A heat treatment method for improving the strength of a GH4169 alloy forging

Abstract

The present application belongs to the field of metal heat treatment, and particularly relates to a heat treatment method for improving the strength of GH4169 alloy forgings. Step one, solution; step two, solution; step three, aging; wherein, the forgings produced by using foreign GH4169 alloy rods are heat treated according to the steps one, two and three; the forgings produced by using domestic GH4169 alloy rods are heat treated according to the steps one, three and repeated step three, and the repeated step three is repeated for 1-3 times when the heat treatment strength requirement is high. The present application fully considers the characteristics of foreign and domestic GH4169 alloy rods, and controls the precipitation amount of delta phase through the adjustment of solution temperature and cooling and different heat treatment modes according to the transformation law of different alloys, promotes the precipitation of strengthening phases gamma prime phase and gamma double prime phase, and improves the strength performance of forgings.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal heat treatment, and particularly relates to a heat treatment method for improving the strength of GH4169 alloy forgings. BACKGROUND

[0002] GH4169 alloy was applied in the 1960s, and it is a precipitation-hardened nickel-based high-temperature alloy with a body-centered cubic γ" phase as the main strengthening phase and a face-centered cubic γ' phase as the auxiliary strengthening phase. The chemical composition of the alloy is slightly different according to the use requirements of different parts, mainly the content of the control elements Nb and trace elements. In recent years, due to the rapid advancement of domestic production, the production of forgings from domestic GH4169 rods often has problems such as unqualified room temperature tensile yield strength and high temperature tensile yield strength. Through a large amount of production experience and data tracking analysis, it is believed that there are differences between domestic GH4169 rods and imported GH4169 rods, and the same heat treatment system has different effects on the microstructure and properties of forgings in the production process. The influence of heat treatment parameters on the microstructure and properties of forgings produced from domestic GH4169 rods has not been systematically studied in the early stage, and the production experience of forgings produced from imported GH4169 rods is blindly followed, which is an important factor causing unstable performance of forgings. Therefore, the influence of different heat treatment systems on the microstructure and properties of forgings produced from domestic GH4169 rods is now tested and explored, the heat treatment process parameters of forgings produced from domestic GH4169 rods are optimized, and the first inspection qualified rate of forgings is improved. SUMMARY

[0003] The present application provides a heat treatment method for improving the strength of GH4169 alloy forgings, which can greatly improve the strength of the alloy, and has a high strength margin, and the endurance, plasticity and creep properties can all meet the specification requirements.

[0004] The present application relates to a heat treatment method for improving the strength of GH4169 alloy forgings, comprising the following steps:

[0005] The present application provides a heat treatment method for improving the strength of GH4169 alloy forgings, comprising the following steps:

[0006] Step one, solution

[0007] The forged GH4169 alloy forgings are heated to 825℃, and then kept for 120-240min, and then heated to a first preset temperature, and then kept for 30-60min, and then kept for 1h, and then air cooled; the preset temperature is determined according to the strength requirement of the forged forgings; the higher the strength requirement, the higher the preset temperature;

[0008] Step two, solution

[0009] The GH4169 alloy forge piece cooled to room temperature in step one is heated to 825℃, and kept for 120-240min, then heated to the second preset temperature, kept for 30-60min, kept for 1h, and water cooled; the preset temperature is determined according to the strength requirement of the forge piece; the higher the strength requirement, the higher the preset temperature;

[0010] Step three, aging

[0011] The GH4169 alloy forge piece cooled to room temperature in step two is heated to 600℃, kept for 30-90min, then heated to 700℃, kept for 30-90min, then heated to 720℃, kept for 8h, furnace cooled to 620℃ at 50℃ / h, kept for 8-16h, and air cooled;

[0012] The forge piece produced by using foreign GH4169 alloy bar is heat treated according to step one, step two, and step three;

[0013] The forge piece produced by using domestic GH4169 alloy bar is heat treated according to step one, step three, and repeated step three.

[0014] Further, the furnace entry temperature of the aged forge piece is not higher than 500℃, and the furnace entry temperature of the solution treated forge piece is not higher than 800℃.

[0015] Further, during the heat treatment process, the disc and shaft type forge pieces are placed in a single layer, the ring type forge pieces are placed in ≤3 layers, and the distance between the forge pieces is ≥100mm.

[0016] Further, the solution treated forge pieces are cooled on the cooling rack with a spacing of ≥200mm, and the transfer time is ≤120s, and the cooling transfer time of step two is ≤60s.

[0017] Further, for the forge pieces with high strength requirements or low final forging temperature, the aging time at 620℃ in step three is extended according to the strength requirements of the forge pieces and the final forging temperature.

