Microstructural study of welded joints in a high temperature martensitic-ferritic ASTM A335 P91 steel

摘要

We have studied the effect of post-weld heat treatments (PWHT's) performed at 760 °C on the microstructure and hardness of ASTM A335 P91 steel welded joints. The welding process used was GMAW and the filler material was a solid wire of the type AWS ER90S-B9. The analysis of cross sections of the welds revealed a narrow heat-affected zone (HAZ) 4 mm wide, composed by a thin (~0.2 mm) coarse-grained layer with high hardness, a fine-grained region exhibiting grains up to 4 um in size, and a soft intercritical region with low hardness, located 3 to 4 mm away from the fusion line. The results of hardness measurements suggest that a PWHT of 2h at 760 °C is enough to reestablish the strength of the P91 steel after the welding process.