention provides a martensitic heat-resistant steel forging, which is made of a steel ingot obtained by smelting molten steel. The molten steel comprises the following components by weight percentage: C 0.13-0.17%, Si < 0.50%, Mn < 0.50%, P < 0.030%, S < 0.015%, Cr 11.00-12.00%, Ni 1.80-2.10%, Mo 1.10-1.65%, V 0.20-0.30%, Nb 0.20-0.30%, W 0.70-1.00%, N 0.02-0.08%, and the remainder is Fe and unavoidable impurities.

[0053] A second aspect of the present invention provides a method for preparing the martensitic heat-resistant steel forging according to the first aspect, the method comprising the following steps:

[0054] S1: Smelting and forging the above raw materials to obtain ingots.

[0055] S2: The ingot is heated and forged to obtain a billet.

[0056] S3: The billet is put into the furnace for cooling along with the furnace, and then normalizing, waiting and fine grain heat treatment are carried out.

[0057] S4: The blank processed in step S3 is subjected to rough turning and flaw detection, and then subjected to performance heat treatment, and cooled to obtain a martensitic heat-resistant steel forging.

[0058] In some embodiments, in step S2, the ingot heating includes two-stage step heating and / or three-stage step heating.

[0059] When the weight of the ingot is ≤4T, and / or the cross-sectional size of the ingot is ≤650mm, two-stage step heating is adopted.

[0060] When the weight of the ingot is greater than 4T and / or the cross-sectional size of the ingot is greater than 650mm, three-stage step heating is adopted.

[0061] The interface size refers to the cross-sectional area, that is, the size of the largest inscribed circle of the ingot cross-sectional size.

[0062] In some embodiments, the two-stage step heating method is: the first forging step temperature is 600-700°C, and the insulation time is 2-4h; the second step temperature is 800-900°C, and the insulation time is ≥0.3min / mm multiplied by the effective thickness of the ingot, and the unit of the effective thickness of the ingot is mm.

[0063] In some embodiments, the three-step step heating method is: the temperature of the first forging step is 650°C, and the insulation time is 2-4h; the temperature of the second step is 850°C, and the insulation time is 0.3min / mm×the effective thickness of the ingot; the temperature of the third step is 1150-1180°C, and the insulation time is 0.4-0.5min / mm multiplied by the effective thickness of the ingot; wherein the unit of the effective thickness of the ingot is mm.

[0064] In some embodiments, in step S2, the forging process includes: heating the ingot, taking it out of the furnace, removing the chilled layer on the surface of the ingot; and then performing two upsetting and two drawing to obtain a forged billet.

[0065] In some embodiments of the present invention, in step S2, after the billet forging heating is completed, it needs to be forged on a press. Since its surface temperature is lower than the set temperature, it needs to be returned to the furnace while hot. When returning to the furnace while hot, the insulation time is reduced to half of the temperature of the last step, which helps to avoid the occurrence of cracks in the billet.

[0066] In some embodiments, the method for removing the chill layer on the surface of the ingot includes: after the ingot is taken out of the furnace, the blank is first lightly pressed around the outer circle, and the pressing amount is controlled to be 50-80mm to break the chill layer on the surface of the ingot.

[0067] It is understandable that the plasticity of the chilled layer is very poor. If it is directly upset, it is easy to form small cracks on the outer circle of the blank. As the upsetting deformation increases, the cracks extend.

[0068] It can be understood that the two upsetting and two drawing operations refer to at least two upsetting operations and two drawing operations during blank making.

[0069] In some embodiments, the deformation of each upsetting of the two upsetting and two drawing is ≥40%, the deformation of each drawing is ≥40%, and the total forging ratio is ≥7; the initial forging temperature of the forging blank is Final forging temperature ≥850℃.

[0070] It is understood that the calculation method of the deformation amount is (ab) / a, where a is the cross-sectional area after upsetting or before drawing; b is the cross-sectional area before upsetting or after drawing. The total forging ratio refers to the sum of the forging ratios of each process, and the sum of the upsetting ratio and the drawing ratio of each time.

