Hot press forming steel plate, formed member using same, and method for manufacturing the plate and member

A method for manufacturing a steel sheet for hot press forming, the method comprising:

• heating a steel slab to a temperature range of 1100° C. to 1300° C., the steel slab comprising, by wt %, C:
• 0.3% to 1.0%, Mn:
• 0.01% to 4.0%, Si:
• 1.0% to 2.0%, Al:
• 0.01% to 2.0%, S:
• 0.015% or less, N:
• 0.01% or less, and the balance of Fe and inevitable impurities;
• performing a finish hot-rolling process at a temperature within a range of Ar3 transformation point to 950° C. to form a steel sheet;
• and
• coiling the steel sheet at a temperature within a range of Ms to 720° C.

A method for manufacturing a steel sheet for hot press forming, the method comprising:

• heating a steel slab to a temperature range of 1100° C. to 1300° C., the steel slab comprising, by wt %, C:
• 0.3% to 1.0%, Mn:
• 0.01% to 4.0%, Si:
• 1.0% to 2.0%, Al:
• 0.01% to 2.0%, S:
• 0.015% or less, N:
• 0.01% or less, and the balance of Fe and inevitable impurities;
• performing a finish hot-rolling process at a temperature within a range of Ar3 transformation point to 950° C. to form a steel sheet;
• coiling the steel sheet at a temperature within a range of Ms to 720° C.;
• pickling the steel sheet;
• cold-rolling the steel sheet;
• continuously annealing the steel sheet at a temperature within a range of 750° C. to 900° C.;
• and
• overaging the steel sheet at a temperature within a range of Ms to 550° C.

A method for manufacturing a steel sheet for hot press forming, the method comprising:

• heating a steel slab to a temperature range of 1100° C. to 1300° C., the steel slab comprising, by wt %, C:
• 0.3% to 1.0%, Mn:
• 0.01% to 4.0%, Si:
• 1.0% to 2.0%, Al:
• 0.01% to 2.0%, S:
• 0.015% or less, N:
• 0.01% or less, and the balance of Fe and inevitable impurities;
• performing a finish hot-rolling process at a temperature within a range of Ar3 transformation point to 950° C. to form a steel sheet;
• coiling the steel sheet at a temperature within a range of Ms to 720° C.;
• pickling the steel sheet;
• cold-rolling the steel sheet;
• continuously annealing the steel sheet at a temperature within a range of 750° C. to 900° C.;
• overaging the steel sheet at a temperature within a range of Ms to 550° C.;
• and
• plating the overaged steel sheet by any one of hot-dip galvanizing, galvannealing, electro galvanizing, and hot-dip aluminizing.

A hot-press formed member comprising, by wt %, C:

• 0.3% to 1.0%, Mn:
• 0.01% to 4.0%, Si:
• 1.0% to 2.0%, Al:
• 0.01% to 2.0%, S:
• 0.015% or less, N:
• 0.01% or less, and the balance of Fe and inevitable impurities, wherein the hot-press formed member has a dual phase microstructure formed by bainite and retained austenite.

A method for manufacturing a hot-press formed member, the method comprising:

• heating a steel sheet to a temperature equal to or higher than Ac3, the steel sheet comprising, by wt %, C:
• 0.3% to 1.0%, Mn:
• 0.01% to 4.0%, Si:
• 1.0% to 2.0%, Al:
• 0.01% to 2.0%, S:
• 0.015% or less, N:
• 0.01% or less, and the balance of Fe and inevitable impurities;
• hot-press forming the heated steel sheet;
• cooling the hot-press formed steel sheet to a temperature range of Ms to 550° C. at a rate of 20° C./sec or higher;
• and
• heat-treating the cooled steel sheet at a temperature within a range of Ms to 550° C. in a heating furnace.