A method of forging a large size superalloy bar

Abstract

This invention relates to the field of forging technology, specifically disclosing a forging method for large-diameter high-temperature alloy bars. The method includes main body forging and surface refinement forging. The main body forging employs a wide anvil and large reduction drawing combined with directional forging, along with stepped cooling and air cooling after each forging pass. The final forging pass involves a temperature recovery and only drawing without upsetting. The surface refinement forging employs a high-temperature, short-time holding combined with a narrow anvil and small reduction drawing and rounding. This invention guides axial metal flow through a wide anvil and large reduction, reducing end shrinkage; directional forging suppresses radial loss; stepped cooling and air cooling work together to prevent grain coarsening; the temperature recovery in the final forging pass ensures plastic deformation; and the high-temperature, narrow anvil, small reduction in the final forging pass achieves a balance between surface refinement and core stabilization. The bars prepared by this invention have uniform microstructure across the entire cross-section, achieve an A-level flaw detection level, and significantly improve yield, meeting the economic requirements of industrial production and showing promising prospects for widespread application.

Description

Technical Field

[0001] This invention relates to the field of forging technology, and in particular to a forging method for large-diameter high-temperature alloy bars. Background Technology

[0002] GH2674 alloy is a high-performance high-temperature alloy with excellent high-temperature strength, oxidation resistance, and corrosion resistance. It is widely used in high-end equipment manufacturing fields such as aerospace, petrochemicals, and energy. With the development of related equipment towards larger sizes and higher performance, the demand for large-diameter GH2674 high-temperature alloy bars (such as those with a diameter of 700 mm and above) is becoming increasingly urgent. However, the forging process of large-diameter GH2674 high-temperature alloy bars presents dual technical challenges: difficulty in microstructure control and low yield. These challenges become more pronounced as the bar size increases.

[0003] At the microstructure control level, the grain size and microstructure uniformity of large-size GH2674 high-temperature alloy bars are difficult to control. Specifically, there is a significant temperature gradient between the surface and core of large-size ingots. The surface of the ingot dissipates heat more quickly, easily causing its temperature to drop below the recrystallization critical temperature, resulting in a coarse-grained microstructure with insufficient recrystallization. In contrast, the core of the ingot is prone to temperature rise due to the accumulation of deformation heat and difficulty in heat dissipation, leading to abnormal grain growth and resulting in an uneven microstructure across the bar cross-section. Furthermore, large-size bars have greater metal flow resistance, making it difficult to effectively transfer deformation to the core. This often results in sufficient surface deformation but insufficient core deformation, further exacerbating microstructure segregation and making it difficult to meet the requirements of high-end equipment for consistent raw material microstructure.

[0004] In terms of yield, the forging yield of large-size GH2674 high-temperature alloy bars is relatively low, mainly due to the following two aspects: Firstly, the metal at the ends of large-size bars suffers severe radial loss under axial pressure, easily forming a central shrinkage defect, leading to an increased amount of material removed from the ends. Traditional processes, to ensure grain size at the core and half-radius position, employ a method of progressively decreasing temperature combined with small reduction in drawing length, further exacerbating the radial loss of end metal and increasing material waste. Secondly, because the coarse grain problem on the surface of large-size bars is difficult to solve, to ensure uniform cross-sectional microstructure in the final product, traditional processes can only remove the coarse grain layer by increasing the machining allowance, further causing material waste.

[0005] Existing forging processes are mostly designed for small and medium-sized bars, and their temperature control and deformation distribution methods do not fully consider the forming characteristics of large-sized bars, making it difficult to balance grain size uniformity and yield. Therefore, developing a forging process for large-sized GH2674 high-temperature alloy bars that can ensure uniform microstructure, achieve A-level flaw detection, and have a high yield has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To address the problem of difficulty in balancing microstructure uniformity and yield in existing large-size high-temperature alloy forging processes, this invention provides a forging method for large-size high-temperature alloy bars.

[0007] To solve the above-mentioned technical problems, the technical solution provided by the embodiments of the present invention is as follows:

[0008] A forging method for large-size high-temperature alloy bars includes heating and holding the steel ingot at a certain temperature and then performing multi-fire forging, wherein the multi-fire forging includes at least 5 fires of main body forging and 1 final fire for surface refinement forging; the main body forging includes at least 4 fires of upsetting and drawing forging and 1 final fire for drawing forging.

[0009] In the main forging process, a wide flat anvil is used for forging. The anvil width is 700-800mm. The drawing operation is carried out with a single hammer reduction of 80-150mm and a single hammer feed of 200-250mm. The drawing time for each forging is 7-9 minutes. During the drawing process, each pass is forged from the head end of the billet to the tail end. After each forging, the billet is air-cooled on the ground for 30-35 minutes and then reheated in the furnace. Except for the last forging, the reheating temperature of each subsequent forging is lower than that of the previous forging, and the reheating temperature of the last forging is higher than that of the previous forging.

[0010] In the surface refinement forging, a narrow flat anvil is used for forging. The anvil width is 400~600mm. The drawing and rounding operation is carried out according to a single hammer pressing amount of 30~60mm. The drawing and rounding time is 4~6min.

