A method for preparing a GH4738 alloy strip

Abstract

The application provides a preparation method of GH4738 alloy strip, and relates to the technical field of high-temperature alloy materials. The method comprises the following steps: preparing a GH4738 alloy ingot by adopting a vacuum induction melting and vacuum self-consumption remelting duplex process; homogenizing; blooming forging; hot rolling; solid solution treatment; multi-pass cold rolling; finished product solid solution treatment; and straightening. In the cold rolling process, the deformation amount of each pass is controlled, thereby maximally avoiding uneven deformation in the cold rolling process, making the strip structure of each pass recrystallize, and avoiding defects such as cracks, camber, wrinkles, pitting and the like. The finished product heat treatment adopts an electric heating furnace or a continuous annealing furnace, so that uniform structure and performance are ensured. Excellent plate shape is obtained through straightening. The strip prepared by adopting the method has the advantages of high size precision, smooth surface, good uniformity and the like.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, specifically a method for preparing GH4738 alloy strip. Background Technology

[0002] GH4738 alloy is a Ni-Cr-Co-Mo precipitation-hardening wrought superalloy with excellent high-temperature strength, creep resistance, and thermal fatigue resistance, making it suitable for long-term service under medium-high temperature and high-stress conditions. The most significant characteristic of GH4738 alloy is the precise proportioning of cobalt, molybdenum, aluminum, and titanium into a nickel-chromium matrix. Aluminum and titanium form a dispersed γ' phase (Ni3(Al,Ti)) precipitation strengthening phase, while cobalt and molybdenum provide solid solution strengthening. This dual strengthening mechanism significantly enhances the alloy's high-temperature mechanical properties and microstructural stability. Compared to ordinary solid solution-strengthened superalloys, this composite strengthening system exhibits superior high-temperature load-bearing capacity and deformation resistance. The alloy can withstand a maximum long-term continuous service temperature of 815℃ and a short-term oxidation-resistant service temperature of 1040℃. In addition, this alloy has excellent oxidation resistance and resistance to gas corrosion in high-temperature gas environments, oxidizing environments, and corrosive atmospheres. It also has good cold and hot working plasticity and weldability, and stable microstructure. Therefore, it is widely used in the preparation of core high-temperature load-bearing components such as turbine disks, blades, sealing rings, and fasteners for aero engines and gas turbines.

[0003] The following are the main problems with GH4738 alloy: 1. Strong cold work hardening: The γ′ phase of GH4738 alloy has a significant strengthening effect, and the cold work hardening effect is much higher than that of conventional solid solution nickel-based high-temperature alloys. During the cold rolling process, the deformation resistance increases sharply, the plasticity decreases rapidly, and it is very easy to produce edge cracks, surface micro-cracks, and plate delamination defects, making it difficult to achieve continuous and stable rolling with large deformation.

[0004] 2. Difficulty in controlling microstructure uniformity: GH4738 alloy has a narrow recrystallization range and is highly sensitive to cold deformation amount, annealing temperature, holding time and cooling rate; traditional single annealing system is difficult to take into account the recrystallization requirements of strips with different cumulative deformation amounts, resulting in uneven grain size and hardness distribution, which greatly deteriorates the tensile properties of the finished product.

[0005] In summary, given the unique material properties of GH4738 alloy, developing a method for preparing GH4738 alloy strip that is adaptable to wide and ultra-thin specifications, can be stably mass-produced, and possesses both uniform microstructure and stable mechanical properties has significant engineering application value and industry promotion significance. Summary of the Invention

[0006] This invention aims to solve the technical problems of high cold rolling deformation resistance, high risk of cracking, poor deformation uniformity, high difficulty in shape control, uneven microstructure, and insufficient dimensional accuracy of GH4738 alloy strip in the prior art. It provides a method for preparing high-precision GH4738 alloy strip, which adopts a multi-pass cold rolling combined with appropriate annealing process to effectively weaken uneven deformation and avoid cold rolling cracking. The finished strip has a uniform microstructure, a defect-free state, excellent shape quality, and stable service performance.

