Tensile Properties of Modified 9Cr–1Mo Steel Clad Tube to End Plug Weld Joint

Abstract

The tensile properties of modified 9Cr-1Mo steel clad tube to end plug TIG weld joint have been studied in as-welded, after post-weld heat treatment (PWHT), at 760 °C and second heat treatment (2HT, at 550 °C) conditions at temperatures 27-550 °C. Heat-affected zone (HAZ) grain size varied from 6 to 28 µm, with coarse grains toward weld and finer grains toward base metal. Weld metal also showed coarse grains (up to 45 µm) after PWHT and PWHT+2HT, with high hardness (367-340 HV0.2) near weld center beyond which hardness gradually decreased through HAZ and attained 210-235 HV0.2 in base metal. Small fraction of polygonal delta ferrite is observed in weld metal. The yield strength (YS) and ultimate tensile strength (UTS), of weld joint at 27 and 550 °C, exhibited increase of 11 MPa and decrease of 20 MPa, respectively, in as-welded condition and showed minimum strength properties after PWHT. However, PWHT+2HT treatment has increased strength values above PWHT condition. The weld joint after PWHT+2HT retains sufficient total elongation over 10% and possess sufficient strength properties (YS: 442-263 MPa and UTS: 639-276 MPa) at 27 and 550 °C. All the weld joint tensile samples failed in base metal by transgranular ductile fracture, irrespective of test temperature and weld joint condition (as-welded, PWHT, 2HT).