A kind of low expansion coefficient iron-nickel-based silicon steel forging rolling hybrid forming process

Abstract

The application discloses a kind of low expansion coefficient iron nickel-based mild steel's forging rolling mixed forming process, including forging process and rolling process;The forging process: blank is heated after forging, heat preservation is carried out between forging fire time;The process of the pre-forging heating process is as follows: blank is preheated in 300~500 DEG C heating furnace;Then with ≤100 DEG C / h heating rate, heat up to 790~810 DEG C and then heat preservation;Then again with ≤100 DEG C / h heating rate, heat up to 1170~1190 DEG C and then heat preservation, after heat preservation, forging is carried out.The heating process determined when forging is summarized by many experiments, which can ensure that the inside and outside of the blank are heated uniformly and the grain boundary is not weakened or even destroyed, the blank will not cause surface crack defects, scarring and other defects due to poor heat distribution and unreasonable forging temperature during forging, forming a complete and mature large ingot shape of invar alloy electroslag ingot heating temperature control process, which provides protection for forging defect-free intermediate blank.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, and in particular to a forging, rolling and forming process for low expansion coefficient iron-nickel based Invar steel. Background Technology

[0002] Invar is an alloy with an extremely low coefficient of thermal expansion below 230℃ (even up to 253℃), primarily composed of 36% Ni-Fe; it is commonly known internationally as Invar alloy. Invar alloy is an iron-based alloy with a high nickel content. The Ni content is typically between 36% and 40%, containing small amounts of C, P, and S elements, and the Fe content is usually around 60%. Ni is an austenitic element. This alloy has a low coefficient of thermal expansion and low thermal conductivity. Although the strength and hardness of the rolled material are not high, the linear strength can be increased to over 1000 MPa through alloy strengthening, grain refinement strengthening, and precipitation strengthening methods without significantly altering the plasticity.

[0003] Due to its wear resistance, corrosion resistance and low coefficient of expansion, this alloy is widely used in power electronic devices, aerospace components, optical measurement systems and other fields, especially as a cored wire for long-distance power cables with excellent performance.

[0004] Low expansion coefficient Invar alloy rolled products suffer from poor surface quality in the forged intermediate billets used, and the internal grains are often accompanied by coarse mixed grains. Improper control of the cooling process during rolling leads to uneven microstructure of the final rolled product, which is prone to the formation of coarse grain rings. The mechanical properties have a small margin, and the rolled product is prone to wire breakage and cracking. This affects the mechanical properties of the rolled product after heat treatment during redrawing, making it unsuitable for use in related material fields and unable to meet market demands. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a forging and rolling hybrid forming process for low expansion coefficient iron-nickel based Invar steel with good rolled material quality.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes a forging process and a rolling process;

[0007] The forging process involves: the billet being preheated before forging and then forged, with heat preservation between forging cycles; the preheating process is as follows: the billet is preheated in a furnace at 300℃~500℃; then heated at a rate of ≤100℃ / h to 790℃~810℃ and held; then heated again at a rate of ≤100℃ / h to 1170℃~1190℃ and held, followed by forging;

[0008] The forging process is as follows: the temperature in the forging zone is reduced from 950℃~1060℃ in the first forging to 900℃~1060℃ in the last forging, and the holding temperature after forging is reduced from 1170℃~1190℃ in the first forging to 1140℃~1160℃ in the penultimate forging.

[0009] Furthermore, in the forging process, the billet is preheated in a heating furnace at 300℃~500℃ for 3.5~4.5 hours, then heated to 790℃~810℃ and held for at least 2 hours, and then heated to 1170℃~1190℃ and held for at least 7 hours.

[0010] Furthermore, the final forging process in the forging process is as follows: First, the edges are chamfered; then one end is forged, and the side length after forging is the target size + (10~15) mm; then the forging material is turned around, and the other end is forged into a square billet with consistent overall size; then one end is finally forged to the target size; finally, the forging material is turned around a second time, and the other end is finally forged to the target size.

[0011] Furthermore, during the forging process: forging temperature ≥1100℃, impact energy 310~320J, single-sided reduction ≤25mm; forging temperature 1000~1100℃, impact energy 280~310J, single-sided reduction ≤20mm; forging temperature 950~1000℃, impact energy 220~280J, single-sided reduction ≤15mm; forging temperature 900~950℃, impact energy 120~220J, single-sided reduction ≤10mm.

[0012] Furthermore, a five-stage forging process is adopted, with the forging temperature controlled as follows: the forging temperature range for the first stage is controlled at 950℃~1060℃, and the holding temperature after forging is 1170℃~1190℃; the forging temperature range for the second stage is controlled at 900℃~1060℃, and the holding temperature after forging is 1170℃~1190℃; the forging temperature range for the third stage is controlled at 900℃~1060℃, and the holding temperature after forging is 1150℃~1170℃; the forging temperature range for the fourth stage is controlled at 900℃~1060℃, and the holding temperature after forging is 1140℃~1160℃; and the forging temperature range for the fifth stage is controlled at 900℃~1060℃.

