Formation of G-phase in 20Cr32Ni1Nb Stainless Steel and its Effect on Mechanical Properties  

作　　者：Xiao-Feng Guo Ying-Ying Ni Jian-Ming Gong Lu-Yang Geng Jian-Qun Tang Yong Jiang Xian-Kai Jia Xin-Yu Yang 

机构地区：[1]School of Mechanical and Power Engineering,Nanjing Tech University,Nanjing 211816,China [2]Key Lab of Design and Manufacture of Extreme Pressure Equipment,Nanjing 210037,China

出　　处：《Acta Metallurgica Sinica(English Letters)》2017年第9期829-839,共11页金属学报（英文版）

基　　金：financially supported by the National Natural Science Foundation of China(No.50775107);the China Petrochemical Corporation(No.315007);the Innovation Program for Graduate Students in Jiang Su Province of China(No.KYLX15_-0800)

摘　　要：A series of tensile tests, Charpy impact tests, optical microscopy observations, and field emission-scanning electron microscopy examinations, were carded out to investigate the mechanical properties and microstructural evolution of 20Cr32NilNb steel. Experimental results indicate that the as-cast microstructure of the steel typically consists of a supersaturated solid solution of austenite matrix with a network of interdendritic primary carbides （NbC and M23C6）. In the ex-service samples, large amounts of secondary carbides precipitate within austenite matrix. Besides the growth and coarsening of NbC and M23C6 carbides during service condition, the Ni-Nb silicides known as G-phase （Nil6Nb6Si7） are formed at the interdendritic boundaries. The microstructural evolution results in the degradation of the mechanical properties of the ex-service steel. In addition, the precipitate rate of G-phase, depending in part on Si content, varies greatly for the 20Cr32NilNb steel, which plays a key role in the long-term microstructural stability of the steel. Based on the X-ray diffraction data, time-temperature-transformation curve for the steel is obtained from the aged specimens.A series of tensile tests, Charpy impact tests, optical microscopy observations, and field emission-scanning electron microscopy examinations, were carded out to investigate the mechanical properties and microstructural evolution of 20Cr32NilNb steel. Experimental results indicate that the as-cast microstructure of the steel typically consists of a supersaturated solid solution of austenite matrix with a network of interdendritic primary carbides （NbC and M23C6）. In the ex-service samples, large amounts of secondary carbides precipitate within austenite matrix. Besides the growth and coarsening of NbC and M23C6 carbides during service condition, the Ni-Nb silicides known as G-phase （Nil6Nb6Si7） are formed at the interdendritic boundaries. The microstructural evolution results in the degradation of the mechanical properties of the ex-service steel. In addition, the precipitate rate of G-phase, depending in part on Si content, varies greatly for the 20Cr32NilNb steel, which plays a key role in the long-term microstructural stability of the steel. Based on the X-ray diffraction data, time-temperature-transformation curve for the steel is obtained from the aged specimens.

关 键 词：20Cr32NilNb EMBRITTLEMENT G-phase TTT dial  ram 

分 类 号：TG142.1[一般工业技术—材料科学与工程]