High-performance GH4738 alloy material and preparation method thereof

Abstract

The invention discloses a high-performance GH4738 alloy material and a preparation method thereof, the grain size of the alloy material is 5-6.5 grade, the metallographic phase is a uniform equiaxed crystal structure, and the alloy material comprises 18.0-21.0 wt% of Cr, 12.0-15.0 wt% of Co, 3.50-5.00 wt% of Mo, 2.75-3.25 wt% of Ti, 1.20-1.60 wt% of Al and the balance Ni. Through the synergistic effect of cold drawing deformation and heat treatment recrystallization, the problem that grains of the GH4738 alloy grow abnormally after standard solution treatment is solved in a breakthrough mode. By means of the process, the grain size is stabilized to the refined 5-6.5 level, and the high-temperature durability requirement in the AMS5708 standard is met at the same time. And the device has the advantages of low equipment cost, low energy consumption and high compatibility, and provides a high-performance material guarantee for key parts of the aero-engine.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of alloy materials, and particularly relates to a high-performance GH4738 alloy material and a preparation method thereof. BACKGROUND

[0002] As a Ni-Cr-Co-based precipitation hardening type high-temperature alloy, GH4738 is widely used in key components such as turbine blades and high-temperature fasteners of an aero-engine due to excellent creep rupture strength and microstructure stability.

[0003] Many units or individuals have carried out a large amount of research on the manufacturing thereof, for example: a Chinese patent with the patent application number CN201911240193.7 discloses a high-quality GH4738 alloy and a preparation method thereof, a GH4738 alloy device and an aero-engine, and provides a high-quality GH4738 alloy and a preparation method thereof, a GH4738 alloy device and an aero-engine, which belong to the technical field of alloy smelting, and the preparation method of the high-quality GH4738 alloy comprises: vacuum electroslag remelting a GH4738 alloy vacuum induction electrode under a protective atmosphere to obtain an electroslag remelting electrode; vacuum consumable remelting smelting the electroslag remelting electrode to obtain a vacuum consumable ingot; and homogenizing annealing the vacuum consumable ingot, wherein ZrO2 is added in the slag system during the electroslag remelting process; the temperature of the homogenizing annealing process is 1180-1210℃, and the time is 60-80h. The preparation method is beneficial to improving the microstructure uniformity of the GH4738 alloy, can control the grain size difference of the GH4738 alloy in the ASTM 2-3 grade range, and almost no metallurgical defects exist in the GH4738 alloy.

[0004] In the prior art, after the GH4738 rolled bar is subjected to standard solid solution treatment at 1080℃, the abnormal grain coarsening (the grain size is usually coarser than 0 grade) is caused due to the release of hot rolling residual stress and the increase of grain boundary activation energy, which leads to uneven mechanical properties and limits the application of the GH4738 rolled bar in the high-performance field. At present, the method of reducing the solid solution temperature to inhibit grain growth will lead to insufficient dissolution of the gamma prime phase, which affects the precipitation strengthening effect; and although the thermal deformation regulation can refine the grain, the process window is narrow and the energy consumption is high. Therefore, a grain refinement process that takes into account the microstructure uniformity and mechanical properties is urgently needed. SUMMARY

[0005] In order to overcome the deficiencies in the prior art, the application discloses a high-performance GH4738 alloy material and a preparation method thereof, and the specific technical solutions are as follows: A high-performance GH4738 alloy material, which has a grain size of 5-6.5, a uniform equiaxed crystal microstructure, and a composition of 18.0-21.0wt% Cr, 12.0-15.0wt% Co, 3.50-5.00wt% Mo, 2.75-3.25wt% Ti, 1.20-1.60wt% Al, and the balance of Ni.

[0006] Further, the alloy material has an elongation δ5 ≥ 27.5%, a reduction of area ψ ≥ 30%, and a hardness HRC of 38.0-38.9.

