Heat treatment method for improving strength of GH4169 alloy forging

Abstract

The invention belongs to the field of metal heat treatment, and particularly relates to a heat treatment method for improving the strength of a GH4169 alloy forge piece. Step 1, solid solution; step 2, solid solution; step 3, aging; wherein a forge piece produced by using a foreign GH4169 alloy bar is subjected to heat treatment according to the first step, the second step and the third step; a forge piece produced by domestic GH4169 alloy bars is subjected to heat treatment according to the first step and the third step, and the third step is repeated for 1-3 times when the strength requirement is high. According to the method, the characteristics of foreign and domestic GH4169 alloy bars are fully considered, the precipitation number of delta phases is reasonably controlled through adjustment of the solid solution temperature and cooling and different heat treatment modes according to the transformation rules of the delta phases of different alloys, precipitation of strengthening phases gamma'and gamma 'is promoted, and the strength performance of forgings is improved.

Description

Technical Field

[0001] The invention belongs to the field of metal heat treatment, and in particular relates to a heat treatment method for improving the strength of GH4169 alloy forgings. Background Art

[0002] GH4169 alloy began to be used in the 1960s. It is a precipitation-hardened nickel-based high-temperature alloy with the γ″ phase of the body-centered cubic structure as the main strengthening phase and the face-centered cubic γˊ phase as the auxiliary strengthening phase. The chemical composition of the alloy is slightly different according to the use requirements of different parts, mainly controlling the content of the element Nb and trace elements. In recent years, due to the rapid advancement of domestic production, for forgings with difficult deformation control, the room temperature tensile yield strength and high temperature tensile yield strength of forgings produced by domestic GH4169 bars are often unqualified. Through a large amount of production experience and data tracking analysis, it is believed that the domestic GH4169 bars are There are differences between domestic GH4169 bars and imported GH4169 bars. The same heat treatment system also has different effects on the microstructure and properties of forgings during the production process. There was no systematic study on the influence of heat treatment parameters on the microstructure and properties of forgings produced by domestic GH4169 bars in the early stage. Instead, the production experience of forgings produced by imported GH4169 bars was blindly used, which was also an important factor causing the unstable performance of forgings. Therefore, we now conduct experiments to explore the influence of different heat treatment systems on the microstructure and properties of forgings produced by domestic GH4169 bars, optimize the heat treatment process parameters of forgings produced by domestic GH4169 bars, and improve the first-time inspection pass rate of forgings. Summary of the invention

[0003] The invention provides a heat treatment method for improving the strength of GH4169 alloy forgings, which can greatly improve the strength of the alloy and simultaneously not only has a higher strength margin, but also has durability, plasticity and creep properties that can meet specification requirements.

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

[0005] Provided is a heat treatment method for improving the strength of GH4169 alloy forgings, comprising the following steps:

[0006] Step 1: Solid solution

[0007] The forged GH4169 alloy forging is heated to 825°C, kept at this temperature for 120 to 240 minutes, then heated to a first preset temperature, heated for 30 to 60 minutes, kept at this temperature for 1 hour, and then cooled in air; the preset temperature is determined according to the strength requirement of the steel forging; the higher the strength requirement, the higher the preset temperature;

[0008] Step 2: Solid solution

[0009] The GH4169 alloy forging cooled to room temperature in step 1 is heated to 825°C, kept at this temperature for 120 to 240 minutes, then heated to a second preset temperature, heated for 30 to 60 minutes, kept at this temperature for 1 hour, and water-cooled; the preset temperature is determined according to the strength requirement of the steel forging; the higher the strength requirement, the higher the preset temperature;

[0010] Step 3: Time limit

[0011] The GH4169 alloy forging cooled to room temperature in step 2 is heated to 600°C and kept at this temperature for 30 to 90 minutes, then heated to 700°C and kept at this temperature for 30 to 90 minutes, then heated to 720°C and kept at this temperature for 8 hours, then furnace cooled to 620°C at 50°C / h, kept at this temperature for 8 to 16 hours, and air cooled;

[0012] Among them, the forgings produced using foreign GH4169 alloy bars are heat treated according to steps one, two and three;

[0013] Forgings produced using domestic GH4169 alloy bars are heat treated according to step 1, step 3, and step 3 is repeated. When the strength requirement is high, step 3 is repeated 1 to 3 times.

[0014] Furthermore, the temperature of aging forgings entering the furnace is not higher than 500°C, and the temperature of solution forgings entering the furnace is not higher than 800°C.

[0015] Furthermore, during the heat treatment process, disc and shaft forgings are placed in a single layer, annular forgings are placed in ≤3 layers, and the spacing between forgings is ≥100mm.