[0011] Compared to existing technologies, the forging method for large-size high-temperature alloy bars provided by this invention employs a wide, flat anvil in the main forging process. By increasing the contact area between the anvil and the billet, deformation energy is more evenly transferred to the core of the forging, effectively avoiding the microstructure segregation problem of sufficient surface deformation but insufficient core deformation in traditional processes. Simultaneously, by controlling the reduction and feed rate, uniform deformation in each pass is ensured, preventing excessive local deformation leading to grain coarsening or insufficient deformation leading to inadequate recrystallization. Furthermore, the large reduction guides the metal to flow axially, suppressing radial metal loss at the ends and reducing central shrinkage defects. Based on this, each pass in the drawing process employs directional forging from the head to the tail end. By fixing the forging direction, the metal is guided to flow directionally from the head to the tail, further suppressing radial metal loss at the tail end, significantly reducing the amount of metal removed from the ends, and thus greatly improving the yield.

[0012] Furthermore, this invention employs a stepped cooling method during the main forging process (except for the last forging pass), and performs air cooling for 30-35 minutes after each forging pass. This air cooling effectively reduces the core temperature of the bar, eliminating the plastic deformation heat effect generated by the previous forging pass and preventing the core temperature from increasing cumulatively during subsequent reheating, thus preventing abnormal grain coarsening at its source. The stepped cooling further suppresses the grain growth trend, keeping the grain size fine and uniform throughout the forging process. This effectively solves the problem of uneven microstructure caused by large temperature gradients in large-diameter bars, significantly improving the consistency of the cross-sectional microstructure of the bar and achieving a flaw detection level that meets Class A requirements.

[0013] In the final heat treatment of the main body forging, the remelting temperature is increased to a higher level than the previous heat treatment to ensure that the metal has sufficient plastic flow capacity during the drawing process. The method of drawing without upsetting avoids the severe core deformation and temperature rise caused by additional upsetting. While ensuring the uniformity of the microstructure, the cross-sectional size is further reduced, creating favorable conditions for the final heat treatment of surface refinement forging.

[0014] In the final forging (surface refinement forging), a narrow anvil and a small reduction are used to concentrate the deformation in the surface and near-surface areas, achieving sufficient recrystallization and refinement of the surface metal, while significantly reducing the amount of core deformation and avoiding excessive heat conversion of deformation work, which would cause the core temperature to rise and coarsen. Short forging time ensures that the surface metal completes recrystallization in the high-temperature range, while avoiding excessive heat accumulation in the core due to prolonged forging time.

[0015] By adopting the above-mentioned process control, this invention effectively overcomes the dual problems of difficult microstructure control and low yield in the forging of large-size bars by traditional processes. The uniformity of the microstructure of the resulting bar cross section is significantly improved, and the flaw detection level stably reaches the A-level requirement. At the same time, due to the reduction of end shrinkage and the controllability of the surface coarse grain layer, the material utilization rate is greatly improved, and the yield meets the economic requirements of industrial production, showing good prospects for promotion and application.

[0016] It should be noted that the forging method for large-size high-temperature alloy bars provided by this invention is applicable to the preparation of bars with a specification of Ф700mm~Ф710mm.

[0017] Specifically, the high-temperature alloy bar is a large-size GH2674 high-temperature alloy bar.

[0018] The chemical composition of the GH2674 high-temperature alloy bar is as follows: C≤0.08%; Mn 1.20~1.70%; Si≤0.70%; S≤0.015%; P≤0.020%; Mo 1.10~1.60%; V 0.20~0.40%; Al≤0.30%; Cr 14.00~16.00%; Ti 1.90-2.40%; Ni 24.00~26.00%; B≤0.010%; Zr≤0.010%; Ce≤0.010%, with the balance being Fe and unavoidable impurity elements.

[0019] Furthermore, the steel ingot is cylindrical with a diameter of 800~820mm.

[0020] It should be noted that the steel ingots described in this invention can be prepared by conventional methods in the art, such as electric furnace smelting, AOD refining, LF refining, VD vacuum refining, casting, and vacuum consumable remelting to obtain Φ810±10mm round consumable ingots.

[0021] Furthermore, the steel ingot is heated to a temperature of 1090~1110℃ and held for 4~6 hours.

[0022] Furthermore, before the upsetting operation, ceramic fibers are placed at both ends of the steel ingot, and the ingot body is also coated with ceramic fibers. Ceramic fibers have excellent thermal insulation properties, reducing heat conduction loss when the ends contact the anvil surface, preventing the formation of coarse-grained structures due to excessively low end temperatures. Simultaneously, the ingot body coating reduces the temperature gradient between the surface and the core, resulting in a more uniform temperature field distribution during deformation. In addition, end insulation helps suppress excessive radial metal loss, reduces end shrinkage, improves material utilization, and enhances the transfer of deformation towards the core, laying the foundation for improved uniformity of the forging structure and increased yield in subsequent forging processes.

[0023] Furthermore, the initial forging temperature is ≥920℃, and the final forging temperature is ≥860℃.

[0024] Furthermore, in the main body forging process, except for the final forging, the reflow temperature of the subsequent forging is 10-30°C lower than the reflow temperature of the previous forging, and the reflow temperature of the final forging is 20-30°C higher than the previous forging.

