Influence of welding process and heat treatment on Δ-ferrite evolution and mechanical properties of P91 weldments

Creep strength enhanced ferritic/martensitic modified 9Cr-1Mo (P9l) also designated as ASTM A335 used for out-of-core and in-core (piping, cladding, ducts, wrappers, and pressure vessel) of Gen IV reactors. In present investigation, a comparative study of effect of autogenous tungsten inert gas welding (A-TIG) with single and double pass and multi-pass gas tungsten arc (GTA) on microstructure evolution in sub-zones and tensile properties of P91 and P92 welded joints was carried out. The microstructure evolution was carried out in as welded and post-weld heat treatment (PWHT) condition. The study also focused on the evolution of δ-ferrite patches and their influence on the tensile properties of welded joints. PWHT was carried out at 760 ° C for 2 h. Presence of higher content of ferrite stabilizer in P92 steel promoted the formation of δ-ferrite patches in weld fusion zone as well as HAZ. For microstructure characterization, field-emission scanning electron microscope (FESEM) with energy dispersive spectroscopy (EOS) and optical microscope were utilized. (author)