Hot-press formed product and method for manufacturing same

#The present invention relates to a hot-press formed product used for structural members of automobile components and capable of adjusting the strength and ductility according to different regions within the formed product and a method for manufacturing the same, and relates more specifically to a hot-press formed product being subjected to a heat treatment simultaneously with impartation of the shape in forming a pre-heated steel sheet (blank) into a predetermined shape and capable of obtaining the strength and ductility according to different regions and a useful method for manufacturing such hot-press formed product.

#As one of the fuel economy improvement measures of an automobile triggered by global environment problems, weight reduction of the vehicle body is advancing, and it is necessary to high-strengthen a steel sheet used for an automobile as much as possible. However, when a steel sheet is high-strengthened for weight reduction of an automobile, elongation EL and r value (Lankford value) drop, and press formability and shape freezing property come to deteriorate.

#In order to solve such problems, a hot-press forming method has been employed for manufacturing components in which a steel sheet is heated to a predetermined temperature (for example, a temperature at which a state of an austenitic phase is achieved), the strength is lowered (that is, forming is facilitated), the steel sheet is thereafter formed using a tool of a temperature (room temperature for example) that is lower compared with the case of a thin steel sheet, thereby impartation of a shape and a rapid heat treatment (quenching) utilizing the temperature difference of the both are executed simultaneously, and the strength after forming is secured.

#FIG. 1 is a schematic explanatory drawing showing a tool configuration for executing hot-press forming.

#FIG. 2 is a schematic explanatory drawing of a forming tool used in the example.

#FIG. 3 is a schematic explanatory drawing showing a shape of a press formed product formed in the example.

#The present inventors carried out studies from various aspects in order to achieve such a hot-press formed product that showed excellent ductility (elongation) while securing the strength matching the required properties of respective different regions after forming in heating a thin steel sheet to a predetermined temperature and thereafter manufacturing the formed product by hot-press forming.

#As a result of the studies, it was found out that, in manufacturing a hot-press formed product by press-forming a thin steel sheet using a press forming tool, when the heating temperature and the conditions of respective forming regions in forming were properly controlled and the structure of the each forming region was adjusted so as to contain retained austenite by 3-20 area %, a hot-press formed product exerting strength-ductility balance according to each forming region could be achieved, and the present invention was completed.

#The reasons for setting the range of the structure (basic structure) in each forming region of the hot-press formed product of the present invention are as follows.