Micro-segregation and Precipitation of Alloy 690 during Isothermal Solidification:the Role of Nitrogen Content  

作　　者：Rong Jiang Bo Chen Xianchao Hao Yingche Ma Shuo Li Kui Liu 

机构地区：[1]Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

出　　处：《Journal of Materials Science & Technology》2012年第5期446-452,共7页材料科学技术（英文版）

基　　金：supported by the National Natural Science Foundation of China (No. 50901076)

摘　　要：The segregation and precipitation behavior of Alloy 690 containing 0.001-0.11 wt% nitrogen during isothermal solidification at 1370 and 1355 ℃ have been investigated using optical microscopy （OM）,electron probe microanalysis （EPMA） and transmission electron microscopy （TEM）.The results indicate that the volume fraction of TiN-type nitride formed during isothermal solidification increases with the nitrogen content of Alloy 690.Segregation of Ti and Cr exists in samples solidified at 1370 and 1355℃.The Ti content in the residual liquid markedly decreases and the concentration of Cr increases when the nitrogen content of Alloy 690 increases.Furthermore,N and S also show segregation to some extent in the residual liquids at 1355℃.Accompanying by the segregation of Cr,Ti,C,N and S,sulfides and chromium nitrides form.In a low nitrogen content Alloy 690,sulfur segregates and precipitates in the form of Ti 4 C 2 S 2 and （Cr,Ti）S,but in the form of （Cr,Ti）S or CrS in a high nitrogen content Alloy 690.（Cr,Ti）N-type nitrides with an fcc crystal structure have been identified in a sample with 0.11 wt% nitrogen.The segregation and precipitation behavior of Alloy 690 containing 0.001-0.11 wt% nitrogen during isothermal solidification at 1370 and 1355 ℃ have been investigated using optical microscopy （OM）,electron probe microanalysis （EPMA） and transmission electron microscopy （TEM）.The results indicate that the volume fraction of TiN-type nitride formed during isothermal solidification increases with the nitrogen content of Alloy 690.Segregation of Ti and Cr exists in samples solidified at 1370 and 1355℃.The Ti content in the residual liquid markedly decreases and the concentration of Cr increases when the nitrogen content of Alloy 690 increases.Furthermore,N and S also show segregation to some extent in the residual liquids at 1355℃.Accompanying by the segregation of Cr,Ti,C,N and S,sulfides and chromium nitrides form.In a low nitrogen content Alloy 690,sulfur segregates and precipitates in the form of Ti 4 C 2 S 2 and （Cr,Ti）S,but in the form of （Cr,Ti）S or CrS in a high nitrogen content Alloy 690.（Cr,Ti）N-type nitrides with an fcc crystal structure have been identified in a sample with 0.11 wt% nitrogen.

关 键 词：Alloy 690 Nitrogen content SOLIDIFICATION MICRO-SEGREGATION PRECIPITATE 

分 类 号：TG146.15[一般工业技术—材料科学与工程] TG244.3[金属学及工艺—金属材料]