[0007] A method for preparing the aforementioned high-performance GH4738 alloy material, comprising the following steps: Step 1: raw material pretreatment: homogenizing treatment is performed on a blank prepared by vacuum induction smelting + vacuum consumable remelting, followed by forging breakdown and hot rolling to a diameter Φ1, and then standard solid solution treatment is completed by keeping at 1080℃ for 4h and air cooling; Step 2: surface finishing: the surface oxide layer is removed by using a centerless grinding skinning process, the size is controlled to Φ2, the ovality is ≤ 0.05mm, the surface defects are eliminated, and the surface is finished to Φ2: 1. The deformation amount is accurately controlled to avoid inaccuracy caused by ovality; 2. For GH4738 high-temperature alloy which is difficult to deform, poor ovality of the blank will intensify the cracking risk in the subsequent cold working process; Step 3: cold drawing deformation: cold drawing is performed at room temperature by using a conical die, and the cold drawing deformation amount is controlled to be 11%-26%, and a lubricant is uniformly applied before deformation, and the lubricant can be D-380 type drawing processing oil produced by Beishan Chemical; Step 4: recrystallization heat treatment: the deformed bar is placed in a heat treatment furnace, kept at 1040-1060℃ for 1h, and then air cooled to promote complete static recrystallization of the deformed structure.

[0008] Further, the final rolling temperature during the hot rolling treatment in step 1 is ≥ 950℃, and the total deformation amount is controlled to be 65%-80%.

[0009] Preferably, it further comprises step 5: heat treatment and inspection: sampling the bar after cold drawing deformation and recrystallization heat treatment, and then performing structure and performance inspection after stabilization treatment and aging treatment.

[0010] Further, the stabilization treatment process in step 5 is keeping at 845℃ for 4h and then air cooling, and the aging treatment process is keeping at 760℃ for 16h and then air cooling.

[0011] Preferably, Φ2 in step 2 is generally reduced by about 2mm based on Φ1 in step 1, which can basically skin clean and meet the subsequent processing requirements.

[0012] The lattice distortion of GH4738 alloy after hot rolling can be converted into the driving force for grain boundary migration during standard solid solution treatment, resulting in abnormal grain growth. The present application realizes the refinement of grain size from coarse 0 to 5-6.5 levels by the synergistic process of drawing deformation-recrystallization heat treatment, which stimulates recrystallization nucleation by introducing deformation storage energy, and inhibits secondary grain growth by precise temperature control. Specifically, first, 11%-26% plastic deformation is introduced in step 3 of cold drawing, so that the dislocation density and deformation storage energy are increased to provide sufficient nucleation power for recrystallization; at the same time, the original coarse grains are broken to form a network of subgrain boundaries, increasing the nucleation sites. Secondly, the recrystallization temperature is controlled at 1040-1060℃, which can ensure the formation of equiaxed grains by subgrain merging and growth, and avoid the secondary coarsening of grains due to high temperature.

[0013] The beneficial technical effects of the present application are: (1) Significant grain refinement: the grain size is refined from coarse 0 level to 5-6.5 level after standard solid solution, meeting the requirements of technical standards; (2) Excellent mechanical properties: the stress rupture life is 30.2-42.9h, the elongation δ5 is ≥27.5%, the reduction of area ψ is ≥30%, and the hardness HRC is 38.0-38.9 under the condition of 816℃ / 328MPa; (3) Strong process compatibility: it can be directly applied to the existing hot-rolled bar production line without the need for new large-scale equipment, and the energy consumption is significantly reduced compared to thermal deformation process; (4) High quality stability and low scrap rate: by controlling the deformation and temperature matching, the batch rejection caused by grain size inconsistency due to standard heat treatment is avoided, and the grain size and stress rupture performance requirements are met after secondary processing, effectively avoiding economic losses; (5) Reduced equipment cost and energy consumption: no new heat treatment equipment is needed, only cold drawing + solid solution recrystallization process is added after standard solid solution treatment, which greatly reduces the equipment cost and energy consumption.

