Effect of lath martensite/bainite microstructure on strength and toughness of a low carbon martensite steel

Effect of lath martensite/bainite mixed structure on strength and toughness of 10CrNi5Mo low carbon martensite steel ultra-heavy plate was investigated by means of electron backscatter diffraction(EBSD) and finite element analysis.The results indicate that no significant variation of metallurgical quality is observed in thick-direction of the ultra-heavy plate,Single martensite microstructure is obtained in the steel plat surface,while lath martensite/bainite mixed structure appears in 1/4 thickness position and center of the ultra-heavy plate of 120 mm thick after quenching.Compared to single martensite structure,lath martensite/bainite mixed structure with finer substructure presents longer high-angle boundaries.thus lath martensite/bainite mixed structure in the center can induce excellent low temperature toughness.Generally,lath martensite/bainite mixed structure improves low temperature toughness of the 10CrNi5Mo steel plate and lowers its ductile-brittle transition temperature,however,it has no significant influence on strength.