A combined process method for blade steel forgings

Abstract

This application provides a combined process method for blade steel forgings, designed specifically for the characteristics of 04Cr15Ni7Cu2MoVNbN blade steel. This method can result in uniform microstructure, stable product performance, increased impact toughness margin, and improved product yield. Addressing the performance issues caused by the high Nb content in the material, this method uses quantitative melting rate control to reduce the melting rate during the electroslag remelting process, ensuring uniform solidification of the molten steel, reducing the precipitation of large NbC precipitates, and controlling the size of the NbC precipitates. Furthermore, a diffusion process for alloy steel elements is specifically designed to address the issues of bulk NbC and Nb segregation, resolving the problem of residual as-cast microstructure caused by insufficient diffusion in traditional processes.

Description

Technical Field

[0001] This invention relates to the field of turbine blade processing technology, specifically a combined process method for turbine blade steel forgings. Background Technology

[0002] Martensitic stainless steel is a commonly used material for turbine blades. Patent documents with publication numbers CN118147411A, CN109517952A, CN109517953A, and CN103103327A all represent processes developed by our company specifically for martensitic stainless steel. Existing processing techniques for martensitic stainless steel typically include the following steps performed sequentially: electroslag remelting (alloy purification), diffusion annealing (homogenization of microstructure), ingot blanking (breaking the as-cast structure), multiple forging stages (gradual shaping) followed by final annealing (final microstructure shaping), billet preparation and die forging (precision shaping), and quenching (strengthening treatment).

[0003] 04Cr15Ni7Cu2MoVNbN is a precipitation-hardening martensitic stainless steel. Its material composition is as follows: Figure 1 As shown, the addition of alloying elements such as Nb, V, and Mo to the material can enhance strength through precipitation strengthening. In the alloy steel to be processed, the Nb content is 8 to 15 times that of C, and Nb forms NbC precipitates with C, which is key to refining the grain and improving strength. Using 04Cr15Ni7Cu2MoVNbN alloy steel as the core material for turbine blades, its service environment requires ultra-high strength and toughness matching. The corresponding standard mechanical property requirements for the blades are referenced... Figure 2 As shown, however, in actual production, it has been found that when processing 04Cr15Ni7Cu2MoVNbN alloy steel based on existing martensitic stainless steel processing technology, forgings are prone to problems such as unqualified impact toughness and small toughness margin, with a pass rate of only about 85%.

[0004] Analysis revealed that the 04Cr15Ni7Cu2MoVNbN material has a high Nb content. During processing with existing technology, the high Nb content and inherent characteristics during solidification after electroslag remelting lead to a typical microstructure characterized by "dendritic depletion and interdendritic enrichment," affecting the overall material performance. Furthermore, during the formation of the NbC precipitate from Nb and C, uneven solidification rates in the molten steel cause Nb atoms to segregate at grain boundaries in the ingot's core, while the Nb content at the edges is significantly lower. The design values ​​result in an uneven microstructure with large, blocky NbC in the core and no effective precipitates at the edges. Furthermore, because 04Cr15Ni7Cu2MoVNbN material is complex, containing multiple alloying elements, if the atomic diffusion kinetic energy of Nb, V, Mo, and other alloying elements is low, dendrite segregation and compositional fluctuations cannot be eliminated through the diffusion process. Moreover, the large-sized blocky NbC and other as-cast dendrite structures generated during casting cannot be broken up through the existing forging deformation process, leading to mixed crystal formation. These issues severely restrict the service life and operational reliability of turbine blades made of 04Cr15Ni7Cu2MoVNbN material. Summary of the Invention

[0005] To address the issue that existing processes developed for martensitic stainless steel are not suitable for processing 04Cr15Ni7Cu2MoVNbN blade steel, this application provides a combined process method for blade steel forgings. This method is designed specifically for the characteristics of 04Cr15Ni7Cu2MoVNbN blade steel, which can result in uniform microstructure of the forgings, stable product performance, increased impact toughness margin, and improved product yield.

