Analysis of microstructure in the welding zone of 9Cr-1 Mo-V-Nb (P91) steel

Under the condition of TIG+SMAW technology, the microstructure in the welding zone of 9Cr-1Mo-V-Nb (P91) heat-resisting steel is researched by means of X-ray diffractometry (XRD) and transmission electron microscope (TEM). The test results indicate that when the weld heat input (E) of TIG is 8.5 ∼ 11.7 kJ/cm and the weld heat input of SMAW is 13.3 ∼ 21.0 kJ/cm, the microstructure in the weld metal is composed of austenite and a little amount of δ ferrite. The substructure of austenite is crypto-crystal martensite, which has included angle. TEM analysis indicates the fine structure in the heat-affected zone is lath martensite. There are some carbide at the boundary of grain and inside the grain, most of which is Cr23C6 and a little amount of (Fe, Me)23C6.