Method for producing small-size rod of gh4141 alloy

Abstract

The application discloses a preparation method of GH4141 alloy small-size rod, which comprises the following steps: step 1, a multi-stage step high-temperature homogenization heat treatment is carried out on a GH4141 ingot, and then 8-12 times of open-die forging is carried out to obtain a Φ120mm-Φ180mm rod; step 2, the Φ120mm-Φ180mm rod after the open-die forging is rolled to a Φ50mm-Φ70mm rod in the middle of one time of rolling; step 3, after the surface of the Φ50mm-Φ70mm intermediate-rolled rod blank is cleaned, one or two times of rolling is carried out to obtain a Φ8mm-Φ32mm rod, and then solid solution heat treatment, aging heat treatment, straightening and grinding are carried out to obtain a Φ7mm-Φ30mm finished rod. The carbide distribution of the GH4141 alloy rod processed by the method is uniform, the solid solution structure is uniform and consistent without mixed crystals, and the rod performance meets the corresponding standard requirements.

Description

Technical Field

[0001] This invention belongs to the technical field of high-temperature alloy processing methods, specifically relating to a method for preparing small-diameter bars of GH4141 alloy. Background Technology

[0002] GH4141 alloy is a highly alloyed Ni-Cr-Co based precipitation-hardening wrought superalloy. It exhibits high tensile and creep strength in the temperature range of 650℃ to 900℃, as well as good yield strength, fatigue resistance, and oxidation resistance. Its microstructure contains three types of carbides: MC, M6C, and M23C6. After high-temperature aging treatment, γ′ precipitation strengthening phase is obtained. The room temperature tensile strength can reach 1200MPa, making it one of the strongest wrought superalloys. It is a commonly selected material for hot-end components of aerospace engines, such as blades, turbine disks, casings, combustion chambers, and guide vanes.

[0003] GH4141 alloy has a total alloy strengthening element content of up to 46%, of which nearly 40% (Co+Cr+Mo) is used for solid solution strengthening and carbide strengthening, and nearly 5% is used for age strengthening of aluminum and titanium. The extremely high degree of alloying makes its processing extremely difficult. GH4141 alloy has dendrites and carbide precipitation. Its deformation resistance is high, forging temperature range is narrow, hot working plasticity is also poor, and yield is low. It is the most difficult nickel-based wrought high-temperature alloy to process and was once known as the "King of High-Temperature Alloys". Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing small-sized GH4141 alloy bars. The GH4141 alloy bars processed using this method have uniform carbide distribution and uniform microstructure without mixed crystals after solid solution treatment.

[0005] The technical solution adopted in this invention is a method for preparing small-diameter bars of GH4141 alloy, which is implemented according to the following steps:

[0006] Step 1: Perform multi-stage stepped high-temperature homogenization heat treatment on GH4141 ingots, and then perform 8 to 12 forging cycles to open the billet to a size of Φ120mm to Φ180mm.

[0007] Step 2: Roll the Φ120mm~Φ180mm bars after the initial forging into Φ50mm~Φ70mm in one pass.

[0008] Step 3: After cleaning the surface of the Φ50mm~Φ70mm intermediate rolled bar billet, roll it one or two times to a specification of Φ8mm~Φ32mm. Then, after solution heat treatment, aging heat treatment, straightening, and grinding, the finished bar with a specification of Φ7mm~Φ30mm is obtained.

[0009] The invention is further characterized by:

[0010] The high-temperature homogenization heat treatment process in step 1 is as follows: hold at 1150℃~1200℃ for no less than 50 hours, and then remove from the furnace and air cool at below 850℃.

[0011] Step 1, the 8 to 12 forging processes, includes 4 to 6 upsetting and drawing processes, 2 to 4 drawing processes, 1 chamfering process, and 1 rounding process. Among these, at least two of the 4 to 6 upsetting and drawing processes involve axial upsetting.

[0012] During the 4th to 6th upsetting and drawing process: the deformation amount is controlled between 15% and 45%, and the deformation amount increases with the increase of the number of upsetting processes. The deformation amount of axial upsetting is not less than 25%. The forging temperature of the first upsetting process is 1120℃ to 1180℃, and then gradually decreases to 1090℃ to 1170℃ with the increase of the number of upsetting processes. Each upsetting process is heated and held for 4 to 7 hours. The final forging temperature is not lower than 900℃. After forging, the process is air-cooled.

