The Rolling Process Study and Mechanical Property of 460MPa Class Steel Plate Used for Hull Structure

Targeted on grain refinement, the effects of different rolling process conditions on mechanical property of 460MPa class steel plate, in terms of tensile and yield strength, low-temperature toughness, arrestability and microstructure, are studied. The rolling process conditions are surface-layer with ultrafine grains process (SUF) and traditional thermo mechanical control process (TMCP). As for SUF process, better surface strength and toughness can be achieved. Yield strength is generally higher than 540MPa.-60℃ impact value of SUF2 is higher than 280J. The surface nil-ductility transition temperature (NDTT) of SUF condition have reached less than-80℃. The fine grain microstructure formed at the surface layer, which is about 4mm thick, contributes to better mechanical property than that in other layers. The microstructure varies gradually from the surface to the centre. There are proeutectoid ferrite and bainite at 1~4mm thickness of surface layer. The microstructure in the 4~10mm thickness layer consists of polygonal ferrite and a considerable amount of bainite. As for the TMCP process, relatively homogenous strength and toughness can be achieved across thickness direction, featuring with higher strength and lower toughness at the surface layer, and lower strength and higher toughness at centre layer, when compared to that of SUF process. The microstructure of the TMCP sample varies gradually from the surface to the centre.