[0013] Furthermore, in the rolling process: the temperature of the soaking zone is 970-1020℃, and the soaking zone holding time reaches 120-150min; the initial rolling temperature is 1030-1070℃, the finishing rolling inlet temperature is 900-950℃, and the wire drawing temperature on the air-cooled roller table of the wire rod is 850-900℃.

[0014] Furthermore, the rolling process includes: water cooling after pre-finishing and finishing rolling; the water cooling pipe after pre-finishing has two sections, with the first section having a water flow rate of 80-85 m³ / h. 3 / h, the second stage water flow rate is 27-31m³ / h. 3 / h; The number of controlled cooling water pipe sections after finishing rolling is 4, with the first section having a water flow rate of 27-31m³ / h. 3 / h, the second stage water flow rate is 23-27m³ / h. 3 / h, the water flow rate of the third section is 29-34m³ / h. 3 / h, the water flow rate of the fourth section is 31-35m³ / h. 3 / h.

[0015] Furthermore, in the rolling process: the air-cooled roller conveyor is fully shut off and the insulation cover is fully opened. The speeds of the roller conveyors in sections 1-9 are: 0.60±0.02m / s, 0.62±0.02m / s, 0.64±0.02m / s, 0.66±0.02m / s, 0.68±0.02m / s, 0.70±0.02m / s, 0.72±0.02m / s, 0.70±0.02m / s, and 0.60±0.02m / s.

[0016] The beneficial effects of adopting the above technical solution are as follows: The heating process determined by this invention during forging is the result of numerous experiments and can ensure uniform heating of the billet inside and out without weakening or even destroying the grain boundaries. During forging, the billet will not suffer from surface cracks, scabs, or other defects due to poor heat uniformity or unreasonable forging temperature. This forms a complete and mature heating temperature control process for larger ingot shapes of Invar alloy electroslag ingots, providing a guarantee for forging defect-free intermediate billets. This invention uses a rapid forging method with temperature control and a double-turn forging method in the final heat stage. By reducing the holding forging temperature during the inter-heating stage, it reduces some grain growth caused by temperature increases, compensating for coarse grain or mixed grain defects in the material due to insufficient deformation during forging. Especially in the final heat, the double-turn method solves the problem of coarse grain or mixed grain formation at the clamping end. This invention uses a controlled cooling process for precision rolling and pre-precision rolling to reasonably accelerate the cooling of the rolled material, inhibit austenite grain growth, form grains of similar size and uniform distribution, improve the uniformity of the material structure, and enhance the strength, hardness, and toughness of the steel. This invention provides a forging method and a rolling method for Invar alloy large-shaped long fixed-length defect-free intermediate billets, which solves the problems of coarse grains and mixed grains in the forged intermediate billets leading to small mechanical property margins, thus meeting the requirements of the high-end market. Attached Figure Description

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0018] Figure 1 This is an internal microstructure diagram of the square billet obtained by forging in Embodiment 1 of the present invention;

[0019] Figure 2 This is an internal microstructure diagram of the square billet obtained by forging in Embodiment 2 of the present invention;

[0020] Figure 3 This is a graph showing the heating process regime of the present invention;

[0021] Figure 4 This is a schematic diagram of the first forging process of the present invention;

[0022] Figure 5 This is a schematic diagram of the second forging process of the present invention;

[0023] Figure 6 This is a schematic diagram of the third fire forging process described in this invention;

[0024] Figure 7 This is a schematic diagram of the fourth fire forging process described in this invention;

[0025] Figure 8 This is a schematic diagram of the fifth forging process described in this invention. Detailed Implementation

[0026] The forging and rolling hybrid forming process of this low-expansion coefficient iron-nickel-based Invar steel includes forging and rolling processes. The billet before forging is a high-quality Invar alloy base material, mainly due to the requirement of controlling harmful elements. The billet contains P≤0.010wt%, S≤0.002wt%, O≤0.0018wt%, and H≤0.0003wt%. High-quality raw materials are the basic prerequisite for forging defect-free intermediate billets and meeting rolling performance requirements. The low content of harmful elements such as S, O, and H in the billet can reduce the amount of sulfides, nitrides, and oxide inclusions, and improve the purity of the alloy. This can significantly improve the surface quality, internal quality, and subsequent processing performance of the material during forging and rolling, ultimately improving the strength, toughness, and other properties of the product, and giving the steel good plastic deformation.

