1 alloy introduction
1. 1 Overview
GH6 159 is a new type of high-strength multiphase cobalt-based superalloy developed on the basis of foreign multiphase cobalt-based superalloy (MP alloy). Its main characteristics are as follows: firstly, cold deformation is used to induce flaky exfoliated ε phase distributed in the face-centered cubic matrix, which prevents the long-range movement of dislocations and strengthens them, and then dispersed Ni3X phase is precipitated after aging treatment for supplementary strengthening. The alloy has comprehensive properties such as ultra-high strength, good plastic toughness and high stress corrosion resistance, and can still maintain high strength at 650℃. The alloy can be widely used not only for high-temperature fastening bolts and other parts of aero-engines, but also for ultra-high strength fasteners of aircraft in stress corrosion environment (such as marine atmospheric environment). The main varieties supplied are cold-drawn steel bars.
1.2, application and special requirements
This alloy is mainly used for fasteners of aero-engines. Its performance is stable at 600℃ and it can be used for a long time. It is the best fastener material for aero-engines at present. The alloy is strengthened mainly by cold deformation to produce a large number of ε phases with gateway distribution. Therefore, the technological parameters of cold drawing deformation should be strictly controlled. The deformation is too small, the strength is insufficient, the deformation is too large, the strength increases, but the plasticity decreases. Practice has proved that the alloy has good comprehensive properties when the cold deformation is controlled at the lower limit.
1.3 material grade
GH6 159？ GH 159？ MP 159 (USA)
1.4, material technical standards
Q/6S 992- 1992 GH 159 alloy cold-drawn bar for high-temperature fasteners
C3S 284- 1993 High temperature fastener GH 159 alloy cold-drawn steel bar
AMS 584 1B vacuum induction+vacuum consumable remelting, solution heat treatment state.
AMS 5842B？ Vacuum induction+vacuum consumable remelting, solution treatment and cold deformation strengthening.
1.6, heat treatment system
1040 ~ 1055℃ solution treatment for 4 ~ 8h, water cooling +48%+0% cold drawing deformation at room temperature+aging treatment at 650 ~ 675℃ for 4~4.5h, and air cooling.
1.7, variety specifications and supply status
Can produce d5~25mm cold-drawn steel bars in cold-drawn state.
1.8, melting and casting process
The alloy is produced by vacuum induction and vacuum arc remelting.
Physical and chemical properties
2. 1. 1, melting temperature range
13 18℃
2.4, magnetic properties
The magnetic permeability of the alloy at 25℃ is 1.00265.
2.5, chemical properties
The alloy has good crevice corrosion resistance and stress corrosion cracking resistance. No crevice corrosion and pitting corrosion were found in typical ferric chloride experiments. No damage occurred in the salt friction test. Alternating impregnation proves that the alloy has good resistance to hydrogen embrittlement and stress corrosion cracking.
3 organizational structure
3. 1, phase transition temperature
The temperature range of γ+ε two-phase region is 540~700℃, and the γ phase below 540℃ is metastable.
3.2, alloy structure
The alloy is a stable face-centered cubic γ phase above the upper critical temperature (about 700℃) and a stable hexagonal ε phase at the lower critical temperature (about 540℃). The two-phase region between the two temperatures is γ+ε. When the alloy is cooled from the upper critical temperature to room temperature, the metastable γ phase can be maintained. Cold deformation at room temperature can induce martensite transformation from γ phase to ε phase. Therefore, all the alloys after solution treatment are metastable γ phases, and some γ phases undergo martensite transformation into stable ε phases during cold deformation. The ε-phase is wavy and distributed in the γ-phase grains of face-centered cubic.
4 process performance and requirements
4. 1, alloy processing
The alloy ingot is limited to1125 ~1180℃ homogenization 18~36h to reduce the formation of microstructure segregation and brittle σ phase. The alloy forging cogging temperature is not higher than 600℃, the heating temperature is 120℃ 10℃, the time is not less than 4h, the forging opening temperature is not lower than 1050℃, and the final forging temperature is not lower than 950℃. The charging temperature of alloy hot rolling cogging is not higher than 700℃, the heating temperature is 1 130℃ 10℃, and the heat preservation is 30 ~ 60 minutes. The maximum deformation of each pass shall not exceed 20%. The final rolling temperature is not lower than 950℃. After hot rolling, the alloy is annealed at 1050~ 1075℃ 1h, and uniform grains are obtained, which is convenient for subsequent cold deformation processing.
4.2, parts heat treatment process
The heat treatment process of bolts is 650~675℃, aging for 4 hours and air cooling.
4.3, surface treatment process
The alloy is insensitive to heating. After hot upsetting into nuts, the surface is treated with cold wire rolling.
GH6 159 Main specifications:
GH6 159 seamless pipe, GH6 159 steel plate, GH6 159 round steel, GH6 159 forging, GH6 159 flange, GH6 159 ring, gh6.
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