[0006] The technical solution of this application is as follows: a combined process method for blade steel forgings, characterized by comprising the following steps: S1: For the batching and primary smelting of alloy stainless steel to be processed; S2: Secondary refining; S3: Electroslag remelting; In the electroslag remelting process, the melting rate is controlled at 4-6 kg / min; S4: Element diffusion process in alloy steel; Specifically, this includes: the sequential execution of the steel ingot heating process, the steel ingot initial billet opening process, and the steel ingot diffusion annealing process; In the steel ingot heating process, the heating temperature is 1200°C-1280°C, and the holding time is 4-10 hours. In the single billet-making process of the steel ingot, the rough deformation amount is 40-60%; In the diffusion annealing process of the steel ingot, the heating temperature is 1240°C-1280°C and the holding time is 20-96 hours. S5: Secondary billet preparation and upsetting forging of steel ingots; In the process of secondary billet preparation of the steel ingot, the heating temperature is 1150°C-1180°C and the holding temperature is 1-3 hours; In the upsetting and drawing forging process, the number of upsetting and drawing operations is greater than 1, and the lengthening deformation is 40-60% each time. S6: Forged finished product; S7: Annealing treatment; S8: Die forging.

[0007] Its further features are: In step S1, the ratio of elements Nb to C is controlled to satisfy 9:1 to 11:1; Step S5, the upsetting and drawing forging process adopts two upsetting and two drawing forging; In step S6, during the forging process, the heating temperature is 1080-1130°C, the deformation is ≥30%, and the final forging temperature is ≥900°C. Step S7, the annealing process is a conventional annealing process; In step S8, the heating temperature during the die forging process is 1080-1120°C. It also includes the following steps: S9: Solution treatment; In the solution treatment process, the temperature is maintained at 1038°C for 1-3 hours, and water mist cooling is used. S10: Time-sensitive processing; In the aging process, the temperature is maintained at 482-502°C for 6-12 hours, followed by air cooling.

[0008] This application provides a combined process method for blade steel forgings. Addressing the product performance issues caused by high Nb content in the material, this method uses quantitative melting rate control. During the electroslag remelting process, the melting rate is controlled at 4-6 kg / min, reducing the melting rate and ensuring uniform solidification of the molten steel. This reduces the tendency for Nb atoms to segregate at grain boundaries, minimizes the Nb content deviation between the core and edges of the ingot, reduces the precipitation of large NbC blocks, and controls the size of the NbC blocks. Based on this, an alloy steel element diffusion process is specifically designed to address the issues of blocky NbC and Nb segregation. In this diffusion process, the low diffusion kinetic energy of alloy elements in this steel grade is addressed. The problem is that the steel ingot is first heated to 1200°C-1280°C for 4-10 hours to ensure uniform temperature inside and outside the ingot. Then, in the first billet-making process, the rough deformation is controlled within the range of 40-60%. The large deformation breaks down the coarse grains and dendrites in the cast state, ensuring uniform element diffusion for subsequent diffusion annealing. Then, combined with the diffusion annealing process of holding at 1240°C-1280°C for 20-96 hours, the microalloying elements such as Nb are fully diffused, completely eliminating dendrite segregation and compositional fluctuations, providing a uniform original structure for subsequent forging. This solves the problem of residual cast structure caused by insufficient diffusion in traditional processes. This application addresses the unique compositional characteristics of 04Cr15Ni7Cu2MoVNbN blade steel by designing a process to control the size of blocky NbC through controlled melting rate. This, combined with a process design involving single-stage ingot preparation and high-temperature, long-duration diffusion in the alloy steel element diffusion process, is highly compatible with the element diffusion characteristics of this steel grade, ensuring effective improvement in product performance and yield. Finally, a combination of low-temperature ingot preparation at 1150°C-1180°C and multi-pass upsetting and drawing forging technology, through the synergy of multi-pass large deformation and high-temperature diffusion, achieves complete fragmentation of the as-cast microstructure and continuous grain refinement. This solves the problems of poor microstructure refinement, resulting in substandard impact toughness and low toughness margin that occur in existing forging processes for 04Cr15Ni7Cu2MoVNbN blade steel. Attached Figure Description

[0009] Figure 1 The chemical composition of 04Cr15Ni7Cu2MoVNbN material; Figure 2 The mechanical property requirements for the chemical composition of 04Cr15Ni7Cu2MoVNbN material; Figure 3 This is a schematic diagram of the combined process method for blade steel forgings in this application; Figure 4 The microstructure diagrams of the products are shown for comparison; 4a shows the effect of the process before improvement, and 4b shows the effect of the process improvement based on this method. Detailed Implementation

[0010] like Figure 3 As shown, this application includes a combined process method for blade steel forgings, which includes the following steps.

[0011] S1: For the batching and primary smelting of alloy stainless steel to be processed.

[0012] The materials are prepared according to the chemical composition of 04Cr15Ni7Cu2MoVNbN material, with the ratio of Nb to C controlled to be 9:1 to 11:1, that is, the Nb content is controlled within the range of 9 to 11 times the C content, so as to avoid abnormal precipitation phases from the source of composition.

