EFFECT OF WELD HEAT INPUT ON MECHANICAL PROPERTIES OF 'SUBMERGED ARC WELDED HSLA-80 STEEL AT A GIVEN PREHEAT TEMPERATURE

Abstract

HSLA-80 weldments were prepared using 12mm thick plates, under submerged arc welding process. ESAB (10.40) flux (AWS5.17) and 4mm diameter filler wire confirming to AWS/ASME SFA- 5.23 were used. During welding, the weld heat input was varied by varying the current and welding speed while keeping the voltage constant. During welding, the preheat temperature was maintained at 125°C The effect of welding heat input on weldment mechanical properties such as hardness, tensile strength and impact toughness and on microstructure of weld deposit and HAZ (at 1.5mm-2mm) have been investigated. Microstructure in the weld deposit was acicular ferrite and some secondary constituents. These secondary constituents increased upon increasing heat input from 1.8 kJ/mm - 3.OkJ/mm. In the CGHAZ, bainite was found upto 2.27kJ/mm and then ferrite at higher heat inputs. Hardness in the weld deposit was more than in the HAZ. With increasing heat input the weld deposit hardness decreased. A soft zone" having hardness lower than base material was found in the HAZ. With increasing heat input the "soft zone" width has increased Yield Strength and ultimate tensile strength values of the weldment were found to be lower than the base material. With increasing heat input,the tensile strength of. the weldment was found to be marginally increasing. fi HAZ (1.5mm from fusion boundary) toughness was always more than base material toughness. On increasing the heat input, toughness values of HAZ decreased. Weld metal notch toughness was found to be lower than base material toughness. At the lowest temperature of -45°C, the weld metal toughness was equal to the base material toughness.