The matching of hot deformation forging process parameters and heat treatment process parameters of GH3230 high-temperature alloy is studied through the hot working process test, and the changes in microstructure and mechanical properties are analyzed. The results show that high-temperature reformed forging can improve the original organization in the forged bar so that the organization is uniformly refined; suitable solid solution heat treatment can make the lumpy aggregated carbides re-dissolve, discrete precipitation, uniform distribution, and size refinement. In the solid solution temperature of 1200 ℃ temperature, GH3230 alloy can be obtained comprehensive mechanical properties of good ring products.
GH3230 high-temperature alloy is a very high degree of alloying nickel-based deformation of high-temperature alloys; the total content of its elements W + Mo + Cr can reach 36%. The alloy through solid solution alloying elements to strengthen the matrix, the W element, and Mo elements added not only improve the creep resistance of the alloy and increase the layer error energy, making the dislocation slip difficult to occur. Due to its organization of high thermal stability, the alloy has good high-temperature strength, oxidation resistance, creep resistance, resistance to hot and cold fatigue performance, and its highest application temperature of up to 1050 °C. Therefore, it is widely used in aero-engine combustion chamber flanges, ground gas turbine combustion chambers, the chemical industry, high-temperature corrosion-resistant parts, aviation engine flame tubes, and other key parts. In production practice, often due to the forging process parameters and heat treatment process parameters not matching, resulting in GH3230 high-temperature alloy in the process of forging process, there is deformation resistance, processing and forming difficulties, forgings are easy to crack, and other issues. In particular, the hot processing of GH3230 high-temperature alloy rings has become a problem in today’s forging industry.
To solve the problem, this paper, through the GH3230 high temperature hot deformation forging process parameters and heat treatment process parameters matching research, to obtain a stable production quality, product microstructure, mechanical properties, and surface quality of good ring rolling process.
1. Test material
Raw material situation
(1) Test material selection.
Through the vacuum induction + vacuum self-consumption remelting of Φ200mm GH3230 high temperature alloy bar for the process test, the chemical composition is shown in Table 1.
(2) Forged bar body low times.
The low time organization of GH3230 high temperature alloy in the forging state and GH3230 high temperature alloy after the solid solution is shown in Figure 1.
As can be seen from Figure 1(a), there are no shrinkage holes, bubbles, voids, flaps, cracks, white spots, inclusions, point-like segregation, etc., visible to the naked eye on the acid-impregnated low times specimen of the forged GH3230 high-temperature alloy. As can be seen from Figure 1(b), there is a ring of coarse crystals of uneven thickness at the edge of the acid-impregnated low times specimen of GH3230 high-temperature alloy after solid solution.
(3) Forged bar body grain size.
The grain size grade is obtained using the comparative method in the ASTM E112-2013 standard, and the organizational state of the three different sampling regions (oblate, R/2, center) of the body of the forged bar after the solid solution is shown in Figure 2.
As can be seen from Figure 2, after air firing, the grain growth at the edge of the forged bar is particularly obvious. The grain growth in the center could be clearer, and the preliminary analysis may be due to the low surface deformation temperature, small deformation, and work hardening.
(4) Mechanical tensile properties.
Mechanical tensile properties are shown in Table 2.
2. Test method
Ring size is: Φ975+5-3mm × Φ860+3-5mm × (130±2) mm. The specific process of ring rolling is as follows: the heated raw materials are forged, forging heating equipment for natural gas furnaces, and solid solution treatment heating equipment for electric furnaces. The forging deformation process is as follows: raw materials → change forging → upsetting cake → punching → grinding exhaust → pre-rolling → final rolling → solid solution → physical and chemical testing → storage. Specific ring forging and heat treatment process parameters are shown in Table 3.
The forging process is based on the idea of reforming forging and then forming, adopting the thermal processing method of high-temperature heating and low strain rate deformation, to satisfy the conditions of dynamic recrystallization under relatively low deformation resistance and to obtain uniform and fine equiaxial grain organization; the heat treatment process adopts the high-temperature solid solution to dissolve large aggregated carbides into the matrix and then precipitates uniformly fine and discrete distribution of carbides.
Numerical simulation analysis
(1) Simulation parameter settings.
GH3230 ring piece simulation parameter settings are shown in Table 4.
(2) Load prediction.
Load prediction is shown in Figure 3; ring rolling simulation is completed, and the predicted radial rolling force is 289 tons, effectively reducing the deformation resistance of high-temperature alloy GH3230 ring parts. Φ2500mm reaming machine equipment tonnage of radial 400 tons can roll this type of ring parts.
Table.1 Chemical composition of GH3230 high temperature alloy bar (wt%)
Fig.1 Raw material low times
Fig.2 Raw material high grade
Table.2 Mechanical Properties of Raw Material
|Inspection results/items||Sample number||Tensile strength/MPa||Yield strength/MPa||Elongation rate/%||Hardness/HB||Sampling direction|
|Room temperature stretching||Result||1||837||414||44||205||Chordwise|
|Inspection results/items||Sample number||Test temperature/℃||Tensile strength/MPa||Elongation rate/%||/||Sampling direction|
|Inspection results/items||Sample number||Test temperature/℃||Test stress/MPa||Test time/h||Elongation rate/%||Sampling direction|
|High temperature endurance||Result||1||927||62||78.6||27.5||Chordwise|
Table.3 Main Process Parameters for Forging and Heat Treatment of GH3230 Ring Parts
|Forging process||Modification forging||Blank||Ring rolling||Solid solution|
|Heating temperature||1180℃||1180℃||1160℃||1200-1246 ℃ water cooling or rapid cooling|
Table.4 Simulation Parameter Settings for GH3230 Ring Parts
|Initial temperature of main roller (°C)||60|
|Initial temperature of core roller (°C)||200|
|Initial temperature of billet (°C)||1160|
|Environmental temperature (°C)||25|
|Heat transfer coefficient between workpiece and mold [N/(s.mm.°C)]||2.5|
|Heat transfer coefficient between workpiece and environment [N/(s.mm.°C)]||5|
|Forming fire||Two fire ring rolling|
|Main roller speed (rad/s)||3.1415|
|Core roller feed speed (mm/s)||0.5|
Fig.3 Simulation prediction of radial rolling force for GH3230 ring piece rolling
(3) Temperature field distribution.