[0013] S2: Secondary refining.

[0014] Secondary refining is based on AOD (Argon-Oxygen Decarburization) and ladle refining methods. The primary molten steel is transferred from the electric furnace or converter to another vessel for secondary refining to improve steel quality. The secondary refining process involves deep deoxidation, desulfurization, and dephosphorization of the material, increasing the purity of the molten steel and reducing the decrease in toughness caused by inclusions.

[0015] S3: Electroslag remelting; In the electroslag remelting process, the melting rate is controlled at 4-6 kg / min.

[0016] In 04Cr15Ni7Cu2MoVNbN material, the formation of NbC precipitates from Nb and C is key to refining grains and improving strength. Compared with other martensitic stainless steels, 04Cr15Ni7Cu2MoVNbN material has a higher Nb content, thus achieving better performance. However, the typical Nb segregation coefficient is 0.3-0.6, indicating that the Nb concentration in the solid phase is significantly lower than that in the liquid phase. This results in uneven chemical composition distribution in the final solidified structure, i.e., segregation in the product. In typical turbine blade smelting and forging processes, electroslag remelting is a commonly used and relatively mature alloy purification process. However, when the Nb content in the material is high, during the solidification process after remelting, the first solidified solid phase continuously pushes Nb elements towards the remaining liquid phase, leading to the continuous enrichment of Nb elements in the liquid phase. This eventually forms a typical microstructure characterized by "dendritic stem depletion and interdendritic enrichment," i.e., microsegregation. At the same time, excessively fast electroslag remelting rates can lead to uneven solidification rates in the molten steel. Nb atoms undergo grain boundary segregation in the core of the ingot, while the Nb content at the edges is far lower than the design value, forming an uneven structure with coarse blocky NbC in the core and no effective precipitates at the edges, i.e., macrosegregation. Subsequent forging cannot eliminate this segregation, ultimately resulting in significant differences in strength and toughness in different parts of the forging.

[0017] Therefore, this application addresses the problem of Nb segregation caused by the high Nb concentration characteristic of 04Cr15Ni7Cu2MoVNbN material. By quantitatively controlling the electroslag remelting rate, the electroslag remelting rate is precisely controlled at 4-6 kg / min. By regulating the solidification kinetics of the molten steel, the solidification rate of the molten steel is made uniform, reducing the probability of microsegregation formation. At the same time, the tendency of Nb atoms to agglomerate at grain boundaries is reduced, and the deviation of Nb content between the core and the edge of the ingot is reduced. This keeps the deviation of Nb content between the core and the edge of the ingot within a very small range, improves the uniformity of the microstructure, reduces the precipitation of coarse blocky NbC, and thus controls the size of blocky NbC and the degree of Nb segregation.

[0018] S4: Element diffusion process in alloy steel; Specifically, this includes the following processes performed sequentially: steel ingot heating, steel ingot initial billet preparation, and steel ingot diffusion annealing.

[0019] While the electroslag remelting process can control the Nb content deviation between the core and edges of the ingot to some extent, it still results in inhomogeneous microstructure caused by coarse blocky NbC and dendritic segregation. Furthermore, due to the complex composition of 04Cr15Ni7Cu2MoVNbN material, the low diffusion kinetic energy of alloying elements such as Nb, V, and Mo makes it difficult to eliminate dendritic segregation and compositional fluctuations through diffusion. If the as-cast dendritic structure is not sufficiently broken up, uneven deformation during subsequent forging can easily lead to mixed crystal formation, significantly reducing the impact toughness of the forging. Therefore, to address the unique problems of the alloy stainless steel to be processed in this application, this solution designs an alloy steel element diffusion process.

[0020] In the steel ingot heating process, the heating temperature is controlled within the range of 1200°C-1280°C and held for 4-10 hours to ensure uniform temperature inside and outside the steel ingot, laying the foundation for uniform deformation in subsequent billet opening and avoiding structural defects caused by uneven local deformation.

[0021] In the first billet-making process of steel ingots, for steel ingots with uniform internal and external temperatures, the rough deformation amount is controlled at 40-60% to carry out large deformation billet-making of steel ingots. The large deformation amount breaks down the coarse grains and dendritic structures in the cast state, which provides a guarantee for the uniform diffusion of elements in the subsequent diffusion annealing.