[0025] Furthermore, the main body forging is carried out in 5 heats, with the remelting temperature of the first heat being 1070~1090℃, the remelting temperature of the second heat being 1060~1080℃, the remelting temperature of the third heat being 1040~1060℃, the remelting temperature of the fourth heat being 1010~1030℃, and the temperature of the fifth heat being 1040~1060℃.

[0026] By quantitatively controlling the temperature difference, the main forging stage achieves both sufficient fragmentation of the as-cast structure due to cumulative deformation from multiple heat treatments and avoids abnormal grain coarsening, providing a billet base with good structural consistency for the final heat treatment surface refinement forging.

[0027] Furthermore, in the main forging process, the reheating time for the four upsetting and drawing forging processes is 3-4 hours; the reheating time for the final drawing forging process is 1.5-2 hours.

[0028] By controlling the holding time within the above range, it can be ensured that the temperature of the core and surface of the billet is fully uniform, providing a temperature basis for the uniform transfer of deformation energy to the core during the subsequent wide anvil and large reduction drawing operation; on the other hand, this holding time avoids the problem of abnormal coarsening of the core grains caused by excessively long holding time.

[0029] Furthermore, in the main body forging, the forging ratio of the upsetting section in the first forging is 1.40~1.53, and the forging ratio of the drawing section is 1.19~1.29;

[0030] The forging ratio of the upsetting section in the second firing is 1.45~1.57, and the section ratio of the drawing section is 1.45~1.57.

[0031] The forging ratio of the upsetting section in the third firing is 1.45~1.57, and the section ratio of the drawing section is 1.45~1.57.

[0032] The forging ratio of the upsetting section in the fourth firing is 1.45~1.57, and the forging ratio of the drawing section is 1.04~1.13;

[0033] The forging ratio for the fifth firing is 1.51 to 1.67.

[0034] Furthermore, the forging ratio of the surface refinement forging is 1.24~1.33.

[0035] It should be noted that the forging ratios mentioned above in this invention refer to the ratio of cross-sectional areas before and after plastic deformation. Specifically, the forging ratio of the upsetting section refers to the ratio of the cross-sectional area after upsetting to the cross-sectional area before upsetting; the forging ratio of the drawing section refers to the ratio of the cross-sectional area before drawing to the cross-sectional area after drawing.

[0036] In this invention, the upsetting and drawing operations in each heat treatment are performed using conventional forging methods in the art. Specifically, the upsetting operation reduces the billet height and increases the diameter by controlling the pressure of the anvil, while the drawing operation reduces the billet cross-sectional area and extends its length by successively feeding and pressing it down.

[0037] Specifically, in the main body forging, the first firing process includes upsetting, drawing the octagon, and pressing the clamp handle. The upsetting speed is 5~10mm / s, and the diameter after upsetting is 970~990mm. The octagon is drawn to a diameter of 870~890mm, and the clamp handle presses the head into a clamp handle of (260~300)mm×(440~460)mm.

[0038] Specifically, in the main body forging, the diameter after the second to third forging is controlled to be 1070~1090mm, and then drawn to an octagon with a diameter of 870~890mm; the diameter after the fourth forging is 1070~1090mm, and then drawn to a square shape of (910~930)mm×(910~930)mm; and the fifth forging is drawn to a square shape of (720~740)mm×(720~740)mm.

[0039] Furthermore, the upsetting speed for the second to fourth firings is 5~10mm / s.

[0040] Furthermore, in the surface refinement forging process, the forging tool is preheated to 400~500℃.

[0041] This preheating measure can effectively prevent the bar surface from cooling rapidly when the cold tumbler comes into contact with the high-temperature billet, preventing the surface temperature from dropping below the recrystallization critical temperature and forming a coarse grain layer that has not been fully recrystallized, thus ensuring uniform microstructure across the entire cross section.

[0042] Specifically, after the surface refinement forging, the process also includes a finishing process, which finishes the bar to Φ700 (+10 / 0) ​​mm.

[0043] In summary, this invention discloses a forging method for large-size GH2674 high-temperature alloy bars. This method includes main body forging and surface refinement forging. The main body forging employs a wide anvil and large reduction drawing combined with directional forging, along with stepped cooling and air cooling after each forging pass. The final forging pass involves a temperature recovery and only drawing without upsetting. The surface refinement forging uses a high-temperature, short-time holding temperature combined with a narrow anvil and small reduction drawing and rounding. This invention guides axial metal flow through a wide anvil and large reduction to reduce end shrinkage, directional forging suppresses radial loss, stepped cooling and air cooling work together to prevent grain coarsening, the temperature recovery in the final forging pass ensures plastic deformation, and the high-temperature, narrow anvil, small reduction in the final forging pass achieves a balance between surface refinement and core stabilization. The bars prepared by this invention have uniform microstructure across the entire cross-section, achieve an A-level flaw detection level, and significantly improve yield, meeting the economic requirements of industrial production and showing good prospects for widespread application. Attached Figure Description

[0044] Figure 1 Metallographic image of the edge of the head of the large-size GH2674 bar prepared in Example 1;

[0045] Figure 2 Metallographic structure at half the radius of the head of the large-size GH2674 bar prepared in Example 1;

[0046] Figure 3 Metallographic structure at the center of the head of the large-diameter GH2674 bar prepared in Example 1;

[0047] Figure 4 Metallographic image of the tail edge of the large-size GH2674 bar prepared in Example 1;

[0048] Figure 5 Metallographic structure at half the radius of the tail portion of the large-diameter GH2674 bar prepared in Example 1;

[0049] Figure 6 Metallographic structure at the center of the tail of the large-size GH2674 bar prepared in Example 1. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0051] To better illustrate the present invention, further examples are provided below.