[0007] To achieve the above objectives, the following technical solution is adopted: This invention provides a method for preparing GH4738 alloy strip, comprising the following steps: (1) Smelting: GH4738 alloy ingots were prepared by a dual process of vacuum induction melting and vacuum consumable remelting; (2) Homogenization: Heat the ingot to 1150-1250℃, hold for 20-50 hours, and then cool it in the furnace to below 600℃ before air cooling. (3) Forging: Heat the ingot to 1100℃~1200℃, control the deformation to 50%~85%, and forge the alloy ingot into a slab. (4) Hot rolling: The slab is heated to 1150℃~1250℃, and the deformation is controlled at 65%~95% to hot roll the slab into a strip. (5) Solution treatment: Hot-rolled strip is subjected to solution treatment at a temperature of 1100℃~1150℃ and a holding time of 30~90 minutes, followed by water cooling. (6) Cold rolling: Multi-pass cold rolling is carried out at room temperature. Each pass includes multiple rolling passes, and intermediate annealing is performed between each pass. The total deformation in each rolling pass is controlled between 30% and 60%, and the deformation in the last rolling pass is between 30% and 70%. During each intermediate annealing process in the cold rolling process, the annealing temperature is 1050℃~1150℃, and water cooling and air cooling are used for cooling, with a cooling rate of >200℃ / s; (7) Solution treatment of finished product: After cold rolling to the target thickness, solution treatment of finished product is carried out. The annealing temperature is 1050℃~1120℃. Water cooling and air cooling are used for cooling, and the cooling rate is >200℃ / s. (8) Tension straightening: The strip shape is straightened by tension straightening machine to eliminate strip shape defects and improve surface and mechanical properties.

[0008] Each step is explained in detail: Step (1) Smelting: The dual process of vacuum induction melting (VIM) and vacuum arc remelting (VAR) is adopted to precisely control the alloy composition, effectively reduce the content of harmful impurities such as oxygen and nitrogen, eliminate as-cast compositional segregation and porosity defects, and obtain GH4738 alloy ingots with dense structure and uniform composition.

[0009] The chemical composition of GH4738 alloy, by mass fraction, includes: C 0.02-0.10%, Co 12.0-15.0%, Cr 18.0-21.0%, Mo 3.5-5.0%, Al 1.2-1.6%, Ti 2.75-3.25%, B 0.003-0.010%, Zr 0.02-0.08%, Si≤0.15%, Mn≤0.10%, P≤0.015%, S≤0.015%, Cu≤0.10%, Fe≤2.0%, with the balance being Ni.

[0010] Vacuum induction melting employs a gradient feeding method to control the burn-off of active elements such as Al and Ti. High-vacuum refining reduces the gas content of the melt, resulting in cast consumable electrodes with uniform composition and fewer defects. The electrodes are then subjected to vacuum consumable arc remelting, using a three-stage stepped power regime of arc initiation, stable melting, and hot capping to stably control the molten pool morphology and melting rate, forming a shallow, flat molten pool for stable directional solidification. This process effectively suppresses dendritic segregation and coarse primary carbide formation in GH4738 alloy, reduces oxide inclusion levels, and minimizes metallurgical defects such as ingot porosity and black spots. The resulting consumable ingot has a dense structure and high compositional uniformity, significantly improving subsequent hot working and cold rolling performance, and reducing strip cracking and mixed-grain defects.

[0011] Step (2) Homogenization: The ingot is heated to 1150–1250℃ and held for 20–50 hours. It is then furnace cooled to below 600℃ and air-cooled. High-temperature solid-state atomic diffusion is used to eliminate / reduce dendritic segregation in the casting state, dissolve non-equilibrium eutectic and low-melting-point phases between dendrites, and make the composition and microstructure of the ingot more uniform. This improves the hot working plasticity of the ingot, eliminates inherited defects in the structure, and stabilizes the structure and mechanical properties of subsequent forgings.

