High-grade non-oriented silicon steel and production method thereof

A production method of non-oriented silicon steel, comprising the following steps:

• 1) Smelting steel by molten iron desulfurization, converter smelting and RH refining in sequence, to obtain a molten steel comprising the following chemical components in percent by mass:
• 0.002-0.004% of C, not greater than 0.003% of S, 1.4-1.7% of Si, 0.7-0.95% of Mn, not greater than 0.03% of P, 0.015-0.035% of Sn, not greater than 0.004% of Nb, not greater than 0.004% of V, not greater than 0.005% of Ti, not greater than 0.004% of Mo, not greater than 0.03% of Cr, not greater than 0.03% of Ni, not greater than 0.03% of Cu, not greater than 0.003% of N, and the balance Fe and inevitable impurities, and 11×([Si]-1.4%)=14×([Mn]-0.7%);
• 2) Continuously casting the molten steel obtained in step 1 into a continuous casting billet with the thickness of more than 200 mm;
• 3) Heating the continuous casting billet obtained in step 2 to reach a temperature between 1,120-1,150° C., and maintaining the temperature for more than 200 min;
• then carrying out multi-pass rough rolling to obtain an intermediate billet with a thickness of 40-45 mm;
• then carrying out multi-pass finish rolling, and coiling to obtain a hot-rolled coil with a thickness of 2.50±0.1 mm, the finishing temperature in finish rolling being (Ar1−40)±15° C., Ar1 representing the temperature for transformation from austenite to ferrite, the rolling reduction of the last pass of finish rolling being not less than 30%, the total rolling reduction of the last two passes of finish rolling being not less than 50%, and the coiling temperature being 650±20° C.;
• and carrying out two-stage cooling on the steel plate obtained by finishing in finish rolling before coiling, the first-stage cooling being natural slow cooling without water cooling and lasting for 3-8 s, and the second-stage cooling being water-cooling rapid cooling;
• 4) Carrying out uncoiling, acid pickling, rinsing, drying, cold rolling and coiling on the hot-rolled coil obtained in step 3, rather than carrying out normalizing treatment, thereby obtaining a cold hard coil with a thickness of 0.500±0.005 mm or 0.350±0.004 mm;
• and
• 5) Carrying out finished product annealing on the cold hard coil obtained in step 4 in a mixed atmosphere of H2+N2 through a continuous annealing furnace, the finished product annealing temperature being 920-980° C., and the annealing time being 60±5 s;
• and carrying out cooling, coating and finishing on the annealed steel strip to obtain a finished product of non-oriented silicon steel.