[0052] Example 1

[0053] This invention provides a forging method for large-diameter GH2674 bars, the steps of which are as follows:

[0054] 1. Steel ingot preparation:

[0055] GH2674 high-temperature alloy steel ingots with a specification of Φ810mm and a weight of 8.05t were selected. The steel ingots were heated to 1100℃ and held for 5 hours to make the overall temperature of the steel ingots uniform before forging.

[0056] 2. Main body forging:

[0057] The main forging process involves five passes. Passes 1 to 4 involve upsetting and drawing, while pass 5 is solely for drawing. Each pass uses a wide, flat anvil (800mm wide) for drawing. The single hammer reduction is 80-150mm, and the single hammer feed is 200-250mm. During the drawing process, each pass involves directional forging from the head end to the tail end.

[0058] First fire:

[0059] After being taken out of the furnace, the ingot body is covered with ceramic fiber, and ceramic fiber is placed at both ends of the steel ingot.

[0060] Upsetting: Control the upsetting speed to 7mm / s, and the diameter after upsetting is Φ985mm;

[0061] Lengthening the octagon: Lengthen to an octagonal shape of 882mm for 7.5 minutes;

[0062] Head clamp handle: The head is clamped into a 280mm×450mm clamp handle;

[0063] After forging, the material is air-cooled for 31 minutes, then reheated in the furnace to 1080℃ and held for 3 hours.

[0064] Second fire:

[0065] Upsetting: Upsetting speed 6mm / s, upset diameter Φ1085mm;

[0066] Lengthening the octagon: Lengthen to an octagonal shape of 885mm and lengthen for 8 minutes;

[0067] After forging, the material is air-cooled for 30 minutes, then reheated in the furnace to 1070℃ and held for 3.5 hours.

[0068] Third fire:

[0069] Upsetting: Upsetting speed 7mm / s, upset diameter Φ1080mm;

[0070] Lengthening the octagon: Lengthen to an octagon of 880mm for 7.5 minutes;

[0071] After forging, the material is air-cooled for 35 minutes, then reheated in the furnace to 1050℃ and held for 3 hours.

[0072] 4th Fire:

[0073] Upsetting operation: Upsetting speed 7mm / s, upset diameter Φ1082mm;

[0074] Lengthening operation: Lengthen to 920mm×920mm, lengthening time 8.5min;

[0075] After forging, the material is air-cooled for 33 minutes, then reheated in the furnace to 1020℃ and held for 3 hours.

[0076] 5th Fire:

[0077] Lengthening operation: Lengthen to 730mm×730mm, lengthen for 8 minutes;

[0078] After forging, the material is air-cooled for 32 minutes, then reheated in the furnace to 1050℃ and held for 1.5 hours.

[0079] 3. Surface Refinement Forging:

[0080] The sixth firing is for surface refinement forging:

[0081] Preheat the hammer to 450℃, use a narrow flat anvil (400mm wide), and perform the stretching and rounding operation with a single hammer pressing down of 45mm. Control the stretching and rounding time to 5 minutes, and round it to Φ725mm.

[0082] 4. Gloss finishing:

[0083] The Φ725mm bar is machined to remove surface oxide scale and minor defects, resulting in a Φ700mm finished bar.

[0084] The GH2674 high-temperature alloy bar prepared in this embodiment was tested and found to have a flaw detection level of A (compliant with GB / T6402-2018 standard). The entire cross-section showed uniform microstructure and no reflected wave defects.

[0085] Grain size inspection: Head edge position, 1 / 2 radius, head center (e.g.) Figures 1-3 The levels shown are 4.0, 4.0, and 4.0 respectively; the tail edge position, half radius, and head center are 4.0, 4.0, and 4.0 respectively.

[0086] The yield of the GH2674 high-temperature alloy bar prepared in this embodiment is 73%.

[0087] Example 2

[0088] This invention provides a forging method for large-diameter GH2674 bars, the steps of which are as follows:

[0089] 1. Steel ingot preparation:

[0090] GH2674 high-temperature alloy steel ingots with a specification of Φ810mm and a weight of 8.05t were selected. The steel ingots were heated to 1100℃ and held for 5 hours to make the overall temperature of the steel ingots uniform before forging.

[0091] 2. Main body forging:

[0092] The main body forging process involves five passes. Passes 1 to 4 involve upsetting and drawing, while pass 5 is solely for drawing. Each pass uses a wide, flat anvil (700mm wide) for drawing. The single hammer reduction is 80-150mm, and the single hammer feed is 200-250mm. During the drawing process, each pass involves directional forging from the head end to the tail end.

[0093] First fire:

[0094] After being taken out of the furnace, the ingot body is covered with ceramic fiber, and ceramic fiber is placed at both ends of the steel ingot.