[0027] 1) Forging process: The billet is heated before forging and then forged, and the temperature is maintained between forging cycles.

[0028] 1.1) The heating process is as follows: Preheat the billet at room temperature in a furnace at 300℃~500℃ for 3.5~4.5 hours, preferably 4 hours; then heat at a rate of ≤100℃ / h, preferably 80~100℃ / h; hold at 790℃~810℃ for 2 hours or more; then heat at a rate of ≤100℃ / h, preferably 80~100℃ / h; hold at 1170℃~1190℃, with the holding temperature target for each interval preferably at the middle limit of the allowable range; hold for 7 hours or more before forging. For the heating process curve matching the steel grade and ingot shape, please refer to the appendix. Figure 3 .

[0029] 1.2) The forging process is as follows: the final forging temperature shall not be lower than 900℃, and forging should be carried out by preheating. In principle, under strict adherence to the process, the higher the initial forging temperature, the better for forging. The initial forging temperature is related to the on-site equipment layout and operation. The holding time between forging passes shall be ≥60min. The preheating temperature of the anvil and jaws before forging shall not be lower than 200℃. In order to improve the internal structure and performance quality of the material, the forging process described in this invention adopts multi-pass cooling forging. Furthermore, in order to achieve the target requirement of no defects on the surface of the intermediate forging billet, the single-pass reduction is controlled by digital control of forging impact energy and positive correlation fitting relationship with temperature. The specific positive correlation relationship is shown in Table 1.

[0030] Table 1: Positive correlation between forging impact energy, forging temperature, and single-sided reduction

[0031] 310～320 ≥1060 ≤25 280～310 1000～1060 ≤20 220～280 950～1000 ≤15 120～220 900～950 ≤10

[0032] Note: Temperature should be frequently monitored during the forging process, and the impact energy and unilateral reduction should be adjusted according to the temperature.

[0033] The following is a detailed description of the initial base material using a large-sized electroslag ingot with a diameter of φ500mm to φ531mm, a weight of 1.0 to 1.5t, a target forging size of a square with a cross-sectional side length of 145mm to 155mm and a length of ≥7m, a total forging ratio of ≥9, and a five-stage forging process.

[0034] First forging pass: The first forging pass is used to open the electroslag ingot, mainly to crush the surface grains. The temperature in the forging zone is controlled at ≥950℃, but a general impact energy of 180J~220J is required to control the deformation. The single-pass single-sided reduction is ≤10mm, and the single-sided feed is 360~400mm. Figure 4 As shown, the forming process is AC surface → BD surface (90°) → EF surface (45°) → GH surface (45°), with two to three passes to ensure uniform grain breaking on each surface; the final forging is an octagonal forging blank with two opposite sides of approximately 430mm ± 10mm, completing the blanking process. After this forging, it is placed in a heating furnace for holding at a temperature of 1170~1190℃.

[0035] Second firing: The second firing process involves large deformation and full-body reduction of the electroslag ingot, quickly completing the reduction deformation from an octagonal end face shape to a rectangular shape; firstly, it is carried out by rapid temperature forging, with the temperature of the forging zone controlled at ≥950℃, and according to the highest temperature of the initial forging, the impact energy is 310J~320J or 290J~310J, and the single-pass single-side reduction is controlled at 15mm~25mm according to the temperature. Figure 5As shown, a rectangular billet with AC and BD as its four sides is rapidly formed, with the EFGH sides gradually transitioning into angular shapes. Under this impact energy, each side undergoes two passes of deformation, rapidly forming a square billet with a side length of approximately 345mm to 355mm. The end faces and the straightness of the forging billet are then corrected to ensure no defects such as de-squaring, bending, or torsion. Next, the forging temperature is controlled at 900℃ to 950℃, using 150J to 200J of impact energy, with a single pass and single-side reduction ≤10mm. The billet undergoes further small deformation reduction, with each side undergoing two to three passes of forging. The rear end face of this forging process has a side length of 310±10mm, completing the large deformation reduction. During the above process, the impact energy decreases proportionally with temperature; as the temperature decreases, the impact energy and reduction also decrease, as shown in Table 1 above. After this forging, the billet is held in a heating furnace at a temperature of 1170℃ to 1190℃.

[0036] The third firing process involves another large deformation and overall reduction in size of the forging billet. To ensure a uniform and fine grain distribution in the final product, the billet undergoes controlled cooling forging after exiting the furnace. The gas-fired furnace temperature is reduced to 1160°C, and the entire cooling process takes 15 minutes. The total forging time for the third firing is approximately 20 minutes, ensuring that the furnace temperature is 1160°C when the billet is placed back into the furnace after this firing process.