[0022] In the diffusion annealing process of steel ingots, the heating temperature is controlled at 1240°C-1280°C and held for 20-96 hours to ensure that the Nb microalloying elements in the broken microstructure after large deformation billet can achieve full diffusion, completely eliminating dendritic segregation and compositional fluctuations caused by high Nb content; and the atomic diffusion kinetic energy of alloying elements such as Nb, V, and Mo is increased by high temperature and long-term holding, so as to achieve uniform distribution of elements in the steel ingot, providing a uniform original microstructure for subsequent forging, effectively solving the problem of residual as-cast microstructure caused by insufficient diffusion in traditional processes, avoiding mixed crystal problems, and improving the impact toughness of forgings.

[0023] S5: Secondary billet preparation and upsetting forging of steel ingots.

[0024] In the secondary billet opening process of steel ingots, the heating temperature is controlled within the range of 1150°C-1180°C and held for 1-3 hours; in the upsetting and drawing forging process, the number of upsetting and drawing is greater than 1, and the lengthening deformation is 40-60% each time; in this embodiment, the upsetting and drawing forging process adopts two upsetting and two drawing forging.

[0025] Through the secondary billet-making process of steel ingots, the microstructure is further broken down and the grains are refined based on the uniform composition established by the alloy steel element diffusion process, avoiding the problem of insufficient deformation in a single billet-making process. Then, through the upsetting and drawing forging process, multiple alternating upsetting and drawing processes with large deformation amounts are carried out to achieve multi-directional deformation of the microstructure, further eliminating segregation, refining the grains, and improving the uniformity of the microstructure.

[0026] S6: Forged finished product; This application employs low-temperature, large-deformation forging in the forging process, precisely controlling the heating temperature within the range of 1080-1130°C, with a deformation amount ≥30% and a final forging temperature ≥900°C. Through "low-temperature, large-deformation" forging, not only can sufficient deformation be guaranteed, effectively breaking up coarse grains and segregation clusters in the cast state, but also the problem of local overheating caused by excessive deformation will not occur. Furthermore, precise control of temperature and deformation amount enables dynamic recrystallization, effectively refining austenite grains, avoiding overheating and coarse grains, while ensuring the dimensional accuracy of the forging.

[0027] In this application, based on the characteristics of 04Cr15Ni7Cu2MoVNbN material, a forging process was designed that consists of "one-time billet preparation with 40-60% deformation + diffusion annealing + secondary billet preparation + two upsetting and two drawing processes with 40-60% deformation + final annealing and low-temperature large deformation (forging material) ≥30%". Through the synergy of multiple large deformations and high-temperature diffusion, the complete fragmentation of the as-cast structure and the continuous refinement of grains are achieved, solving the problem of poor microstructure refinement caused by insufficient deformation and improper temperature matching in traditional forging.

[0028] S7: Annealing treatment; In the annealing process, a conventional annealing process at 650℃ is adopted to eliminate forging stress, improve machinability, and avoid subsequent machining cracks caused by stress accumulation.

[0029] S8: Die forging.

[0030] In the turbine blade manufacturing process, die forging is a key step in blade forming. The austenitizing temperature range of 04Cr15Ni7Cu2MoVNbN material is narrow. If the die forging temperature is too high (>1130℃), it will cause the austenite grains to grow rapidly, forming a coarse-grained structure, which will lead to a significant decrease in toughness. If the temperature is too low (<1080℃), the steel will have insufficient plasticity, high resistance to forging deformation, and be prone to work hardening. At the same time, insufficient deformation will prevent the coarse grains from being broken up, forming a mixed-grain structure in which coarse and fine grains coexist, resulting in a deterioration in overall performance. This application addresses the growth characteristics of austenite grains in 04Cr15Ni7Cu2MoVNbN material. During the die forging process, the heating temperature is 1080-1120°C to control grain growth within a suitable size range. This precise control is within the optimal austenitizing temperature range for the steel grade, ensuring both the plasticity and deformation capacity of the steel while preventing austenite grain growth. This achieves "refining and homogenization" of austenite grains, ensuring that the grain size of the forging reaches level 6 or above, without coarse grains or mixed grains.

[0031] S9: Solution treatment; In the solution treatment process, the temperature is controlled and maintained at 1038°C for 1-3 hours, followed by water mist cooling. Water mist cooling replaces traditional oil cooling, achieving uniform cooling by controlling the water mist flow rate and cooling time. This satisfies the cooling rate requirements for martensitic transformation while avoiding the impact of oil fume pollution or the insufficient cooling rate of air cooling quenching. The water mist cooling technology is more environmentally friendly and lower in cost, solving the problem of unstable impact toughness caused by air cooling in the quenching process and the serious pollution hazards of oil fume emissions from oil cooling. It is particularly suitable for processing products made of 04Cr15Ni7Cu2MoVNbN material.