[0012] Step (3) Forging: The ingot is heated to 1100℃~1200℃ and held at that temperature for 4h~8h to ensure uniform temperature before forging begins. The total deformation is controlled at 50%~85%, and the ingot is forged into a slab with a thickness of 40mm~70mm. By breaking up the coarse as-cast dendrite structure, dynamic recrystallization is achieved, the grains are refined, and the tiny porosity and micropores inside the ingot are welded together, thereby increasing the density, further improving the compositional uniformity, and weakening residual segregation, laying a good microstructure foundation for subsequent rolling.

[0013] Step (4) Hot rolling: The slab is heated to 1150℃~1250℃ and held for 0.5h~2h to ensure complete austenitization of the alloy and sufficient uniformity of the microstructure; the total deformation is 65%~95%, and the thickness of the strip after hot rolling is 4.0mm~6.0mm; relying on high temperature and large deformation, the grains are further refined, and the deformation uniformity in the ultra-wide direction is ensured at the same time, weakening the difference in transverse microstructure and properties.

[0014] Step (5) Solution treatment: Hot-rolled strip is subjected to high-temperature solution treatment at 1100℃~1150℃ for 30~90 minutes and then water-cooled. This allows the carbides precipitated during hot rolling to fully dissolve into the austenite matrix, resulting in a uniform supersaturated solid solution that completely restores the alloy's plasticity and eliminates residual stress from previous hot working.

[0015] Step (6) Cold rolling: The rolling process is carried out at room temperature, with the rolling speed controlled at 10–100 m / min. The deformation amount of each cold rolling pass is 30%–60%, and the deformation amount of the last cold rolling pass is 30%–70%.

[0016] Intermediate annealing is performed between each rolling pass: annealing temperature 1050℃~1150℃, heat treatment holding time for strip 1~15 minutes, cooling method of water cooling + air cooling, cooling rate >200℃ / s.

[0017] Step (7) Solution treatment of the finished product: After cold rolling to the minimum target thickness of 0.1 mm, the finished product is solution treated in an electric heating furnace at a temperature of 1050℃~1120℃ for 5~20 minutes, using a water-cooling + air-cooling method with a cooling rate of >200℃ / s.

[0018] Step (8) Straightening: The finished strip is preliminarily straightened by a tension straightening machine, which eliminates most of the macroscopic residual stress, corrects obvious shape defects such as camber and edge waviness, and initially improves the straightness of the strip.

[0019] The minimum thickness of the prepared strip is 0.1±0.01mm, and the width is more than 300mm.

[0020] Compared with the prior art, the present invention has the following significant advantages: On a multi-roll cold rolling mill, GH4738 alloy strip is cold-rolled at room temperature with a minimum thickness of 0.1mm ± 0.01mm and a width of over 300mm. During the cold rolling process, the deformation amount of each pass is controlled to minimize uneven deformation, ensuring recrystallization of the strip microstructure in each pass and preventing defects such as cracks, camber, wrinkles, and pitting.

[0021] The heat treatment of the finished product in this invention uses an electric heating furnace or a continuous annealing furnace to ensure uniform microstructure and properties. Excellent strip shape is obtained through tension straightening. The strip prepared using the method described in this invention has advantages such as high dimensional accuracy, smooth surface, and good uniformity. It saves raw materials and labor time, and the method is simple, economical, and efficient, meeting higher application requirements.

[0022] While specific embodiments of the present invention have been described in detail above, these embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention. Furthermore, the actual application effects of the present invention are not limited to any scientific theories or mechanisms of action mentioned herein. Attached Figure Description

[0023] Figure 1 Photo of a 55mm thick hot-forged slab.

[0024] Figure 2 Photograph of a 0.5mm thick strip.