[0071] In some embodiments, in step S2, when the blank is a ring forging, the forging process further includes punching, and / or reaming, and / or ring rolling; wherein, when the wall thickness ratio before and after ring rolling is less than 2, punching is performed after forging, and the blank is formed by ring rolling; when the wall thickness ratio before and after ring rolling is ≥2, punching and reaming are performed after forging, and finally ring rolling is performed to obtain the blank.

[0072] In some embodiments, in step S2, when the blank is a shaft forging and / or a disc forging, the blank is directly obtained after upsetting during forging, and the deformation amount of the last tempering is ≥25%.

[0073] It can be understood that the deformation amount of the last fire = (cross-sectional area before deformation - cross-sectional area after deformation) / cross-sectional area before deformation * 100%, A = (S0-S1) / S0*100%.

[0074] In some embodiments of the present invention, in step S2, before the forging blank is formed by the last fire, the forging holding temperature needs to be reduced to

[0075] In some embodiments, in step S3, the furnace cooling is to place the billet in a heat treatment furnace or a forging furnace for furnace cooling. And / or, the furnace temperature of the furnace cooling is ≤850°C; and / or, before the normalizing, the surface temperature of the billet is 400-500°C.

[0076] In some embodiments, in step S3, the normalizing process includes: heating the blank to 1130±10°C at a rate of ≤120°C / h, keeping the temperature, and air cooling after exiting the furnace;

[0077] In some embodiments, the holding time is ≥ 90 min + the effective heat treatment thickness of the forging blank multiplied by 0.7-1.2 min / mm, wherein the unit of the effective heat treatment thickness of the forging blank is mm;

[0078] In some embodiments, the air cooling after leaving the furnace refers to air cooling until the surface temperature of the blank is 150±50° C. The waiting time is 2-3 hours.

[0079] In some embodiments, in step S3, the specific process of the fine grain heat treatment includes: heating at a rate of ≤130°C / h to First insulation: Turn off the power and cool the furnace until the surface temperature of the forging blank is Carry out the second heat preservation; after cutting off the power and cooling the furnace again, take it out of the furnace and air cool it to room temperature.

[0080] It can be understood that the normalizing treatment of the present invention is combined with the grain refining heat treatment. Normalizing is used to make the metal austenitized and the resulting structure after air cooling to be martensite due to its high alloy component content, so as to adjust the structure and make the carbide distribution more uniform and refine the grains at the same time. The grain refining process is then used to eliminate the heredity of the forging's structure grains, solve the problem of mixed crystals, and prepare the structure in advance for the fine grain size of subsequent quenching and tempering.

[0081] In some embodiments, the first holding time is the effective heat treatment thickness of the blank multiplied by (1.5-3) min / mm.

[0082] In some embodiments, the second holding time is the effective heat treatment thickness of the blank multiplied by (2.0-3) min / mm, preferably (2.5-3) min / mm.

[0083] It is understandable that the above-mentioned forging method can break up the cast structure and turn it into a forged structure. In free forging, due to the large size of the billet, the deformation amount of each part of the billet is different, and the original grain size will be different, that is, the original grains at different positions of the forging billet are coarse and fine. Since the material has grain inheritance, after forging, if a normal annealing, normalizing or tempering process is used for performance heat treatment, and normal annealing, normalizing and quenching cannot eliminate grain inheritance, the final grain size of the product depends to a great extent on the grain size of the billet when the billet is opened. The risk of doing so is very high, so a fine grain heat treatment method needs to be adopted in the post-forging treatment. The fine grain heat treatment of the present invention is carried out by heating the forging to a temperature higher than A. c3 The line is kept at 30℃-50℃ to fully dissolve the cementite, and then cooled to A c1 Keeping the temperature below the line at 30℃-50℃ makes the carbides in the metal aggregate and grow into granular pearlite, blocking the aggregation and growth of the grains in the metal structure from austenite to martensite during subsequent quenching, and preventing the grains from growing on the habitual surface. This ensures the stability and reliability of product quality to a great extent, and can also eliminate the risk of uneven grain size caused by blanking.