[0014] In summary, the present application solves the problem of abnormal grain growth of GH4738 alloy after standard solid solution treatment by the synergistic effect of cold drawing deformation and heat treatment recrystallization. The process not only stabilizes the grain size to 5-6.5 level, but also meets the high temperature stress rupture performance requirements (816℃ / 328MPa, τ≥23h, A≥8%) in AMS5708 standard. Moreover, it has the advantages of low equipment cost, low energy consumption and high compatibility, providing high performance material guarantee for key components of aircraft engines. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The grain structure (grain size 0 level) after traditional standard solid solution treatment is Example 1; Figure 2Grain structure after Example 1 treatment (grain size 5); Figure 3 Grain structure after Example 2 treatment (grain size 6); Figure 4 Grain structure after Example 3 treatment (grain size 6.5); Figure 5 Grain structure after Example 4 treatment (grain size 5); Figure 6 Grain structure after Comparative Example 2 treatment (grain size 0); Figure 7 Grain structure after Comparative Example 3 treatment (grain size 3); Figure 8 Grain structure after Comparative Example 4 treatment (grain size 3); Figure 9 Grain structure after Comparative Example 5 treatment (grain size 0). DETAILED DESCRIPTION

[0016] The above technical solutions of the present application will be described in detail below through specific examples.

[0017] Example 1

[0018] GH4738 alloy rod was prepared according to the following method steps: Step 1: The blank was homogenized by vacuum induction melting (VIM) + vacuum consumable remelting (VAR), then was forged to break down, and was hot rolled to Φ1 = 17.5 mm, and then was subjected to standard solution treatment at 1080 °C for 4 h and air cooling, and the composition of the blank was 18.0-21.0 wt% Cr, 12.0-15.0 wt% Co, 3.50-5.00 wt% Mo, 2.75-3.25 wt% Ti, 1.20-1.60 wt% Al, and the balance of Ni; Step 2: The rolled rod after standard solution treatment was peeled, and the size was controlled to Φ2 = 15.7 mm, and the ovality was ≤0.05 mm, and the surface defects were eliminated.

[0019] Step 3: Cold drawing deformation: the peeled rod was cold drawn at room temperature, and the size after drawing was Φ3 = 14.8 mm, and the drawing deformation was 11%.

[0020] Step 4: Recrystallization heat treatment: the drawn rod was heat treated, the holding temperature was 1060 °C, the holding time was 1 h, and the cooling mode was air cooling.

[0021] Step 5: performance heat treatment and detection: after the cold drawing deformation + recrystallization treatment of the rod, after the stabilization treatment + aging treatment, the microstructure and performance are detected. The stabilization treatment process is 845℃ for 4h air cooling; the aging treatment process is 760℃ for 16h air cooling.

[0022] The microstructure of the GH4738 alloy rod prepared in this example is shown in Figure 2 , the grain size is about 5 levels according to ASTM E112 "Standard Test Method for Determining Average Grain Size", and the grains are uniform. It can be seen that the grain size of the GH4738 alloy rod treated by the method of this example is uniform, which meets the standard requirements. The measured high temperature stress rupture performance is shown in Table 1.

[0023] Example 2

[0024] Different from example 1 is: Step 3: cold drawing deformation, the cold drawing deformation is carried out on the stripped rod, and the size after drawing is Φ3=14.1mm, and the drawing deformation is 19.3%.

[0025] Step 4: recrystallization heat treatment, the heat treatment temperature is 1050℃.

[0026] The microstructure of the GH4738 alloy rod prepared in this example is shown in Figure 3 , the grain size is about 6 levels according to ASTM E112 "Standard Test Method for Determining Average Grain Size", and the grains are uniform. It can be seen that the grain size of the GH4738 alloy rod treated by the method of this example is uniform, which meets the standard requirements. The measured high temperature stress rupture performance is shown in Table 1.

