High-performance gh4738 alloy material and preparation method thereof

Abstract

The application discloses a kind of high-performance GH4738 alloy material and preparation method thereof, the grain size of the alloy material is 5~6.5 level, metallographic is uniform equiaxed crystal organization, and 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 of Ni.By the synergistic effect of cold drawing deformation and heat treatment recrystallization, the abnormal grain growth problem of GH4738 alloy after standard solid solution treatment is solved.The process not only stabilizes the grain size to 5~6.5 level, but also meets the high-temperature durability requirements in AMS5708 standard.Simultaneously, it has the advantages of low equipment cost, low energy consumption and high compatibility, providing high-performance material guarantee for aero-engine key components.

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 the following steps: vacuum electroslag remelting of a GH4738 alloy vacuum induction electrode is carried out under a protective atmosphere to obtain an electroslag remelting electrode; vacuum consumable remelting smelting is carried out on the electroslag remelting electrode to obtain a vacuum consumable ingot; and homogenization annealing treatment is carried out on the vacuum consumable ingot, wherein ZrO2 is added in the slag system during the electroslag remelting process; the temperature of the homogenization annealing treatment is 1180-1210 DEG C, and the time is 60-80 h. 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 range of ASTM 2-3 grade, 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 DEG C, 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; 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 which 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 scheme is as follows:

[0006] 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.

[0007] 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.

[0008] A method for preparing the aforementioned high-performance GH4738 alloy material, comprising the following steps:

[0009] Step 1: raw material pretreatment: homogenization 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, standard solid solution treatment is completed at 1080℃ for 4h and air cooling;

[0010] 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.

[0011] Step 3: cold drawing deformation: cold drawing is performed at room temperature through a conical die, the cold drawing deformation amount is controlled to be 11%-26%, and a lubricant is uniformly applied before deformation, which can be D-380 type drawing processing oil produced by Beishan Chemical;

[0012] Step 4: recrystallization heat treatment: the deformed rod is placed in a heat treatment furnace, and after being kept at 1040-1060℃ for 1h and air cooling, complete static recrystallization of the deformed structure is promoted.

[0013] 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%.

[0014] Preferably, step 5: heat treatment and inspection is further included: the rod after cold drawing deformation and recrystallization heat treatment is sampled, after stabilization treatment and aging treatment, the structure and performance are inspected.

[0015] Further, the stabilization treatment process in step 5 is air cooling after being kept at 845℃ for 4h; and the aging treatment process is air cooling after being kept at 760℃ for 16h.

[0016] Preferably, the Φ2 in the step 2 is generally reduced by about 2mm on the basis of the Φ1 in the step 1, so that the peeling is basically clean and the subsequent processing requirements can be met.

[0017] The residual 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 by the drawing deformation-recrystallization heat treatment synergistic process, by introducing deformation storage energy to stimulate recrystallization nucleation, and combining with precise temperature control to inhibit secondary grain growth. Specifically, first, 11%-26% plastic deformation is introduced in the cold drawing of step 3, so that the dislocation density and deformation storage energy are increased, providing 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 merging and growth of subgrains to form equiaxed grains, and avoid the secondary coarsening of grains due to too high temperature.

[0018] The beneficial technical effects of the present application are:

[0019] (1) Significant grain refinement: the grain size is refined from coarse 0 to 5-6.5 under standard solid solution, meeting the requirements of technical standards;

[0020] (2) Excellent mechanical properties: the stress rupture life is 30.2-42.9h under the condition of 816℃ / 328MPa, the elongation δ5 is ≥27.5%, the reduction of area ψ is ≥30%, and the hardness HRC is 38.0-38.9;

[0021] (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 with thermal deformation process;

[0022] (4) High quality stability and low scrap rate: by controlling the deformation and temperature matching, batch scrap caused by grain size not meeting the standard heat treatment is avoided, and the grain size and stress rupture performance requirements are met after secondary processing, effectively avoiding economic losses;

[0023] (5) Reduced equipment cost and energy consumption: no new thermal processing 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.

[0024] In summary, the 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 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

[0025] Figure 1 The grain structure after the treatment of Comparative Example 1, i.e. the grain size of 0 level after traditional standard solid solution treatment;

[0026] Figure 2 The grain structure after the treatment of Example 1, i.e. the grain size of 5 level;

[0027] Figure 3 The grain structure after the treatment of Example 2, i.e. the grain size of 6 level;

[0028] Figure 4 The grain structure after the treatment of Example 3, i.e. the grain size of 6.5 level;

[0029] Figure 5 The grain structure after the treatment of Example 4, i.e. the grain size of 5 level;

[0030] Figure 6 The grain structure after the treatment of Comparative Example 2, i.e. the grain size of 0 level;

[0031] Figure 7 The grain structure after the treatment of Comparative Example 3, i.e. the grain size of 3 level;

[0032] Figure 8 The grain structure after the treatment of Comparative Example 4, i.e. the grain size of 3 level;

[0033] Figure 9 The grain structure after the treatment of Comparative Example 5, i.e. the grain size of 0 level. DETAILED DESCRIPTION

[0034] The above technical solutions of the application will be described in detail through specific examples.

