Microstructural evolution of 9Cr–1Mo deposited metal subjected to weld heating

The microstructural evolution and the final microstructure of 9Cr–1Mo deposited metal in as-welded condition are analyzed and discussed in this paper. The concept of “weld bead heat affected zone” (WBHAZ) is proposed. Different zones of WBHAZ are in different temperature interval during weld heating. The microstructures in different zones are observed using optical microscopy, scanning electron microscopy and transmission electron microscopy. The type and the process of phase transformation taking place in different zones of WBHAZ are established according to the thermal cycles they were subjected to. Based on these studies, the microstructural evolution process and the microstructure of 9Cr–1Mo deposited metal are deduced. This research will provide foundation for analyzing the microstructural features in as-welded condition, the microstructural evolution of 9Cr–1Mo or other Cr–Mo deposited metal after post-weld heat treatment and in the long-term operations at elevated temperature.