[0013] During the 2nd to 4th heating and drawing process: the deformation amount is controlled at 30% to 50%, the heating temperature is 1070℃ to 1150℃, the heating and holding time is 4 to 6 hours, the final forging temperature is not lower than 800℃, and air cooling is performed after forging.

[0014] The deformation during chamfering is controlled at 10% to 30%, and the deformation during rounding is controlled at 3% to 10%. The heating temperature for chamfering and rounding processes is 1060℃ to 1140℃, and the heating and holding time is 3 to 5 hours. The final forging temperature is not lower than 750℃, and air cooling is performed after forging.

[0015] In step 1, intermediate heat preservation can be carried out in the furnace according to the actual forging temperature drop; the tooling is preheated during the forging process, and the preheating temperature is not lower than 400℃. When the forging interval exceeds 30 minutes, the tooling is reheated; the transfer time of the billet during the forging process is controlled within 90 seconds.

[0016] Step 2 specifically involves rolling Φ120mm~Φ180mm bars onto a 650 reversible rolling mill or a 550 three-roll tandem rolling mill to a specification of Φ50mm~Φ70. The heating temperature is 1100℃~1200℃, and the holding time is 3.5~24 hours. The rolling passes are 6~16, and the deformation per pass is controlled at 10%~30%. The interval between each pass is 5s~25s, and the final temperature is greater than 950℃. After rolling, the bars are air-cooled.

[0017] The rolling process in step 3 is as follows: for bars with a finished diameter of less than Φ15mm, two-fire rolling is used, and for bars with a diameter of more than Φ15mm, one-fire rolling is used; the heating temperature during rolling is 1100℃~1200℃, the holding temperature is 0.75~3 hours, the final temperature is greater than 950℃, and the bars are air-cooled after rolling; the number of rolling passes is 6~16, the deformation per pass is controlled at 10%~25%, and the interval between each pass is 0s~10s.

[0018] In step 3: the solution heat treatment temperature is 1079℃, held for 0.5 to 1.5 hours, and then air-cooled; the aging heat treatment temperature is 760℃, held for 15 to 20 hours, and then air-cooled.

[0019] The beneficial effects of this invention are:

[0020] This invention eliminates interdendritic crystals, carbide re-dissolution, and elemental segregation within the alloy through multi-stage, step-like high-temperature homogenization heat treatment. By employing a rational high-speed forging mill forging and rolling deformation processing technology, it eliminates carbide banding in the bar stock, resulting in a more uniform carbide distribution. Precise control of factors such as temperature, time, and deformation amount during deformation avoids surface cracking and differences in microstructure between the edge and core of the bar stock. By adopting the above methods, this invention improves the hot working plasticity of GH4141 high-temperature alloy steel ingots, reduces the processing difficulty of the material, and enhances the consistency and stability of the bar stock's microstructure and properties. It ensures uniform low-magnification transverse and longitudinal microstructure and carbide distribution in small-diameter bars (Φ7mm~Φ30mm), resulting in a homogeneous microstructure free of mixed crystals after solution treatment, with a grain size reaching 8.5~9.0 grade. Simultaneously, the properties of the heat-treated bars meet the corresponding standard requirements. Attached Figure Description

[0021] Figure 1 This is a carbide distribution diagram of the forged state of the Φ150mm intermediate bar in an embodiment of the present invention, wherein a, b, and c are carbide distribution diagrams of the core, 1 / 2R and edge, respectively;

[0022] Figure 2 This is a forged microstructure diagram of a Φ150mm intermediate bar in an embodiment of the present invention, wherein a, b, and c are microstructure diagrams of the core, 1 / 2R section, and edge section, respectively.