[0037] First, to avoid corner cracks and excessively rapid cooling at the corners, the forging zone temperature is controlled at 1000℃~1060℃, using 130J~160J of impact energy, with a single-pass single-sided reduction ≤10mm, and the edges are quickly chamfered to a length of 10~20mm; then, the forging zone temperature is controlled at 950℃~1030℃, using 290J~310J of impact energy, with a single-pass single-sided reduction ≤25mm, such as... Figure 6 As shown, large deformation reduction is rapidly performed on the four faces AC and BD. After a single forging pass on face A, face C is immediately rotated 180° for reduction, face B is rotated 90° for reduction, and face D is rotated 180° for rotation. This process is repeated cyclically. Any twisting or deflection must be corrected promptly. During the reduction process, the transition area between the reduction end and the clamping end should be a stepped transition, avoiding any abrupt jumps in the reduction. At this point, the end face dimension is approximately 230±10mm. Then, the forging temperature is controlled at 900℃~950℃, using 150J~200J of impact energy, with a single-pass single-side reduction ≤10mm, for small deformation reduction and surface finishing. After this forging pass, the side length of one end face is 190±10mm, completing the large deformation reduction at one end. After this forging pass, the surface is held in a heating furnace at a temperature of 1150℃~1170℃.

[0038] Fourth forging: The fourth forging involves large deformation and full-body reduction forging of the billet, and the furnace temperature is lowered again to 1140℃~1160℃ to ensure that the furnace temperature is 1140℃~1160℃ after the forging is completed. The temperature is lowered again to control the forging and obtain the best grain size and uniformity.

[0039] In this forging process, the other end is reduced in length to form a square billet. Firstly, to avoid corner cracks and excessively rapid cooling at the corners, the forging temperature is controlled at 1000℃~1060℃, using 130J~160J of impact energy, with a single-pass single-sided reduction ≤10mm, and the edges are quickly chamfered to a length of 10~20mm. Then, the forging temperature is controlled at 950℃~1030℃, using 290J~310J of impact energy, with a single-pass single-sided reduction ≤20mm. Figure 7 As shown, large deformation reduction is rapidly performed on the four faces AC and BD. After a single pass of forging on face A, face C is immediately rotated 180° for reduction, face B is rotated 90° for reduction, and face D is rotated 180° for rotation. This process is repeated cyclically. Any twisting or deflection must be corrected promptly. During the reduction process, the transition area between the reduction end and the clamping end should be a stepped transition, avoiding any abrupt transitions. At this point, the end face dimension is approximately 230±10mm. Then, the forging temperature is controlled at 900℃~950℃, using 150J~200J of impact energy, with a single-pass single-side reduction ≤10mm, for small deformation reduction and surface finishing. After this forging pass, the side length of one end face is 190±10mm, completing the large deformation reduction on the other end. In the stepped transition zone, to prevent folding cracks, a striking energy of 180J–230J is used for forging, with a single-pass single-side reduction of ≤15mm. The forging direction transitions from the higher step to the lower step, with a single-side feed of ≤300mm. After this forging, the forged billet has a total side length of 190±10mm. After this forging, it is held in a heating furnace at a temperature of 1140℃–1160℃.

[0040] Fifth firing: This is the last firing. Figure 8As shown, the riser end is first forged into a clamping end. The forging temperature is controlled at 1000℃~1060℃. First, using 130J~160J impact energy, the single-pass single-side reduction is ≤10mm, and the edges are quickly chamfered to a length of 10~20mm. Then, using 290J~310J impact energy, the single-pass single-side reduction is ≤20mm, and two passes of forging are performed to quickly forge a square billet clamping end with a length of approximately 500mm and an end face side length of 165±10mm. The side length of the clamping end is the target size with a 10~15mm deformation allowance, i.e., target size + (1 The 0-15 mm diameter is mainly due to the fact that the forging of the billet ends first, which tends to fall within the material recrystallization temperature range. Without deformation, secondary carbide chains and grain growth are likely to occur, causing fluctuations in the microstructure and grain size quality. If the billet is forged to form the clamping end first, and then quickly turned around to uniformly forge the other end, and then turned around again just before reaching the final forging temperature, the clamping end that is about to be formed is forged again, so that the clamping end has forging deformation again. This allows some of the grains that have grown due to the high forging temperature to be broken up again, achieving the purpose of uniform grain size and completing two forging cycles. Then, the forging is quickly reversed, and the other section is forged. The forging temperature is controlled at 960℃~1010℃, and 290J~310J of impact energy is used to quickly form a square billet with a side length of 160mm~165mm. Two more forging passes are then performed, with the forging temperature controlled at 930℃~960℃ and 150J~210J of impact energy used to quickly form one end into a square billet with a final forged side length of 145mm~155mm. Frequent adjustments are made during the process to avoid defects such as de-squaring and twisting. The forging is then reversed a second time to finalize the clamping end. The forging temperature is controlled at 900℃~930℃, and 150J~210J of impact energy is used for two forging passes to quickly form the clamping end into a square billet with a final forged side length of 145mm~155mm. Finally, the entire forging is completed into a 150×150mm square billet (allowable tolerance ±10mm). During the fifth forging process, in order to ensure the straightness of the length, a laser level is placed parallel to the elongation direction of the forging material to assist in the timely correction of bending during the forging process.