Temperature field distribution is shown in Figure 4; ring rolling simulation is completed after the temperature field is more uniform; the temperature range is 970-1000 ℃.
Figure.4 GH3230 ring rolled after the completion of the temperature field distribution
(4) Strain field distribution.
The strain field distribution is shown in Figure 5. After the ring rolling simulation, the strain is more uniform, and the equivalent effect becomes 0.6-1.
Figure.5 GH3230 ring rolled after the completion of strain field distribution
Physical and chemical testing results and analysis
(1) Microstructure under different solid solution temperatures.
The ring piece is divided into two parts, respectively, at 1200 ℃ and 1230 ℃ for solid solution treatment, holding temperature 80min after water cooling. The microstructure of the ring after solid solution treatment is shown in Figure 6.
As shown in Figure 6, after the solid solution, the massive carbides in the microstructure of the ring piece are reduced compared with the bar body (Figure 2). This is mainly due to the ring part in the forming before the reforging, the bar of the original grain further broken, the reforging process occurs in the dynamic recrystallization so that the organization uniformity, refinement; in the subsequent solid solution treatment carbide re-dissolved into the matrix, and converted to a discrete distribution of uniformly small carbides, in the morphology, size, distribution of the changes that occurred after the heat treatment using water-cooled to a greater extent Retained the solid solution homogenization of the organization, and has the effect of grain refinement.
From Figure 6(a), and Figure 6(d), two diagrams can be seen, 1200 ℃ solid solution treatment after the organization of the grain than 1230 ℃ solid solution treatment after the grain is more fine, uniform, which indicates that the temperature increases, the grain growth phenomenon; from Figure 6(b), Figure 6(e) two diagrams can be seen, 1230 ℃ solid solution treatment after the organization of the carbide distribution is relatively homogeneous, the degree of dispersion is greater, while 1200 ℃ solid solution treatment of carbides in the organization of individual aggregation phenomenon. This is consistent with the higher the temperature, the better the degree of carbide solid solution; Figure 6 (c), Figure 6 (f) two diagrams can be seen, through the solid solution heat treatment, a large number of carbides dissolved into the alloy matrix, which can play a role in solid solution strengthening, and at the same time to see precipitation of carbide is a fine granular, chain distribution, play a role in pegging, can be effective in preventing the growth of the grain.
Figure.6 Microstructure under different solid solution temperatures
Table.5 Performance data of GH3230 under different solid solution temperatures
|Inspection results/items||Sample number||Tensile strength/MPa||Yield strength/MPa||Elongation rate/%||Hardness/HB||Heat treatment system||Sampling direction|
|Room temperature stretching||Result||1||869||384||43.5||213||1200℃ x 80min,water-cooling||Chordwise|
|1||886||405||43||217||1230℃ x 80min,water-cooling|
|Inspection results/items||Sample number||Test temperature/℃||Tensile strength/MPa||Elongation rate/%||/||Heat treatment system||Sampling direction|
|Elevated temperature||Result||1||950||221||78||1200℃ x 80min, water-cooling||Chordwise|
|1||224||64.5||/||1230℃ x 80min, water-cooling|
|Inspection results/items||Sample number||Test temperature/℃||Test stress/MPa||Test time/h||Elongation rate/%||Heat treatment system||Sampling direction|
|High temperature endurance||Result||1||927||62||30.4||38.5||1200℃ x 80min, water-cooling||Chordwise|
|1||25.8||38||1230℃ x 80min, water-cooling|
(2) Mechanical properties under different solid solution temperatures.
The ring was solid solution treated at 1200℃ and 1230℃, respectively, and water-cooled after holding for 80min. Mechanical properties data after solid solution treatment are shown in Table 5.
It can be seen from the performance data using 1200 ℃ solution treatment after the room temperature tensile strength data results, although lower than the 1230 ℃ data, its data fluctuations are small and relatively stable; at the same time, the use of 1200 ℃ solution treatment of high-temperature tensile, high-temperature endurance data results are fluctuations are small, relatively stable; therefore, if the forging process described in this paper after rolling the ring is recommended to use 1200 ℃ solution treatment, can improve the microstructure of nickel-based high temperature alloy GH3230, improve its comprehensive mechanical properties.
This also further indicates that the use of suitable heat treatment process parameters matched with the forging process plays an important role in the stability of product quality of GH3230 high temperature alloy ring parts.
- (1) High-temperature alloy GH3230 ring parts using a higher forging deformation temperature while matching the relatively low strain rate, in the case of reducing the forging deformation resistance to meet the tonnage limitations of the equipment, but still meet the conditions of dynamic recrystallization, you can get a uniformly fine hot working equiaxial organization.
- (2) High-temperature alloy GH3230 through forging to get uniform fine isometric organization for heat treatment provides the organization preparation, the use of appropriate heat treatment process parameters, that is, in 1200 ℃ under the solution treatment, can improve the GH3230 alloy carbides in the morphology, size, distribution, etc., to obtain the organization of uniformity, the comprehensive performance of the ring parts of the product is excellent.
Author: Cao Yuru, Shi Zhankui, Cao Yigao