A comparison between induction pre-heating and induction post-heating of laser-induction hybrid welding on S690QL steel

Abstract

In this paper, the differences of microstructure and performance of S690QL steel between induction pre-heating laser-induction hybrid welding (LIHW) and post-heating LIHW were compared via scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), electrical back-scattered diffraction (EBSD), and mechanical machines. The t8/5 values of both pre-heating and post-heating LIHW joints were shown to increase with inductor output power increasing from 60% to 80% and 100%, and each temperature curve of the post-heating LIHW weld center (WC) and heat-affected zone (HAZ) has two peak values. Through experimental and theoretical analyses, pre-heating LIHW joints were determined to mainly contain ferrite, bainite and little martensite, while the post-heating LIHW joints have more bainite. Except for the 80% inductor output power post-heating sample, the microstructures demonstrate dispersing phenomena, as well as weld defects. With increasing pre-heating LIHW inductor output powers, the proportion of ferrite rises, martensite and bainite contents decrease, and dislocation pileup occurs; these will lead to the decrease of microhardness and an increase in plasticity. However, in post-heating LIHW joints, the amounts of ferrite and martensite show a decreasing tendency, and the proportion of bainite tends to increase. The fracture pattern of pre-heating LIHW joints and post-heating LIHW joints is shown to be a dimple fracture, and the pre-heating LIHW joints have a better tensile strength and toughness. Thus, compared with post-heating LIHW, pre-heating LIHW is shown to be superior.