沉淀强化钢中两相区NiAl相和富Cu相的析出特点

PRECIPITATION CHARACTERIZATION OF Ni Al AND Cu-RICH PHASES IN DUAL-PHASE REGION OF PRECIPITATION STRENGTHENING STEEL

沉淀强化钢在900℃固溶2 h后水淬,500℃时效1 h,利用原子探针层析技术(APT)研究了残余奥氏体和马氏体两相区强化相的析出特点.结果表明,残余奥氏体中没有析出相,马氏体和马氏体/残余奥氏体界面处均有强化相析出,马氏体中靠近界面处有一层析出贫化区.界面处强化相的等效半径和间距均大于马氏体中的强化相,界面处富Cu相和Ni Al相中Cu,Ni和Al的含量均大于马氏体中的富Cu相和Ni Al相,而且界面处富Cu相和Ni Al相的分离趋势要大于马氏体,这是因为界面处存在大量缺陷,促进了强化相的长大,使得界面处和马氏体中的强化相处于长大的不同阶段.

Precipitation strengthening plays an important role on improving the mechanical properties of steels, Ni Al and Cu-rich phases are two kinds of common precipitates. This work aims to reveal the precipitation characteristics of these two phases in martensite and retained austenite in precipitation strengthening steel by atom probe tomography（APT）. The hot rolled samples were aged at 500 ℃ for 1 h after solution treatment at 900 ℃for 2 h, followed by microstructure analysis. The results show that Ni Al and Cu- rich phases form in martensite phase as well as at martensite/austenite phase boundaries, while no precipitate develops in retained austenite. Precipitation was not observed near the phase boundaries in martensite. Equivalent radius, spacing and concentration of the strengthening phases at phase boundary are larger than that inside martensite. In addition, Ni Al phase tend to separate from Cu-rich phase, and the separated tendency becomes stronger at phase boundaries than in martensite.Besides, the growth of Ni Al and Cu- rich phases at phase boundary differs from that within martensite, which should be induced by the defect density difference between them.