Effect of Weld Thermal Cycles on Microstructures and Mechanical Properties in Simulated Heat Affected Zone of a HY 85 Steel

Abstract

Physical weld simulation for single and two-pass weld of a HY 85 steel has been done using thermo mechanical simulator at constant heat input of 22 kJ/cm. Attempt has been made to investigate the causes behind the deterioration of mechanical properties in the coarse grain heat affected zone (CGHAZ) in single pass and subsequent improvement in the mechanical properties of CGHAZ region in the two-pass weld. HY 85 steel finds wide applications in the making of ship hull. Impact toughness at −50 °C for CGHAZ in the single pass weld has been found to be 49 J. However, impact toughness improves to 122 J in the super critical reheated CGHAZ region for two-pass weld. This improvement in the impact toughness has been observed due to reaustenitization of fine prior austenite grains of average size of 44 µm from 99 µm, refinement of bainitic ferrite lath, and M–A constituents during second pass weld.