Improvement of weld characteristics by variation in welding processes and parameters in joining of thick wall 304LN stainless steel pipe

Abstract

Various properties of weld joints of 25 mm thick wall 325 mm O. D, 304LN austenitic stainless steel pipe prepared by using different welding process and conventional V-groove as per AWS specification have been compared. The welding was carried out by commonly used shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and pulsed current gas metal arc welding (P-GMAW) processes. In P-GMAW process the influence of pulse parameters have been studied by considering their summarized influence defined by a dimensionless hypothetical factor ø=[(1b//p) f-tb] where, t b=[(1/f) - tp]. The characteristics of weld joints with respect to their metallurgical, mechanical, corrosion and fracture mechanics properties as well as residual stresses have been studied and compared. Welding of thick wall stainless steel pipe by P-GMAW process significantly improves the tensile properties, reduces the inclusion and porosity content, increases initiation fracture toughness and lowers residual stresses of weld joint in comparison to those observed of SMA and GMA weld joints. The influence of ø on properties of P-GMA weld joints is primarily attributed to the reduction in severity of weld thermal cycle and refinement of microstructure of weld deposit. © 2008 ISIJ.