Forming method for improving grain size of Ni2 steel

Abstract

The invention discloses a forming method for improving the grain size of a Ni2 steel forged piece, and provides a forming method for effectively improving the grain size of Ni2 steel aiming at the problems that the internal quality of the forged piece is poor, the grain size is low, the grain size grade difference is large and the like in the forging process of the Ni2 steel. The forming method adopted for solving the technical problems comprises the following steps: step 1) homogenizing heat treatment before forging; step 2), staggering an ingot protection plate; the Ni2 steel forged piece forming method comprises the steps of (1) forging, (2) forging, (3) upsetting, (4) drawing and rounding, (5) forging an intermediate blank, (6) completely annealing the intermediate blank, (7) heating the intermediate blank, (8) forging a finished product and (9) completely annealing the finished product. The Ni2 steel forged piece forming method can fully cut off Ni2 steel structure inheritance, improve the internal quality and grain size uniformity of the forged piece and reduce the grain size grade difference.

Description

Technical Field

[0001] The invention belongs to the technical field of metal plastic processing, and particularly relates to a forming method for improving the grain size of Ni2 steel, which can effectively improve the internal quality and grain size uniformity of Ni2 steel forgings and reduce the grain size difference. Background Art

[0002] The higher Ni content in Ni2 steel gives it higher hardenability and good comprehensive mechanical properties. It is often used to manufacture large forgings with high strength and high toughness, and is widely used in key load-bearing and pressure-bearing components in large equipment such as petroleum equipment, power station equipment, and transportation equipment. Therefore, Ni2 steel forgings are subjected to harsh service environments and complex stress states during service. Although this type of steel has good innate advantages, it also has strong organizational inheritance. The austenite grains produced during the heating process are difficult to refine, which reduces the strength and toughness of the material at the same time. This will greatly shorten the service life of Ni2 steel forgings, cause the entire set of equipment to stop production, and generate huge economic losses.

[0003] At present, the traditional forming method of Ni2 steel is to heat it to the forging temperature and then upset and pull the blank apart. When the surface of the forging drops below 800℃, it is returned to the furnace for heating for two hours and then forged again. Although this forming method can effectively form the finished product size and shape, the grain size of the forged product is about 5 levels, and there are 3-level grains, which cannot meet the needs of high-end products. In order to effectively improve the internal quality and grain size uniformity of Ni2 steel forgings and reduce the grain size difference, it is necessary to make full use of the "forming" and "forming properties" characteristics of forging to refine the internal organization grains, cut off the organization inheritance, and obtain Ni2 steel forgings with fine and uniform grains. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a forming method for improving the grain size of Ni2 steel, so as to improve the uniformity of the internal grain size of Ni2 steel forgings, reduce the grain size difference, and at the same time improve the forging efficiency, reduce the overall production cost, and improve the overall quality of Ni2 steel forgings.

[0005] The present invention achieves the above-mentioned purpose through the following technical solutions: A forming method for improving the grain size of Ni2 steel, the forming steps are as follows: Step 1) Homogenization heat treatment before forging: Load the electroslag ingot into the heating furnace and heat it to 1230℃~1260℃ in three stages for 20~25 hours to ensure uniform heating; Step 2) staggering the ingot guard plate: placing the electroslag ingot after being taken out of the furnace on the hydraulic press, using upper and lower flat anvils to stagger the ingot guard plate at the tail of the electroslag ingot, and leveling the tail end surface of the electroslag ingot; Step 3), upsetting: the electroslag ingot completed in step 2) is upset on a hydraulic press using an upsetting plate and a lower plate, the upsetting deformation is 50% to 60%, and the height-to-diameter ratio of the electroslag ingot after upsetting is 0.6 to 0.75; Step 4) Lengthening: The electroslag ingots completed in step 3) are stretched, squared and rounded on a hydraulic press using upper and lower flat anvils. The deformation of each stretching pass is 20%~30%; Step 5), forging of intermediate billet: forging the intermediate billet completed in step 4) to the shape and size of the intermediate billet, with a deformation of 25%~45% per pass; a forging ratio of 1.5~3.0 is reserved from the size of the intermediate billet to the size of the finished product; Step 6), complete annealing of the intermediate billet: normalizing + hydrogen expansion + complete annealing to room temperature after forging the intermediate billet of step 5); Step 7) Heating the intermediate billet: Rapidly heat the intermediate billet from step 6) to 950°C~1050°C at low temperature and keep it warm for 4~6 hours to ensure uniform heating; Step 8) Finished product forging: Forge the intermediate billet obtained in step 7) to the finished product shape and size; the deformation amount of each pass is 25%~45%; Step 9), complete annealing of finished product: normalize and completely anneal the finished product after forging in step 8) to room temperature.