[0095] Upsetting: Control the upsetting speed to 7mm / s, and the diameter after upsetting is Φ985mm;

[0096] Lengthening the octagon: Lengthen to an octagonal shape of 882mm for 7 minutes;

[0097] Head clamp handle: The head is clamped into a 280mm×450mm clamp handle;

[0098] After forging, the material is air-cooled for 30 minutes, then reheated in the furnace to 1070℃ and held for 4 hours.

[0099] Second fire:

[0100] Upsetting: Upsetting speed 6mm / s, upset diameter Φ1085mm;

[0101] Lengthening the octagon: Lengthen to an octagonal shape of 885mm, and lengthen for 9 minutes;

[0102] After forging, the material is air-cooled for 35 minutes, then reheated in the furnace to 1060℃ and held for 4 hours.

[0103] Third fire:

[0104] Upsetting: Upsetting speed 7mm / s, upset diameter Φ1080mm;

[0105] Lengthening the octagon: Lengthen to an octagonal shape of 880mm and lengthen for 7 minutes;

[0106] After forging, the material is air-cooled for 30 minutes, then reheated in the furnace to 1040℃ and held for 4 hours.

[0107] 4th Fire:

[0108] Upsetting operation: Upsetting speed 7mm / s, upset diameter Φ1082mm;

[0109] Lengthening operation: Lengthen to 920mm×920mm, lengthen for 9 minutes;

[0110] After forging, the material is air-cooled for 30 minutes, then reheated in the furnace to 1010℃ and held for 4 hours.

[0111] 5th Fire:

[0112] Lengthening operation: Lengthen to 730mm×730mm, lengthen for 9 minutes;

[0113] After forging, the material is air-cooled for 35 minutes, then reheated in the furnace to 1040℃ and held for 2 hours.

[0114] 3. Surface Refinement Forging:

[0115] The sixth firing is for surface refinement forging:

[0116] Preheat the hammer to 500℃, use a narrow flat anvil (500mm wide), and perform the stretching and rounding operation with a single hammer pressing down of 45mm. Control the stretching and rounding time to 4 minutes, and round it to Φ725mm.

[0117] 4. Gloss finishing:

[0118] The Φ725mm bar is machined to remove surface oxide scale and minor defects, resulting in a Φ700mm finished bar.

[0119] The GH2674 high-temperature alloy bar prepared in this embodiment was tested and found to have a flaw detection level of A (compliant with GB / T6402-2018 standard). The entire cross-section showed uniform microstructure and no reflected wave defects.

[0120] Grain size inspection: The head edge position, half radius, and head center are grade 4.0, 4.0, and 4.0, respectively; the tail edge position, half radius, and head center are grade 4.0, 4.0, and 4.0, respectively.

[0121] The yield of the GH2674 high-temperature alloy bar prepared in this embodiment is 71%.

[0122] Example 3

[0123] This invention provides a forging method for large-diameter GH2674 bars, the steps of which are as follows:

[0124] 1. Steel ingot preparation:

[0125] GH2674 high-temperature alloy steel ingots with a specification of Φ810mm and a weight of 8.05t were selected. The steel ingots were heated to 1100℃ and held for 5 hours to make the overall temperature of the steel ingots uniform before forging.

[0126] 2. Main body forging:

[0127] The main forging process involves five passes. Passes 1 to 4 involve upsetting and drawing, while pass 5 is solely for drawing. Each pass uses a wide, flat anvil (900mm wide) for drawing. The single hammer reduction is 80-150mm, and the single hammer feed is 200-250mm. During the drawing process, each pass involves directional forging from the head end to the tail end.

[0128] First fire:

[0129] After being taken out of the furnace, the ingot body is covered with ceramic fiber, and ceramic fiber is placed at both ends of the steel ingot.

[0130] Upsetting: Control the upsetting speed to 7mm / s, and the diameter after upsetting is Φ985mm;

[0131] Lengthening the octagon: Lengthen to an octagonal shape of 882mm for 9 minutes;

[0132] Head clamp handle: The head is clamped into a 280mm×450mm clamp handle;

[0133] After forging, the material is air-cooled for 35 minutes, then reheated in the furnace to 1090℃ and held for 3 hours.

[0134] Second fire:

[0135] Upsetting: Upsetting speed 6mm / s, upset diameter Φ1085mm;

[0136] Lengthening the octagon: Lengthen to an octagonal shape of 885mm for 7 minutes;

[0137] After forging, the material is air-cooled for 32 minutes, then reheated in the furnace to 1080℃ and held for 3 hours.

[0138] Third fire:

[0139] Upsetting: Upsetting speed 7mm / s, upset diameter Φ1080mm;

[0140] Lengthening the octagon: Lengthen to an octagonal shape of 880mm and lengthen for 9 minutes;

[0141] After forging, the material is air-cooled for 31 minutes, then reheated in the furnace to 1060℃ and held for 3 hours.

[0142] 4th Fire:

[0143] Upsetting operation: Upsetting speed 7mm / s, upset diameter Φ1082mm;

[0144] Lengthening operation: Lengthen to 920mm×920mm, lengthen for 7 minutes;

[0145] After forging, the material is air-cooled for 35 minutes, then reheated in the furnace to 1030℃ and held for 3 hours.