[0084] It can be understood that the present invention controls the first heating rate of fine grain heat treatment to ≤120℃ / h. Due to the high alloy content of the material, if the heating rate is too fast, it will lead to a large temperature difference between the surface and the core of the forging, and there will be large thermal stress during the heating process, and there is a risk of cracking during the heating process; by controlling the holding time of each stage, if the holding time is too long, the grain size will grow, and if the holding time is too short, the cementite is not completely dissolved in the austenite structure, the organizational transformation is insufficient, and the effect of completely eliminating organizational inheritance cannot be achieved.

[0085] In some embodiments, when the effective heat treatment thickness of the forging blank is ≥500mm, the second power-off furnace cooling refers to furnace cooling until the surface temperature of the blank is ≤200°C; when the effective heat treatment thickness of the forging blank is <500mm, the second power-off furnace cooling refers to furnace cooling until the surface temperature of the blank is ≤400°C.

[0086] In some embodiments, before the grain refinement heat treatment, the temperature of the heat treatment furnace is ≤200°C.

[0087] In some embodiments, in step S4, the performance heat treatment includes quenching, annealing, and tempering.

[0088] It can be understood that the performance heat treatment of the present invention will improve the impact performance of the forgings. In particular, by controlling the method of cooling after quenching and heat preservation during the performance heat treatment, the risk of quenching cracking is reduced. By controlling the tempering temperature and the cooling method after the furnace, the tempering brittleness range is avoided, thereby ensuring the high impact value of the forgings.

[0089] In some embodiments, the quenching process is to heat up to 1120±10°C at a rate of ≤90°C / h, keep warm for (0.7-1.2min)*effective heat treatment thickness of forging blank+90min, and cool out of the furnace;

[0090] In some embodiments, the furnace cooling process includes: firstly, liquid cooling and air cooling are repeatedly alternately cooled to a surface temperature of the forging blank of 200-250°C, and then air cooling is performed to a surface temperature of the forging blank of 100-150°C; the waiting time is 1-2h;

[0091] In some embodiments, the tempering process includes: heating to 680±10°C at a rate of ≤80°C / h, keeping warm for (1.2-1.5)*effective thickness of forging blank+120min, then water cooling to 300-350°C, and air cooling to room temperature after being taken out of the furnace.

[0092] In some embodiments, the liquid cooling-air cooling repeated alternating cooling method is: first liquid cooling (3-4) min, then air cooling (1-1.5) min, then liquid cooling (3-4) min again, air cooling (1.5-2) min, and repeating liquid cooling and air cooling until the surface temperature is 200-250°C.

[0093] In some embodiments of the present invention, the performance heat treatment may further include a stress relief annealing process.

[0094] In some embodiments of the present invention, the stress relief annealing process is: heating to 300±10°C at a rate of ≤120°C / h, keeping the temperature for 8-12h, and then air cooling.

[0095] The present invention will be further described below by way of examples.

[0096] Example 1

[0097] The raw materials of ring forging 1Cr12Ni2WMoVNbN include the following components by mass percentage: 0.14% C, 0.31% Si, 0.41% Mn, 0.018% P, 0.0015% S, 11.3% Cr, 2.04% Ni, 1.46% Mo, 0.25% V, 0.25% Nb, 0.76% W, 0.049% N, and the balance is Fe and indispensable impurities.

[0098] The preparation method of ring forging 1Cr12Ni2WMoVNbN is as follows:

[0099] (1) Smelting the above raw materials to obtain an ingot weighing 9.6 tons;

[0100] (2) Ingot forging heating, forging blanking, punching, horse frame hole expansion, and ring rolling (the wall thickness ratio before and after ring rolling is 3) to obtain the blank.

