Investigation of the effect of heat input on the properties of HSLA 100 steel weld joints produced by SMAW process

The microstructure and mechanical properties of HSLA-100 steel weld joints was investigated. Welding with three heat input of 0.820, 1.176 and 1.392 kJ / mm was performed using E12018 electrode. Microstructural studies were performed using scanning electron and optical microscopes. The mechanical properties of welded joints were evaluated by impact and microhardness tests. Microstructural studies showed that with increasing the heat input, the amount of acicular ferrite in the weld metal decreased and the amount of polyhedral and quasi-polygonal ferrite increased. It was found that with increasing the heat input, the amount of layered bainite in the heat affected zone increased and the amount of granular bainite decreased. Due to the decrease in the amount of acicular ferrite in the weld metal microstructure with increasing inlet temperature, the amount of hardness and impact energy decreased. The results showed that the increase in heat input due to the reduction of the acicular ferrite of the weld metal and the dissolution of precipitates in the coarse grain heat affected zone has caused a decrease in hardness in these zones. It was found that with increasing the heat input due to decreasing the acicular ferrite, the impact energy of the weld metal decreased by 29% (from 45 joules at an heat input of 0.82 to 32 joules at an heat input of 1.392 kJ / mm). It was found that at all heat inputs, the impact energy of the base metal is greater than the impact energy of the weld metal.