Optical microscope

micro-hardness tester

scanning electron microscope（SEM）

energy dispersive spectrometer（EDS） and X-ray diffractometer（XRD） were applied to analyze the microstructure and phase transformation of Shielded Metal Arc Welding（SMAW） joint for T91 heat resistant steel under 760 ℃+different holding time of annealing treatment. The test results show that the hardness of welded joints decreases obviously

and the hardness distribution decreases from base metal to heat affected zone by different holding time of annealing treatment. In the same time

the microstructure in the weld zone transforms from lath martensite to acicular martensite or plate martensite with different holding time of annealing treatment. Fine dispersed precipitated phases are mainly distributed in grain boundaries and martensitic boundaries and interior after annealing treatment of holding 6 h. The properties of materials are relatively excellent by second phase strengthening.