Abstract
Optical microscope, micro-hardness tester, scanning electron microscope (SEM) and X-ray diffractometer (XRD) were applied to analyze the microstructure and properties of tungsten inert-gas arc welding (TIG) joint for P91 heat resistant steel under the different holding time of annealing treatment. The test results show that the martensite structure and retained austenite structure had a change in weld zone and heat affected zone (HAZ) with the increase of the holding time from 4 to 6 h with 760 °C annealing. The microstructure in the weld zone shows the finer characteristic. The hardness in all regions tends to decrease after the annealing treatment, and the hardness is about 200–240 HV. However, the hardness in the weld zone is about 200–270 HV. The highest hardness in the weld zone and HAZ was observed when the holding time was 6 h, and some carbide was dissolved partially with the increase of the holding time. Moreover, when the holding time was 6 h with 760 °C annealing, some small dispersed precipitated phases were distributed in the substrate. Thus, the microstructure and properties of TIG welded joint used for holding time 6 h are better than those for holding time 4 and 5 h.

Key words
P91 heat-resistant steel, annealing, holding

Full text (983 KB)