Influence of the Heat Flow Transient State on the Microstructure and Microhardness of ASTM-A36 and SAE-1045 Steels Welded by GMAW Process

Abstract

The quasi-stationary state may not be achieved in electrical arc welding of small parts and/or materials of higher thermal conductivity. However, the transient state will always occur at the beginning and end of the welding. In this case, the variation of the energy flow through heat can promote microstructural variations and, consequently, variations of physical properties. Therefore, the objective of this study is to analyze the hardness and microstructure variations along the weld bead in the transient and quasi-stationary states, with the GMAW process and consumable ER70S-6, in the ASTM-A36 and SAE-1045 steels. The welds were carried on plate and collected thermal cycles on the face opposite the welded face, from thermocouples welded in different positions along a line parallel to the center line of the welds. Also, microhardness test and metallography were carried out. Higher cooling rates were obtained at the beginning of the cord during the transient regime, resulting in larger volumetric fractions of acicular ferrite and smaller fractions ferrite of the grain contour and Widmanstätten. Consequently, a hardness increase was obtained at around 20% at the beginning of the weld, with reference to the hardness values of the quasi-stationary state.

Keywords:
Heat transfer in welding; Transient and quasi-stationary states; Microhardness Vickers; Thermal cycles; GMAW process