[0016] Furthermore, the forgings are solution cooled out of the furnace and scattered on the cooling rack, the scattering spacing is ≥200mm, the transfer time is ≤120 seconds, and the cooling transfer time in step two is ≤60 seconds.

[0017] Furthermore, for forgings with high strength requirements or low final forging temperature, the aging holding time at 620° C. in step three is extended according to the strength requirements of the forgings and the final forging temperature.

[0018] Furthermore, for forgings whose die forging deformation cannot meet the requirements, if steps 1-3 still cannot meet the strength requirements, step 1 is no longer executed, and step 2 is directly repeated n times, and then step 3 is repeated m times, where m and n are integers greater than 1.

[0019] Furthermore, the first preset temperature is lower than the second preset temperature.

[0020] Furthermore, for forgings produced using foreign GH4169 alloy bars, the first preset temperature is 970-990°C; for forgings produced using domestic GH4169 alloy bars, the second preset temperature is 960-975°C.

[0021] The heat treatment method of GH4169 alloy forgings provided by the present invention has the following advantages:

[0022] (1) The present invention requires that the aging furnace temperature of GH4169 alloy forgings is not higher than 500°C, and the solution furnace temperature is not higher than 800°C, so as to reduce the internal stress of the forgings caused by the heating process and ensure that the forgings have uniform structure and flat appearance.

[0023] (2) The present invention adds an aging process before the conventional solid solution + aging heat treatment. There are core differences between foreign GH4169 alloy bars and domestic GH4169 alloy bars in smelting technology on the one hand, and in element content on the other hand. After forging, this difference will be further amplified. Compared with domestic GH4169 alloy bars, foreign GH4169 alloy bars mostly show a higher Nb content, and comparable Al and Ti contents. 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 and hinder the grain growth during the solid solution process, thereby obtaining 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 will increase the amount of γ″ and γˊ phases in the matrix, and improve the stability of the two strengthening phases, thereby ensuring the tensile properties of the forgings. For this reason, it is necessary to formulate precise heat treatment processes based on the differences in alloys.

[0024] The improved strength is greatly improved, while the elongation does not change much.

[0025] In summary, the present invention describes in detail the heat treatment process parameters applicable to forgings produced from different alloy bars by considering the differences between foreign and domestic GH4169 alloy bars, and can obtain a grain size of 8 to 10 and a microstructure with δ phase dispersed distribution at the grain boundary by controlling the forging microstructure transformation and phase precipitation, and can meet all performance parameters required by the specification. The process is stable, the operation is convenient, and it is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the microstructure (100μm) of foreign GH4169 alloy forgings after heat treatment.

[0027] Figure 2 Schematic diagram of the microstructure (100μm) of domestic GH4169 alloy forgings after heat treatment. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] The heat treatment method of GH4169 alloy forgings provided by the present invention comprises:

[0030] Foreign GH4169 bars refer to alloys with high content of high temperature resistant elements Nb and Ni and initial dissolution temperature of δ phase above 1000℃, while domestic GH4169 bars refer to alloys with relatively low content of high temperature resistant elements Nb and Ni and initial dissolution temperature of δ phase below 1000℃. Due to the large gap between domestic and foreign smelting methods, the content of high temperature resistant elements in domestically produced GH4169 alloy bars is relatively low, such as the Nb content is relatively low. This is because when the Nb content is high, during the solidification and crystallization process of the steel ingot during smelting, when the Nb content is high, it is easy to form segregated Nb, resulting in the precipitation of white blocky Laves phase between the branches rich in Nb elements, and segregation will affect the performance stability and organizational uniformity of the finished forgings.

[0031] Due to the differences in smelting methods and elements, foreign GH4169 alloy bars are more suitable for high-temperature solid solution to improve the strength of forgings without causing grain growth; domestic GH4169 alloy bars are suitable for relatively low solid solution temperatures. This is because when the solid solution temperature is high, the grain boundary δ phase melts and cannot stabilize the grains, causing grain growth and affecting the comprehensive performance of the forgings.

[0032] Step 1: Solid solution

[0033] The forged GH4169 alloy forging is heated to 825°C, kept at this temperature for 120-240 minutes, then heated to a first preset temperature, heated for 30-60 minutes, kept at this temperature for 1 hour, and then air-cooled; the preset temperature is determined according to the strength requirement of the steel forging; the higher the strength requirement, the higher the preset temperature.

[0034] Step 2: Solid solution

[0035] The GH4169 alloy forging cooled to room temperature in step 1 is heated to 825°C, kept at this temperature for 120 to 240 minutes, then heated to a second preset temperature, heated for 30 to 60 minutes, kept at this temperature for 1 hour, and water-cooled; the preset temperature is determined according to the strength requirement of the steel forging; the higher the strength requirement, the higher the preset temperature.

