A forging method for improving the grain size of austenitic stainless steel pipes with nozzles

Abstract

This invention relates to a forging method for improving the grain size of austenitic stainless steel pipes with nozzles. The method involves taking an electroslag ingot with a diameter of Φ1000–1200 mm, holding it at 1180±10℃ for 9–12 hours, and then drawing it to form a billet. After returning the billet to the furnace, the temperature is raised to 1200±10℃ and held for 7–8 hours. The billet is then upset with a flat upsetting cap, drawn into a flat square shape, and marked to form a flat square billet. This flat square billet is held at 1180±10℃ for 3–4 hours, drawn to lengthen both ends, and staggered to form a billet with a staggered nozzle. This staggered nozzle billet is held at 1150–1180±10℃ for 3–4 hours and then drawn, completing the forging process in one firing. This four-firing forging method for pipes with nozzles achieves a grain size ≥4 in the forging body, significantly improving the overall grain size of the austenitic stainless steel pipe with nozzle.

Description

Technical Field

[0001] This invention belongs to the field of forging technology, specifically relating to a forging method for improving the grain size of austenitic stainless steel pipes with nozzles. Background Technology

[0002] Stainless steel pipes are one of the key components of nuclear power plants. They are austenitic stainless steel forgings, which have extremely high technical requirements. Typically, the overall austenitic grain size must be ≥4, making forging extremely difficult. In addition to the rounded ends, some pipes also have nozzles in the middle. The nozzles are large-section flat square parts, and controlling their grain size is even more difficult than that of the rounded ends.

[0003] Since austenitic stainless steel does not undergo structural transformation during heating and cooling, the grains can only be refined through forging deformation. However, the nozzle cross-section is relatively large and requires multiple furnace heating cycles, making it difficult to achieve the required overall grain size for the nozzle. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problem that it is difficult to achieve an overall grain size of ≥4 in austenitic stainless steel pipes with nozzles, and to provide a forging method for improving the grain size of austenitic stainless steel pipes with nozzles.

[0005] The objective of this invention is achieved in the following ways:

[0006] This invention involves heating and four-times forging austenitic stainless steel electroslag ingots at different temperatures, as detailed below:

[0007] 1) Electroslag ingots with a diameter of Φ1000~1200mm are heated at 1180±10℃ for 9~12 hours and then taken out of the furnace and stretched into billets;

[0008] 2) After the billet is returned to the furnace, the furnace temperature is raised to 1200±10℃ and kept at that temperature for 7-8 hours. After that, the billet is taken out of the furnace with a flat upsetting cap, and then flattened and marked to form a flat square billet.

[0009] 3) After the flat square billet is fully heated at 1180±10℃ for 3 to 4 hours, it is taken out of the furnace, the two ends are stretched and staggered out of the nozzle to form the billet after staggered nozzle. The billet after staggered nozzle is reserved for deformation.

[0010] 4) After the nozzle is shifted, the billet is kept at 1150~1180±10℃ for 3~4 hours before being taken out of the furnace. After taking out of the furnace, it is completed in one firing. The completion is carried out sequentially from the bottom end to the handle end. First, the bottom circular rod is formed, and then the nozzle is formed. The nozzle part must be pressed down to close the process size with a large amount of anvil in both the height and thickness directions, and then finely shaped with a small amount of deformation. After the large amount of nozzle pressing is completed, the circular rod part of the handle end is formed to obtain the forging.

[0011] Further, the specific process of step 1) is as follows: cut off 40-50mm from both ends of the electroslag ingot with a diameter of Φ1000-1200mm. After holding the electroslag ingot at 300-350℃ for 4-5 hours, raise the temperature to 850±10℃ at a heating rate of ≤50℃ / h and hold for 5-7 hours. Then raise the temperature to 1180±10℃ at a heating rate of ≤60℃ / h and hold for 9-12 hours before removing it from the furnace. On a press with a tonnage of 8000t or above, the manipulator clamps the bottom of the electroslag ingot and uses a flat anvil to press the ingot body at the riser end of the electroslag ingot. After the clamp is pressed, the electroslag ingot is turned around, and the manipulator clamps the clamp to draw the ingot body 10-30mm on one side to form a billet.

[0012] Further, the specific process of step 2) is as follows: the billet is placed in the upsetting tray, a flat upsetting cap is placed on the billet for upsetting, and then a flat anvil is used to draw the flat billet to form a flat billet. The cross-sectional height of the flat billet = process nozzle height + deformation allowance reserved for the last firing + shrinkage allowance, the shrinkage allowance is 150~200mm, and the cross-sectional thickness of the flat billet = process nozzle thickness + deformation allowance reserved for the last firing + 150~200mm.

[0013] Furthermore, the upsetting diameter needs to ensure that the forging ratio of the nozzle is 6 to 10.

[0014] Furthermore, in step 3), the calculation method for the last deformation allowance of the nozzle and rod is as follows: Deformation of the flat square nozzle = (Area before completion - Area after completion) ÷ Area before completion; Deformation of the round rod = (Diameter before completion - Diameter after completion) ÷ Diameter before completion.