[0032] S10: Time-sensitive processing; In the aging process, the temperature is maintained at 482-502°C for 6-12 hours, followed by air cooling. This process achieves fine and uniform precipitation of NbC and other phases on a uniform martensitic matrix, fully leveraging the precipitation strengthening effect. While ensuring high strength, it significantly improves impact toughness, achieving an optimal balance between strength and toughness.

[0033] This application proposes a comprehensive technical system for the alloying characteristics of 04Cr15Ni7Cu2MoVNbN steel. This system includes precise compositional proportions (Nb / C ratio), controlled smelting segregation (precise melting rate), uniform diffusion in forging (combined processes of ingot heating + single-stage roughing + diffusion annealing), controlled grain size in die forging (final heating followed by low-temperature large deformation), water mist quenching, and aging precipitation strengthening. This comprehensive process, tailored to the specific compositional characteristics of this steel, addresses the underlying mechanisms of performance defects in each stage of hot working of 04Cr15Ni7Cu2MoVNbN steel, optimizing the manufacturing process and achieving stable performance improvements. Based on this solution, the product qualification rate can be increased from 85% to over 99%, solving the problems of large fluctuations in impact toughness and non-compliance associated with traditional processes. Figure 4 As shown, 4a represents the effect of the process before improvement, where a mixed-grain structure can be seen; 4b represents the effect after the process improvement based on this method, where a uniform fine-grain structure can be seen. Based on this method, the grain size of forgings can be stably achieved to level 6-8, without coarse grains or mixed grains. The compositional deviation between the core and edge of the steel ingot is reduced to within 5%, and precipitates such as NbC are fine and uniformly distributed, significantly improving the performance consistency of different parts of the forging.

[0034] To make the technical solution and advantages of this application clearer, the technical solution of this application will be clearly and completely described below in conjunction with the embodiments and comparative examples of this application.

[0035] Example 1: Electroslag remelting with low melting rate + low temperature long-term diffusion annealing + high die forging temperature + low temperature long-term aging; This embodiment addresses the production conditions where Nb segregation is severe. It employs electroslag remelting with a low melting rate to enhance segregation control, combined with low-temperature long-term diffusion annealing to fully eliminate segregation, high forging temperature to ensure plasticity, and low-temperature long-term aging to achieve sufficient and uniform precipitation of the precipitated phase.

[0036] S1.1: Ingredients: As per attached Figure 1 The chemical composition requires specific ingredient formulation, with the Nb / C ratio controlled within the range of 9-11.

[0037] S1.2: Primary smelting: electric furnace smelting, controlling the tapping temperature at 1580-1650°C to ensure sufficient melting of alloying elements.

[0038] S1.3: Secondary refining: AOD + ladle refining, deep deoxidation, desulfurization and dephosphorization, steel purity ≥99.99%.

[0039] S1.4: Electroslag remelting: The melting rate is controlled at 4 kg / min (low melting rate) to reduce Nb element segregation and improve the uniformity of steel ingot composition.

[0040] S1.5: Steel ingot heating: Hold at 1200°C for 8-10 hours to ensure uniform temperature inside and outside the steel ingot.

[0041] S1.6: Steel ingot first-time billet: rough deformation amount 60%, broken cast coarse grain and dendritic structure.

[0042] S1.7: Diffusion annealing: Hold at 1240°C for 60-96 hours (low temperature long time) to promote the full diffusion of alloying elements such as Nb and V and eliminate compositional segregation.

[0043] S1.8: Secondary billet preparation of steel ingot: heat preservation at 1180°C for 3 hours, rough deformation amount of 60%, further crushing the structure.

[0044] S1.9: Upsetting and drawing: Hold at 1180°C for 3-5 hours, deformation amount 60%, multi-directional deformation to refine grains.

[0045] S1.10: Two upsetting and two drawing: heat treatment at 1150°C for 3-5 hours, deformation amount 60%, improving the uniformity of the structure.

[0046] S1.11: Forging finished product: Hold at 1130°C for 1-3 hours, low temperature large deformation forging (deformation amount 35%), final forging temperature ≥900°C, to obtain a bar stock with a specification of Φ150mm.

[0047] S1.12: Annealing treatment: Conventional full annealing to eliminate forging stress.

[0048] S1.13: Blade cutting: According to the turbine blade size requirements, the bar stock is cut into Φ150mm×380mm blanks.

[0049] S1.14: Billet preparation: Hold at 1120°C for 1-3 hours (high die forging temperature), pre-deform and divide the material, with a deformation amount of 35%.

