Manufacturing process of high-co high-ni high-toughness low-carbon high-alloy steel

Abstract

The application relates to a manufacturing process of high-Co high-Ni high-toughness low-carbon high-alloy steel, which adopts gas furnace heating and heat preservation, an oil press is used for blooming, a radial precision forging machine is used for forming, hot saw cutting is performed, stress relieving annealing and normalizing are performed after forging, overaging treatment is performed, one upsetting and one drawing are performed to generate larger deformation in the steel ingot, internal defects of the steel ingot are effectively forged, compactness and uniformity of the product are increased, and the longitudinal and transverse performances of the workpiece are effectively considered; the defects at the two ends of the forging are removed through hot saw cutting; the organization and grain size are further refined through stress relieving annealing, normalizing and overaging treatment after forging; after heat treatment of the sample, the mechanical performance reaches the requirements of Rm>=1620Mpa, Rp0.2>=1480Mpa, A>=10%, Z 纵 >=55%, and Z 横 >=55%.

Description

Technical Field

[0001] This invention belongs to the field of precision forging and first heat treatment technology, specifically relating to a production method of using a hydraulic press for billet opening + radial precision forging machine forming + hot sawing and the manufacturing process of high-Co, high-Ni, high-strength and high-toughness, low-carbon, high-alloy steel after forging stress-relief annealing + normalizing + over-aging treatment. Background Technology

[0002] High-Co, high-Ni, high-strength, high-toughness, low-carbon, high-alloy steel can be used to produce components for critical load-bearing positions in artillery. When combined with advanced manufacturing techniques, the static mechanical properties of these key components can be significantly improved, thereby extending their service life. This steel has a high alloy content and poor thermal conductivity. By designing reasonable heating temperatures and holding times, forging hammer reduction and drawing speeds, and forging temperature ranges, and employing a production method of hydraulic press for billet preparation followed by radial precision forging, machining allowances can be reduced, lowering production costs. Furthermore, due to its high alloy content and strong hardenability, it is prone to cracking during post-forging heat treatment, necessitating the development of a reasonable post-forging heat treatment process. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing forging equipment and technology, and to provide a manufacturing process for high-Co, high-Ni, high-strength, high-toughness, low-carbon, high-alloy steel by comprehensively considering factors such as heating, forging, and post-forging heat treatment. This process involves heating and holding the steel in a gas furnace, opening the billet with a hydraulic press, forming it with a radial precision forging machine, hot sawing, stress-relief annealing, normalizing, and over-aging treatment after forging.