[0041] 1.3) In the forging process, during the drawing and feeding of the billet, the feeding amount for each forging is within the range of 330-460mm; compressed air pipes are used to blow away the iron oxide scale on the working surface during the billet turning gap, so as to achieve defect-free intermediate billet forging and solve the defects of surface cracks, corner cracks and no scabs; after the forging billet is forged to the target specification, it is air-cooled.

[0042] 1.4) This invention controls the positive correlation between impact energy and single-pass reduction, and simultaneously determines the corresponding ingot heating process matching Invar alloy during forging. It uses a stepped controlled cooling forging method to solve the coarse grain mixed crystal phenomenon inside the forging intermediate billet, improves the uniformity of the structure, and promotes the transmission of forging stress from the surface to the core through multi-pass deformation forging, improving the uniformity of deformation in the elongation direction, providing high-quality intermediate billets for the rolled product. Finally, the rolling adopts a controlled cooling process, which effectively and uniformly refines the deformed austenite structure, refines the grains, improves the strength and toughness of the steel, and ensures the performance of the final product. Ultimately, it realizes a composite production process method for forging and rolling Invar alloy ingots with longer fixed lengths.

[0043] The obtained Invar alloy forging intermediate billet has a specification of 150×150mm square billet, an effective length of ≥7m, no cracks or defects on the surface and corners, no scars or pits, a difference of ≤5mm between the two long diagonals, a total curvature of ≤120mm, no torsion, and a grain size of ≥5 for the forging intermediate billet, which solves the problem of mixed grains and coarse grains and provides a high-quality intermediate billet for subsequent rolling.

[0044] 2) Rolling process: Controlled cooling is adopted. The temperature of the soaking zone is 970-1020℃, and the holding time in the soaking zone is 120-150 minutes. The initial rolling temperature is 1030-1070℃, the finishing rolling inlet temperature is 900-950℃, and the wire drawing temperature on the air-cooled roller table for φ10mm-φ13mm wire is 850-900℃. Water cooling is performed after pre-finishing and finishing rolling. The water cooling pipe section after pre-finishing is 2 sections, and the water flow rate of the first section is 80-85m³. 3 / h, the second stage water flow rate is 27-31m³ / h. 3 / h, the number of controlled cooling water pipe sections after finishing rolling is 4, the water flow rate of the first section is 27-31m³ / h. 3 / h, the second stage water flow rate is 23-27m³ / h. 3 / h, the water flow rate of the third section is 29-34m³ / h. 3 / h, the water flow rate of the fourth section is 31-35m³ / h. 3 / h. After the air-cooled roller conveyor is fully shut off and the insulation cover is fully open, the speeds of roller conveyors 1-9 are: 0.60±0.02m / s, 0.62±0.02m / s, 0.64±0.02m / s, 0.66±0.02m / s, 0.68±0.02m / s, 0.70±0.02m / s, 0.72±0.02m / s, 0.70±0.02m / s, 0.60±0.02m / s.

[0045] The resulting Invar alloy rolled products are round bars with diameters of φ10mm, φ12mm, and φ13mm. Their tensile strength is approximately 590 MPa, yield strength is approximately 410 MPa, and expansion coefficient is generally 1.5 × 10⁻⁶. -6 / ℃, elongation after fracture A=30~45%, forging impact toughness AK=130~310J / cm 2 It is relatively stable at room temperature from -80℃ to 230℃; its linear strength can be increased to over 1000 MPa through alloy strengthening, fine grain strengthening, precipitation strengthening, and cold deformation, while maintaining good plasticity.

[0046] Example 1: The forging and rolling hybrid forming process of this low expansion coefficient iron-nickel-based Invar steel is described in detail below.

[0047] (1) The electroslag ingot base material used has a diameter of 500mm and a weight of 1.35t. The ingot is a cold ingot at room temperature. The mass percentage of harmful elements in the base material is shown in Table 2. The forging intermediate billet has a size of 150×150mm, and the rolled round steel has a size of φ13mm. The specific process steps are as follows:

[0048] (2) Forging process: The cold electroslag ingot is loaded into a gas-fired heating furnace at a furnace temperature of 350℃ and preheated for 4 hours. The billet is placed in the furnace away from the furnace door. Then, the temperature is increased at a rate of 90℃ / h until it reaches 800℃. Then, it is held at the same temperature for 2 hours. Then, the temperature is increased at a rate of 100℃ / h until it reaches 1180℃. After holding at this temperature for 7.1 hours, the billet is taken out of the furnace for forging.