[0006] The whole forging process is completed by two firings, among which step 2), step 3), step 4), step 5) are the first firing, and step 8) is the second firing. Step 4), step 5), step 8), the electroslag ingot is formed separately in the hydraulic press, or after being forged to the appropriate size in the hydraulic press, it is forged by the precision forging machine.

[0007] The beneficial effects of the present invention are as follows: The present invention performs homogenization heat treatment on the electroslag ingot before forging, improves the internal segregation of the electroslag ingot through high-temperature diffusion, and improves the coarse grain mixed crystal caused by component segregation. The core of the electroslag ingot is fully deformed by using a hydraulic press to perform large deformation upsetting and stretching, the core cast structure is broken, and the loose shrinkage cavities of the core are welded. The core is fully dynamically recrystallized, sub-dynamically recrystallized, and statically recrystallized after deformation by high temperature and large deformation to fully refine the core grains. The surface of the electroslag ingot is fully deformed by inverting and rounding, and the surface grains are refined, so as to obtain an intermediate billet with uniform overall deformation and fine grains. After the intermediate billet is completely annealed to room temperature and the tissue inheritance is cut off, it is quickly heated to the deformation temperature of the finished product to prevent the grain coarsening caused by heating in the internal grains of the intermediate billet. The intermediate billet has a large deformation margin relative to the finished product, and the internal tissue grains are further refined by low-temperature deformation of the intermediate billet. After forging to the shape and size of the finished product, it is fully annealed again to cut off the tissue inheritance to provide a good internal grain structure state for subsequent quenching and tempering heat treatment. For example, in step 3) and step 4), the upsetting plate and the lower flat plate are used on the hydraulic press to upset the electroslag ingot with a large deformation, and the deformation is 50%~60%. After upsetting, the height-to-diameter ratio of the electroslag ingot is 0.6~0.75. The upper and lower flat anvils are used to stretch the electroslag ingot with a large deformation, and the deformation of each pass is 20%~30%. By opening the electroslag ingot with a large deformation, the internal cast structure of the electroslag ingot is fully broken, the defects of the electroslag ingot core are compacted and welded, so that the internal deformation of the electroslag ingot is uniform, dynamic recrystallization occurs fully, and the grains are refined.

[0008] The invention only needs one firing process to convert the electroslag ingot into the intermediate billet and forge the intermediate billet into the finished product, which effectively prevents the grain coarsening of the internal grains of the Ni2 steel caused by heating and effectively improves the production efficiency.

[0009] The Ni2 steel deformation method of the present invention can effectively improve the internal quality and grain size uniformity of forgings, reduce grain size differences, and simultaneously improve forging production efficiency and reduce comprehensive production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic flow chart of a forming method for improving the grain size of Ni2 steel according to the present invention.

[0011] Figure 2 This is a dimension diagram of an intermediate billet forging of a hydraulic press according to an embodiment of the forming method for improving the grain size of Ni2 steel of the present invention.

[0012] Figure 3 This is a dimension diagram of an intermediate billet forging of a precision forging machine in an embodiment of a forming method for improving the grain size of Ni2 steel according to the present invention.

[0013] Figure 4 This is a dimension diagram of a semi-finished forging of a hydraulic press according to an embodiment of the forming method for improving the grain size of Ni2 steel of the present invention.

[0014] Figure 5 This is a dimension diagram of a semi-finished forging of a precision forging machine in accordance with an embodiment of the forming method for improving the grain size of Ni2 steel according to the present invention.

[0015] Figure 6 This is a dimension diagram of a finished forging of a hydraulic press according to an embodiment of a forming method for improving the grain size of Ni2 steel described in the present invention.

[0016] Figure 7 This is a dimension diagram of a finished forging of a precision forging machine in accordance with an embodiment of a forming method for increasing the grain size of Ni2 steel according to the present invention.

[0017] Figure 8 This is a grain size diagram at 1 / 2 radius of three finished electroslag ingots produced in Example 1 of a forming method for improving the grain size of Ni2 steel described in the present invention.