[0027] Example 3

[0028] Different from example 1 is: Step 3: cold drawing deformation, the cold drawing deformation is carried out on the stripped rod, and the size after drawing is Φ3=13.5mm, and the drawing deformation is 26%.

[0029] Step 4: recrystallization heat treatment, the heat treatment temperature is 1040℃.

[0030] The microstructure of the GH4738 alloy rod prepared in this example is shown in Figure 4 , the grain size is about 6.5 levels according to ASTM E112 "Standard Test Method for Determining Average Grain Size", and the grains are uniform. It can be seen that the grain size of the GH4738 alloy rod treated by the method of this example is uniform, which meets the standard requirements. The measured high temperature stress rupture performance is shown in Table 1.

[0031] Example 4

[0032] Different from example 1 is: Step 3: Cold drawing deformation, the peeled rod is cold drawn at room temperature, and the size after drawing is Φ3=13.5 mm, and the drawing deformation is 26%.

[0033] Step 4: Recrystallization heat treatment, the heat treatment temperature is 1050℃.

[0034] The microstructure of the GH4738 alloy rod prepared in this example is shown in Figure 5 , and the grain size is about 5 levels according to ASTM E112 "Standard Test Method for Determining Average Grain Size", and the grain is uniform. It can be seen that the grain size of the GH4738 alloy rod treated by the method of this example is uniform, which meets the standard requirements. The measured high temperature stress rupture performance is shown in Table 1.

[0035] Comparative Example 1 The rod with a diameter of Φ1=17.5 mm after vacuum induction melting, vacuum consumable remelting, homogenization heat treatment, forging breakdown and hot rolling is subjected to standard solid solution treatment, that is, 1080℃ for 4h, and air cooling after discharge.

[0036] The metallographic structure of the rolled rod after completing the standard solid solution heat treatment is shown in Figure 1 , and it can be seen from Figure 1 that the rod has excessively coarse grain structure, and the grain size level is above 0 level.

[0037] Comparative Example 2 The GH4738 alloy rod is prepared according to the following steps: Step 1: VIM+VAR billet is subjected to homogenization treatment, then forged breakdown, and hot rolled to Φ1=17.5 mm, and standard solid solution treatment is completed at 1080℃ for 4h air cooling; Step 2: The rolled rod after standard solid solution treatment is peeled, and the size is controlled to Φ2=15.7 mm, and the ovality is ≤0.05 mm, and the surface defects are eliminated.

[0038] Step 3: Cold drawing deformation: the peeled rod is cold drawn at room temperature, and the size after drawing is Φ3=14.8 mm, and the drawing deformation is 11%.

[0039] Step 4: The rod after drawing is subjected to heat treatment, the holding temperature is 1000℃, the holding time is 1h, and the cooling mode is air cooling.

[0040] The metallographic structure of the rod prepared in Comparative Example 2 is shown in Figure 6 , and the metallograph shows that the 11% drawing deformation + 1000℃ heat treatment still has 0 level large grain structure.

[0041] Comparative Example 3 The GH4738 alloy rod is prepared according to the following steps: Step 1: VIM+VAR ingot was homogenized, then forged and hot rolled to Φ1=17.5mm, and standard solid solution treatment was completed by 1080℃x4h air cooling; Step 2: The rolled bar after standard solid solution treatment was peeled, and the size was controlled to Φ2=15.7mm, the ovality was ≤0.05mm, and the surface defects were eliminated.

[0042] Step 3: Cold drawing deformation: the peeled bar was cold drawn at room temperature, and the size after drawing was Φ3=14.8mm, and the drawing deformation was 11%.

[0043] Step 4: The drawn bar was heat treated, the holding temperature was 1100℃, the holding time was 1h, and the cooling mode was air cooling.

[0044] The metallographic structure photograph of the bar prepared in Comparative Example 3 is shown in Figure 7 The metallographic structure showed that the metallographic structure after 11% drawing deformation+1100℃ heat treatment was 3-grade grain structure. Although there was a recrystallization homogenization, the grain size grade did not meet the requirement of the grain size finer than 3-grade specified in AMS5708 standard and the like. The high temperature durability measured is shown in Table 1.

