Patent ID: 8449698

Claim:
A method of manufacturing a dual phase steel sheet for interior and exterior panels of automobiles, comprising: reheating a steel slab, the steel slab comprising C: 0.05˜0.10% by weight (wt %), Si: 0.03˜0.50 wt %, Mn: 1.50˜2.00 wt %, P: greater than 0 wt %˜0.03 wt %, S: greater than 0 wt %˜0.003 wt %, Al: 0.03˜0.50 wt %, Cr: 0.1˜0.2 wt %, Mo: 0.1˜0.20 wt %, Nb: 0.02˜0.04 wt %, B: greater than 0 wt %˜0.005 wt %, N: greater than 0 wt %˜0.01 wt %, and the balance of Fe and other unavoidable impurities; hot-rolling the steel slab to prepare a hot-rolled steel sheet; coiling the hot-rolled steel sheet to prepare a hot-rolled coil; pickling and cold-rolling the steel sheet after uncoiling the hot-rolled coil to prepare a cold-rolled steel sheet; and annealing the cold-rolled steel sheet to prepare an annealed steel sheet having a dual phase, wherein the annealing is performed on a continuous annealing line, the continuous annealing line including an annealing line on which the steel sheet is heated to a temperature of 750˜850° C. at 10˜20° C./sec and annealed for 100˜110 seconds, a cooling line on which the annealed steel sheet is cooled to 460˜540° C. at 3˜15° C./sec, and an over-aging line on which the cooled steel sheet is subjected to over-aging at 460˜540° C. for 100˜200 seconds.