[0049] Before forging, the anvil and jaws are preheated at a temperature of 210℃.

[0050] The first forging temperature was 1055℃, with an impact energy of approximately 200J and a single-pass single-sided reduction of 10mm. Surface grain breaking was then initiated, forming an octagonal ingot with an end-to-edge distance of 429mm. The final forging temperature was 950℃. The second forging temperature was 1055℃, with an impact energy of approximately 300J and a single-pass single-sided reduction of 15mm. Large deformation and scaling were initiated. After three passes of scaling, the end-face dimensions were 355×355mm, and the billet temperature was 951℃. Slight de-squarening of the end face was observed, so corner pressing was initiated for end-face correction. Then, with an impact energy of approximately 190J and a single-pass single-sided reduction of 10mm, micro-scaling deformation was performed. After two passes of deformation, a 315×315mm square billet was formed, with a final forging temperature of 901℃. The third forging temperature was 1057℃. At this point, the gas furnace temperature dropped to 1160℃ after 11 minutes. Using 135J of impact energy, the single-pass single-sided reduction was 10mm. The edges were quickly chamfered to a length of 10mm. After chamfering, the temperature was measured at 1000℃. Using 310J of impact energy, the single-pass single-sided reduction was 20mm. After three passes of deformation, the end face size was 235mm×235mm. At this point, the forging temperature was 949℃. Using 150J of impact energy, the single-pass single-sided reduction was 10mm. After two passes, the end size was 189mm×189mm. The fourth forging temperature is 1061℃. At this time, the gas furnace temperature drops to 1150℃ after 7 minutes. 140J of impact energy is used, with a single-pass single-sided reduction of 10mm. The other end is quickly chamfered with a length of 10mm. After chamfering, the temperature is 998℃. 310J of impact energy is used, with a single-pass single-sided reduction of 20mm. After three passes of deformation, the end face size is 233mm×233mm. At this time, the forging temperature is 957℃. 150J of impact energy is used, with a single-pass single-sided reduction of 10mm. After two passes, one end size is 187mm×187mm. The forging of the stepped transition area is fed in 380mm per pass, using 260J of impact energy. The fifth forging pass is at a temperature of 1040℃, using 135J of impact energy to quickly chamfer the edges to an 8mm length. Then, using 310J of impact energy, the single-pass single-side reduction is ≤20mm. Through two passes, a square billet clamping end with a length of approximately 560mm and an end face side length of 166mm is forged. Then, the billet is quickly turned around, the temperature is measured at 1000℃, and 290J of impact energy is used. Through two passes, a square billet with a side length of 163mm is forged. Then, using 180J of impact energy, one end is forged into a 150mm×150mm square billet. The billet is turned around again, and the clamping end is forged, the temperature is measured at 933℃, and 150J of impact energy is used. Through two passes, the clamping end is forged into a 150×150mm square billet. During the forging process, frequent adjustments are made, and a laser level is used to assist in avoiding bending and torsion defects.

[0051] (3) Rolling process: Controlled cooling is adopted. The temperature of the soaking zone during rolling is 1010℃, and the holding time in the soaking zone is 135min. The initial rolling temperature is 1055℃, the finishing rolling inlet temperature is 941℃, and the wire ejection temperature of the upper air-cooled roller table is 900℃. Water cooling is performed after pre-finishing and finishing rolling. The number of water pipe sections for controlled cooling after pre-finishing is 2, and the water flow rate of the first section is 85m³ / h. 3 / h, the second section's water flow rate is 29m³ / h. 3 / h, the number of controlled cooling water pipe sections after finishing rolling is 4, and the water flow rate of the first section is 29m³ / h. 3 / h, the second section's water flow rate is 25m³ / h. 3 / h, the water flow rate of the third section is 31m³ / h. 3 / h, the water flow rate of the fourth section is 33m³ / h. 3 / h. The rear fan of the upper air-cooled roller conveyor is completely turned off, and the insulation cover is fully open. The roller conveyor speeds for sections 1-9 are: 0.62m / s, 0.63m / s, 0.65m / s, 0.66m / s, 0.68m / s, 0.71m / s, 0.70m / s, 0.70m / s, and 0.60m / s.

[0052] The surface quality, internal grain size, and mechanical properties of the rolled round steel in this embodiment of low-expansion iron-nickel-based Invar steel forging and rolling composite forming are shown in [reference needed]. Figure 1 Tables 3 and 4.