[0015] Furthermore, in step 4), if the total length of the forging is greater than or equal to 3m, the heating temperature of the final forging is 1180±10℃; if the total length of the forging is less than 3m, the heating temperature of the final forging is 1150~1180℃, and the final forging surface temperature is controlled at 800~900℃.

[0016] Compared with existing technologies, the advantages of this invention are as follows: This invention heats austenitic stainless steel pipe forgings with nozzles at different temperatures and employs a four-fire forging process. For pipes of different specifications, the high-temperature holding temperature and time are selected according to the diameter of the electroslag ingot and the size of the pipe. Forging is carried out according to the forging process specified for each fire, which can greatly improve the overall grain size of the pipe with nozzle. The grain size of both the forging rod and the nozzle body can reach ≥4 level. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the pipe forging with nozzle according to the present invention;

[0018] Figure 2 Schematic diagram of the blank clamp handle;

[0019] Figure 3 This is a schematic diagram of billet upsetting.

[0020] Figure 4 This is a schematic diagram of the stamp after the square is flattened;

[0021] Figure 5 A schematic diagram of the forging after reserving deformation allowance. Detailed Implementation

[0022] The method of the present invention will be further explained below with reference to the accompanying drawings:

[0023] The method of this invention includes heating austenitic stainless steel electroslag ingots at different temperatures and forging them using a four-heat process. Specifically:

[0024] 1)Reference Figure 2 Before forging, 40-50mm is sawn off from both ends of an electroslag ingot with a diameter of Φ1000-1200mm. After holding the ingot at 300-350℃ for 4-5 hours, the temperature is increased to 850±10℃ at a rate of ≤50℃ / h and held for 5-7 hours. Then, the temperature is increased to 1180±10℃ at a rate of ≤60℃ / h and held for 9-12 hours before being removed from the furnace. On a press with a tonnage of 8000t or above, the manipulator clamps the bottom of the electroslag ingot, and a flat anvil with a top and bottom width of 800mm is used to press the ingot body at the riser end. After the clamp is in place, the electroslag ingot is turned around, and the manipulator, holding the clamp, pulls the ingot body with a small reduction of 10-30mm on each side to elongate it into a billet. The small reduction and slight elongation of the ingot body is to eliminate pits or grinding protrusions on the surface of the electroslag ingot and to avoid folds or cracks on the outer circle during the upsetting process.

[0025] 2)Reference Figure 3 , Figure 4 After the billet is returned to the furnace, the furnace temperature is raised to 1200±10℃ and held for 7-8 hours before being taken out of the furnace. The billet is placed in an upsetting tray, and a flat upsetting cap is placed on the billet for upsetting. The diameter of the upsetting cap must ensure that the forging ratio of the nozzle is 6-10. Then, a flat anvil with an upper and lower width of 800mm is used to draw a flat square billet. The cross-sectional height of the flat square is equal to the height of the process nozzle + the deformation allowance reserved for the last heat + the shrinkage allowance, which is 150-200mm. The cross-sectional thickness of the flat square is equal to the thickness of the process nozzle + the deformation allowance reserved for the last heat + 150-200mm.

[0026] Then use a marking knife to mark the blank as deeply as possible, but the depth should not exceed the height of the bevel of the marking knife. Otherwise, the bottom edge of the bevel of the marking knife will leave an indentation on the blank. This indentation will extend into a crack during the subsequent drawing process. The deeper the indentation, the deeper the crack will be. In order for the second firing to complete the upsetting, drawing, and marking processes, the heating temperature of this firing needs to be increased to 1200±10℃.

[0027] 3)Reference Figure 5The flat square billet is held at 1180±10℃ for 3-4 hours before being removed from the furnace. Both ends are then elongated and offset to form the billet with the offset nozzle. The billet with the offset nozzle is then reheated after allowing for a certain amount of deformation. The calculation method for the allowable deformation in the final forging of the nozzle and rod is as follows: Deformation of the flat square nozzle = (Area before completion - Area after completion) ÷ Area before completion; Deformation of the round rod = (Diameter before completion - Diameter after completion) ÷ Diameter before completion. The grain size of the pipe with the nozzle is mainly affected by the forging process parameters of the final forging, namely the deformation amount and final forging temperature. To obtain a fine and uniform microstructure, the deformation amount in the final forging is best controlled between 30% and 45%.

[0028] 4)Reference Figure 1 After the nozzle is misaligned, the billet is kept at 1150~1180±10℃ for 3~4 hours before being taken out of the furnace. After being taken out of the furnace, it must be completed in one furnace. The completion process is carried out sequentially from the bottom end to the handle end. First, the bottom circular rod is formed, and then the nozzle is formed. The nozzle part must be pressed down to close to the process size by the large amount of deformation in the height and thickness directions with an anvil, and then finely shaped with a small amount of deformation. After the large amount of deformation of the nozzle is completed, the circular rod part of the handle end is formed to obtain the forging.

