Non-oriented electrical steel sheets with excellent magnetic properties and method for manufacturing the same
The present invention relates to technology for manufacturing electrical steel sheets having excellent magnetic properties through the control of a hot-rolled texture using the phase transformation of steel. More particularly, it relates to a non-oriented electrical steel sheet that has reduced iron loss and increased magnetic flux density by controlling alloy component elements and optimizing hot-rolling conditions, even though hot-rolled sheet annealing is not carried out, as well as a manufacturing method thereof. More specifically, the invention provides a non-oriented electrical steel sheet which has excellent magnetic properties while hot-rolled sheet annealing can be omitted, the steel sheet being comprised of 0.005 wt % or less of C, 1.0-3.0 w % of Si, 0.1-2.0 wt % of Mn, 0.1 wt % or less of P, 0.1-1.5 wt % of Al, and a remainder of Fe and other inevitable impurities, in which the relationship between the elements Mn and Al satisfies an equation of −0.2<m(=Mn−Al)<1.0, and a slab for the steel sheet, when reheated, has a two-phase region of austenite+ferrite at a temperature ranging from ArI to 1250° C.
1. A method for manufacturing a non-oriented electrical steel sheet that has excellent magnetic properties while hot-rolled sheet annealing can be omitted, the method comprising the steps of:
reheating a slab comprising 0.005 wt % or less of C, 1.0-3.0 wt % of Si, 0.1-2.0 wt % of Mn, 0.1 wt % or less of P, 0.1-1.5 wt % of Al, wherein the elements Mn and Al satisfy an equation of −0.2<Mn−Al<1.0 and a remainder of Fe and other inevitable impurities, to a temperature ranging from Ar1 to 1250° C.;
hot-rolling the reheated slab in such a manner that 70% or more of a total hot finish rolling is performed in a two-phase region of austenite+ferrite, and the remaining reduction ratio is performed in a ferrite single-phase region, in which the reduction ratio in a final pass becomes {20−(960−finish rolling end temperature)/20}% or less;
winding the hot-rolled steel sheet at a temperature of 650-800° C.;
cold-rolling the wound steel sheet to a predetermined thickness; and
subjecting the cold-rolled steel sheet to final annealing.
2. The method of claim 1 , wherein the slab additionally contains 0.007-0.15 wt % of at least one element selected from Sb and Sn.
3. The method of claim 1 , wherein the impurities contained in the steel sheet are comprised of 0.003 wt % or less of S, 0.003 wt % or less of N, 0.002 wt % or less of Nb, and 0.002 wt % or less of Ti.
4. The method of claim 1 , wherein the final annealing step is carried out at a temperature elevation rate of 10˜40° C./sec.
5. The method of claim 1 , wherein the Ar1 temperature of the slab is 960-1060° C.
6. The method of claim 1 , wherein the start temperature of the hot finish rolling is Ar1+50° C. or more, and the end temperature of the hot finish rolling is Ar1−80° C. or more.