[0146] 5th Fire:

[0147] Lengthening operation: Lengthen to 730mm×730mm, lengthen for 7 minutes;

[0148] After forging, the material is air-cooled for 30 minutes, then reheated in the furnace to 1060℃ and held for 1.5 hours.

[0149] 3. Surface Refinement Forging:

[0150] The sixth firing is for surface refinement forging:

[0151] Preheat the hammer to 400℃, use a narrow flat anvil (600mm wide), and perform the stretching and rounding operation with a single hammer pressing down of 45mm. Control the stretching and rounding time to 6 minutes, and round it to Φ725mm.

[0152] 4. Gloss finishing:

[0153] The Φ725mm bar is machined to remove surface oxide scale and minor defects, resulting in a Φ700mm finished bar.

[0154] The GH2674 high-temperature alloy bar prepared in this embodiment was tested and found to have a flaw detection level of A (compliant with GB / T6402-2018 standard). The entire cross-section showed uniform microstructure and no reflected wave defects.

[0155] Grain size inspection: The head edge position, half radius, and head center are grade 4.0, 4.0, and 4.0, respectively; the tail edge position, half radius, and head center are grade 4.0, 4.0, and 4.0, respectively.

[0156] The yield of the GH2674 high-temperature alloy bar prepared in this embodiment is 72%.

[0157] Comparative Example 1

[0158] This comparative example provides a forging method for large-size GH2674 bars. The only difference from Example 1 is that in the main forging process, the reheating temperature of the second to fifth forging passes is 1080°C. All other process parameters are exactly the same as in Example 1, and will not be repeated here.

[0159] The bar prepared in Comparative Example 1 was tested and found to be at level B, failing to reach level A and not meeting the requirements of GB / T 6402-2018 standard. The grain size inspection results were: 4.0 grade at the head edge, 2.0 grade at half the radius, and 1.0 grade at the core, exhibiting obvious grain inhomogeneity, with severe coarse grains in the core. Due to the failure to pass the flaw detection test, the prepared bar was scrapped.

[0160] The above test results show that when the main body forging process does not adopt a stepped cooling strategy but adopts constant temperature heating (1080℃), even though the other process parameters are the same, the core of the bar stock will grow abnormally due to repeated heating and lack of air cooling to eliminate the heat accumulation of deformation. As a result, the flaw detection level cannot meet the Class A requirement.

[0161] Comparative Example 2

[0162] This comparative example provides a forging method for large-size GH2674 bars. The only difference from Example 1 is that in the sixth forging process, which is a surface refinement forging process, an 800mm wide flat anvil is used and the single hammer reduction is 110mm. All other process parameters are exactly the same as in Example 1, and will not be repeated here.

[0163] The bar prepared in Comparative Example 2 was tested and found to be at level B, failing to reach level A and not meeting the requirements of GB / T 6402-2018 standard. The grain size inspection results were: 4.0 grade at the head edge, 2.0~4.0 grade (mixed grains) at half the radius, and 2.0 grade at the core, exhibiting obvious grain inhomogeneity, with severe coarse grains in the core. Due to the failure to pass the flaw detection test, the bar was ultimately scrapped.

[0164] As can be seen from the comparison between Comparative Example 2 and Example 1, when the surface refining forging adopts a wide anvil and large reduction (anvil width 800mm, reduction 110mm), due to the large contact area of ​​the anvil surface and the large reduction, the deformation energy not only acts on the surface layer, but also penetrates deep into the core, resulting in large deformation of the core. The deformation work is converted into heat, which raises the temperature of the core and causes abnormal grain coarsening. At the same time, the wide anvil forging has a limited refining effect on the surface metal, and the deformation of the surface layer and the subsurface layer is uneven, forming a mixed grain structure.

[0165] Comparative Example 3

[0166] This comparative example provides a forging method for large-size GH2674 bars. The only difference from Example 1 is that in the main forging process, the drawing time for the 3rd, 4th, and 5th forging passes is 5 min, 5.5 min, and 4.5 min, respectively. All other process parameters are exactly the same as in Example 1, and will not be repeated here.

[0167] The bar prepared in Comparative Example 3 was tested and found to be at level B, failing to reach level A and not meeting the requirements of GB / T 6402-2018 standard. The grain size inspection results were: 5.0 grade at the head edge, 1.0~4.0 grade (mixed grains) at half the radius, and 1.0 grade at the core, exhibiting obvious grain inhomogeneity, with severe coarse grains in the core. Due to the failure to pass the flaw detection test, the bar was ultimately scrapped.

[0168] The experimental results show that when the drawing time of each heat in the main body forging is shortened, the heat accumulation in the core cannot be fully released through sufficient forging time, the core temperature continues to rise, and abnormal grain coarsening occurs. At the same time, insufficient drawing time causes the metal in the deformation zone to stay in the recrystallization temperature range for too short a time, resulting in insufficient recrystallization and the formation of mixed crystal structure.

[0169] Comparative Example 4

[0170] This comparative example provides a forging method for large-size GH2674 bars. The only difference from Example 1 is that in the sixth forging process of surface refinement, the drawing and rounding time is controlled to 8 minutes. All other process parameters are exactly the same as in Example 1, and will not be repeated here.