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a manufacturing process for high-Co, high-Ni, high-strength, high-toughness, low-carbon, high-alloy steel, employing a gas furnace for heating and holding, hydraulic press for billet preparation followed by radial precision forging, and post-forging stress-relief annealing + normalizing + over-aging treatment. The specific manufacturing process steps are as follows: Step 1) Place the steel ingot, which has been evenly coated with an anti-oxidation coating, in the effective zone of the trolley-type gas-fired heating furnace and heat it according to a four-stage heating curve: preheat at 400-450℃ for 1-2 hours / 100mm, then raise the temperature to 650-750℃ for a limited time and preheat for 1-2 hours / 100mm to further reduce the temperature difference between the inner and outer surfaces; then raise the temperature to 1250±10℃ for a limited time for high-temperature diffusion for 3-5 hours / 100mm to further homogenize the composition and structure of the billet and reduce the deformation resistance during forging; then cool down to 1180-1200℃ and hold for a period of time before removing the billet from the furnace for forging. Step 2) Forging is performed using a hydraulic press with one upsetting and one drawing operation, and a radial precision forging machine. The hydraulic press uses upsetting and drawing to fully deform the billet, weld internal defects, and further homogenize the microstructure. The radial precision forging machine performs rapid forging within a small temperature range, controlling the forming temperature and degree of deformation to ensure a dense microstructure, fine grain size, and uniform deformation of the product. Considering that higher temperatures tend to coarsen the microstructure, while lower temperatures result in greater deformation resistance, software simulations show that the microstructure above 800℃ is austenitic. Therefore, the initial forging temperature is 1150℃~950℃, and the final forging temperature is ≥800℃. The parameters for the upsetting and drawing control of the hydraulic press are as follows: upsetting is performed using an upper upsetting plate and a lower platform, followed by two drawing passes using the upsetting plate and the lower platform, then drawing the square shape on a flat anvil and then the octagonal shape; the material is then transferred to a radial precision forging machine and forged at a temperature of 1050~800℃, a reduction of 30-60mm per pass, and a drawing speed of less than 3m / min. Step 3) Hoist the forging to the hot saw, hot saw the defects at both ends to remove the crack source, and hoist it to the annealing bay for post-forging heat treatment; Step 4) Post-forging heat treatment employs stress-relief annealing + normalizing + over-aging treatment, specifically as follows: The forging is immediately placed in a 600~650℃ trolley-type gas-fired annealing furnace to await material processing. This is to prevent the workpiece from cooling too quickly, causing microstructural transformation and resulting in stress cracks. After the material is awaited, it is held at 600-650℃ for 2~4 hours / 100mm, then cooled to 60~100℃ at ≤10℃ / h, followed by air cooling. This aims to remove forging stress and obtain a ferrite-carbide microstructure. Finally, it is preheated to 650±20℃ at ≤60℃ / h for 1~2 hours / 100mm to reduce the temperature difference between the outer surface and the core of the forging. Due to temperature differences, the forging is rapidly heated to the normalizing temperature of 880–910℃ and held for ≥3–5 hours per 100 mm to fully austenitize it. The forging is then lifted off the trolley and placed in a dedicated cooling area for air cooling to room temperature, ensuring uniform cooling and maximizing the transformation of austenite. After aging treatment at 650–700℃ for 6–10 hours per 100 mm, it is air-cooled to obtain tempered sorbite and transform the retained austenite. Hardness and straightness are tested, and the aging temperature and time are adjusted. The forging is then straightened and air-cooled to room temperature for further testing. This process prepares the microstructure for subsequent machining and performance heat treatment.