[0035] Example 1

[0036] The GH4738 alloy rod was prepared according to the following method steps:

[0037] Step 1: The billet 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 solid solution treatment at 1080 ℃ for 4 h and air cooling, and the composition of the billet 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;

[0038] Step 2: The rolled bar subjected to the standard solid 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.

[0039] Step 3: Cold drawing deformation: the peeled bar was subjected to cold drawing deformation at room temperature, and the size after drawing was Φ3 = 14.8 mm, and the drawing deformation was 11%.

[0040] Step 4: Recrystallization heat treatment: the bar after drawing was subjected to heat treatment, the holding temperature was 1060 ℃, the holding time was 1 h, and the cooling mode was air cooling.

[0041] Step 5: Performance heat treatment and detection: the bar after cold drawing deformation + recrystallization treatment was sampled, and after being subjected to stabilization treatment + aging treatment, the structure and performance were detected. The stabilization treatment process was 845 ℃ for 4 h and air cooling; the aging treatment process was 760 ℃ for 16 h and air cooling.

[0042] The structure of the GH4738 alloy bar prepared in this embodiment is referred to Figure 2 , and the grain size was about grade 5 according to ASTM E112 "Standard Test Method for Determining Average Grain Size", and the grains were uniform. It can be known that the grain size of the GH4738 alloy bar treated by the method of this embodiment is uniform, and meets the standard requirements. The measured high-temperature durability performance is shown in Table 1.

[0043] Example 2

[0044] Different from Example 1 is that:

[0045] In Step 3, the cold drawing deformation was performed on the peeled bar, and the size after drawing was Φ3 = 14.1 mm, and the drawing deformation was 19.3%.

[0046] In Step 4, the recrystallization heat treatment was performed at a heat treatment temperature of 1050 ℃.

[0047] The structure of the GH4738 alloy bar prepared in this embodiment is referred to Figure 3, the grain size is about 6.5 grade, 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.

[0048] Example 3

[0049] Different from Example 1 is that:

[0050] Step 3, cold deformation, the peeled rod is cold drawn, the size after drawing is Φ3=13.5mm, and the drawing deformation is 26%.

[0051] Step 4, recrystallization heat treatment, the heat treatment temperature is 1050℃.

[0052] The microstructure of the GH4738 alloy rod prepared in this example is referred to Figure 4 , the grain size is about 5 grade, 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.

[0053] Example 4

[0054] Different from Example 1 is that:

[0055] Step 3, cold deformation, the peeled rod is cold drawn, the size after drawing is Φ3=13.5mm, and the drawing deformation is 26%.

[0056] Step 4, recrystallization heat treatment, the heat treatment temperature is 1050℃.

[0057] The microstructure of the GH4738 alloy rod prepared in this example is referred to Figure 5 , the grain size is about 5 grade, 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.

[0058] Comparative Example 1

[0059] The rod which is vacuum induction smelted, vacuum consumable remelted, homogenization heat treated, forged, and hot rolled to Φ1=17.5mm is subjected to standard solid solution treatment, that is, kept at 1080℃ for 4h, and air cooled after discharging.

[0060] The metallographic structure photograph of the rolled rod after completing the standard solid solution heat treatment is shown in Figure 1 , and the grain size is about 8 grade. Figure 1It can be seen that the bar has excessive coarse grain structure, and the grain size level is above 0 level.

[0061] Comparative Example 2

[0062] The GH4738 alloy bar was prepared by the following method steps:

[0063] Step 1: The VIM+VAR billet was subjected to homogenization treatment, then was forged to break down, and was hot rolled to Φ1=17.5 mm, and was subjected to standard solid solution treatment at 1080°C for 4h and air cooling.

[0064] Step 2: The rolled bar subjected to standard solid 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.

[0065] Step 3: Cold drawing deformation: the peeled bar was subjected to cold drawing deformation at room temperature, and the size after drawing was Φ3=14.8 mm, and the drawing deformation was 11%.

[0066] Step 4: The drawn bar was subjected to heat treatment, the holding temperature was 1000°C, the holding time was 1h, and the cooling mode was air cooling.