[0101] Among them, the ingot forging heating is carried out in a three-stage step heating process, first heated to 650℃, kept warm for 3h, then heated to 850℃, kept warm again for 920mm*0.3min / min, then heated to 1180℃, kept warm for 920mm*0.4min / min to complete the ingot heating.

[0102] The specific process of forging billet is as follows: after the ingot is heated, it is taken out of the furnace, the chilled layer on the surface of the ingot is removed, and then the billet is obtained by two upsetting and two drawing, and the deformation of each upsetting is 40%; the deformation of each drawing is 40%, the total forging ratio is 8.5, and the deformation of the last fire is 31%. The initial forging temperature of the forging billet is 1180℃, and the final forging temperature is 850℃.

[0103] (3) Place the billet in a heat treatment furnace at 850°C and cool it down until the surface temperature of the billet reaches 400°C. Then, perform normalizing, waiting, and grain refinement heat treatment.

[0104] Among them, the process of normalizing, waiting and fine grain heat treatment is: heating the billet to 1130℃ at a rate of 80℃ / h, holding time is 90min+effective heat treatment thickness of forging billet 183mm multiplied by 0.7min / mm, air cooling to the billet surface temperature of 150℃ to complete normalizing treatment, and then the waiting time is 2h, after that, the temperature of the heat treatment furnace is ensured to be ≤200℃, heating to 870℃ at a rate of 80℃ / h, holding for the first time, and the holding time is 183mm multiplied by 1.5min / mm of the effective heat treatment thickness of the billet; turning off the power to cool the furnace to 700℃, holding for the second time, and the holding time is 183mm multiplied by 2.5min / mm of the effective heat treatment thickness of the billet; turning off the power to cool the furnace to 400℃ again, air cooling to room temperature after taking out of the furnace to complete fine grain heat treatment.

[0105] (4) The blank treated in step (3) is subjected to rough turning and flaw detection, and then subjected to performance heat treatment, and cooled to obtain a martensitic heat-resistant steel forging. The performance heat treatment includes quenching, waiting, and tempering treatment, specifically, heating to 1120±10°C at a rate of ≤80°C / h, keeping the temperature for 300 minutes, then cooling to 200°C by intermittent liquid cooling, then air cooling to 120°C, completing the quenching treatment, and then waiting for 2 hours, and finally heating to 680±10°C at a rate of 55°C / h, keeping the temperature for 360 minutes, then water cooling to 300°C, and air cooling to room temperature after being taken out of the furnace.

[0106] Example 2

[0107] The raw materials of ring forging 1Cr12Ni2WMoVNbN include the following components by mass percentage: 0.17% C, 0.35% Si, 0.38% Mn, 0.020% P, 0.0015% S, 11.35% Cr, 1.75% Ni, 1.36% Mo, 0.22% V, 0.26% Nb, 0.75% W, 0.052% N, and the balance is Fe and indispensable impurities.

[0108] The preparation method of the ring forging 1Cr12Ni2WMoVNbN is the same as that in Example 1.

[0109] Example 3

[0110] The raw materials and proportions of the ring forging 1Cr12Ni2WMoVNbN are the same as those in Example 1.

[0111] The preparation method of the ring forging 1Cr12Ni2WMoVNbN is basically the same as that of Example 1, except that the heating rate of the fine grain heat treatment in step (3) is changed. In this embodiment, the heating rate of the fine grain heat treatment in step (3) is 130°C / h. The metallographic structure diagram of the obtained forging is shown in FIG. Figure 6As shown in Figures a and b.

[0112] Example 4

[0113] The raw materials and proportions of the ring forging 1Cr12Ni2WMoVNbN are the same as those in Example 1.

[0114] The preparation method of the ring forging 1Cr12Ni2WMoVNbN is basically the same as that of Example 1, except that the first holding time of the fine grain heat treatment in step (3) is changed. In this embodiment, the first holding time of the fine grain heat treatment in step (3) is 1 min / mm multiplied by the thickness of the billet 183 mm.

