METHOD OF REDUCING SIZE OF COARSE CRYSTALLINE GRAINS THE HUMS OF SURFACE OF UNTEXTURED TRANSFORMER STEEL

摘要

Method for improving surface coarse grains of non-oriented silicon steel is disclosed. The method comprises the following steps: 1) smelting and casting, wherein the non-oriented silicon steel, having the components (in wt%) as follows: C 0.001-0.005%, Si 0.1-1.80%, Mn 0.10-0.80%, P ≤0.04%, Al 0.20-0.80%, S ≤ 0.005%, N ≤ 0.005% and balance Fe, is subjected to smelting and RH refining process, and then casting the molten steel into blank; 2) hot rolling into steel plate; 3) normalizing at a temperature of 800-900℃ and for a soaking time of 15-30 sec., with O₂ content being controlled as less than 0.5% in normalizing furnace, thereafter in the steel plate, the ratio of maximum grain size to average grain size is less than 3; 4) pickling, cold rolling, annealing and coating to obtain the non-oriented silicon steel product. Under existing conditions of this invention, the problem of surface coarse grains of non-oriented silicon steel is solved without adding heating treatment process or parallel hot working.