The effect of microstructure on hardness and toughness of low carbon welded steel using inert gas welding

The heat affected zone (HAZ), has a great influence on the properties of welded joints since it can alter the microstructure and residual stresses. In this paper, the effect of welding parameters and heat input on the HAZ and grain growth has been investigated. The role of grain size on hardness and toughness of low carbon steel has also been studied. It was observed that, at high heat input, coarse grains appear in the HAZ which results in lower hardness values in this zone. For example raising the voltage from 20 to 30 V decreased the grain size number from 12.4 to 9.8 and hardness decreased from 160 to 148 HBN. High heat input and low cooling rates produced fine austenite grains, resulting in the formation of fine grained polygonal ferrites at ambient temperature.