Effect of Single and Multiple Thermal Cycles on Microstructure and Mechanical Properties of Simulated HAZ in Low Carbon Bainitic Steel

The correlation of microstructure and mechanical properties in simulated heat affected zone (HAZ) of a low carbon bainitic steel plate of thickness 28mm using single and multiple thermal cycles was investigated in the Gleeble 3800 Thermo Mechanical Simulator. Optical microscopy, field emission scanning electron microscopy, hardness, and impact strength measurements were done to characterize theweld HAZ simulated steel samples. Peak temperatures (Tp) of 1300, 1150, 1000, 900, 800, 700, and 600 degrees C with heat input 50 kJ/cm were used for single pass weld. In two pass weld cycles, peak temperature (Tp1) 1300 degrees C, and (Tp2) of 1100, 1000, 900, 800, and 700 degrees C were used. This heat input is in line with the submerged arc welding (SAW) process extensively used in the fabrication of ship building industries. The impact toughness of weld HAZ simulated specimens was determined at -50 degrees C by using a Charpy impact tester. Best impact toughness values (minimum 75 J) in weld HAZ simulated specimen were observed at the peak temperatures from 600 to 1150 degrees C in single pass weld and from 1000 to 1100 degrees C in two pass weld HAZ thermal cycles.