[0025] Figure 3 The grain structure of the strip is 0.3 mm thick. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0027] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0028] Example 1 GH4738 alloy ingots were prepared by vacuum induction melting and vacuum arc remelting. The raw material composition of GH4738 alloy (in mass fraction) is accurately weighed according to the target alloy composition ratio as follows: C: 0.06%, Co: 14.0%, Cr: 19.5%, Mo: 4.25%, Al: 1.4%, Ti: 3.0%, B: 0.007%, Zr: 0.05%, Si≤0.15%, Mn≤0.10%, P≤0.015%, S≤0.015%, Cu: 0.05%, Fe: 1.5%, with the balance being Ni.

[0029] According to the target composition ratio of GH4738 alloy, electrolytic nickel, electrolytic cobalt, metallic chromium, metallic molybdenum, pure iron, electrolytic aluminum, sponge titanium, and graphite raw materials were accurately weighed and sequentially loaded into the crucible of a vacuum induction melting furnace. The furnace body was evacuated, and the raw materials were melted by heating under vacuum. After all the metal raw materials were completely melted into a homogeneous molten steel, a high vacuum environment was maintained for refining to thoroughly remove gaseous impurities such as oxygen, hydrogen, and nitrogen, as well as trace amounts of harmful inclusions, thus purifying the molten steel. After successful refining, the high-temperature molten steel was smoothly poured into a preheated ingot mold. After static solidification and demolding, it was air-cooled to room temperature, yielding an alloy electrode rod with satisfactory surface and internal quality.

[0030] The prepared alloy electrode rods were clamped and fixed inside a vacuum arc remelting furnace. After the furnace was evacuated to a high vacuum, the arc was ignited to initiate melting. The entire process of electrode melting, droplet refining, and sequential solidification in the crystallizer was completed under vacuum conditions. After the smelting operation was completed, the formed ingot was subjected to gradient slow cooling and heat preservation cooling treatment to finally obtain GH4738 vacuum arc remelting steel ingot with uniform structure, stable composition, and high purity.

[0031] After being held at 1180℃ for 35 hours, the furnace was cooled to below 600℃ and then air-cooled to room temperature to complete the homogenization process. The resulting slab was then forged at 1150℃ into a 55mm thick slab with a deformation of approximately 65%. The prepared slab is shown below. Figure 1 As shown, the strip is heated to 1180℃ and hot-rolled into a 4.5mm strip with a deformation of approximately 92%. It is then held at 1120℃ for 60 minutes and water-cooled to room temperature to complete the solution treatment. The strip is then cold-rolled and annealed four times to produce a 0.8mm × 300mm strip. The cold rolling process parameters are shown in Table 1.

[0032] Table 1 Cold rolling process parameters of the example

[0033] After cold rolling, the finished product undergoes solution treatment: electric heating furnace, holding temperature: 1080℃, holding time: 16min, followed by water cooling + air cooling, cooling rate > 200℃ / s; then tension straightening is performed to eliminate strip shape defects and improve surface and mechanical properties.

[0034] Example 2 The hot-rolled strip blank of Example 1 was subjected to cold rolling and annealing five times to produce a 0.5mm × 300mm strip. The cold rolling process parameters are shown in Table 2.

[0035] Table 2 Cold rolling process parameters of the example

[0036] After cold rolling, the finished product undergoes solution treatment: electric heating furnace, holding temperature: 1100℃, holding time: 12min, followed by water cooling + air cooling, cooling rate > 200℃ / s; then tension leveling is performed to correct the strip shape, eliminate strip shape defects, and improve surface and mechanical properties.

[0037] Example 3 The hot-rolled strip blank of Example 1 was subjected to cold rolling and annealing repeated 6 times to produce a 0.3mm × 300mm strip. The cold rolling process parameters are shown in Table 3.

[0038] Table 3 Cold rolling process parameters in the examples

[0039] After cold rolling, the finished product undergoes solution treatment: electric heating furnace, holding temperature: 1110℃, holding time: 8min, followed by water cooling + air cooling, cooling rate > 200℃ / s; then tension straightening is performed to correct the strip shape, eliminate strip shape defects, and improve surface and mechanical properties.

