Hot-pressed steel plate member and manufacturing method therefor

A manufacturing method of a hot-pressed steel plate member using a raw steel plate comprising, with respect to the chemical composition of the steel plate, 0.15 to 0.4 wt % of C, 1.0 to 5.0 wt % of Mn or of a total of Mn and at least one of Cr, Mo, Cu, and Ni, 0.02 to 2.0 wt % of at least any one of Si and Al, and the remainder being Fe and unavoidable impurities, and providing physical properties of a martensite phase average grain diameter of 5 μm or less and a tensile strength of 1200 MPa or higher by being subjected to hot pressing, the hot pressing comprising:

• a heating process for heating the steel plate member to a highest heating temperature T° C. of 675 to 950° C. at a rate of temperature increase of 10° C./sec or higher;
• a temperature keeping process for keeping the highest heating temperature 1° C. for (40-T/25) sec or less;
• and
• a cooling process for cooling the steel plate member to not more than an Ms point that is a temperature of formation of the martensite phase at a cooling rate of 1.0° C./sec or higher from the highest heating temperature T° C. while pressing the steel plate member.