[0005] The present invention has the following advantages over the prior art: The high-Co, high-Ni, high-strength, high-toughness, high-low-carbon alloy steel produced using this invention, based on the actual composition of the material, is analyzed using software simulation to obtain the phase transformation point and austenitic transformation products at different temperatures. This allows for the design of a reasonable heating process and constant forging temperature. The hydraulic press's upsetting and drawing process induces significant deformation within the ingot, effectively forging and closing internal defects, increasing the product's density and microstructure uniformity, and effectively balancing the longitudinal and transverse properties of the workpiece. Hot sawing removes crack initiation points at both ends of the forging. Post-forging stress-relief annealing, normalizing, and over-aging treatment further refines the microstructure and grain size. After heat treatment, the mechanical properties of the samples reach Rm≥1620MPa, Rp0.2≥1480MPa, A≥10%, and Zn≥10%. 纵 ≥55%, Z 横 The requirement is ≥55%. Detailed Implementation

[0006] The following embodiments are a detailed description of the present invention. These embodiments are merely descriptions of the best implementation of the present invention and do not limit the scope of the present invention in any way.

[0007] Example 1: A method for manufacturing high-Co, high-Ni, high-strength, high-toughness, low-carbon, high-alloy steel. The forging dimensions are Φ250*950+Φ235*2900. The manufacturing method is as follows: The chemical composition of the high-Co, high-Ni, high-strength, high-toughness, low-carbon, high-alloy steel ingot is shown in Table 1. The forging process employs a method of upsetting and drawing the billet using a hydraulic press, forming it using a radial precision forging machine, hot sawing, stress-relief annealing after forging, normalizing, and over-aging treatment. The manufacturing process steps are as follows: Table 1 Chemical composition (mass percentage) content 0.16 13.5～14.5 10.01 1.92 0.93 0.019 0.0026 Step 1) Place a 1.53T steel ingot (390mm in diameter) in the effective heating zone of a trolley-type gas-fired furnace and heat it according to the four-stage heating curve for cold ingots: first, preheat at 400-450℃ for 5.5 hours; then, raise the temperature to 650-750℃ for 5 hours within a specified time to preheat for another 5.5 hours to reduce the temperature difference between the surface and the core; then, raise the temperature to 1200-1260℃ for 12 hours within a specified time to allow for high-temperature diffusion, so that the steel is fully austenitized and the segregation of chemical composition and the inhomogeneity of fiber structure are eliminated or reduced; then, cool down to 1180-1200℃ and hold for 2 hours, forging in a range with good plastic deformation. Step 2) Forging is carried out by using a hydraulic press for upsetting and drawing to open the billet, and then transferring it to a radial forging machine for precision forging. The initial forging temperature is 1150℃~950℃, and the final forging temperature is ≥800℃. The parameters controlled by upsetting and drawing are as follows: using a 500mm flat anvil for upsetting H=650mm (to trim the side bend), using a flat anvil for drawing in two passes, drawing 300mm square on the flat anvil, then turning octagonal to 320mm, returning to 1100±20℃ and holding for no more than 2 hours, then transferring to a radial precision forging machine for forging at a temperature between 1050~800℃, with a deformation heat of φ280 to hot φ254, and after handover according to the drawing, deformation heat of φ254 to hot φ239, with a drawing speed of less than 3m / min, and precision forging. Step 3) Hoist the forging to the hot saw and hot saw the defects at both ends to remove the crack source; Step 4) Stress-relief annealing + normalizing + over-aging treatment: Immediately after forging, place the forging in the effective heating zone of a 600~650℃ trolley-type gas annealing furnace to await material; after the material is awaited, hold at 600-650℃ for 5 hours (to ensure uniform temperature inside and outside the forging and relieve stress), cool to 60~100℃ at ≤10℃ / h, then air cool to room temperature, and must be placed in the furnace within 2 hours; preheat to 650±20℃ at ≤60℃ / h for 3 hours, then rapidly heat to the normalizing temperature of 880~910℃, hold for 6 hours, and then remove from the trolley and place on a dedicated... The forgings were cooled to room temperature in a dispersed air-cooled area, and turned over every 30 minutes to prevent drafts and ensure uniform cooling, maximizing the transformation of austenite. After stress-relief tempering at 650-700℃, they were air-cooled again to reduce hardness and promote the transformation of residual austenite. Hardness and straightness were tested, and the temperature and time of the second aging process were adjusted according to the hardness level. The temperature was increased to 650-700℃ at a rate of ≤60℃ / h and held for 10 hours for heat calibration. After air cooling to room temperature, the hardness and straightness were tested to meet the requirements for subsequent processing. Test pieces were cut after forging and subjected to heat treatment according to standard requirements (aging temperature 510℃). The mechanical property test results are shown in Table 2. Table 12 Mechanical property test results of Example 1 Vertical 1 1686 1558 14 66 Vertical 2 1677 1561 13 66 Vertical 3 1723 1578 13.5 64 Vertical 4 1696 1571 12 62 Horizontal 1 1695 1585 14.5 71 Horizontal 2 1675 1566 13.5 71 Horizontal 3 1710 1577 14.5 71 Horizontal 4 1684 1571 14.5 71 Post-forging heat treatment test results show that using a hydraulic press for upsetting and drawing effectively breaks down the as-cast structure, welds internal defects in the billet, further homogenizes the microstructure, and effectively balances the longitudinal and transverse properties of the workpiece. Rapid forging within a narrow temperature range using a radial precision forging machine controls the forming temperature and deformation degree, ultimately ensuring a dense microstructure, refined grain size, and uniform deformation. Hot sawing at both ends of the forging removes crack initiation points. Post-forging stress-relief annealing, normalizing, and over-aging further refines the microstructure and grain size, reduces hardness, and prepares the microstructure for material processing and performance heat treatment. After heat treatment, the mechanical properties of the samples meet the requirements of Rm≥1620MPa, Rp0.2≥1480MPa, A≥10%, Z longitudinal ≥55%, and Z transverse ≥55%.