[0040] Example 4 The hot-rolled strip blank of Example 1 was subjected to cold rolling and annealing repeated 7 times to produce a 0.1mm × 300mm strip. The cold rolling process parameters are shown in Table 4.

[0041] Table 4. Cold rolling process parameters in Example 4

[0042] After rolling, the finished product undergoes solution treatment: electric heating furnace, holding temperature: 1100℃, holding time: 6min, followed by water cooling + air cooling, cooling rate > 200℃ / s; then tension straightening is performed to correct the strip shape, eliminate strip shape defects, and improve surface and mechanical properties.

[0043] Comparative Example 1 A 0.3mm × 300mm strip was obtained using the same process as in Example 3. During the solution heat treatment of the finished product, it was cooled in air after the heat preservation was completed, with a cooling rate of <200℃ / s.

[0044] Comparative Example 2 A 0.1mm × 300mm strip was obtained using the same process as in Example 4. After rolling, the strip underwent solution treatment: an electric heating furnace was used to maintain the temperature at 1100℃ for 6 minutes. The strip was then cooled in air at a rate of <200℃ / s. Finally, a tension leveling process was used to correct the strip shape, eliminate shape defects, and improve surface and mechanical properties.

[0045] Comparative Example 3 Hot-rolled strip blanks were obtained using the same process as in Example 2. These strip blanks were then cold-rolled and annealed. During the second rolling pass, when the strip was cold-rolled to 1.1 mm, the deformation was 63.3%, exceeding 60%, causing cracks at the strip edge. After removing the cracked portions, the strip underwent intermediate annealing and was rolled into 0.5 mm × 300 mm strips. The cold rolling process parameters are shown in Table 6.

[0046] Table 6 Comparative Example 3 Cold Rolling Process Parameters

[0047] After cold rolling, the finished product undergoes solution treatment: electric heating furnace, holding temperature: 1100℃, holding time: 15min, followed by water cooling + air cooling, cooling rate > 200℃ / s; then tension leveling is performed to correct the strip shape, eliminate strip shape defects, and improve surface and mechanical properties.

[0048] Performance testing: The GH4738 alloy strip products obtained in the examples and comparative examples were subjected to the following tests: Room temperature tensile properties: GB / T 228.1 Metallic materials, tensile testing—Part 1: Test at room temperature; Grain size rating: GB / T 6394 "Method for determination of average grain size of metals"; Hardness: GB / T 4340.1 "Metallic materials - Vickers hardness test - Part 1: Test method"; Roughness: GB / T 1031 "Product Geometric Specification (GPS) Surface Structure Profile Method Surface Roughness Parameters and Their Values".

[0049] Two sets of data were tested for each sample, and the results are shown in the table below:

[0050] Results Analysis: As can be seen from the performance test results of Examples 1-4 and Comparative Examples 1-3 above, the GH4738 alloy precision strip prepared by the present invention through multi-stage cold rolling deformation control, intermediate annealing and high-speed cooling of >200℃ / s after solution treatment of finished product fully meets the technical requirements.

[0051] In Examples 3 and 4, the finished products underwent solution treatment and were cooled using a combination of water and air cooling at a rate >200℃ / s. In Comparative Examples 1 and 2, all other process parameters remained identical to those of Examples 3 and 4, except for the cooling method after solution treatment, which was changed to air cooling at a rate <200℃ / s. The mechanical properties, hardness, and grain size of these examples did not meet the technical requirements. This was due to insufficient cooling, which caused work hardening of the alloy matrix and a significant deterioration in plasticity.

[0052] In Comparative Example 3, except that the total deformation in the second rolling pass reached 63.3%, exceeding the maximum deformation limit of 60% for the rolling pass specified in this invention, the remaining processes of smelting, homogenization, forging, hot rolling, heat treatment, and tension leveling were consistent with those of Example 2. In Comparative Example 3, edge cracking defects appeared in the strip during the second rolling pass, requiring the cracked edges to be removed before further rolling could continue, thus reducing the material yield.