[0018] Further, for the forge pieces that cannot meet the requirements of die forging deformation, if the strength requirements cannot be met by using steps one to three, step one is not executed, and steps two and three are repeated n and m times respectively, and m and n are integers greater than 1.

[0019] Further, the first preset temperature is less than the second preset temperature.

[0020] Further, the first preset temperature of the forge piece produced by using foreign GH4169 alloy bar is 970-990℃, and the second preset temperature of the forge piece produced by using domestic GH4169 alloy bar is 960-975℃.

[0021] The heat treatment method of the GH4169 alloy forge piece provided by the application has the following advantages:

[0022] (1) When the application is used for the GH4169 alloy forge piece, the aging furnace-in temperature is not higher than 500 DEG C, and the solid solution furnace-in temperature is not higher than 800 DEG C, thereby reducing the internal stress of the forge piece caused by the heating process and ensuring uniform forge piece organization and flat shape.

[0023] (2) The application adds an aging process before the conventional solid solution + aging heat treatment. The foreign GH4169 alloy bar and the domestic GH4169 bar differ in the smelting technology and the element content, and the difference is further enlarged after forging. The foreign GH4169 alloy bar has a higher Nb content than the domestic GH4169 alloy bar, and the Al and Ti contents are equivalent. On the one hand, the Nb content is the main forming element of the δ phase, which can ensure the high-temperature stability of the δ phase, hinder the grain growth during the solid solution process, and thus obtain a higher tensile strength. On the other hand, Nb is the main forming element of γ"-Ni3Nb, and Al and Ti are the main forming elements of γˊ-Ni3(Al, Ti, Nb). Increasing the Nb and Al contents within a certain range can increase the number of γ" and γˊ phases in the matrix and improve the stability of the two strengthening phases, thereby ensuring the tensile properties of the forge piece. Therefore, a precise heat treatment process needs to be formulated according to the difference between the alloys.

[0024] The strength is greatly improved, and the elongation changes little.

[0025] In summary, the application describes the heat treatment process parameters suitable for the forge pieces produced by different alloy bars in detail by considering the difference between the foreign and domestic GH4169 alloy bars. The grain size of the forge piece is 8-10, the grain boundary has a δ phase dispersed distribution, and all the performance parameters required by the specification can be met by controlling the forge piece organization transformation and phase precipitation. The process is stable, easy to operate, and suitable for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a schematic diagram of the microstructure (100 μm) of the foreign GH4169 alloy forge piece after heat treatment.

[0027] Figure 2 It is a schematic diagram of the microstructure (100 μm) of the domestic GH4169 alloy forge piece after heat treatment. DETAILED DESCRIPTION

[0028] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0029] The present application provides a heat treatment method of GH4169 alloy forgings, comprising:

[0030] The foreign GH4169 bar refers to an alloy with high content of high-temperature-resistant elements Nb and Ni, and the initial dissolution temperature of the δ phase is above 1000℃, while the domestic GH4169 bar refers to an alloy with relatively low content of high-temperature-resistant elements Nb and Ni, and the initial dissolution temperature of the δ phase is below 1000℃. Due to the great difference between the smelting methods at home and abroad, the content of high-temperature-resistant elements in the domestic GH4169 alloy bar is relatively low, for example, the Nb content is relatively low. This is because when the Nb content is high, during the smelting ingot solidification crystallization process, the high Nb content is easy to form segregated Nb, which causes the white block Laves phase to precipitate between the Nb-rich elements, and the segregation will affect the performance stability and organizational uniformity of the finished forgings.

[0031] Due to the difference between the smelting methods and elements, the foreign GH4169 alloy bar is more suitable for high-temperature solid solution to improve the strength of the forgings without causing grain growth; the domestic GH4169 alloy bar is suitable for relatively low solid solution temperature. This is because when the solid solution temperature is high, the grain boundary δ phase melts and cannot play a role in stabilizing the grain, causing grain growth and affecting the comprehensive performance of the forgings.

[0032] Step one, solid solution

[0033] The GH4169 alloy forgings in the as-forged state are heated to 825℃, and then kept for 120-240min, and then heated to a first preset temperature, soaked for 30-60min, kept for 1h, and then scattered and air-cooled; the preset temperature is determined according to the strength requirement of the as-forged forgings; the higher the strength requirement, the higher the preset temperature.

[0034] Step two, solid solution

[0035] The GH4169 alloy forgings cooled to room temperature in step one are heated to 825℃, and then kept for 120-240min, and then heated to a second preset temperature, soaked for 30-60min, kept for 1h, and then water-cooled; the preset temperature is determined according to the strength requirement of the as-forged forgings; the higher the strength requirement, the higher the preset temperature.