[0023] Figure 3 This is a carbide distribution diagram of the Φ53mm intermediate bar in an embodiment of the present invention, where a and b are carbide distribution diagrams of the core and edge, respectively;

[0024] Figure 4 This is a microstructure diagram of a Φ53mm intermediate bar in an embodiment of the present invention, where a and b are microstructure diagrams of the core and edge, respectively;

[0025] Figure 5These are low-magnification microstructure images of a Φ12mm bar in an embodiment of the present invention, where a and b are microstructure images of the head and tail, respectively;

[0026] Figure 6 These are high-magnification microstructure images of a Φ12mm bar in the solution-treated and aged state in an embodiment of the present invention, where a and b are microstructure images of the head and tail, respectively. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] The method for preparing small-diameter GH4141 alloy bars of the present invention is specifically implemented according to the following steps:

[0029] Step 1: Perform a multi-stage, stepped high-temperature homogenization heat treatment on the GH4141 ingot. Specifically, hold at 1150℃~1200℃ for no less than 50 hours, then remove from the furnace and air-cool at below 850℃. This aims to improve elemental segregation and reduce carbide precipitates.

[0030] After high-temperature homogenization heat treatment, the billet is forged through multiple upsetting and drawing processes to a bar size of Φ120mm~Φ180mm. The forging process involves 8~12 forging cycles, including the first 4~6 forging cycles, the 2~4 drawing cycles, the 1st chamfering cycle, and the 1st rounding cycle. These multiple forging cycles ensure the refinement, homogenization, and surface quality of the billet while reducing carbide banding, ensuring smooth operation of the subsequent rolling process. The forging is performed on a high-speed forging mill. The first 4~6 forging cycles employ a large deformation amount of 15%~45%, with the deformation increasing with each forging cycle. At least two of the 4~6 forging cycles involve axial upsetting, with an axial upsetting deformation amount of not less than 25%. This large deformation process effectively and thoroughly breaks down and homogenizes the microstructure, thereby reducing carbide banding and further refining the grains, improving the microstructure, and enhancing performance. The billet is heated to 1120℃~1180℃ for the first heat, gradually decreasing to 1090℃~1170℃ with each subsequent heat. Each heat is held for 4~7 hours, with a final forging temperature not lower than 900℃. After forging, the billet is air-cooled. During drawing, the deformation is further increased to 30%~50%, further refining and homogenizing the microstructure and improving performance. The heating temperature is 1070℃~1150℃, held for 4~6 hours, with a final forging temperature not lower than 800℃. After forging, the billet is air-cooled. The deformation during chamfering is controlled at 10%~30%, and during rounding, the deformation is controlled at 3%~10%. These two heats primarily transform the cross-section of the bar from square to octagonal before rounding it to Φ120mm~Φ180mm. The heating temperature for chamfering and rounding is 1060℃~1140℃, held for 3~5 hours, with a final forging temperature not lower than 750℃. After forging, the billet is air-cooled.

[0031] The forging temperature window for GH4141 alloy is narrow. Too low a forging temperature can lead to severe cracking during deformation, while too high a temperature may result in a coarse microstructure, affecting subsequent processing. Therefore, strict control of temperature and deformation during forging is necessary. Intermediate reheating can be performed during the forging interval based on the actual temperature drop. The upper and lower hammers, anvils, and other related tools and dies of the high-speed forging mill must be preheated to a temperature not lower than 400℃. If the forging interval exceeds 30 minutes, the tools and dies must be reheated. Furthermore, the billet transfer time should be controlled within 90 seconds. The bar stock must be covered with a soft sleeve to prevent surface temperature drop. This step combines upsetting, square forging, and octagonal forging methods to minimize dendritic structures, prevent deformation dead zones, improve microstructure uniformity, and provide qualified billets for subsequent rolling processing.

[0032] Step 2: After the billet is forged and the surface is cleaned, the Φ120mm~Φ180mm bar is rolled once to a specification of Φ50mm~Φ70mm.

[0033] Φ120mm~Φ180mm bars are rolled to Φ50mm~Φ70 on a 650 reversible rolling mill or a 550 three-roll tandem rolling mill. The heating temperature is 1100℃~1200℃, and the holding time is 3.5~24 hours. To prevent the temperature difference between the edge and the center from being too large and causing poor uniformity of the microstructure, the deformation per pass is controlled at 10%~30%, and the interval between each pass is 5s~25s. The final temperature is greater than 950℃, and the bars are air-cooled after rolling.

