Bake-hardened hot-dip galvanized steel sheet with excellent powdering resistance, and manufacturing method therefor

A method for manufacturing a bake-hardened hot-dip galvanized steel sheet having excellent powdering resistance, comprising operations of:

• re-heating a steel slab including:
• by wt %, 0.0001 to 0.005% of carbon (C), 0.1 to 1.2% of manganese (Mn), 0.02% or less of silicon (Si), 0.01 to 0.04% of phosphorus (P), 0.01% or less of sulfur (S), 0.01% or less of nitrogen (N), 0.01 to 0.06% of aluminum (sol.Al), 0.003 to 0.015% of niobium (Nb), 0.0005 to 0.0035% of boron (B), 0.01 to 0.1% of chromium (Cr), 0.005 to 0.05% of molybdenum (Mo), and a balance of Fe and inevitable impurities, satisfying the following relationships 1 and 2, at a temperature of 1000 to 1250° C.;
• hot-rolling the re-heated steel slab at a temperature in a range of 900 to 1100° C.;
• cooling the hot-rolled steel sheet to a temperature in a range of 500 to 700° C. at an average cooling rate of 10 to 70° C./sec, and then winding the steel sheet;
• cold-rolling the wound hot-rolled steel sheet at a reduction rate of 70 to 90%, and then performing continuous annealing in a temperature range of 740 to 850° C.;
• immersing the continuous annealed cold-rolled steel sheet in a hot-dip galvanized plating bath, and then alloying the steel sheet in a temperature range of 450 to 540° C. to manufacture a hot-dip galvanized steel sheet;
• and
• performing skin pass rolling on the manufactured hot-dip galvanized steel sheet in a range of a reduction rate of 0.5 to 2.0%, wherein the following relationship 4 is satisfied,
• [Nb]/((93/12)×[C])<0.55 [Relationship 1]
• [Mn]/((55/28)×[Si])>10 [Relationship 2]
• Powdering=[−14.2+0.0362×(GA)−0.970×(CGL SPM El.)]<3 [Relationship 4]
• where, (GA) is a hot-dip galvanizing alloying temperature (° C.), and (CGL SPM EL.) is skin pass rolling elongation in a continuous hot-dip galvanizing line.