[0053] Example 2: The forging and rolling hybrid forming process of this low expansion coefficient iron-nickel-based Invar steel is described in detail below.

[0054] (1) The electroslag ingot base material used has a diameter of 500mm and a weight of 1.31t. The mass percentage of harmful element components in the base material is shown in Table 2. The forging intermediate billet has a size of 150×150mm, and the rolled round steel has a diameter of 13mm. The specific process steps are as follows:

[0055] (2) Forging process: The ingot is a cold ingot at room temperature. The cold electroslag ingot is loaded into a gas-fired heating furnace at a furnace temperature of 330℃ and preheated for 4.4 hours. The billet is placed in the furnace away from the furnace door. Then, the temperature is increased at a rate of 100℃ / h. After reaching 800℃, it is held at the same temperature for 2 hours. Then, the temperature is increased at a rate of 100℃ / h. It is held at 1180℃ for 7.2 hours before being taken out of the furnace for forging.

[0056] Before forging, the anvil and jaws are preheated to 203℃.

[0057] The first forging temperature is 1067℃, with an impact energy of approximately 210J and a single-pass single-side reduction of 10mm. Surface grain breaking begins, forming an octagonal ingot with an end-to-side distance of 425mm. The final forging temperature is 937℃. The second forging temperature is 1060℃, with an impact energy of approximately 310J and a single-pass single-side reduction of 15mm. Large deformation and scaling begin. After three passes, the end-face dimensions are 350×350mm, and the billet temperature is 960℃. Then, with an impact energy of approximately 180J and a single-pass single-side reduction of 10mm, micro-scaling deformation is performed. After two passes, a 309×309mm square billet is formed, with a final forging temperature of 908℃. The third forging temperature was 1061℃. At this point, the gas furnace temperature dropped to 1160℃ after 10 minutes. Using 140J of impact energy, the single-pass single-sided reduction was 10mm. The edges were quickly chamfered to a length of 12mm. After chamfering, the temperature was 1011℃. Using 310J of impact energy, the single-pass single-sided reduction was 20mm. After three passes of deformation, the end face size was 227mm×227mm. At this point, the forging temperature was 956℃. Using 160J of impact energy, the single-pass single-sided reduction was 10mm. After two passes, the end size was 185mm×185mm. The fourth forging temperature is 1066℃. At this time, the gas furnace temperature drops to 1150℃ after 6 minutes. 140J of impact energy is used, with a single-pass single-sided reduction of 10mm. The other end is quickly chamfered, with a chamfer length of 11mm. The temperature after chamfering is 1000℃. 310J of impact energy is used, with a single-pass single-sided reduction of 20mm. After three passes of deformation, the end face size is 229mm×229mm. At this time, the forging temperature is 964℃. 160J of impact energy is used, with a single-pass single-sided reduction of 10mm. After two passes, one end size is 185mm×185mm. The forging of the stepped transition area is fed in 380mm each time, using 270J of impact energy. The fifth forging pass is at a temperature of 1050℃, using 150J of impact energy to quickly chamfer the edges to a length of 10mm. Then, using 310J of impact energy, the single-pass single-side reduction is ≤20mm. Through two passes, a square billet clamping end with a length of approximately 530mm and an end face side length of 169mm is forged. Then, the billet is quickly turned around, and the temperature is measured at 1015℃. Using 300J of impact energy, through two passes, a square billet with a side length of 165mm is forged. Then, using 180J of impact energy, one end is forged into a 150mm×150mm square billet. The billet is turned around again, and the clamping end is forged, and the temperature is measured at 940℃. Using 160J of impact energy, through two passes, the clamping end is forged into a 150×150mm square billet. During the forging process, frequent adjustments are made, and a laser level is used to assist in avoiding bending and torsion defects.

[0058] (3) Rolling process: Controlled cooling is adopted. The temperature of the soaking zone during rolling is 1000℃, and the holding time in the soaking zone is 140min. The initial rolling temperature is 1050℃, the finishing rolling inlet temperature is 935℃, and the wire ejection temperature of the upper air-cooled roller table is 880℃. Water cooling is performed after pre-finishing and finishing rolling. The number of water pipe sections for controlled cooling after pre-finishing is 2, and the water flow rate of the first section is 86m³ / h. 3 / h, the second section's water flow rate is 30m³ / h. 3 / h, the number of controlled cooling water pipe sections after finishing rolling is 4, and the water flow rate of the first section is 31m³ / h. 3 / h, the second section's water flow rate is 26m³ / h. 3 / h, the water flow rate of the third section is 30m³ / h. 3 / h, the water flow rate of the fourth section is 35m³ / h. 3 / h. The rear fan of the upper air-cooled roller conveyor is completely turned off, and the insulation cover is fully open. The roller conveyor speeds for sections 1-9 are: 0.60m / s, 0.62m / s, 0.63m / s, 0.65m / s, 0.68m / s, 0.70m / s, 0.71m / s, 0.69m / s, and 0.60m / s.