[0036] Step 3: Time limit

[0037] The GH4169 alloy forging cooled to room temperature in step 2 is heated to 600°C and kept for 30-90 min, then heated to 700°C and kept for 30-90 min, then heated to 720°C and kept for 8 h, furnace cooled to 620°C at 50°C / h, kept for 8-16 h, and air cooled.

[0038] Optionally, the furnace temperature for aging forgings is not higher than 500°C, and the furnace temperature for solution forgings is not higher than 800°C, so 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] Optional: disk and shaft forgings are placed in a single layer, ring forgings are placed in ≤3 layers, and the spacing between forgings is

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

[0041] Optionally, the forgings are solution-cooled out of the furnace and scattered on the cooling rack, with a scattering spacing of ≥200mm and a transfer time of ≤120 seconds. The cooling transfer time in step two is ≤60 seconds, so as to improve the solution effect and obtain a uniform supersaturated solid solution, laying a good foundation for the precipitation of strengthening phases in the subsequent aging process.

[0042] Optionally, the aging time at 620℃ in step 3 can be extended for forgings with high strength requirements or low final forging temperatures, depending on the strength requirements and final forging temperature of the forgings. When the forgings are kept at 620℃, the γ' phase is mainly precipitated. Extending the 620℃ holding time can also precipitate a small amount of strengthening phase. Data show that the tensile and yield strengths of the discs increased by about 50MPa after long-term aging at 650℃ for 200 hours, which is due to the continued precipitation of the γ" phase and the γ' phase for supplementary strengthening.

[0043] Optionally, forgings produced using foreign GH4169 alloy bars can be heat treated according to step one, step two, and step three; forgings produced using domestic GH4169 alloy bars can be heat treated according to step one, step three, and repeating step three. When the strength requirement is high, step three can be repeated 1 to 3 times. Fully consider the characteristics of foreign and domestic GH4169 alloy bars, and according to the transformation law of the δ phase of different alloys, for example, when the foreign GH4169 alloy is solution treated according to step one and step two, the alloy solid solution effect can be enhanced, and the precipitation of the δ phase can be effectively inhibited, which is beneficial to the full precipitation of the strengthening phases γˊ phase and γ″ phase in the later aging process of the forgings, thereby improving the strength performance of the forgings. When the domestic GH4169 alloy is subjected to aging heat treatment according to step three and repeating step three, the effect of enhanced aging can be achieved, and more grain boundary δ phases can be converted into strengthening phases.

[0044] γˊ phase and γ″ phase strengthen forgings.

[0045] Optionally, for forgings with unsatisfactory forging deformation, if the strength requirements cannot be met using claim 1, heat treatment is performed in the order of step 2, repeating step 2, step 3, and repeating step 3. Increasing the solution temperature and increasing the solution cooling rate can reduce the precipitation of the δ phase, and the constituent elements of the δ phase and the strengthening phase γ″ are similar, so reducing the precipitation of the δ phase helps promote the precipitation of the strengthening phase γ″ during the aging process, further strengthening the forgings and improving the strength performance of the forgings.

[0046] Optionally, the first preset temperature is 975° C. and the second preset temperature is 985° C. Fully considering the characteristics of foreign and domestic GH4169 alloy bars, the effect of solution temperature on the dissolution and precipitation of δ phase, and accurately setting the solution temperature, thereby obtaining a satisfactory δ phase morphology and quantity, and comprehensively improving the strength of forgings.

[0047] Furthermore, for forgings produced using foreign GH4169 alloy bars, the first preset temperature is 970-990°C; for forgings produced using domestic GH4169 alloy bars, the second preset temperature is 960-975°C. Within a certain range of solid solution temperature, as the solid solution temperature increases, the elements are fully diffused, the chemical composition of the alloy is homogenized, and the component segregation is reduced, which plays a role in adjusting the quantity, morphology and distribution of the γˊprecipitated phase in the alloy, thereby achieving the purpose of improving the alloy performance. To this end, we fully consider the characteristics of foreign and domestic GH4169 alloy bars and reasonably formulate the solid solution temperature range to adapt to the heat treatment production of forgings with different performance requirements.