[0034] Step 3: After cleaning the surface of the Φ50mm~Φ70mm intermediate rolled bar billet, roll it to Φ8mm~Φ32mm in one or two heat treatments. After solution heat treatment, subsequent aging heat treatment, straightening and grinding, the finished bar stock with Φ7mm~Φ30mm that meets the standard requirements is obtained.

[0035] Intermediate rolling of Φ50mm~Φ70mm bars is performed on a 350 three-roll tandem mill to a final size of Φ8mm~Φ32 before grinding. To ensure microstructure and properties, bars with a finished diameter of Φ15mm or less are rolled in two passes, while bars with a diameter of Φ15mm or more are rolled in one pass. The heating temperature is 1100℃~1200℃, and the holding time is 0.75~3 hours. The deformation per pass is controlled at 10%~25%, with an interval of 0s~10s between passes. The final temperature is greater than 950℃, and the bars are air-cooled after rolling. The solution heat treatment temperature is 1079℃, and the holding time is 0.5~1.5 hours, followed by air cooling. The subsequent aging heat treatment temperature is 760℃, and the holding time is 15~20 hours, followed by air cooling.

[0036] The preheating in steps 2 and 3 should be carried out slowly, with stepped heat treatment before rising to the rolling temperature to avoid cracking of the rolled piece due to excessive thermal stress. The rolling process should be carried out at a relatively high temperature, and the rolls need to be preheated to a temperature not less than 100°C to avoid surface cracking and microstructure differences in the finished bar due to temperature drop. The number of rolling passes should be 6 to 16. Too few passes will result in insufficient deformation and unsatisfactory microstructure, while too many passes will lead to an excessively low final rolling temperature.

[0037] Example 1

[0038] Step 1: The GH4141 alloy ingot with a diameter of Ф500mm undergoes a multi-stage high-temperature homogenization heat treatment, held at 1180℃ for 58 hours. The initial forging is carried out on an 8000T high-speed forging mill, involving eight upsetting and drawing processes to obtain a Φ150mm bar. The deformation process consists of four upsetting and drawing processes, two drawing processes, one chamfering process, and one rounding process. The deformation amounts in the four upsetting and drawing processes are 25%, 28%, 30%, and 45% respectively, gradually increasing with each heat. The heating temperature is 1120℃~1180℃, gradually decreasing to 1090℃~1170℃ with each heat. Heating and holding are performed for 4~7 hours, with a final forging temperature not lower than 900℃. After forging, the bar is air-cooled. The first two forging passes result in a 50% elongation deformation. The heating temperature is 1070℃~1150℃, and the holding time is 4~6 hours. The final forging temperature is not lower than 800℃, and air cooling is performed after forging. The second forging pass results in a 26% deformation deformation, and the third forging pass results in a 6% deformation deformation. The heating temperature is 1060℃~1140℃, and the holding time is 3~5 hours. The final forging temperature is not lower than 750℃, and 100% of the defects are removed after forging. Intermediate reheating and heat preservation can be performed during the forging process based on the actual temperature drop. The upper and lower hammers, anvils, and other related tools and dies of the high-speed forging mill must be preheated to a temperature not lower than 400℃. If the forging interval exceeds 30 minutes, the relevant tools and dies must be reheated. The billet transfer time should be controlled within 90 seconds. The bar stock is covered with a soft sleeve to prevent surface temperature drop.

[0039] Step 2: Roll GH4141 Φ150mm bars to Φ63mm bars on a 650 reversible rolling mill. The heating temperature is 1150℃, and the temperature is held for 4 hours. Rolling is done in 8 passes, with the deformation per pass controlled at 15% to 25%. The average interval between each pass is 15 seconds. The surface temperature of the billet after rolling is 1020℃. After rolling, air cooling is performed to remove 100% of the defects.

[0040] Step 3: Roll the Φ63mm bar to Φ32.0mm bar on a three-roll tandem mill. The heating temperature is 1120℃, held for 1.5 hours, and rolled in 6 passes. The deformation per pass is controlled between 15% and 25%, with an average interval of 10 seconds between each pass. The surface temperature of the billet after rolling is 1030℃. After rolling, it is air-cooled. Subsequently, it is straightened and ground to Φ30.5mm.

