Hot stamping method
Provided is a method for manufacturing vehicle parts having ultra-high strength of 500 Mpa or more by using hot stamping. The method includes: forming a heated blank in a press forming apparatus; and taking out the formed blank from the press forming apparatus and consecutively cutting the blank with a trimming die. A blank temperature at the time of trimming may be 150° C. to 330° C.
1. A hot stamping method comprising:
(a) heating a blank to an austenitization temperature of the blank or more;
(b) forming the heated blank in a press forming apparatus, wherein the forming of the blank is started at a temperature of 600° C. to 900° C. and the heated blank is cooled to below a martensite transformation start temperature (Ms) of the blank at a speed of 25° C./sec or more; and
(c) taking out the formed blank from the press forming apparatus and consecutively cutting the formed blank with a trimming die, wherein a blank temperature at the time of cutting is 150° C. to 330° C.,
wherein, in the step (c), the formed blank is taken out from the press forming apparatus at a temperature 250° C. to 350° C.; the formed blank is sequentially cut by using at least two trimming dies; the formed blank is not reheated during the entire process of trimming; and a final trimming is performed at 170° C. or higher.
2. The hot stamping method of claim 1 , wherein, the formed blank temperature at the time of cutting is 190° C. to 320° C.
3. The hot stamping method of claim 2 , wherein, in the step (c) of sequentially cutting by using at least two trimming dies, the temperature of the formed blank cut in the first trimming die after press forming is 220° C. to 320° C., and the temperature of the formed blank cut in the second trimming die is 190° C. to 300° C.