[0048] The present invention is further described in detail below in conjunction with an actual production example: A GH4169 alloy forging with an overall size of Φ351×Φ269×274 is used, and its effective thickness is 35 mm. Foreign GH4169 bars and domestic GH4169 alloy bars were used for forging respectively, and then heat treated: forgings produced by foreign GH4169 alloy forgings: the first step is to heat the forged state to 825℃, keep warm for 120min, then heat to 975℃, evenly heat for 30min, keep warm for 1h, disperse air cooling, and transfer to the cooling rack within 120s, with an air cooling spacing of ≥200mm; the second step is to heat the forgings cooled to room temperature in the first step to 825℃, keep warm for 120min, then heat to 985℃, evenly heat for 30min, keep warm for 1h, water cool, transfer to a water tank within 60s, and water cool for 30min; the third step is to heat the forgings cooled to room temperature in the second step to 600℃ and keep warm for 60min, then heat to 700℃ and keep warm for 60min, then heat to 720℃, keep warm for 8h, furnace cool to 620℃ at 50℃ / h, keep warm for 8h, and air cool. Forgings produced by domestic GH4169 alloy forgings: The first step is to heat the forged state to 825℃, keep it warm for 120min, then heat it to 975℃, heat it for 30min, keep it warm for 1h, disperse air cooling, and transfer it to the cooling rack within 120s, and the disperse air cooling spacing is ≥200mm; the second step is to heat the forgings cooled to room temperature in the first step to 600℃ and keep it warm for 60min, then heat it to 700℃ and keep it warm for 60min, then heat it to 720℃ and keep it warm for 8h, and cool it to 620℃ at 50℃ / h, keep it warm for 8h, and cool it in air. The third step is to heat the forgings cooled to room temperature in the second step to 600℃ and keep it warm for 60min, then heat it to 700℃ and keep it warm for 60min, then heat it to 720℃ and keep it warm for 8h, and cool it in air at 50℃ / h.

[0049] The mechanical properties of GH4169 alloy forgings are shown in Table 1 (foreign GH4169 alloy) and Table 2 (domestic GH4169 alloy bars). Figure 1 (foreign GH4169 alloy) and Figure 2 (domestic GH4169 alloy rod), where 100μm means the magnification is 100 times.

[0050] Table 1

[0051]

[0052] Table 2

[0053]

Claims

1. A heat treatment method for improving the strength of GH4169 alloy forgings, characterized in that: The following steps are involved: Step 1: Solid solution The forged GH4169 alloy forging is heated to 825°C, kept at this temperature for 120 to 240 minutes, then heated to a first preset temperature, heated for 30 to 60 minutes, kept at this temperature for 1 hour, and then cooled in air; the preset temperature is determined according to the strength requirement of the steel forging; the higher the strength requirement, the higher the preset temperature; Step 2: Solid solution The GH4169 alloy forging cooled to room temperature in step 1 is heated to 825°C, kept at this temperature for 120 to 240 minutes, then heated to a second preset temperature, heated for 30 to 60 minutes, kept at this temperature for 1 hour, and water-cooled; the preset temperature is determined according to the strength requirement of the steel forging; the higher the strength requirement, the higher the preset temperature; Step 3: Time limit The GH4169 alloy forging cooled to room temperature in step 2 is heated to 600°C and kept at this temperature for 30 to 90 minutes, then heated to 700°C and kept at this temperature for 30 to 90 minutes, then heated to 720°C and kept at this temperature for 8 hours, then furnace cooled to 620°C at 50°C / h, kept at this temperature for 8 to 16 hours, and air cooled; Among them, the forgings produced using foreign 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 step 1, step 3, and step 3 is repeated. When the strength requirement is high, step 3 is repeated 1 to 3 times.

2. The method according to claim 1, characterized in that The furnace temperature for aging forgings shall not exceed 500℃, and the furnace temperature for solution forgings shall not exceed 800℃.

3. The method according to claim 1, characterized in that During the heat treatment process, disc and shaft forgings are placed in a single layer, annular forgings are placed in ≤3 layers, and the spacing between forgings is ≥100mm.

4. The method according to claim 1, characterized in that: The forgings are solution cooled and scattered on the cooling racks, with a spacing of ≥200mm and a transfer time of ≤120 seconds. The cooling transfer time in step 2 is ≤60 seconds.

5. The method according to claim 1, characterized in that: For forgings with high strength requirements or low final forging temperature, the aging holding time at 620℃ in step three shall be extended according to the strength requirements and final forging temperature of the forgings.

6. The method according to claim 1, characterized in that For forgings whose die forging deformation cannot meet the requirements, if steps 1-3 still cannot meet the strength requirements, step 1 is no longer executed, and step 2 is directly repeated n times, and then step 3 is repeated m times, where m and n are integers greater than 1.

7. The method according to claim 1, characterized in that The first preset temperature is lower than the second preset temperature.

8. The method according to claim 1, characterized in that For forgings produced using foreign GH4169 alloy bars, the first preset temperature is 970-990°C; for forgings produced using domestic GH4169 alloy bars, the second preset temperature is 960-975°C.

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