[0041] Example 2

[0042] Step 1: Same as in Example 1, the GH4141 alloy ingot with a diameter of Φ500mm undergoes a high-temperature homogenization heat treatment, held at 1180℃ for 56 hours. It is then forged into a bar stock with a diameter of Φ150mm. Details will not be repeated here.

[0043] Step 2: Roll Φ150mm bars to Φ53mm bars on a 550 tandem rolling mill. The heating temperature is 1150℃, and the temperature is held for 4 hours. Roll 10 times, and the deformation per pass is controlled between 14% and 26%. The average interval between each pass is 9 seconds. The surface temperature of the billet after rolling is 1016℃. After rolling, air cool and 100% of the defects are removed.

[0044] Step 3: Roll the Φ53mm bar to Φ18.5mm on a 350 tandem rolling mill. The heating temperature is 1100℃, held for 1 hour, and rolled in 10 passes. The deformation per pass is controlled between 15% and 25%, with an average interval of 4 seconds between passes. The surface temperature of the billet after rolling is 1002℃. After rolling, it is air-cooled. It is then straightened and ground to Φ17mm.

[0045] Example 3

[0046] Steps 1 and 2 are the same as in Example 2, and will not be repeated here.

[0047] Step 3: Roll the Φ53mm bar into a Φ8.5mm bar in two passes on a 350 three-roll tandem mill. The first pass rolls the bar to a Φ26.5mm intermediate billet. The first pass is heated to 1100℃, held for 1 hour, and rolled in 6 passes. The deformation per pass is controlled between 16% and 25%, with an average interval of 8 seconds between passes. The surface temperature of the billet after rolling is 1021℃. The second pass is heated to 1170℃, held for 0.75 hours, and rolled in 12 passes. The deformation per pass is controlled between 10% and 25%, with an average interval of no more than 2 seconds between passes. The surface temperature of the rolled piece after rolling is 990℃ (the length of the Φ26.5mm intermediate billet should not exceed 1000mm; otherwise, the final rolling temperature will be less than 950℃). After rolling to Φ8.5mm, air cooling is performed. Subsequent straightening and grinding are then performed to Φ7.0mm.

[0048] Example 4

[0049] Steps 1 and 2 are the same as in Example 2, and will not be repeated here.

[0050] Step 3: Roll the Φ53mm bar to Φ13.5mm in two passes on a transverse rolling mill. The first pass is the same as in Example 3 and will not be repeated here. The second pass is heated to 1170℃ and held for 0.75 hours, with 8 passes. The deformation per pass is controlled between 10% and 21%, and the average interval between passes is no more than 4 seconds. The surface temperature of the rolled piece is 993℃. After rolling to Φ13.5mm, it is air-cooled. It is then straightened and ground to Φ12.0mm.

[0051] Performance testing of GH4141 high-temperature alloy bars prepared using the method of this invention:

[0052] The carbide distribution and microstructure uniformity of the Φ150mm, Φ53mm, and Φ12mm intermediate bars in the examples were tested, and the test results are as follows: Figures 1-6 As shown.

[0053] In addition, multiple batches of production were carried out using the method of the present invention, producing multiple GH4141 high-temperature alloy bars with a specification of Φ12mm. Their performance was tested, and the combined creep performance data are shown in Table 1, while the mechanical property data such as room temperature tensile and high temperature tensile are shown in Table 2.

[0054] As can be seen from Tables 1 and 2, the properties of the produced bars meet the standard requirements, and the composite creep performance has a large margin. (From Tables 1 and 2...) Figures 1-6 The results show that the GH4141 high-temperature alloy small-size bars produced by the method of this invention have a uniform microstructure. The bars are uniform in the transverse direction at low magnification and are free from metallurgical defects such as shrinkage cavities, cracks, and inclusions. The microstructure in the transverse and longitudinal directions at high magnification is relatively uniform and fine, with uniform distribution of carbides in both the edge and center. The microstructure after solution treatment is uniform and free of mixed crystals, with an average grain size of 8.5 to 9.0. The performance test results fully meet the standard requirements.

