GH925高温耐蚀合金升温相态转变行为及热处理工艺研究

Study on the phase transformation behaviors with rising temeprature and heat treatment process of the GH925 high-temperature and corrosion-resistant alloy

采用差示扫描量热法(DSC)、扫描电镜(SEM)、电子探针(EMPA)等表征方法,对GH925合金的锻态相转变行为、固溶时效态热处理工艺性能及显微组织进行了研究。研究表明合金从室温25~1 100℃升温区间的相转变序列为:MC相(转变温度为540℃-终止析出温度为1 043℃,下同);γ′相(578~978℃);M23C6-M7C3(679~758℃);σ相(723.5~879℃);η相(807~978℃)。合金锻态组织经(990~1 010℃)×2h固溶+740℃-760℃×8h时效处理,可以获得最佳的综合力学性能。1 000℃×2h固溶+780℃×8h时效热处理,沿晶界有大量的脆硬针片状σ相析出,造成合金冲击韧性的急剧下降。

The phase transformation behaviors, solid-solution aging heat treatment processes, mecnanlc proper- ties and microstructure of the forged GH925 alloy were investigated by means of differential scanning calorime- try （DSC）, scanning electron microscopy （SEM）, electron probe mieroanalysis （EPMA） characterization meth- ods, etc. The research results show that the phase transformation sequence of the forged alloy during elevated temperature from 25 to 1 100 ℃ is MC phase （initial transformation temperature is 540 ℃, terminated transfor- mation temperature is 1 043 ℃, the same below）, 7r phase （578-978 ℃）, M2sC6-MTCs （679-758 ℃）, a phase （723.5-879 ℃ ） and η phase （807-978 ℃）. The optimum comprehensive mechanical properties of the forged alloy can be obtained by 990-1 010 ℃ × 2 h solid-solution and 740-760 ℃ × 8 h aging heat-treatment. An amount of hard and brittle needle flake σ phase precipitates along the grain boundaries after the heat-treatment of 1 000 ℃ × 2 h solid-solution and 780 ℃ × 8 h aging, resulting in a sharp decline of the aolly＇s impact toughness at this aging temperature.