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

• Published in: Journal of materials science & technology 2012-05, Vol.28 (5), p.446-452
• Main Authors: Jiang, Rong, Chen, Bo, Hao, Xianchao, Ma, Yingche, Li, Shuo, Liu, Kui
• Format: Article
• Language: English
• Subjects: 690合金; Alloy 690; Micro-segregation; Nitrogen content; Precipitate; Solidification; 凝固过程; 微观偏析; 氮化钛; 氮含量; 等温; 透射电子显微镜; 降水
• ISSN: 1005-0302; 1941-1162
• DOI: 10.1016/S1005-0302(12)60081-4

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.