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

• 来源期刊: 金属学报（英文版）
• 年，卷（期）: 2017,（9）
• 页码范围: 829-839
• 页数: 11页
• 语种: 英文
• DOI: 10.1007/s40195-017-0589-0

摘要

A series of tensile tests,Charpy impact tests,optical microscopy observations,and field emission-scanning electron microscopy examinations,were carried 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 (Ni16Nb6Si7) 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 20Cr32Ni1Nb steel,which plays a key role in the long-term microstroctural stability of the steel.Based on the X-ray diffraction data,time-temperature-transformation curve for the steel is obtained from the aged specimens.