[0115] Example 5

[0116] The raw materials and proportions of the ring forging 1Cr12Ni2WMoVNbN are the same as those in Example 1.

[0117] The preparation method of the ring forging 1Cr12Ni2WMoVNbN is basically the same as that of Example 1, except that the first holding time of the fine grain heat treatment in step (3) is changed. In this embodiment, the first holding time of the fine grain heat treatment in step (3) is 3 min / mm multiplied by the thickness of the billet 183 mm.

[0118] Example 6

[0119] The raw materials and proportions of the ring forging 1Cr12Ni2WMoVNbN are the same as those in Example 1.

[0120] The preparation method of the ring forging 1Cr12Ni2WMoVNbN is basically the same as that of Example 1, except that the heating rate of quenching in the performance heat treatment in step (4) is changed. In this embodiment, the heating rate of quenching is 90°C / h.

[0121] Example 7

[0122] The raw materials and proportions of the ring forging 1Cr12Ni2WMoVNbN are the same as those in Example 1.

[0123] The preparation method of the ring forging 1Cr12Ni2WMoVNbN is basically the same as that of Example 1, except that after the performance heat treatment in step (4), a stress relief annealing process is also included, that is, the temperature is raised to 300°C at a rate of 120°C / h, kept at this temperature for 10h, and then taken out of the furnace and air-cooled to obtain a martensitic heat-resistant steel forging.

[0124] Example 8

[0125] The raw materials and proportions of the shaft forgings 1Cr12Ni2WMoVNbN are the same as those in Example 1.

[0126] The preparation method of shaft forgings 1Cr12Ni2WMoVNbN is basically the same as that of Example 1, except that the method of cooling after holding the temperature during the quenching stage in the performance heat treatment in step (4) is changed. In this embodiment, the method of cooling after quenching and holding the temperature is direct air cooling.

[0127] Example 9

[0128] The raw materials and proportions of the ring forging 1Cr12Ni2WMoVNbN are the same as those in Example 1.

[0129] The preparation method of the ring forging 1Cr12Ni2WMoVNbN is basically the same as that of Example 1, except that the forging is a ring forging, and the wall thickness ratio before and after ring rolling is 1.5. Therefore, in step (2), after forging the blank, it also includes punching and ring rolling to obtain the blank.

[0130] Example 10

[0131] The raw materials and proportions of the shaft forgings 1Cr12Ni2WMoVNbN are the same as those in Example 1.

[0132] The preparation method of the shaft forging 1Cr12Ni2WMoVNbN is basically the same as that of Example 1, except that the forging is a shaft forging, so in step (2), the blank is directly obtained after forging.

[0133] Embodiment 11

[0134] The raw materials and proportions of shaft forgings 1Cr12Ni2WMoVNbN are the same as those in Example 10.

[0135] The preparation method of the shaft forging 1Cr12Ni2WMoVNbN is basically the same as that of Example 10, except that in step (2), after the shaft forging is forged, the deformation amount of the last fire is 20%.

[0136] Comparative Example 1

[0137] Ring forging 1Cr12Ni2WMoVNbN, calculated by mass percentage, includes the following components: 0.14% C, 0.31% Si, 0.41% Mn, 0.018% P, 0.0015% S, 11.3% Cr, 1.65% Ni, 1.46% Mo, 0.25% V, 0.25% Nb, 0.76% W, 0.049% N, and the balance is Fe and indispensable impurities.

[0138] The preparation method of the ring forging 1Cr12Ni2WMoVNbN is the same as that in Example 1.

[0139] Comparative Example 2

[0140] The raw materials and proportions of the shaft forgings 1Cr12Ni2WMoVNbN are the same as those in Example 1.