[0029] The final heating temperature depends on the finished product. If the total length of the forging is greater than or equal to 3m and the finished product is relatively large, the heating temperature for the final heating is 1180±10℃. If the total length of the forging is less than 3m and the finished product is relatively small, the temperature is between 1150 and 1180℃. Generally, four temperatures are selected: 1150±10℃, 1160±10℃, 1170±10℃, and 1180±10℃. The final forging surface temperature is controlled between 800 and 900℃.

[0030] 5) Pipe forgings with nozzles (see...) Figure 1 After completion, the forging is water-cooled to room temperature before being lifted out.

[0031] This invention involves heating austenitic stainless steel pipe forgings with nozzles at different temperatures using a four-fire forging process. For pipes of different specifications, the high-temperature holding temperature and time are selected based on the diameter of the electroslag ingot and the pipe dimensions. Forging is performed according to a specified forging procedure for each fire, significantly improving the overall grain size of the pipe with nozzle. The grain size of both the forging rod and the nozzle body can reach ≥4. This method is applicable to all pipes with nozzles forged from electroslag ingots with diameters of Φ1000–1200 mm. After sufficient high-temperature holding at different temperatures, the forging process is controlled to be completed in four fires, with a certain amount of deformation reserved in the final fire. The forging of each part of the forging is performed in a specific sequence and method, with strict control over the final forging temperature. This method offers good adaptability and flexibility. Pipes with nozzles obtained using this forging method can achieve a grain size of ≥4.

Claims

1. A forging method for improving the grain size of austenitic stainless steel pipes with nozzles, characterized in that: The forging method is as follows: 1) Electroslag ingots with a diameter of Φ1000~1200mm are heated at 1180±10℃ for 9~12 hours and then taken out of the furnace and stretched into billets; 2) After the billet is returned to the furnace, the furnace temperature is raised to 1200±10℃ and kept at that temperature for 7~8 hours. After that, the billet is taken out of the furnace with a flat upsetting cap, and then flattened and marked to form a flat square billet. 3) After the flat square billet is fully heated at 1180±10℃ for 3~4 hours, it is taken out of the furnace, the two ends are stretched and staggered out of the nozzle to form the billet after staggered nozzle. The billet after staggered nozzle is reserved for deformation. 4) After the nozzle is misaligned, the billet is kept at (1150~1180)±10℃ for 3~4 hours before being taken out of the furnace. After being taken out of the furnace, it is completed in one firing. The completion is carried out sequentially from the bottom end to the handle end. First, the bottom circular rod is formed, and then the nozzle is formed. The nozzle part must be pressed down to close to the process size by the reserved deformation amount in the height and thickness directions with a large pressing amount of an anvil, and then finely shaped with a small deformation amount. After the large pressing amount of the nozzle is completed, the circular rod part of the handle end is formed to obtain the forging. The specific process of step 2) is as follows: the billet is placed in the upsetting tray, a flat upsetting cap is placed on the billet for upsetting, and then a flat anvil is used to draw the flat square to form a flat square billet. The cross-sectional height of the flat square = process nozzle height + deformation allowance reserved for the last heat + shrinkage allowance, the shrinkage allowance is 150~200mm, and the cross-sectional thickness of the flat square = process nozzle thickness + deformation allowance reserved for the last heat + 150~200mm. In step 3), the calculation method for the last deformation allowance of the nozzle and rod is as follows: Deformation of the flat square nozzle = (Area before completion - Area after completion) ÷ Area before completion; Deformation of the round rod = (Diameter before completion - Diameter after completion) ÷ Diameter before completion. In step 4), if the total length of the forging is greater than or equal to 3m, the heating temperature of the final heat is 1180±10℃; if the total length of the forging is less than 3m, the heating temperature of the final heat is 1150~1180℃, the final forging surface temperature is controlled at 800~900℃, and the deformation amount of the final heat is controlled at 30%~45%. The upsetting diameter must ensure that the forging ratio of the nozzle is 6~10.

2. The forging method for improving the grain size of austenitic stainless steel pipe with nozzle according to claim 1, characterized in that: The specific process of step 1) is as follows: Cut off 40-50mm from both ends of the electroslag ingot with a diameter of Φ1000~1200mm. After holding the electroslag ingot at 300~350℃ for 4~5 hours, raise the temperature to 850±10℃ at a heating rate of ≤50℃ / h and hold for 5~7 hours. Then raise the temperature to 1180±10℃ at a heating rate of ≤60℃ / h and hold for 9~12 hours before removing it from the furnace. On a press with a tonnage of 8000t or above, the operating machine clamps the bottom of the electroslag ingot and uses a flat anvil to step on the ingot body at the riser end of the electroslag ingot to press the clamp handle. After the clamp handle is pressed, the electroslag ingot is turned around and the operating machine clamps the clamp handle to stretch the ingot body by 10~30mm on one side to form a billet.

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