Experimental Study on Monitoring of Heat Input in Continuous CO2 Laser Butt Welding of Dissimilar Thin Steels

Abstract

In the present study, CO2 laser with the continuous wave was used for the welding of dissimilar thin steels i.e., low carbon steel (LCS) and AISI 304 stainless steel (SS 304). In laser welding, the most significant process parameters are laser power (Plaser) and laser scanning speed i.e., welding speed (V). The heat input per unit length (J/mm) was considered in this study, which was calculated by the Plaser/V ratio. The effect of heat input on mechanical properties, weld bead dimensions and residual deformation was investigated. Micro and macrostructural characteristics of welded samples were evaluated using an optical microscope and EDX system equipped with a scanning electron microscope. Within the present working range of the heat input (i.e., 150 to 300 J/mm), the tensile samples were fractured in the LCS side under a ductile manner. The heat input of 210 J/mm was experienced the full depth of penetration and maximum tensile strength of 387.94 MPa. The fusion zone was exhibited the vermicular δ–ferrite at the dendritic core in the austenite matrix. The LCS was showed the recrystallisation in the heat affected zone (HAZ), whereas the grain coarsening was occurred in SS 304. The dendrites width was found to reduce with a decrease in heat input, which resulted in higher hardness values in the fusion zone. The residual deformation was increased by 26.4% with an increase in the heat input from 150 to 300 J/mm and the extreme deformation of 0.211 mm was obtained at a heat input of 300 J/mm.