METHOD FOR MANUFACTURING PRESS-FORMED PRODUCT, AND PRESS-FORMED PRODUCT

摘要

A method of the present invention includes the steps of heating a steel sheet for hot pressing use to a temperature of Ac3 transformation point or above and 950° C. or below, the steel sheet for hot pressing use containing a predetermined chemical component composition, some of Ti-containing precipitates contained in the steel sheet, each of which having an equivalent circle diameter of 30 nm or less, having an average equivalent circle diameter of 3 nm or more, and the precipitated Ti amount and the total Ti amount in the steel fulfilling the relationship represented by formula (1) shown below, thereafter starting press forming, and being held at the bottom dead point and being cooled to a temperature lower than martensite transformation starting temperature Ms while securing the average cooling rate of 20° C./s or more within a tool.;Precipitated Ti amount (mass %)−3.4[N]≧0.5×[total Ti amount (mass %)−3.4[N]]  (1);(In the formula (1), [N] represents the content (mass %) of N in the steel.)

主权项

1. A method for manufacturing a press-formed product, the method comprising:
heating a steel sheet to a temperature of Ac3 transformation point or above and 950° C. or below, thereafter starting press forming; and holding the steel sheet at a bottom dead point and cooling the steel sheet to a temperature lower than martensite transformation starting temperature Ms while securing an average cooling rate of 20° C./s or more within a tool, wherein the steel sheet comprises: by mass %,
C: 0.15-0.5%;Si: 0.2-3%;Mn: 0.5-3%;P: 0.05% or less, exclusive of 0%;S: 0.05% or less, exclusive of 0%;Al: 0.01-1%;B: 0.0002-0.01%;Ti: 3.4[N]+0.01% or more and 3.4[N]+0.1% or less, where[N] represents mass % of N;N: 0.001-0.01%; andiron some Ti-containing precipitates in the steel sheet have an equivalent circle diameter of 30 nm or less, while these Ti-containing precipitates have an average equivalent circle diameter of 3 nm or more, and a relationship between precipitated Ti amount and a total Ti amount in the steel sheet is represented by formula (1):
Precipitated Ti]−3.4[N]≧0.5×{[Ti]−3.4[N]}  (1)where [Precipitated Til, [N], and [Ti] represent mass % of the precipitated Ti amount, N, and the total amount Ti amount in the steel sheet, respectively.