[0171] The bars prepared in Comparative Example 4 were tested and found to be at level A, meeting the requirements of GB / T 6402-2018 standard. The grain size inspection results were as follows: grain size at the head edge was 2.0~5.0 (mixed grains), at 1 / 2 radius it was 4.0, and at the center it was 4.0, exhibiting obvious grain inhomogeneity. The yield was 67%.

[0172] Comparing Comparative Example 4 with Example 1, it can be seen that when the drawing and rounding time for surface refinement forging is extended to 8 minutes, although the flaw detection level can still reach Grade A, the uniformity of the microstructure decreases significantly, with coarse grains and mixed grains appearing at the edges, and the yield also decreases to 67%. This is because the excessive drawing and rounding time causes the surface metal to remain in the high-temperature range for too long, intensifying heat dissipation. In some areas, the temperature drops below the recrystallization critical temperature, forming a coarse-grained microstructure that has not fully recrystallized. Simultaneously, the prolonged forging time increases the heat accumulation in the core. Although this does not cause core coarsening, it exacerbates the uneven deformation of the surface and subsurface layers, leading to mixed grains. Due to the presence of mixed grains at the edges, to ensure the uniformity of the final product's cross-section, the machining allowance needs to be increased to remove the surface coarse grains and mixed grain layers, resulting in material waste and a significant decrease in yield.

[0173] Comparative Example 5

[0174] This comparative example provides a forging method for large-size GH2674 bars. The only difference from Example 1 is that after the main forging process, the reheating temperature of the fifth furnace charge is 1020°C. All other process parameters are exactly the same as in Example 1, and will not be repeated here.

[0175] The bars prepared in Comparative Example 5 were tested and found to be at level A, meeting the requirements of GB / T 6402-2018 standard. The grain size inspection results were as follows: grain size at the head edge was 2.0~5.0 (mixed grains), at 1 / 2 radius it was 4.0, and at the center it was 4.0, exhibiting obvious grain inhomogeneity. The yield was 66%.

[0176] As can be seen from the comparison between Comparative Example 5 and Example 1, when the reheat temperature of the fifth forging pass in the main body is reduced from 1050℃ to 1020℃, although the flaw detection level can still reach Grade A, the uniformity of the microstructure is significantly reduced, mixed crystals appear at the edges, and the yield is reduced to 66%. This is because the fifth forging pass, as the final forging pass in the main body, undertakes the critical deformation task of drawing from 920mm square to 730mm square. The lower reheat temperature leads to reduced metal plasticity and increased deformation resistance. During the drawing process, deformation is difficult to be uniformly transmitted to the surface and sub-surface areas, resulting in insufficient recrystallization in some areas and the formation of a mixed crystal structure. Simultaneously, the lower base temperature weakens the high-temperature compensation effect of the subsequent final forging pass, making it difficult to obtain a uniform recrystallized microstructure during surface refinement forging. Due to the presence of mixed crystals at the edges, in order to ensure the uniformity of the final product cross-section microstructure, the machining allowance needs to be increased to remove the mixed crystal layer on the surface, resulting in material waste and a significant decrease in yield.

[0177] Comparative Example 6

[0178] This comparative example provides a forging method for large-size GH2674 bars. The only difference from Example 1 is that in the main forging process, the third to fifth forging passes are all performed from the tail end to the head end of the forging head. All other process parameters are exactly the same as in Example 1, and will not be repeated here.

[0179] The bars prepared in Comparative Example 6 were tested and found to be at level A, meeting the requirements of GB / T 6402-2018 standard. The grain size inspection results were: 4.0 grade at the head edge, 4.0 grade at half the radius, and 4.0 grade at the center, exhibiting obvious grain inhomogeneity. The yield was 67%.

[0180] Reverse forging from tail to head causes a mismatch between the metal flow direction and the temperature and stress field distribution of the billet. This leads to increased radial metal loss at the tail and an increase in end shrinkage defects, requiring the removal of more end material and thus reducing the yield.

[0181] Comparative Example 7

[0182] This comparative example provides a forging method for large-size GH2674 bars. The only difference from Example 1 is that after the first to fifth forging in the main forging process, the bars are directly reheated in the furnace without the step of air cooling after forging. All other process parameters are exactly the same as in Example 1, and will not be repeated here.

[0183] The bar prepared in Comparative Example 7 was tested and found to be at level B, failing to reach level A and not meeting the requirements of GB / T 6402-2018 standard. The grain size inspection results were: 4.0 grade at the head edge, 2.0 grade at half the radius, and 1.0 grade at the core, exhibiting obvious grain inhomogeneity, with severe coarse grains in the core. Due to the failure to pass the flaw detection test, the bar was ultimately scrapped.

[0184] Because the core of the bar stock lacks an air cooling step to eliminate deformation heat, the plastic deformation heat generated in the previous forging process accumulates inside the billet. After reheating, the core temperature rises exponentially, causing the core temperature to far exceed the set temperature, resulting in abnormal grain coarsening. At the same time, the temperature gradient between the core and the surface further expands, the microstructure uniformity deteriorates severely, and the flaw detection level cannot meet the Class A requirements.