[0036] Step three, aging

[0037] The GH4169 alloy forgings cooled to room temperature in step two are heated to 600℃ and held for 30-90 minutes, then heated to 700℃ and held for 30-90 minutes, then heated to 720℃ and held for 8 hours, then furnace cooled to 620℃ at 50℃ / h and held for 8-16 hours, and finally air cooled.

[0038] Optionally, the furnace temperature for aging forgings should not exceed 500℃, and the furnace temperature for solution-treated forgings should not exceed 800℃, to ensure that the forgings have sufficient time to be heated, promote uniform surface and core structure, reduce thermal stress during heating, and reduce the risk of dimensional changes in forgings.

[0039] Optionally, disc and shaft forgings can be arranged in a single layer, while ring forgings can be arranged in ≤3 layers, with varying spacing between forgings.

[0040] ≥100mm, to ensure heat flow during the heating process of the forging and promote the uniformity of the heating process during heat treatment of the forging.

[0041] Optionally, the forgings are cooled after solution treatment and spread out on a cooling rack with a spacing of ≥200mm and a transfer time of ≤120 seconds. The cooling transfer time in step two is ≤60 seconds, which improves the solution treatment effect and obtains a uniform supersaturated solid solution, laying a good foundation for the precipitation of strengthening phases in the subsequent aging process.

[0042] Optionally, depending on the strength requirements and final forging temperature of the forging, for forgings with high strength requirements or low final forging temperatures, the holding time at 620℃ in step three can be extended. Holding the forging at 620℃ primarily precipitates the γ' phase; extending the holding time at 620℃ can further supplement the precipitation of a small amount of strengthening phase. Data shows that after long-term aging at 650℃ for 200 hours, the tensile and yield strengths of discs both increased by approximately 50 MPa, due to the continued precipitation and supplementary strengthening by the γ' and γ' phases.

[0043] Optionally, forgings produced using imported GH4169 alloy bars are heat-treated according to steps one, two, and three. Forgings produced using domestic GH4169 alloy bars are heat-treated according to steps one, three, and repeating step three. For high strength requirements, step three can be repeated 1 to 3 times. Taking into full account the characteristics of imported and domestic GH4169 alloy bars, and based on the transformation laws of the δ phase in different alloys, for example, when imported GH4169 alloy undergoes solution treatment according to steps one and two, the solution treatment effect is enhanced, effectively suppressing the precipitation of the δ phase. This is beneficial for the full precipitation of the strengthening phases γˊ and γ″ during the later aging process of the forging, improving the strength performance of the forging. Conversely, when domestic GH4169 alloy undergoes aging heat treatment according to step three and repeating step three, the aging effect is enhanced, and more grain boundary δ phases are converted into strengthening phases.

[0044] γˊ phase and γ″ phase, for strengthening forgings.

[0045] Optionally, for the forging which is not ideal in forging deformation, if the strength requirement cannot be met by using the method of claim 1, the heat treatment is performed according to the sequence of step two, repeating step two, step three, and repeating step three. Increasing the solid solution temperature and increasing the solid solution cooling rate can reduce the precipitation of δ phase, and the composition elements of δ phase are similar to those of the strengthening phase γ", so reducing the precipitation of δ phase helps to promote the precipitation of the strengthening phase γ" during aging process, further strengthens the forging, and improves the strength performance of the forging.

[0046] Optionally, the first preset temperature is 975℃, and the second preset temperature is 985℃. The characteristics of foreign and domestic GH4169 alloy bars, the influence of solid solution temperature on the dissolution and precipitation of δ phase are fully considered, the solid solution temperature is accurately determined, and then the satisfactory δ phase morphology and quantity are obtained, and the strength of the forging is comprehensively improved.

[0047] Further, for the forgings produced by using foreign GH4169 alloy bars, the first preset temperature is 970-990℃; for the forgings produced by using domestic GH4169 alloy bars, the second preset temperature is 960-975℃. Within a certain range of solid solution temperature, with the increase of the solid solution temperature, the elements are fully diffused, the chemical composition of the alloy is homogenized, the composition segregation is reduced, the number, morphology and distribution of γˊ precipitated phase in the alloy are adjusted, and the purpose of improving the alloy performance is achieved. Therefore, we fully consider the characteristics of foreign and domestic GH4169 alloy bars, and reasonably determine the solid solution temperature range to adapt to the heat treatment production of forgings with different performance requirements.

