A Study on the Microstructure and Mechanical Properties of the Coarse Grain Heat Affected Zone in EH40 Grade High Strength Structural Steels

Abstract

In this paper, the effect of the electro gas arc welding (EGW) process with a heat input of 600 kJ/cm on the microstructural and mechanical characteristics was investigated for two types of EH40 high strength hull structural steels, containing Ti and Nb. The coarse grain heat affected zone (CGHAZ), with a peak temperature of 1450 °C, was simulated for both alloys using a material thermal cycle simulator. Tensile and Charpy impact toughness tests were performed to determine the mechanical properties of the CGHAZ, and microstructural analysis was performed using scanning electron microscopy and transmission electron microscopy. Both alloys exhibited a significant loss of impact toughness because of the welding thermal cycle, causing the formation of a brittle phase and the growth of precipitates. The experimental results indicated that although the addition of Ti and Nb had several benefits on mechanical properties, this might be unsuitable for the EGW process owing to the resulting deterioration in impact toughness.