[0045] Comparative Example 4 The GH4738 alloy bar was prepared according to the following method steps: Step 1: VIM+VAR ingot was homogenized, then forged and hot rolled to Φ17.5mm, and standard solid solution treatment was completed by 1080℃x4h air cooling; Step 2: The rolled bar after standard solid solution treatment was peeled, and the size was controlled to Φ15.7mm, the ovality was ≤0.05mm, and the surface defects were eliminated.

[0046] Step 3: Cold drawing deformation: the peeled bar was cold drawn at room temperature, and the size after drawing was Φ13.1mm, and the drawing deformation was 30%.

[0047] Step 4: The drawn bar was heat treated, the holding temperature was 1050℃, the holding time was 1h, and the cooling mode was air cooling.

[0048] The metallographic structure photograph of the bar prepared in Comparative Example 4 is shown in Figure 8 The metallographic structure showed that the metallographic structure after 30% drawing deformation+1050℃ heat treatment was also 3-grade grain structure. The grain size grade still did not meet the requirement of the grain size finer than 3-grade specified in AMS5708 standard and the like. The high temperature durability measured is shown in Table 1.

[0049] Comparative Example 5 The GH4738 alloy bar was prepared according to the following method steps: Step 1: VIM+VAR billets are homogenized, then forged to break down, and hot rolled to Φ17.5mm, and standard solid solution treatment is completed by 1080℃×4h air cooling; Step 2: The rolled bar after standard solid solution treatment is peeled, and the size is controlled to Φ15.7mm, the ovality is ≤0.05mm, and the surface defects are eliminated.

[0050] Step 3: Cold deformation: the peeled bar is cold drawn at room temperature, and the size after drawing is Φ15.2mm, and the drawing deformation is 6%.

[0051] Step 4: The drawn bar is heat treated, the holding temperature is 1050℃, the holding time is 1h, and the cooling mode is air cooling.

[0052] The metallographic structure photograph of the bar prepared in Comparative Example 5 is shown in Figure 9 The metallographic structure shows that after 6% drawing deformation + 1050℃ heat treatment, it is 0 grade large grain structure.

[0053] Table 1: Comparison of measured structure and performance of Examples 1-4 and Comparative Examples 1-5

[0054] As shown in Table 1, Figures 1-9 It can be seen that, by the cold drawing deformation-recrystallization heat treatment synergistic process, the grain size of GH4738 alloy is successfully refined from the traditional heat treatment coarse 0 grade (Comparative Example 1) to 5-6.5 grade, and the stress rupture property meets the AMS5708 standard requirement. The technical principle and key advantages are as follows: 1. Grain refinement mechanism: (1) Deformation energy storage driving, recrystallization cold drawing (11-26% deformation), high dislocation density and deformation energy storage are introduced in the alloy, which provides nucleation driving force for recrystallization. If the deformation is too low, the stored energy is insufficient, and complete recrystallization cannot be triggered (Comparative Example 5, 6% deformation); if it is too high, the stored energy is high, and the recrystallization is quickly completed and enters the growth stage, resulting in coarse grains (Comparative Example 4, 30% deformation); (2) Precise temperature control to inhibit secondary coarsening, the recrystallization temperature is strictly limited to 1040-1060℃ (Examples 1-4). Below this range, recrystallization is difficult to activate (Comparative Example 2, 1000℃); above this range, although recrystallization occurs, the grain boundary migrates too quickly, resulting in grain growth to 3 grade (Comparative Example 3, 1100℃), which cannot meet the AMS5708 standard of finer than 3 grade or the AMS5544 standard of finer than 5 grade.