[0018] Fig. 9 This is a grain size diagram at 1 / 2 radius of three finished electroslag ingots produced in Example 2 of a forming method for improving the grain size of Ni2 steel described in the present invention. DETAILED DESCRIPTION

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. The embodiments of the present invention and the features in the embodiments can be combined with each other without conflict. Example 1: This example provides a forming method for improving the grain size of Ni2 steel. The electroslag ingot specification is Φ725mm / Φ790mm, the length is 1461mm, and the finished product size is as follows: Figure 6 , 7 As shown, the forming steps are as follows: Step 1), put the electroslag ingot into the heating furnace, heat it to 1230±10℃ in three stages, keep it warm for 25 hours, and diffuse the high temperature to ensure uniform heating; Step 2), place the electroslag ingot after being taken out of the furnace on the hydraulic press, use the upper and lower flat anvils to remove the tail guard plate of the electroslag ingot, and level the tail end surface of the electroslag ingot; Step 3), the electroslag ingot completed in step 2) is upset on the hydraulic press using an upsetting plate and a lower plate, and the upsetting is performed to H=700mm (~Φ1120mm); Step 4), the electroslag ingot completed in step 3) is stretched and squared on a hydraulic press using upper and lower flat anvils; the deformation amount of each stretching pass is 20%, the square is stretched to 400mm, and the square is squared to 420mm; and the rounding is to Φ420mm; Step 5) Forge the electroslag ingot completed in step 4) on a hydraulic press. Figure 2 Forging size drawing of hydraulic press intermediate billet, notch at the small diameter position to stretch from Φ420mm to Φ300mm; Step 6), air-cool the intermediate billet after step 5) to 250°C~280°C, load it into a furnace for normalizing + hydrogen expansion + complete annealing to room temperature; Step 7), quickly heat the intermediate billet obtained in step 6) to 1050±10°C at low temperature, and keep it warm for 4 hours to ensure uniform heating; Step 8) Forge the intermediate billet obtained in step 7) on a hydraulic press in two passes to the finished product shape and size; the first pass presses the forging into Figure 4 The semi-finished product of the hydraulic press is stretched according to the forging size diagram. The large diameter is forged from Φ420mm to Φ355mm, and the small diameter is forged from Φ300mm to Φ240mm. The second pass is to press the forging Figure 4 The finished product forging dimensions of the hydraulic press are forged to be lengthened, with the major diameter forged from Φ355mm to Φ305mm, and the minor diameter forged from Φ240mm to Φ195mm; Step 9), air-cool the finished product of step 8) to 250°C~280°C, put it into a furnace for normalizing + complete annealing to room temperature.

[0020] The electroslag ingot is forged to the intermediate billet size in one pass without returning to the furnace for heating. The intermediate billet is forged to the finished product size in one pass without returning to the furnace for heating.

[0021] In this embodiment 1, three electroslag ingots are produced. Figure 8 This is the grain size diagram of the finished forging at 1 / 2 radius. The grains are uniform and fine, and the grain size is about 8~9.

[0022] Embodiment 2: This embodiment provides a forming method for improving the grain size of Ni2 steel. The electroslag ingot specification is Φ725mm / Φ790mm, the length is 1461mm, and the finished product size is as follows: Figure 6 , 7 shown.

[0023] Step 1), put the electroslag ingot into the heating furnace, heat it to 1230±10℃ in three stages and keep it warm for 25 hours, and diffuse the high temperature to ensure uniform heating; Step 2), place the electroslag ingot after being taken out of the furnace on the hydraulic press, use the upper and lower flat anvils to remove the tail guard plate of the electroslag ingot, and level the tail end surface of the electroslag ingot; Step 3), the electroslag ingot completed in step 2) is upset on the hydraulic press using an upsetting plate and a lower plate, and the upsetting is performed to H=700mm (~Φ1120mm); Step 4) The electroslag ingots completed in step 3) are stretched and squared on a hydraulic press using upper and lower flat anvils; the deformation amount of each stretching pass is 20%, the square is drawn to 480mm, the squaring is to 500mm, and the rounding is to Φ500mm. The billet is transferred to the fine forging machine for radial forging, and the pulling and beating are forged to Φ420mm in one pass, the pulling and beating speed is ≥3m / min, and the forging frequency is 180 times / minute; Step 5) radially forge the electroslag ingot obtained in step 4) on a precision forging machine. Figure 3 The forging size drawing of the intermediate billet of the precision forging machine is forged, and the lengthening is carried out at the small diameter position, from Φ420mm to Φ320mm, the pulling speed is ≥3m / min, and the forging frequency is 180 times / minute; Step 6), air-cool the intermediate billet after step 5) to 250°C~280°C, load it into a furnace for normalizing + hydrogen expansion + complete annealing to room temperature; Step 7), quickly heat the intermediate billet obtained in step 6) to 1050±10°C at low temperature, and keep it warm for 2.5 hours to ensure uniform heating; Step 8) The intermediate billet completed in step 7) is radially forged on a fine forging machine, and forged in two passes to the finished product shape and size; the first pass presses the forging Figure 5 The semi-finished product forging size diagram of the precision forging machine is stretched, the large diameter is forged from Φ420mm to Φ355mm, and the small diameter is forged from Φ320mm to Φ240mm. The pulling speed is ≥3m / min, and the forging frequency is 180 times / minute; the second pass presses the forging Figure 5 The finished product forging size of the precision forging machine is stretched and lengthened, with the large diameter forged from Φ355mm to Φ305mm, and the small diameter forged from Φ240mm to Φ195mm. The pulling speed is ≥6m / min, and the forging frequency is 180 times / minute; Step 9), air-cool the finished product of step 8) to 250°C~280°C, put it into a furnace for normalizing + complete annealing to room temperature.

