Effect of heat treatment process and NbV-N microalloying on mechanical property and microstructure of grade ship plate steel

In order to obtain a 390 MPa grade ship plate steel with good strengthen and toughness matching, the NbV-N composite microalloying and different heat treatment process（normalizing＋tempering or quenching＋tempering）were applied, and the room temperature tensile properties, impact properties at －40 ℃, microstructure and precipitated phase of the laboratory steel plate were analyzed. The results showed that the addition of V and Nb can effectively refine the grain size, and the increase of N mass fraction can make the fine grain effect more obvious, which can result in the increase of the strength and toughness, especially the impact toughness. Compared with the hot rolling state, the normalizing＋tempering and quenching＋tempering states could significantly improve the mechanical properties of steel, especially the low temperature toughness, which benefited from a large member of the dispersed precipitations of the microalloyed carbonitrides during tempering and the obvious refinement of the effective grain size in steel during the normalizing/quenching＋tempering process.