BAKING HARDENING TYPE COLD ROLLED STEEL SHEET HAVING INCREASED YIELD STRENGTH AND PROCESS FOR PRODUCING THE SAME

摘要

IF steel fine in a complex system of Ti and Nb (Mn, Cu) by S precipitates and the AlN precipitates yield strength and in-plane anisotropy is provided a cold-rolled steel sheet and a method of manufacturing is improved. ; This is a cold-rolled steel sheet in weight%,, C: 0.001-0.01%, Cu: 0.01-0.2%, Mn: 0.01-0.3%, S: 0.005-0.08%, Al: 0.1% or less, N: 0.004-0.02%, P: 0.2% or less, B: 0.0001-0.002%, Ti: 0.005 ~ 0.15%, Nb: 0.002-0.04%, and the balance of Fe and other unavoidable impurities in the composition, ; The Cu, Mn, S, Al, N, C, Ti, Nb is ; Cu + Mn: 0.05-0.4%, (Mn / 55 + Cu / 63.5) / (S ^* / 32): 1-30, (Al / 27) / (N ^* / 14): 1-10, ; Cs (solute carbon): 5 meet the -30 and ; [Here, S ^* = S-0.8x (Ti-0.8x (48/14) xN) x (32/48), ; N ^* = N-0.8x (Ti-0.8x (48/32) xS)) x (14/48), Cs = (C -Nbx12 / 93-Ti ^* x12 / 48) x10000, ; Ti ^* = Ti-0.8x ((48/14) xN + (48 / 32) xS) However, Ti ^* & if 0 Ti ^* = referred to as 0] ; (Mn, Cu) S precipitates and The average size of the AlN precipitate is made below 0.2 . ; In the present invention, unlike the precipitation technique and used in the technique of the -Cu, or Cu for adding Cu to the corrosion resistance in the IF steel, while using the Cu as fine CuS precipitates and AlN precipitates precipitate MnS and to use together.