Method of producing press-formed product
A method of producing a press-formed product includes a steel plate heating step, a hot forging step and a hot stamping step. In the steel plate heating step, a steel plate is heated to 950° C. or more. In the hot forging step, the heated steel plate is forged to form a varying-thickness steel plate. In the hot stamping step, the heated varying-thickness steel plate is subjected to press-working by a press tooling to form a press-formed product, and the press-formed product that is formed is cooled inside the press tooling. Thus, a press-formed product that has high strength and for which a reduction in weight is possible can be produced.
1. A method of producing a press-formed product, comprising:
heating a steel plate to 950° C. or more,
forging the steel plate using a first press apparatus to form a varying-thickness steel plate,
water cooling the varying-thickness steel plate,
heating the varying-thickness steel plate to a temperature that is not less than an A c3 transformation point and not more than an A c3 transformation point+150° C., and
using a second press apparatus different from the first press apparatus, forming the varying-thickness steel plate into a press-formed product by means of a press tooling of the second press apparatus, and cooling the press-formed product inside the press tooling.
2. The method of producing a press-formed product according to claim 1 , wherein:
the varying-thickness steel plate includes a portion having a large thickness and a portion having a small thickness, and a ratio t 1 /t 2 between a plate thickness t 1 of the portion having a large thickness and a plate thickness t 2 of the portion having a small thickness is more than 1.8.
3. The method of producing a press-formed product according to claim 1 , wherein:
a tensile strength of the press-formed product is 1300 MPa or more.
4. The method of producing a press-formed product according to claim 1 , wherein:
the steel plate consists of, by mass %, C: 0.15 to 0.60%, Si: 0.001 to 2.0%, Mn: 0.5 to 3.0%, P: 0.05% or less, S: 0.01% or less, sol. Al: 0.001 to 1.0%, N: 0.01% or less and B: 0.01% or less, with the balance being Fe and impurities.
5. The method of producing a press-formed product according to claim 4 , wherein:
the steel plate comprises, in lieu of a part of Fe, 0.03 to 1.0% in total of one or more types of element selected from the group consisting of Ti, Nb, V, Cr, Mo, Cu and Ni.