[0050] S1.15: Die forging: Hold at 1120°C for 1-3 hours, forge and press to form turbine blade profile dimensions with an accuracy of ±0.5mm.

[0051] S1.16: Solution treatment (quenching): Hold at 1038°C for 1-3 hours, then transfer to a sealed water mist cooling chamber with a water mist flow rate of 5L / min and a cooling time of 20 minutes to achieve uniform cooling.

[0052] S1.17: Aging treatment: Hold at 482°C for 12 hours (low temperature, long time), then air cool to achieve full and uniform precipitation of the precipitated phase.

[0053] S1.18: Physicochemical testing: Mechanical properties shall be tested according to GB / T 228 and GB / T 229, and grain size shall be tested according to GB / T 6394.

[0054] The test results for Example 1 are as follows: transverse Rm=1290MPa, Rp0.2=1200MPa, Rp0.02=1080MPa, A=14%, Z=64%, KV=70~88J; longitudinal Rm=1292MPa, Rp0.2=1202MPa, Rp0.02=1086MPa, A=16%, Z=66%, KV=145~162J; grain size grade 6; no mixed crystal phenomenon.

[0055] Example 2: Electroslag remelting with medium melting rate + medium temperature and medium time diffusion annealing + medium die forging temperature + medium temperature and medium time aging; This embodiment represents the optimal process scheme for industrial-scale mass production. It employs electroslag remelting with a melting rate that balances production efficiency and segregation control, medium-temperature and medium-time diffusion annealing that balances element diffusion and production cycle, medium-die forging temperature to achieve the optimal balance between grain refinement and plasticity, and medium-temperature and medium-time aging that balances precipitation strengthening and production efficiency.

[0056] S2.1: Ingredients: As per attached Figure 1 The chemical composition requires specific ingredient formulation, with the Nb / C ratio controlled within the range of 9-11.

[0057] S2.2: Primary smelting - secondary refining: Same as Example 1.

[0058] S2.3: Electroslag remelting: The melting rate is controlled at 5 kg / min (medium melting rate) to balance segregation control and production efficiency.

[0059] S2.4: Steel ingot heating: Hold at 1240°C for 5-7 hours to ensure uniform temperature inside and outside the steel ingot.

[0060] S2.5: Steel ingot first-time billet: rough deformation amount 50%, broken cast coarse dendritic structure.

[0061] S2.6: Diffusion annealing: Hold at 1260°C for 40-60 hours (medium temperature and time) to achieve uniform diffusion of elements and shorten the production cycle.

[0062] S2.7: Secondary billet preparation of steel ingot: heat preservation at 1180°C for 2 hours, rough deformation amount 50%.

[0063] S2.8: One upsetting and one drawing - two upsetting and two drawing: Same as Example 1, deformation amount 50%.

[0064] S2.9: Forging finished product: Hold at 1100°C for 2 hours, low temperature large deformation forging (deformation amount 32%), final forging temperature ≥900°C, to obtain a bar stock with a specification of Φ150mm.

[0065] S2.10: Annealing treatment - blade cutting: Same as in Example 1.

[0066] S2.11: Billet preparation - die forging: 1100°C holding for 2 hours (medium die forging temperature), pre-deformation material distribution + die forging, deformation amount 32%, blade profile dimension accuracy ±0.4mm.

[0067] S2.12: Solution treatment: Hold at 1038°C for 2 hours, then cool with water mist at a flow rate of 6 L / min for 18 minutes.

[0068] S2.13: Aging treatment: 492°C for 9 hours (medium temperature and medium time), then air cooling.

[0069] S2.14: Physicochemical testing: Same as Example 1.

[0070] The test results for Example 2 are as follows: transverse Rm=1270MPa, Rp0.2=1180MPa, Rp0.02=1040MPa, A=14%, Z=65%, KV=82~86J; longitudinal Rm=1275MPa, Rp0.2=1184MPa, Rp0.02=1045MPa, A=16%, Z=68%, KV=172~188J; grain size 6-7; uniform structure without mixed crystals.

[0071] Example 3: Electroslag remelting with high melting rate + high temperature short-time diffusion annealing + low die forging temperature + high temperature short-time aging; This embodiment is designed for high-efficiency production conditions. It adopts electroslag remelting with a high melting rate to improve production efficiency, combined with high-temperature short-time diffusion annealing to achieve element diffusion in a short time, low die forging temperature to strengthen grain refinement, and high-temperature short-time aging to quickly achieve precipitation strengthening, thus taking into account both production efficiency and performance requirements.

[0072] S3.1: Ingredients: As per attached Figure 1 The chemical composition requires specific ingredient formulation, with the Nb / C ratio controlled within the range of 9-11.