[0141] The preparation method of shaft forgings 1Cr12Ni2WMoVNbN is basically the same as that of Example 1, except that step (3) does not include fine grain heat treatment, and normalizing and waiting are followed by tempering. The specific process of tempering is as follows: heating at a heating rate of 100°C / h, heating to 750°C, and keeping warm for a time equal to the effective heat treatment thickness of the blank 183mm multiplied by 2min / mm, and air cooling to room temperature after being taken out of the furnace. The metallographic structure diagram of the obtained forging is as follows: Figure 6 As shown in Figures c and d.

[0142] Test Case

[0143] 1. Forging Characterization

[0144] The metallographic examination diagrams of the forgings prepared in the examples and comparative examples are shown in the following table. Figure 6 As shown in the figure, it can be seen that the present invention can significantly improve the unevenness of product grain size and the fineness of grain size by adding a fine grain process after forging.

[0145] 2. Forging strength test

[0146] 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. The method for measuring grain size is: GB / T 6394. The test results are shown in Table 1.

[0147] Table 1 Performance tests of embodiments and comparative examples

[0148]

[0149]

[0150] It can be seen from the above table that the holding time of each step in the fine grain process has a significant effect on the subsequent grain size. If the holding is not sufficient, the fine grain effect will be significantly reduced; the heating rate in the performance heat treatment has no significant effect on the strength of the forging; the pre-forging process of the ring forging adopts the mounting process to improve the grain size and performance of the forging compared with the direct ring rolling process; the deformation of the forging in the last fire is low, which is easy to cause coarse grains and affect the impact performance of the forging; the strength, grain size and impact value of the forging are significantly reduced when the air cooling is used for quenching during the performance heat treatment and the alternating liquid cooling is used for quenching; the comparison between the forging with and without the fine grain process can clearly reflect that the fine grain process has a significant improvement on the grain size of the forging after the performance heat treatment; if the forging does not adopt the performance heat treatment and is directly tempered, the strength and impact value will be significantly reduced.

[0151] 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 martensitic heat-resistant steel forging, characterized in that: The martensitic heat-resistant steel forging is made of steel ingots obtained by smelting molten steel. The molten steel includes the following components by weight: C0.13-0.17%, Si<0.50%, Mn<0.50%, P<0.030%, S<0.015%, Cr11.00-12.00%, Ni1.80-2.10%, Mo1.10-1.65%, V0.20-0.30%, Nb0.20-0.30%, W0.70-1.00%, N0.02-0.08%, and the balance is Fe and unavoidable impurities.

2. A method for preparing the martensitic heat-resistant steel forging according to claim 1, characterized in that: The preparation method comprises the following steps: S1: smelting and forging the above raw materials to obtain ingots; S2: heating the ingot, forging and blanking to obtain the blank; S3: Put the billet into the furnace for cooling along with the furnace, and then carry out normalizing, waiting and fine grain heat treatment; S4: The blank processed in step S3 is subjected to rough turning and flaw detection, and then subjected to performance heat treatment, and cooled to obtain a martensitic heat-resistant steel forging.

3. The preparation method according to claim 2, characterized in that: In step S2, the ingot heating includes two-stage step heating and / or three-stage step heating; When the weight of the ingot is ≤4T, and / or the cross-sectional size of the ingot is ≤650mm, two-stage step heating is adopted; When the weight of the ingot is greater than 4T and / or the cross-sectional size of the ingot is greater than 650mm, three-stage step heating is adopted; Preferably, the two-stage step heating method is: the temperature of the first forging step is 600-700°C, and the insulation time is 2-4h; the temperature of the second step is 800-900°C, and the insulation time is ≥0.3min / mm multiplied by the effective thickness of the ingot, and the unit of the effective thickness of the ingot is mm; Preferably, the three-stage step heating method is: the temperature of the first forging step is 650°C, and the insulation time is 2-4h; the temperature of the second step is 850°C, and the insulation time is 0.3min / mm×the effective thickness of the ingot; the temperature of the third step is 1150-1180°C, and the insulation time is 0.4-0.5min / mm multiplied by the effective thickness of the ingot; wherein the unit of the effective thickness of the ingot is mm.