[0067] The metallographic structure photograph of the bar prepared in Comparative Example 2 is shown in Figure 6 The metallographic structure shows that the bar still has 0 level coarse grain structure after 11% drawing deformation and 1000°C heat treatment.

[0068] Comparative Example 3

[0069] The GH4738 alloy bar was prepared by the following method steps:

[0070] Step 1: The VIM+VAR billet was subjected to homogenization treatment, then was forged to break down, and was hot rolled to Φ1=17.5 mm, and was subjected to standard solid solution treatment at 1080°C for 4h and air cooling.

[0071] Step 2: The rolled bar subjected to standard solid 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.

[0072] Step 3: Cold drawing deformation: the peeled bar was subjected to cold drawing deformation at room temperature, and the size after drawing was Φ3=14.8 mm, and the drawing deformation was 11%.

[0073] Step 4: The drawn bar was subjected to heat treatment, the holding temperature was 1100°C, the holding time was 1h, and the cooling mode was air cooling.

[0074] The metallographic structure photograph of the bar prepared in Comparative Example 3 is shown in Figure 7As shown, the metallographic structure after 11% drawing deformation and 1100℃ heat treatment exhibits a grade 3 grain structure. Although there is some recrystallization homogenization, the grain size does not meet the requirement of a grain size finer than grade 3 as specified in standards such as AMS5708. Its measured high-temperature creep performance is shown in Table 1.

[0075] Comparative Example 4

[0076] Prepare GH4738 alloy bars according to the following steps:

[0077] Step 1: The VIM+VAR billet is homogenized, then forged and hot-rolled to Φ17.5mm, and then air-cooled at 1080℃ for 4h to complete the standard solution treatment.

[0078] Step 2: Peel the rolled bars that have undergone standard solution treatment, control the dimensions to Φ15.7mm, ellipticity ≤0.05mm, and eliminate surface defects.

[0079] Step 3: Cold drawing deformation: The stripped bar is cold drawn at room temperature, and the drawn size is Φ13.1mm with a drawing deformation of 30%.

[0080] Step 4: Heat treat the drawn bar stock at 1050℃ for 1 hour, and air cool.

[0081] The metallographic images of the rods prepared in Comparative Example 4 are as follows: Figure 8 As shown in the metallographic data, even after 30% drawing deformation and heat treatment at 1050℃, the microstructure still exhibits a grade 3 grain structure. The grain size still does not meet the requirement of a grain size finer than grade 3 as specified in standards such as AMS5708. The measured high-temperature creep rupture properties are shown in Table 1.

[0082] Comparative Example 5

[0083] Prepare GH4738 alloy bars according to the following steps:

[0084] Step 1: The VIM+VAR billet is homogenized, then forged and hot-rolled to Φ17.5mm, and then air-cooled at 1080℃ for 4h to complete the standard solution treatment.

[0085] Step 2: Peel the rolled bars that have undergone standard solution treatment, control the dimensions to Φ15.7mm, ellipticity ≤0.05mm, and eliminate surface defects.

[0086] Step 3: Cold drawing deformation: The stripped bar is cold drawn at room temperature, and the drawn size is Φ15.2mm with a drawing deformation amount of 6%.

[0087] Step 4: heat treatment of the drawn rod, holding temperature 1050℃, holding time 1h, cooling mode air cooling.

[0088] The metallographic structure photograph of the rod prepared in Comparative Example 5 is shown in Figure 9 The metallographic structure shows 0-grade coarse grain structure after 6% drawing deformation + 1050℃ heat treatment.

[0089] Table 1: comparison of measured structure and performance of Examples 1-4 and Comparative Examples 1-5

[0090]

[0091] As can be seen from Table 1, Figures 1-9 The grain size of GH4738 alloy is successfully refined from coarse 0-grade after traditional heat treatment (Comparative Example 1) to 5-6.5 grade by the cold drawing deformation-recrystallization heat treatment synergistic process of Examples 1-4, and the endurance performance meets the requirements of AMS5708 standard. The technical principle and key advantages are as follows: 1. Grain refinement mechanism: (1) Deformation energy storage driving, recrystallization cold drawing (11-26% deformation), introducing high dislocation density and deformation energy storage in the alloy, providing nucleation driving force for recrystallization. If the deformation is too low, the stored energy is insufficient to trigger complete recrystallization (Comparative Example 5, 6% deformation); if it is too high, the stored energy is high, and the recrystallization is completed quickly and enters the growth stage, resulting in coarse grains (Comparative Example 4, 30% deformation); (2) Precise temperature control to inhibit secondary coarsening, 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 requirement of most standards such as AMS5544 of finer than 5-grade.