[0073] S3.2: Primary smelting - secondary refining: Same as Example 1.

[0074] S3.3: Electroslag remelting: The melting rate is controlled at 6 kg / min (high melting rate) to improve production efficiency and eliminate segregation in conjunction with subsequent high-temperature diffusion annealing.

[0075] S3.4: Steel ingot heating: Hold at 1280°C for 4-6 hours to improve the plasticity of the steel ingot and shorten the heating time.

[0076] S3.5: Steel ingot first-time billet: rough deformation amount 40%, broken as-cast structure.

[0077] S3.6: Diffusion annealing: Hold at 1280°C for 20-40 hours (high temperature short time) to improve atomic diffusion kinetic energy and eliminate component segregation in a short time.

[0078] S3.7: Secondary billet preparation of steel ingot: heat preservation at 1180°C for 1 hour, rough deformation amount 40%.

[0079] S3.8: One upsetting and one drawing - two upsetting and two drawing: Same as Example 1, deformation amount 40%.

[0080] S3.9: Forging finished product: Hold at 1080°C for 1 hour, low temperature large deformation forging (deformation amount 30%), final forging temperature ≥900°C, to obtain a bar stock with a specification of Φ60mm.

[0081] S3.10: Annealing treatment - blade cutting: Same as in Example 1.

[0082] S3.11: Billet preparation - die forging: 1080°C holding for 1-3h (low die forging temperature), pre-deformation material distribution + die forging, deformation amount 25%, blade profile dimension accuracy ±0.3mm, strengthening grain refinement.

[0083] S3.12: Solution treatment: Hold at 1038°C for 1 hour, then cool with water mist at a flow rate of 7 L / min for 15 minutes.

[0084] S3.13: Aging treatment: Hold at 502°C for 6 hours (high temperature short time), then air cool to quickly achieve precipitation enhancement.

[0085] S3.14: Physicochemical testing: Same as Example 1.

[0086] Test results: Transverse Rm=1253MPa, Rp0.2=1140MPa, Rp0.02=1030MPa, A=15%, Z=67%, KV=112~125J; Longitudinal Rm=1252MPa, Rp0.2=1142MPa, Rp0.02=1035MPa, A=18%, Z=70%, KV=196~208J; Grain size 7-8 grade, fine and uniform grains, maximum excess impact toughness.

[0087] Comparative Example: The existing processing technology for martensitic stainless steel is adopted, specifically including the following steps: 1) Ingredients: As per attached... Figure 1 The chemical composition requires formulation, controlling the Nb to C ratio within the range of 9:1 to 11:1; 2) Primary smelting - secondary refining: Same as Example 1.

[0088] 3) Electroslag remelting: melting rate 7-8 kg / min; 4) Diffusion annealing: 1200℃, hold for 24 hours; 5) Steel ingot blanking: 1160~1200 degrees Celsius, heat preservation for 4-6 hours, deformation amount 30%-50%; 6) The final heat treatment stage produces timber at a temperature of 1145℃; Multi-heat forging, with the final heating cycle forming the forging, transforms the billet into a finished forging that meets the microstructure and performance requirements; 7) Billet preparation and die forging temperature: 1145℃, holding time 1.5-3h; 8) Quenching, based on oil cooling or air cooling; 9) Physicochemical testing: Mechanical properties shall be tested according to GB / T 228 and GB / T 229, and grain size shall be tested according to GB / T 6394.

[0089] Test results: Transverse Rm=1258MPa, Rp0.2=1142MPa, Rp0.02=1025MPa, A=15%, Z=68%, KV=36-46J; Longitudinal Rm=1256MPa, Rp0.2=1145MPa, Rp0.02=1046MPa, A=18%, Z=72%, KV=122-132J, grain size grade 5.

[0090] The lateral performance comparison of the embodiments and comparative examples is shown in Table 1; Table 1: Results of Lateral Performance Testing

[0091] In the table, Rm is the tensile strength, Rp0.2 is the yield strength, Rp0.02 is the conditional yield strength, A is the elongation, Z is the reduction of area, and KV is the transverse and longitudinal impact toughness. As can be seen from the data comparison in Table 1, comparing the comparative examples using existing technologies with the three embodiments of this solution, it can be seen that the grain size of the products processed in the three embodiments of this solution all reach level 5 or above. With the adjustment of the processing conditions in the electroslag remelting and alloy steel element diffusion processes in Examples 1-3, the grain size of the products gradually becomes finer. Based on the appendix Figure 2 The mechanical properties of the 04Cr15Ni7Cu2MoVNbN material were verified according to the chemical composition requirements. The grain size of all three examples met the requirements; in particular, the grain size of Examples 2 and 3 reached level 6 or above, proving that this method can effectively improve the uniformity of the forging structure. Comparing the transverse impact toughness data KV2J, it can be seen that the transverse impact toughness of the forgings corresponding to Examples 1-3 is stable at >70J, while the KV2J in the comparative example is 36-46J, proving that this method can significantly improve the impact toughness margin and solve the problem of large fluctuations in impact toughness in traditional processes.