[0048] The application is further described in detail in combination with actual production examples. The GH4169 alloy forgings with the outer dimensions of Φ351×Φ269×274 and the effective thickness of 35 mm are used. The foreign GH4169 bars and the domestic GH4169 alloy bars are used respectively for forging, and then heat treatment is carried out. The forgings produced by the foreign GH4169 alloy forgings: the first step is to heat the forged state to 825℃, keep for 120 min, then heat to 975℃, keep for 30 min, keep for 1 h, air cool, transfer to the cooling rack within 120 s, and the air cooling interval is ≥200 mm; the second step is to heat the forgings cooled to room temperature in the first step to 825℃, keep for 120 min, then heat to 985℃, keep for 30 min, keep for 1 h, water cool, transfer to the water tank within 60 s, and water cool for 30 min; the third step is to heat the forgings cooled to room temperature in the second step to 600℃, keep for 60 min, then heat to 700℃, keep for 60 min, then heat to 720℃, keep for 8 h, furnace cool to 620℃ at the rate of 50℃ / h, keep for 8 h, and air cool. The forgings produced by the domestic GH4169 alloy forgings: the first step is to heat the forged state to 825℃, keep for 120 min, then heat to 975℃, keep for 30 min, keep for 1 h, air cool, transfer to the cooling rack within 120 s, and the air cooling interval is ≥200 mm; the second step is to heat the forgings cooled to room temperature in the first step to 600℃, keep for 60 min, then heat to 700℃, keep for 60 min, then heat to 720℃, keep for 8 h, furnace cool to 620℃ at the rate of 50℃ / h, keep for 8 h, and air cool. The third step is to heat the forgings cooled to room temperature in the second step to 600℃, keep for 60 min, then heat to 700℃, keep for 60 min, then heat to 720℃, keep for 8 h, furnace cool to 620℃ at the rate of 50℃ / h, keep for 8 h, and air cool.

[0049] The mechanical property parameters of the GH4169 alloy forgings are shown in Table 1 (foreign GH4169 alloy) and Table 2 (domestic GH4169 alloy bar), and the microstructures are shown in Figure 1 (foreign GH4169 alloy) and Figure 2 (domestic GH4169 alloy bar), wherein 100 μm represents the magnification of 100 times.

[0050] Table 1

[0051]

[0052] Table 2

[0053]

Claims

1. A method of heat treating a GH4169 alloy forging to increase strength, characterized by, It comprises the following steps: Step one, solution The forged GH4169 alloy piece is heated to 825℃, and kept for 120-240 minutes, then heated to the first preset temperature, kept for 30-60 minutes, and then cooled by air cooling; the preset temperature is determined according to the strength requirement of the forged piece; the higher the strength requirement, the higher the preset temperature; Step two, solution The GH4169 alloy piece cooled to room temperature in step one is heated to 825℃, and kept for 120-240 minutes, then heated to the second preset temperature, kept for 30-60 minutes, and then cooled by water; the preset temperature is determined according to the strength requirement of the forged piece; the higher the strength requirement, the higher the preset temperature; Step three, aging The GH4169 alloy piece cooled to room temperature in step two is heated to 600℃, kept for 30-90 minutes, then heated to 700℃, kept for 30-90 minutes, then heated to 720℃, kept for 8 hours, then cooled by furnace at 50℃ / h to 620℃, kept for 8-16 hours, and then cooled by air; The aging forged piece is not higher than 500℃ in temperature, and the solution forged piece is not higher than 800℃ in temperature; The forged piece produced by using foreign GH4169 alloy bar is heat treated according to step one, step two and step three; The forged piece produced by using domestic GH4169 alloy bar is heat treated according to step one, step three and repeated step three, and the forged piece with high strength requirement is repeated step three for 1-3 times; The first preset temperature is less than the second preset temperature; The first preset temperature is 970-990℃ for the forged piece produced by using foreign GH4169 alloy bar, and the second preset temperature is 960-975℃ for the forged piece produced by using domestic GH4169 alloy bar.

2. The method of claim 1, wherein, During the heat treatment, the disc and shaft forged pieces are placed in single layer, and the ring forged pieces are placed in no more than 3 layers, and the distance between the forged pieces is no less than 100mm.

3. The method of claim 1, wherein, The solution forged piece is cooled on the cooling rack with a distance no less than 200mm, and the transfer time is no more than 120 seconds, and the transfer time in step two is no more than 60 seconds.

4. The method of claim 1, wherein, For the forged piece with high strength requirement or low final forging temperature, the aging time at 620℃ in step three is prolonged according to the strength requirement and the final forging temperature of the forged piece.

5. The method of claim 1, wherein, For the forged piece with forging deformation that cannot meet the requirement, if the strength requirement cannot be met by using step one to step three, step one is not executed, and step two is repeated n times, and step three is repeated m times, and m and n are integers greater than 1.

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