[0092] Through comparative tests, the core process window is determined: the effective parameter range of cold drawing deformation is 11-26%, deformation <11% has the risk of insufficient stored energy to trigger recrystallization, and deformation >26% will lead to grain coarsening. The effective parameter range of recrystallization temperature is 1040-1060℃, temperature <1040℃ will lead to inactivation of recrystallization, and temperature >1060℃ will affect the secondary growth of grains.

[0093] Theoretically, the lower grain size rating (coarser grains) should increase the alloy's stress-rupture life, with more time for plastic deformation, and the plasticity should increase. However, in the case of GH4738 alloy, the strengthening phase γ' coarsens during long-term stress-rupture testing, which weakens the plastic deformation ability of the intracrystalline, offsetting the theoretical increase in plasticity of coarse grains. At the same time, the grain boundary weakens at high temperatures for a long time, and the applicant speculates that these two points may cause the theoretical plasticity advantage to be offset, and the plasticity of Comparative Examples 3 and 4 and the examples is similar.

[0094] However, the core value of the present application is to break through the technical bottleneck of abnormal coarsening of GH4738 alloy grains after standard solid solution (≥0 grade), and to stabilize the grain size at 5-6.5 grade through a cold drawing-recrystallization synergistic process, to meet the mandatory requirements of AMS5708 and other standards for grain size (finer than 3 grade), and to avoid batch rejection due to coarse grains. Although the stress-rupture time of Comparative Examples 3 and 4 (grain size 3 grade) is slightly higher than that of the examples, their grain size does not meet the standard requirements and does not meet the requirements of AMS5708 standard for grain size (which needs to be finer than 3-5 grade), and is only used as a process boundary reference. However, under the premise of ensuring the grain size compliance, the stress-rupture 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, The grain size thereof is 5-6.5, the metallography is uniform equiaxed crystal organization, the 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 of Ni; the elongation δ5 is ≥27.5%, the reduction of area ψ is ≥30%, the hardness HRC is 38.0-38.9, and the alloy is prepared by the following method: step 1, raw material pretreatment: the blank prepared by vacuum induction smelting + vacuum consumable remelting is subjected to homogenization treatment, then is forged to break down, and is hot rolled to a diameter Φ1, and is subjected to standard solid solution treatment under the condition of 1080 ℃ for 4h and air cooling; Step 2, surface finishing: the surface oxidation layer is removed by using the centerless grinding skinning process, the size is controlled to Φ2, the ovality is ≤0.05mm, and the surface defects are eliminated; Step 3, cold drawing deformation: the cold drawing is carried out at room temperature through a conical die, the deformation amount is controlled to be 11%-26%, and the lubricant is uniformly smeared before the cold drawing deformation; Step 4, recrystallization heat treatment: the deformed rod material obtained in step 3 is placed in a heat treatment furnace, is kept for 1h under the condition of 1040-1060 ℃, and is air cooled after keeping, so that the deformed organization is completely statically recrystallized.

2. A method of making the high performance GH4738 alloy material of claim 1, characterized by, The following steps are included: Step 1, raw material pretreatment: the blank prepared by vacuum induction smelting + vacuum consumable remelting is subjected to homogenization treatment, then is forged to break down, and is hot rolled to a diameter Φ1, and is subjected to standard solid solution treatment under the condition of 1080 ℃ for 4h and air cooling; Step 2, surface finishing: the surface oxidation layer is removed by using the centerless grinding skinning process, the size is controlled to Φ2, the ovality is ≤0.05mm, and the surface defects are eliminated; Step 3, cold drawing deformation: the cold drawing is carried out at room temperature through a conical die, the deformation amount is controlled to be 11%-26%, and the lubricant is uniformly smeared before the cold drawing deformation; Step 4, recrystallization heat treatment: the deformed rod material obtained in step 3 is placed in a heat treatment furnace, is kept for 1h under the condition of 1040-1060 ℃, and is air cooled after keeping, so that the deformed organization is completely statically recrystallized.

3. The method of making high performance GH4738 alloy material of claim 2, wherein, The final rolling temperature in the hot rolling treatment in step 1 is ≥950 ℃, and the total deformation amount is controlled to be 65%-80%.

4. The method of making high performance GH4738 alloy material of claim 2, wherein, Step 5, heat treatment and inspection: the rod material after the cold drawing deformation and the recrystallization heat treatment is sampled, is subjected to stabilization treatment and aging treatment, and then is subjected to organization and performance inspection.

5. The method of making high performance GH4738 alloy material of claim 4, wherein, The stabilization treatment process in step 5 is air cooling after keeping for 4h at 845 ℃; and the aging treatment process is air cooling after keeping for 16h at 760 ℃.

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