Abstract: The EH40 ship plate steel is welded with submerged arc welding process, and the microstructure and mechanical property of welded joint are analyzed. The results show that the main microstructures of weld metal are acicular ferrite, a few proeutectoid ferrite and small area of M-A. Acicular ferrite dividing the original austenitic grain, effective grain size of weld metal is 3.2 μm. Large angle grain boundaries account for 78.6% of the grain boundaries in the analysis area of weld metal, and large angle grain boundaries mainly distribute between 50 degree and 60 degree, which are good for the impact toughness of weld metal. Few evenly distributed M-A with small size is not harmful to the toughness of weld metal. The microstructures of the coarse grained heat affected zone (CGHAZ) consist bainite, acicular ferrite and proeutectoid ferrite. The toughness in the CGHAZ is improved for the existing high melting point granule precipitated phases (TiO, Al2O3, MgO, TiN), which prohibit the growing of grain and promote the formation of acicular ferrite. The results of mechanical property show that good property joint is obtained, which is consistent with the results of microstructures

Key words: High heat input, Microstructure, Ship plate steel, Toughness