Claims

1. A manufacturing process for high-Co, high-Ni, high-strength, high-toughness, low-carbon, high-alloy steel, characterized in that: The chemical composition (by weight percentage) of the high-Co, high-Ni, high-strength, high-toughness, low-carbon, high-alloy steel includes C 0.16%, Co 13.5-14.5%, Ni 10.01%, Cr 1.92%, Mo 0.93%, Si 0.019%, Mn 0.0026%, with the balance being iron. The manufacturing process employs a gas-fired furnace for heating and holding, hydraulic press for billet preparation followed by radial precision forging, and post-forging stress-relief annealing, normalizing, and over-aging treatment. The manufacturing steps are as follows: Step 1) Place the steel ingot, which has been evenly coated with an anti-oxidation coating, in the effective zone of the trolley-type gas-fired heating furnace and heat it according to a four-stage heating curve: preheat at 400-450℃ for 1-2 hours / 100mm, then raise the temperature to 650-750℃ for a limited time and preheat for 1-2 hours / 100mm to further reduce the temperature difference between the inner and outer surfaces; then raise the temperature to 1250±10℃ for a limited time for high-temperature diffusion for 3-5 hours / 100mm to further homogenize the composition and structure of the billet and reduce the deformation resistance during forging; then cool down to 1180-1200℃ and hold for a period of time before removing the billet from the furnace for forging. Step 2) Forging is performed using a hydraulic press with one upsetting and one drawing operation, and a radial precision forging machine. The hydraulic press uses upsetting and drawing to fully deform the billet, weld internal defects, and further homogenize the microstructure. The radial precision forging machine performs rapid forging within a small temperature range, controlling the forming temperature and degree of deformation to ensure a dense microstructure, fine grain size, and uniform deformation of the product. Considering that higher temperatures tend to coarsen the microstructure, and lower temperatures result in greater deformation resistance, the software... The simulation shows that the structure above 800℃ is austenitic, so the initial forging temperature is 1150℃~950℃ and the final forging temperature is ≥800℃. The parameters for the hydraulic press to control the upsetting and drawing are as follows: upsetting is done on the upper upsetting plate and the lower platform, followed by two passes of upsetting plate and lower platform drawing, with the flat anvil drawing the square shape and the inverted octagon shape. The material is then transferred to a radial precision forging machine and forged at a temperature of 1050~800℃, a reduction of 30-60mm per pass, and a drawing speed of less than 3m / min. Step 3) Hoist the forging to the hot saw, hot saw the defects at both ends to remove the crack source, and hoist it to the annealing furnace for post-forging heat treatment; Step 4) Post-forging heat treatment employs stress-relief annealing + normalizing + over-aging treatment, specifically as follows: After forging, the forging is immediately placed in a 600~650℃ trolley-type gas furnace for annealing to prevent excessively rapid cooling and microstructural transformation, which could lead to stress cracking. After annealing, it is held at 600-650℃ for 2~4 hours / 100mm, then cooled to 60~100℃ at a rate of ≤10℃ / h, followed by air cooling to remove forging stress and obtain a ferrite-carbide microstructure. Finally, it is preheated to 650±20℃ at a rate of ≤60℃ / h for 1~2 hours / 100mm to reduce surface and core defects. The forging is rapidly heated to the normalizing temperature of 880–910℃ due to a temperature difference, and held for ≥3–5 hours per 100 mm to fully austenitize it. The forging is then lifted off the trolley and placed in a dedicated cooling area for air cooling to room temperature, ensuring uniform cooling and austenitic transformation. The forging is then heated to 650–700℃ and held for 6–10 hours per 100 mm for over-aging, followed by air cooling to obtain tempered sorbite, transforming the retained austenite and reducing hardness. Hardness and straightness are tested, and the over-aging temperature and time are adjusted. The forging is then straightened and air-cooled to room temperature for further testing. This process prepares the microstructure for subsequent machining and performance heat treatment.