4. The preparation method according to claim 2, characterized in that: In step S2, the forging process includes: heating the ingot, taking it out of the furnace, removing the chill layer on the surface of the ingot; and then performing two upsetting and two drawing to obtain a forged billet; The deformation of each upsetting of the two upsetting and two drawing is ≥40%, the deformation of each drawing is ≥40%, and the total forging ratio is ≥7; The initial forging temperature of the forging blank is 1180 -8 0 0℃, final forging temperature ≥850℃.

5. The preparation method according to claim 2, characterized in that: In step S2, when the blank is a ring forging, the forging process further includes punching, and / or horse frame expansion, and / or ring rolling; Among them, when the wall thickness ratio before and after ring rolling is less than 2, punching is performed after forging, and the blank is formed by ring rolling; when the wall thickness ratio before and after ring rolling is ≥2, punching and horse frame expansion are performed after forging, and finally the blank is formed by ring rolling; In step S2, when the blank is a shaft forging and / or a disc forging, the blank is directly obtained after upsetting and drawing of the forging blank, and the deformation amount of the last fire is ≥25%.

6. The preparation method according to claim 2, characterized in that: In step S3, the furnace cooling is to place the blank in a heat treatment furnace or a forging furnace for furnace cooling; And / or, the furnace temperature of the furnace cooling is ≤850°C; and / or, before the normalizing, the temperature of the billet surface is 400-500°C.

7. The preparation method according to claim 2, characterized in that: In step S3, the normalizing process includes: heating the blank to 1130±10°C at a rate of ≤120°C / h, keeping the temperature, and air cooling after leaving the furnace; Preferably, the holding time is ≥90 min+effective heat treatment thickness of the forging blank multiplied by 0.7-1.2 min / mm, wherein the unit of the effective heat treatment thickness of the forging blank is mm; Preferably, the air cooling after leaving the furnace refers to air cooling until the surface temperature of the blank is 150±50°C; The waiting time is 2-3 hours.

8. The preparation method according to claim 2, characterized in that: In step S3, the specific process of the fine grain heat treatment includes: heating at a rate of ≤130°C / h to First insulation: Turn off the power and cool the furnace until the surface temperature of the forging blank is Carry out the second heat preservation; after the power is turned off and the furnace is cooled again, it is taken out of the furnace and air-cooled to room temperature; Preferably, the first heat preservation time is the effective heat treatment thickness of the blank multiplied by (1.5-3) min / mm; Preferably, the second heat preservation time is the effective heat treatment thickness of the blank multiplied by (2.0-3) min / mm; Preferably, when the effective heat treatment thickness of the forging blank is ≥500mm, the second power-off furnace cooling refers to furnace cooling until the surface temperature of the blank is ≤200°C; when the effective heat treatment thickness of the forging blank is <500mm, the second power-off furnace cooling refers to furnace cooling until the surface temperature of the blank is ≤400°C. Before the fine grain heat treatment, the temperature of the heat treatment furnace is ≤200°C.

9. The preparation method according to claim 2, characterized in that: In step S4, the performance heat treatment includes quenching, waiting and tempering.

10. The preparation method according to claim 9, characterized in that: The quenching process is to heat up to 1120±10°C at a rate of ≤90°C / h, keep warm for (0.7-1.2min / mm)*effective heat treatment thickness of forging blank+90min, and cool out of the furnace; Preferably, the process of cooling after being taken out of the furnace comprises: firstly, cooling the forging blank by repeated alternation of liquid cooling and air cooling until the surface temperature of the forging blank is 200-250°C, and then cooling the forging blank by air until the surface temperature of the forging blank is 100-150°C; The waiting time is 1-2h; The tempering process includes: heating to 680±10°C at a speed of ≤80°C / h, keeping warm for (1.2-1.5)*effective thickness of forging blank+120min, then water cooling to 300-350°C, and air cooling to room temperature after being taken out of the furnace.

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