Microstructures and mechanical properties of joints of microalloyed EH40 ship steel plate with high heat-input welding

The weldability of EH40 ship steel plate by submerged-arc welding with high heat-input was studied by the tensile test, impact test, hardness test and microstructure.Experiment results show that the impact absorbing energy value were 116 J and 80.5 J in the coarse grain zones with the high heat-input 40 kJ cm and 60 kJ cm.The strength of the welded joint was better than the one of the base metal and there wasn't soft zone in HAZ.The main macrostructures were lath bainite, granular bainite and a few blocklike ferrite in the coarse grain heat affected zone with 40 kJ cm, while less lath bainite and more block-like ferrite and a few acicular ferrite appear in the some zone with 60 kJ cm.The toughness in the coarse grain heat affected zone is improved for the existing carbides and nitrides of Ti and Nb, which prohibit the original austenite grain from coarsening in high heat-input.