[0059] The surface quality, internal grain size, and mechanical properties of the rolled round steel in this embodiment of low-expansion iron-nickel-based Invar steel forging and rolling composite forming are shown in [reference needed]. Figure 2 Tables 3 and 4.

[0060] Table 2: Content of harmful elements in each embodiment / %

[0061] 1 0.0036 0.0015 0.0017 0.0002 2 0.003 0.0012 0.0015 0.00016

[0062] Table 3: Quality of intermediate billets in each embodiment

[0063]

[0064] Table 4: Test results of mechanical properties of rolled round steel in each embodiment

[0065]

Claims

1. A forging and rolling hybrid forming process for low expansion coefficient iron-nickel-based Invar steel, characterized in that: This includes forging and rolling processes; The forging process involves: the billet being preheated before forging and then forged, with heat preservation between forging cycles; the preheating process is as follows: the billet is preheated in a furnace at 300℃~500℃; then heated at a rate of ≤100℃ / h to 790℃~810℃ and held; then heated again at a rate of ≤100℃ / h to 1170℃~1190℃ and held, followed by forging; The forging process is as follows: the temperature in the forging zone is reduced from 950℃~1060℃ in the first forging to 900℃~1060℃ in the last forging, and the holding temperature after forging is reduced from 1170℃~1190℃ in the first forging to 1140℃~1160℃ in the penultimate forging. The final forging process in the forging process is as follows: First, the edges are chamfered; then one end is forged, and the side length after forging is the target size + (10~15) mm; then the forging material is turned around, and the other end is forged to form a square billet with consistent overall size; then one end is finally forged to the target size; finally, the forging material is turned around a second time, and the other end is finally forged to the target size. During the forging process: forging temperature ≥1060℃, impact energy 310~320J, single-sided reduction ≤25mm; forging temperature 1000~1060℃, impact energy 280~310J, single-sided reduction ≤20mm; forging temperature 950~1000℃, impact energy 220~280J, single-sided reduction ≤15mm; forging temperature 900~950℃, impact energy 120~220J, single-sided reduction ≤10mm. Five-stage forging is employed, with the forging temperature controlled as follows: the forging temperature range for the first stage is 950℃~1060℃, and the holding temperature after forging is 1170℃~1190℃; the forging temperature range for the second stage is 900℃~1060℃, and the holding temperature after forging is 1170℃~1190℃; the forging temperature range for the third stage is 900℃~1060℃, and the holding temperature after forging is 1150℃~1170℃; the forging temperature range for the fourth stage is 900℃~1060℃, and the holding temperature after forging is 1140℃~1160℃; the forging temperature range for the fifth stage is 900℃~1060℃. The rolling process includes: a soaking zone temperature of 970–1020℃ and a soaking zone holding time of 120–150 min; an initial rolling temperature of 1030–1070℃; a finishing rolling inlet temperature of 900–950℃; and a wire drawing temperature of 850–900℃ on the air-cooled roller table. Water cooling is performed after pre-finishing and after finishing rolling. The water cooling pipe after pre-finishing has two sections, with the first section having a water flow rate of 80–85 m³ / h. 3 / h, the second stage water flow rate is 27-31m³ / h. 3 / h; The number of controlled cooling water pipe sections after finishing rolling is 4, with the first section having a water flow rate of 27-31m³ / h. 3 / h, the second stage water flow rate is 23-27m³ / h. 3 / h, the water flow rate of the third section is 29-34m³ / h. 3 / h, the water flow rate of the fourth section is 31-35m³ / h. 3 / h.

2. The forging, rolling, and hybrid forming process for a low-expansion-coefficient iron-nickel-based Invar steel according to claim 1, characterized in that: In the forging process, the billet is preheated in a furnace at 300℃~500℃ for 3.5~4.5 hours, then heated to 790℃~810℃ and held for at least 2 hours, and then heated to 1170℃~1190℃ and held for at least 7 hours.

3. The forging, rolling, and hybrid forming process for a low-expansion-coefficient iron-nickel-based Invar steel according to claim 1 or 2, characterized in that, The rolling process is as follows: the air-cooled roller conveyor is fully shut off, the insulation cover is fully opened, and the speeds of roller conveyors 1-9 are 0.60±0.02m / s, 0.62±0.02m / s, 0.64±0.02m / s, 0.66±0.02m / s, 0.68±0.02m / s, 0.70±0.02m / s, 0.72±0.02m / s, 0.70±0.02m / s, and 0.60±0.02m / s, respectively.

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