[0092] The longitudinal performance comparison of the embodiments and comparative examples is shown in Table 2; Table 2: Results of longitudinal performance comparison

[0093] As can be seen from the data comparison in Table 2, the longitudinal impact toughness KV corresponding to the three embodiments of this scheme is also higher than the longitudinal impact toughness KV data of the comparative example.

[0094] Referring to Tables 1 and 2, it can be seen that this method, through precise control of forging temperature, low-temperature large deformation grain refinement, and aging precipitation strengthening, enables forgings to meet the ultra-high strength requirements of Rm1240-1350MPa and Rp0.2≥1120MPa while maintaining high toughness, elongation after fracture ≥13%, and reduction of area ≥45%, thus meeting the stringent service requirements of turbine blades and effectively improving the product qualification rate.

[0095] By employing the technical solution of this application, starting from the mechanism of performance defects, and through precise optimization and synergistic control of key parameters in each process—smelting, diffusion annealing, forging, die forging, and heat treatment—a combined process method for material modification is achieved through precise control of multiple process parameters. This fundamentally eliminates problems such as Nb segregation, uneven microstructure, abnormal grains, quenching fume pollution, or insufficient air cooling rate, ensuring uniform microstructure and stable performance of the forgings, increasing the impact toughness margin, and meeting the stringent requirements of turbine blades. All process parameters in this application are quantitatively designed, and the equipment used is conventional equipment in the metallurgical forging field, requiring no additional specialized equipment. Process adjustment is simple, facilitating large-scale industrial mass production, and is suitable for the large-scale manufacturing of 04Cr15Ni7Cu2MoVNbN steel forgings for turbine blades.

Claims

1. A combined process method for blade steel forgings, characterized in that, It includes the following steps: S1: For the batching and primary smelting of alloy stainless steel to be processed; S2: Secondary refining; S3: Electroslag remelting; In the electroslag remelting process, the melting rate is controlled at 4-6 kg / min; S4: Element diffusion process in alloy steel; Specifically, this includes: the sequential execution of the steel ingot heating process, the steel ingot initial billet opening process, and the steel ingot diffusion annealing process; In the steel ingot heating process, the heating temperature is 1200°C-1280°C, and the holding time is 4-10 hours. In the single billet-making process of the steel ingot, the rough deformation amount is 40-60%; In the diffusion annealing process of the steel ingot, the heating temperature is 1240°C-1280°C and the holding time is 20-96 hours. S5: Secondary billet preparation and upsetting forging of steel ingots; In the process of secondary billet preparation of the steel ingot, the heating temperature is 1150°C-1180°C and the holding temperature is 1-3 hours; In the upsetting and drawing forging process, the number of upsetting and drawing operations is greater than 1, and the lengthening deformation is 40-60% each time. S6: Forged finished product; S7: Annealing treatment; S8: Die forging.

2. The combined process method for blade steel forgings according to claim 1, characterized in that: In step S1, the ratio of elements Nb and C is controlled to satisfy 9:1 to 11:

1.

3. The combined process method for blade steel forgings according to claim 1, characterized in that: Step S5, the upsetting and drawing forging process adopts two upsetting and two drawing forging.

4. The combined process method for blade steel forgings according to claim 1, characterized in that: In step S6, during the forging process, the heating temperature is 1080-1130°C, the deformation is ≥30%, and the final forging temperature is ≥900°C.

5. The combined process method for blade steel forgings according to claim 1, characterized in that: Step S7, the annealing process is a conventional annealing process.

6. The combined process method for blade steel forgings according to claim 1, characterized in that: In step S8, the heating temperature during the die forging process is 1080-1120°C.

7. The combined process method for blade steel forgings according to claim 1, characterized in that: It also includes the following steps: S9: Solution treatment; In the solution treatment process, the temperature is maintained at 1038°C for 1-3 hours, and water mist cooling is used. S10: Time-sensitive processing; In the aging process, the temperature is maintained at 482-502°C for 6-12 hours, followed by air cooling.

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