[0055] Table 1 Mechanical properties of GH4141 high-temperature alloy bars

[0056]

[0057] Table 2 High-Temperature Alloy Bar Mechanical Properties (Indoor Pull-out)

[0058]

Claims

1. A method for preparing small-diameter bars of GH4141 alloy, characterized in that, The specific steps are as follows: Step 1: Perform multi-stage stepped high-temperature homogenization heat treatment on GH4141 ingots, and then perform 8~12 forging cycles to open the billet to a size of Φ120mm~Φ180mm. Step 2: Roll the Φ120mm~Φ180mm bar stock after the initial forging into a specification of Φ50mm~Φ70mm in one pass. Step 3: After cleaning the surface of the Φ50mm~Φ70mm intermediate rolled bar billet, roll it one or two times to a specification of Φ8mm~Φ32mm. Then, after solution heat treatment, aging heat treatment, straightening and grinding, the finished bar with a specification of Φ7mm~Φ30mm is obtained. The high-temperature homogenization heat treatment process in step 1 is as follows: hold at 1150℃~1200℃ for no less than 50 hours, and then remove from the furnace and air cool at below 850℃; Step 1, the 8-12 forging cycles, includes 4-6 upsetting cycles, 2-4 drawing cycles, 1 chamfering cycle, and 1 rounding cycle. Among these, at least two of the 4-6 upsetting cycles involve axial upsetting. During the 4th to 6th upsetting and drawing process: the deformation amount is controlled between 15% and 45%, and the deformation amount increases with the number of upsetting processes. The deformation amount of axial upsetting is not less than 25%. The forging temperature of the first upsetting process is 1120℃ to 1180℃, and then gradually decreases to 1090℃ to 1170℃ with the number of upsetting processes. Each upsetting process is heated and held for 4 to 7 hours. The final forging temperature is not lower than 900℃. After forging, the process is air-cooled. During the 2nd to 4th heating and drawing process: the deformation amount is controlled at 30% to 50%, the heating temperature is 1070℃ to 1150℃, the heating and holding time is 4 to 6 hours, the final forging temperature is not lower than 800℃, and the forging is air-cooled. The deformation during chamfering is controlled at 10% to 30%, and the deformation during rounding is controlled at 3% to 10%. The heating temperature for chamfering and rounding processes is 1060℃ to 1140℃, and the heating and holding time is 3 to 5 hours. The final forging temperature is not lower than 750℃, and air cooling is performed after forging. In step 1, intermediate heat preservation can be carried out in the furnace according to the actual temperature drop during forging; the tooling is preheated during forging, and the preheating temperature is not lower than 400℃. When the forging interval exceeds 30 minutes, the tooling is reheated; the transfer time of the billet during forging is controlled within 90 seconds. Step 2 specifically involves rolling Φ120mm~Φ180mm bars onto a 650 reversible rolling mill or a 550 three-roll tandem rolling mill to a specification of Φ50mm~Φ70. The heating temperature is 1100℃~1200℃, and the holding time is 3.5~24 hours. The rolling passes are 6~16, and the deformation per pass is controlled at 10%~30%. The interval between each pass is 5s~25s, and the final rolling temperature is greater than 950℃. After rolling, the bars are air-cooled. The rolling process in step 3 is as follows: for bars with a finished diameter of less than Φ15mm, two-fire rolling is used, and for bars with a diameter of more than Φ15mm, one-fire rolling is used; the heating temperature during rolling is 1100℃~1200℃, the holding temperature is 0.75~3 hours, the final rolling temperature is greater than 950℃, and the bars are air-cooled after rolling; the number of rolling passes is 6~16, the deformation per pass is controlled at 10%~25%, and the interval between each pass is 0s~10s.

2. The method for preparing small-diameter GH4141 alloy bars according to claim 1, characterized in that, In step 3: the solution heat treatment temperature is 1079℃, held for 0.5~1.5 hours, and then air-cooled; the aging heat treatment temperature is 760℃, held for 15~20 hours, and then air-cooled.

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