[0055] Through the comparative test, the core process window is determined: the effective parameter range of cold drawing deformation is 11-26%, the deformation <11% has insufficient stored energy to trigger recrystallization risk, and the deformation >26% will lead to grain coarsening. The effective parameter range of recrystallization temperature is 1040-1060℃, the temperature <1040℃ will lead to inactivation of recrystallization, and the temperature >1060℃ will affect the secondary growth of grains.

[0056] Theoretically, the lower the grain size grade (the coarser the grain), the longer the alloy's endurance time, the more time for plastic deformation, and the plasticity should increase. However, in the long-term endurance test of GH4738 alloy, the strengthening phase γ' phase coarsening weakens the intragranular plastic deformation ability, offsetting the theoretical increase of plasticity of coarse grains. At the same time, the grain boundary weakens in long-term high temperature, and the applicant guesses that these two points may lead to the offset of the theoretical plasticity advantage, and the plasticity of Comparative Examples 3 and 4 and the embodiment is similar.

[0057] However, the core value of the present application is to break through the technical bottleneck of abnormal grain coarsening (≥0 grade) after standard solid solution of GH4738 alloy, and to stabilize the grain size at 5-6.5 grade through the cold drawing-recrystallization synergistic process, to meet the mandatory requirements of AMS5708 standard on grain size (finer than 3 grade), and to avoid batch rejection due to coarse grains. Although the endurance time of Comparative Examples 3 and 4 (grain 3 grade) is slightly higher than that of the embodiment, the grain size does not meet the standard requirements, and does not meet the requirements of AMS5708 standard on grain size (need to be finer than 3-5 grade), and is only used as a process boundary reference. While ensuring the compliance of the grain size, the endurance performance (30.2-38.9h) of the present application is far superior to the AMS5708 standard (≥23h), and the elongation (δ5≥27.5%) and surface reduction (ψ≥30%) are significantly better than the traditional coarse grain structure.

Claims

1. A high performance GH4738 alloy material, characterized in that: Its grain size is 5~6.5, and the metallographic structure is uniform equiaxed crystal structure. Its composition is 18.0-21.0wt%Cr, 12.0-15.0wt%Co, 3.50-5.00wt%Mo, 2.75-3.25wt%Ti, 1.20-1.60wt%Al and the balance Ni; its elongation δ5≥27.5%, cross-sectional shrinkage ψ≥30%, and hardness HRC: 38.0~38.

9.

2. A method for preparing the high-performance GH4738 alloy material according to claim 1, characterized in that: The following steps are involved: Step 1: Raw material pretreatment: The blank prepared by vacuum induction smelting + vacuum consumable remelting is homogenized, then forged and hot rolled to a diameter of Φ1, and then subjected to standard solution treatment at 1080℃ for 4 hours and air-cooled; Step 2: Surface finishing: Use centerless grinding and peeling process to remove the surface oxide layer, control the size to Φ2, ovality ≤ 0.05mm, and eliminate surface defects; Step 3: Cold drawing deformation: cold drawing is performed through a tapered die at room temperature, and the deformation is controlled at 11%~26%. Lubricant is evenly applied before cold drawing deformation; Step 4: Recrystallization heat treatment: Place the deformed bar obtained in step 3 in a heat treatment furnace, keep it at 1040~1060℃ for 1h, and then air-cool it to promote complete static recrystallization of the deformed structure.

3. The method for preparing a high-performance GH4738 alloy material according to claim 2, characterized in that: The final rolling temperature during the hot rolling treatment in step 1 is ≥950°C, and the total deformation is controlled at 65% to 80%.

4. The method for preparing a high-performance GH4738 alloy material according to claim 2, characterized in that: It also includes step 5: heat treatment and inspection: sampling the bars after cold drawing deformation and recrystallization heat treatment, and conducting microstructure and performance inspections after stabilization treatment and aging treatment.

5. The method for preparing a high-performance GH4738 alloy material according to claim 4, characterized in that: In step 5, the stabilization treatment process is to keep the temperature at 845° C. for 4 hours and then air-cool; and the aging treatment process is to keep the temperature at 760° C. for 16 hours and then air-cool.

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