Effect of Heat Input on Microstructure and Corrosion Behavior of High Strength Low Alloy Steel Welds

Abstract

High strength low alloy (HSLA) steel was welded by metal active gas arc welding (MAG), and the effect of heat input on microstructure and corrosion behavior of HSLA welds was investigated by optical microscope (OM), scanning electron microscopy (SEM), potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) in this study. Results indicated that the volume percent of acicular ferrite (AF) in the weld increases first and then decreases with the increase of heat input, when the heat input is 11.9kJ ·cm^-1, the proportion of acicular ferrite obtained in the weld reaches the maximum value. It is found that the type of microstructure has significant effect on corrosion behavior of the weld metal, the increase in the amount of acicular ferrite can result in corrosion property of the weld metal becoming worse in 3.5wt% NaCl solution. Moreover, the thickness and density of corrosion product on the surface of samples play a very important role in the corrosion behavior of the weld metal. When the corrosion product is loose, porous and defective, it provides minor protection for the weld metal, in this case, corrosion rate of the weld metal increases.