[0053] Only by simultaneously satisfying the following conditions: ① the deformation amount in each cold rolling stroke is controlled within 30%-60%, and the deformation in the final rolling stroke is 30%-70%; ② the cooling rate after intermediate annealing and solution treatment of the finished product is >200℃ / s; can the technical problems of high cold rolling deformation resistance, easy cracking, high residual stress, and uneven microstructure of GH4738 alloy be solved, and ultra-thin precision strip of aerospace-grade GH4738 alloy with high dimensional accuracy, smooth surface, and uniform and stable microstructure and properties be obtained. If any key process parameter deviates from the protection scope of this invention, one or more defects such as cracking, insufficient plasticity, excessive hardness, and coarse grains will occur, and the product will not meet the requirements of high-end equipment.

[0054] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for preparing GH4738 alloy strip, characterized in that, Includes the following steps: (1) Smelting: GH4738 alloy ingots were prepared by a dual process of vacuum induction melting and vacuum consumable remelting; (2) Homogenization: Heat the ingot to 1150-1250℃, hold for 20-50 hours, and then cool it in the furnace to below 600℃ before air cooling. (3) Forging: Heat the ingot to 1100℃~1200℃, control the deformation to 50%~85%, and forge the alloy ingot into a slab. (4) Hot rolling: The slab is heated to 1150℃~1250℃, and the deformation is controlled at 65%~95% to hot roll the slab into a strip. (5) Solution treatment: Hot-rolled strip is subjected to solution treatment at a temperature of 1100℃~1150℃ and a holding time of 30~90 minutes, followed by water cooling. (6) Cold rolling: Multi-pass cold rolling is carried out at room temperature. Each pass includes multiple rolling passes, and intermediate annealing is performed between each pass. The total deformation in each rolling pass is controlled between 30% and 60%, and the deformation in the last rolling pass is between 30% and 70%. During each intermediate annealing process in the cold rolling process, the annealing temperature is 1050℃~1150℃, and water cooling and air cooling are used for cooling, with a cooling rate of >200℃ / s; (7) Solution treatment of finished product: After cold rolling to the target thickness, solution treatment of finished product is carried out. The annealing temperature is 1050℃~1120℃. Water cooling and air cooling are used for cooling, and the cooling rate is >200℃ / s. (8) Tension straightening: Plate shape correction is performed using a tension straightening machine.

2. The method according to claim 1, characterized in that, The chemical composition of GH4738 alloy in step (1) by mass fraction includes: C: 0.02-0.10%, Co: 12.0-15.0%, Cr: 18.0-21.0%, Mo: 3.5-5.0%, Al: 1.2-1.6%, Ti: 2.75-3.25%, B: 0.003-0.010%, Zr: 0.02-0.08%, Si≤0.15%, Mn≤0.10%, P≤0.015%, S≤0.015%, Cu≤0.10%, Fe≤2.0%, with the balance being Ni.

3. The method according to claim 1, characterized in that, In step (3), the thickness of the slab after forging is 40mm to 70mm.

4. The method according to claim 1, characterized in that, In step (4), the thickness of the hot-rolled strip is 4.0 mm to 6.0 mm.

5. The method according to claim 1, characterized in that, In step (6), the rolling speed is 10 to 100 meters per minute.

6. The method according to claim 1, characterized in that, In step (6), the holding time for each intermediate annealing treatment during the cold rolling process is 1 to 15 minutes.

7. The method according to claim 1, characterized in that, In step (7), the solution treatment of the finished product is kept at a constant temperature for 5 to 20 minutes.

8. The method according to any one of claims 1-7, characterized in that, The minimum thickness of the prepared strip is 0.1±0.01mm, and the width is more than 300mm.

Images