Strengthening-toughening mechanism of cost-saving marine steel plate with 1000 MPa yield strength

One kind of cost-saving marine steel plate with 1000 MPa yield strength was successfully processed based on the alloying concept of nano-particles precipitation in a lath martensitic matrix. The conventional quenching and tempering heat treatment was adopted to optimize the mechanical properties. The experimental steel with lower alloy content exhibited excellent performance, i.e., the yield strength above 1030 MPa at room temperature, and the impact energy above 69 J at -40 degrees C. The microstructural evolution, precipitation behavior and dislocation density were systematically studied by optical microscopy, field emission scanning electron microscopy, X-ray diffraction and transmission electron microscopy. It was shown that the high strength resulted from grain refinement, dislocation strengthening, solid solution strengthening and precipitation strengthening. The role of every strengthening mechanism was quantitively evaluated so that the yield strength could be accurately estimated. Base on this study, it could be concluded that the precipitation strengthening had a significant contribution to yield strength. In addition, the excellent impact toughness of the steel was attributed to its unique microstructure characteristics of fine film-like stable austenite and delamination structure.