Evaluation of microstructure and mechanical properties of Fe–1.2Mn–0.3Cr–1.4Ni–0.4Mo–C steel welded joints

Abstract

The microstructural variations in different sub-regions of the Fe–1.2Mn–0.3Cr–1.4Ni–0.4Mo-C steel welded joint were investigated by means of optical microscope and scanning electron microscope equipped with electron backscattered diffraction. This study focused on the correlation between microstructural characteristics and mechanical properties of the welded joint which was carried out by gas metal arc welding. The microhardness of the fusion line (FL) and fine-grained heat affected zone was inferior to other locations of welded joint due to the diffusion of alloy elements and granular bainite phase transformation, respectively. The tensile strength of the welded joint was about 980 MPa, which reached the required strength of the 1000 MPa grade steel plate for hydropower station. The final fracture was located at the weld metal (WM) because that the crack easily nucleated and propagated in proeutectoid ferrite. The impact toughness at −60 °C of various sampling locations for welded joint was higher than 47 J. The low temperature impact toughness improved gradually as the distance between the V-notch and weld center line increased. The inclusions in the WM and non-uniformity of microstructure and composition near the FL could increase the deterioration on impact toughness at −60 °C.