[0024] The electroslag ingot is forged to the intermediate billet size in one pass without returning to the furnace for heating. The intermediate billet is forged to the finished product size in one pass without returning to the furnace for heating.

[0025] In this embodiment 2, three electroslag ingots are produced. Fig. 9 This is the grain size diagram of the finished forging at 1 / 2 radius. The grains are uniform and fine, and the grain size is about 8~9.

Claims

1. A forming method for increasing the grain size of Ni2 steel, characterized in that: It includes the following steps: Step 1) Homogenization heat treatment before forging: Load the electroslag ingot into the heating furnace, heat it to 1230℃~1260℃ in three stages, and keep it warm for 20~25 hours to ensure uniform heating; Step 2) staggering the ingot guard plate: placing the electroslag ingot after being taken out of the furnace on the hydraulic press, using upper and lower flat anvils to stagger the ingot guard plate at the tail of the electroslag ingot, and leveling the tail end surface of the electroslag ingot; Step 3), upsetting: the electroslag ingot completed in step 2) is upset on a hydraulic press using an upsetting plate and a lower plate, the upsetting deformation is 50% to 60%, and the height-to-diameter ratio of the electroslag ingot after upsetting is 0.6 to 0.75; Step 4) Lengthening: The electroslag ingots completed in step 3) are stretched, squared and rounded on a hydraulic press using upper and lower flat anvils. The deformation of each stretching pass is 20%~30%; Step 5), forging of intermediate billet: forging the intermediate billet completed in step 4) to the shape and size of the intermediate billet, with a deformation of 25%~45% per pass; a forging ratio of 1.5~3.0 is reserved from the size of the intermediate billet to the size of the finished product; Step 6), complete annealing of the intermediate billet: normalizing + hydrogen expansion + complete annealing to room temperature after forging the intermediate billet of step 5); Step 7) Heating the intermediate billet: Rapidly heat the intermediate billet from step 6) to 950°C~1050°C at low temperature and keep it warm for 4~6 hours to ensure uniform heating; Step 8) Finished product forging: Forge the intermediate billet obtained in step 7) to the finished product shape and size; the deformation amount of each pass is 25%~45%; Step 9), complete annealing of finished product: normalize and completely anneal the finished product after forging in step 8) to room temperature.

2. A forming method for improving the grain size of Ni2 steel according to claim 1, characterized in that: The entire forging process is completed by two firings, of which step 2), step 3), step 4), and step 5) are the first firing, and step 8) is the second firing to prevent the internal grain coarsening of the forging caused by reheating.

3. A forming method for improving the grain size of Ni2 steel according to claim 1, characterized in that: Step 1) Before forging, the electroslag ingot is subjected to homogenization heat treatment, and the internal segregation of the electroslag ingot is improved by high-temperature diffusion through heating the electroslag ingot to 1230°C~1260°C in three stages and keeping the temperature for 20~25 hours.

4. A forming method for improving the grain size of Ni2 steel according to claim 1, characterized in that: Step 4), step 5), step 8), the electroslag ingot is formed by a hydraulic press alone, or after being forged to a suitable size by a hydraulic press, it is forged by a precision forging machine.

5. A forming method for improving the grain size of Ni2 steel according to claim 1, characterized in that: In step 6), the electroslag ingot is forged to the size of the intermediate billet. After a forging ratio of 1.5 to 3.0 is reserved from the size of the intermediate billet to the finished product size, the intermediate billet is air-cooled to 250°C to 280°C and loaded into a furnace for normalizing + hydrogen expansion + complete annealing to room temperature to cut off the internal tissue inheritance of the intermediate billet.

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