| Abstract: | Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy,electron backscatter diffraction and mechanical testing.Comparing with the coarse-grained heat-affected zone (CGHAZ),the weld metal presents higher toughness (129.3 J vs.37.3 J) as it contains a large number of acicular ferrites with high-angle grain boundaries (frequency 79.2％) and special grain boundary Σ3 (frequency 55.3％).Moreover,coarse austenite grains in CGHAZ and slender martensite-austenite constituents between bainite laths may likely facilitate crack propagation.Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5,which is the main reason for the occurrence of tensile fracture. |