[0185] Based on the comparison results of the above embodiments and Comparative Examples 1-7, it can be seen that the forging method for large-size GH2674 high-temperature alloy bars proposed in this invention effectively avoids the problems of abnormal grain coarsening and uneven microstructure in the core by using stepped cooling in the main forging stage and air cooling after each forging pass; by controlling the drawing time of each forging pass to 7-9 minutes, the deformation rate and temperature rise control are matched; by using the method of temperature recovery in the final forging pass of the main forging and only drawing without upsetting, a good temperature basis is provided for the surface refinement forging in the final forging pass while ensuring the large deformation drawing in the final forging pass; by using a narrow anvil and small reduction in the final forging pass and controlling the drawing and rounding time to 4-6 minutes, a balance is achieved between sufficient recrystallization refinement of the surface and stable core temperature; at the same time, by using directional forging from the head clamp end to the tail end throughout the process, the end shrinkage defect is effectively suppressed, and the yield is significantly improved. Comparative Examples 1-7 verified the necessity of each of the above-mentioned key technical features. When any feature deviates from the scope defined by the present invention, it will lead to a decrease in tissue uniformity, a decrease in flaw detection level, or a significant decrease in yield.

[0186] In summary, this invention overcomes the dual technical difficulties of difficult microstructure control and low yield in large-size bar forging by synergistically controlling process elements such as temperature, deformation, forging time, and forging direction in multi-fire forging. While ensuring that the flaw detection level consistently reaches Grade A and the microstructure is uniform across the entire cross section, it achieves a high yield and fully meets the economic requirements of industrial production.

[0187] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of forging a large-size superalloy bar, characterized by, The process includes heating and holding the steel ingot at a certain temperature before performing multi-stage forging. The multi-stage forging includes five stages of main forging and one final stage of surface refining forging. The main forging includes four stages of upsetting and drawing forging and one final stage of drawing forging. In the main forging process, a wide flat anvil is used for forging. The anvil width is 700-800mm. The drawing operation is carried out with a single hammer reduction of 80-150mm and a single hammer feed of 200-250mm. The drawing time for each forging is 7-9 minutes. During the drawing process, each pass is forged from the head end of the billet to the tail end. After each forging, the billet is air-cooled on the ground for 30-35 minutes and then reheated in the furnace. Except for the last forging, the reheating temperature of each subsequent forging is lower than that of the previous forging, and the reheating temperature of the last forging is higher than that of the previous forging. In the surface refinement forging, a narrow flat anvil is used for forging. The anvil width is 400~600mm. The drawing and rounding operation is carried out according to a single hammer pressing amount of 30~60mm. The drawing and rounding time is 4~6min. The diameter of the large-size high-temperature alloy bar is 700mm~710mm; In the main body forging process, except for the final forging, the remelting temperature of each subsequent forging is 10-30°C lower than that of the preceding forging, and the remelting temperature of the final forging is 20-30°C higher than that of the preceding forging. The remelting temperature of the first forging of the main body is 1070-1090°C, the second forging is 1060-1080°C, the third forging is 1040-1060°C, the fourth forging is 1010-1030°C, and the fifth forging is 1040-1060°C. The remelting holding time for the upsetting and drawing forging of the four forging processes is 3-4 hours. The remelting holding time for the drawing forging of the final forging is 1.5-2 hours.

2. The method of claim 1, wherein the large size superalloy bar is forged at a temperature of 1,100°C to 1,300°C. The steel ingot is cylindrical with a diameter of 800-820 mm; and / or The steel ingot is heated to a temperature of 1090~1110℃ and held for 4~6 hours.

3. The forging method for large-diameter high-temperature alloy bars as described in claim 1, characterized in that, In the main body forging process, the forging ratio of the upsetting section in the first forging pass is 1.40~1.53, and the forging ratio of the drawing section is 1.19~1.

29. The forging ratio of the upsetting section in the second firing is 1.45~1.57, and the section ratio of the drawing section is 1.45~1.

57. The forging ratio of the upsetting section in the third firing is 1.45~1.57, and the section ratio of the drawing section is 1.45~1.

57. The forging ratio of the upsetting section in the fourth firing is 1.45~1.57, and the forging ratio of the drawing section is 1.04~1.13; The forging ratio for the fifth firing is 1.51 to 1.

67.

4. The forging method for large-diameter high-temperature alloy bars as described in claim 1 or 3, characterized in that, The forging ratio for the surface refinement forging is 1.24~1.

33.

5. The forging method for large-diameter high-temperature alloy bars as described in claim 1, characterized in that, In the main body forging process, the first firing process includes upsetting, drawing the octagon, and pressing the clamp handle. The upsetting speed is 5~10mm / s, and the diameter after upsetting is 970~990mm. The octagon is drawn to a diameter of 870~890mm, and the clamp handle presses the head into a clamp handle of (260~300)mm×(440~460)mm.

6. The forging method for large-diameter high-temperature alloy bars as described in claim 1 or 3, characterized in that, In the main body forging process, the diameter after the second to third forging is controlled to be 1070~1090mm, and then drawn to an octagon with a diameter of 870~890mm; after the fourth forging, the diameter is 1070~1090mm, and then drawn to a square shape of (910~930)mm×(910~930)mm; and after the fifth forging, the shape is drawn to a square shape of (720~740)mm×(720~740)mm.

7. The forging method for large-diameter high-temperature alloy bars as described in claim 1, characterized in that, In the surface refinement forging process, the forging tool is preheated to 400~500℃.

Images