METHOD FOR MANUFACTURING LOW REMANENCE 5NI STEEL PLATE WITH EXCELLENT SURFACE QUALITY

Disclosed is a method for manufacturing a 5Ni steel plate with a low remanence and an excellent surface quality to be used in a ship. The process flow thereof comprises: converter smelting -> LF refining -> RH high vacuum degassing -> treatment with Ca -> continuous casting -> a slow cooling treatment to the slab -> cleaning the surface of the slab -> heating -> rolling -> quenching twice -> tempering. The constituents comprise a low content of carbon, a low content of silicon, and 5% Ni, with V and Nb being added thereto, which improves the hardenability, improves the toughness at a low temperature, and imporves the starting temperature of non-recrystallization of austenite. The steel plate can be subjected to high-temperature rolling and high-temperature quenching so as to significantly improve the shape of the plate, thus being applicable to the production of thin products. The method modifies the element design, the process control, the structure of base material, the center segregation, the quenching and tempering temperatures, the time, etc., and thus ensures that the steel plate has a good elongation, a good impact toughness at a low temperature of -130 °C, an excellent surface quality, and a low remanence, while achieving a high-strength 5Ni steel plate.