Preparation And Properties Of Shipboard Steel With Gradient Structure

Container shipping is a major force in global trade and transportation.In order to improve its transportation volume and economic benefits,the capacity level of container ships has been continuously improved.As the main material of the hull structure,container ship steel plate not only bears the load of cargo,but also faces the challenge of the impact of sea waves and the low-temperature environment in some sea area.Thus,it is of great significance to study the container ship steel with ultra-high strength and high toughness.Container ship steels usually have two important properties:tensile strength and low-temperature toughness.It is found that the EH47 steel which has lath bainite on its surface,granular bainite and polygonal ferrite in its core can be prepared by TMCP and rapid cooling process,this steel plate has a gradient structure in the direction of thickness and has excellent strength and toughness.According to the relevant literatures,this topic used the microwave-assisted heating technology to form a temperature gradient in the direction of the thickness of the steel plate in order to achieve the purpose of preparing the container Marine steel plate with gradient structure,and the samples were cold-rolled in order to deepen the gradient of the microstructure.The effect of gradient structure on the strength and toughness of ship plate steel was studied through microstructure observation and mechanical properties testing.Apart from that,two components were designed to investigate the effects of tempering and niobium content on the gradient microstructure and mechanical properties of ship plate steel.The results show that after microwave quenching and cold rolling,the microstructure of ship plate steel presents gradient structure distribution in thickness direction.After quenching with microwave insulation for 10min and cold rolling,the hardness difference between the surface and the core of the ship sheet steel is the largest,which is 127 HV.Compared with the traditional quenching process,the tensile strength is increased by 57%,which is 1218 MPa,but it has a slight weakening effect on the low temperature impact toughness.The optimal tempering process of container ship sheet steel with gradient structure is 600℃+30 min.At this time,the ship sheet steel with high Nb content has the best precipitation strengthening effect,and the low temperature impact toughness also reaches the highest value,which is 1146.2 k J/m~2,which is higher than the impact toughness of the traditional heat treatment sample of 1092.4 k J/m~2,achieving the best match of strength and toughness.