Steel sheet heating device, method for producing press-formed part, and press-formed part

Abstract

It is provided a steel sheet heating device that heats a flat steel sheet, including: a hot plate having a flat heating surface brought into close contact with the steel sheet; and a plurality of heating equipment able to heat a plurality of heating regions, formed by dividing the heating surface of the hot plate into a plurality of sections, to different heating temperatures at the same time, wherein the steel sheet is heated to different temperatures at various portions based on the heating temperatures of the plurality of heating regions of the heating surface, at the same time through a single heating treatment.

1 . A steel sheet heating device that heats a flat steel sheet, comprising:
 a hot plate having a flat heating surface brought into close contact with the steel sheet; and   a plurality of heating equipment able to heat a plurality of heating regions, formed by dividing the heating surface of the hot plate into a plurality of sections, to different heating temperatures at the same time, wherein   the steel sheet is heated to different temperatures at various portions based on the heating temperatures of the plurality of heating regions of the heating surface, at the same time through a single heating treatment.   
     
     
         2 . The steel sheet heating device according to  claim 1 , wherein:
 the hot plate is made of a single plate member;   the heating equipment include multiple heaters disposed in the plate member at predetermined intervals so as to be positioned within a single plane parallel to the heating surface, and multiple temperature control circuits disposed so as to correspond to the multiple heaters and able to control heating temperatures of the heaters independently of each other; and   the number of the plurality of heating regions that differ in heating temperature and ranges of the plurality of heating regions are able to set to any given number and any given ranges, respectively.   
     
     
         3 . The steel sheet heating device according to  claim 2 , wherein the heating temperature of the heater disposed near a boundary between the plurality of heating regions is made higher or lower than the heating temperature of the other heaters in the same heating region to alleviate an influence of the heating temperature of the contiguous heating region. 
     
     
         4 . The steel sheet heating device according to  claim 1 , wherein the hot plate includes a plurality of plate members that are aligned so as to correspond to the plurality of heating regions and that differ in heating temperature. 
     
     
         5 . The steel sheet heating device according to  claim 4 , wherein a heat insulator is disposed at a boundary between the plurality of plate members. 
     
     
         6 . The steel sheet heating device according to  claim 1 , wherein:
 there are provided a pair of the hot plates each of which has the flat heating surface brought into close contact with the steel sheet, the plurality of heating regions formed by dividing the heating surface into the plurality of sections being heated by the plurality of heating equipment; and   the steel sheet is sandwiched between the hot plates and heated from both sides.   
     
     
         7 . The steel sheet heating device according to  claim 1 , wherein:
 the steel sheet is a steel sheet for hot-pressing; and   at least part of the steel sheet for hot-pressing is heated to a temperature equal to or higher than a transformation point Ac 3  by heating at least part of the plurality of heating regions to a temperature equal to or higher than the transformation point Ac 3 .   
     
     
         8 . A method for producing a prescribed press-formed part, in which tensile strength varies at different portions, by subjecting a steel sheet for hot-pressing to press-forming, comprising:
 a heating process in which the steel sheet for hot-pressing is heated to different temperatures at various portions at the same time through a single heating treatment such that at least part of the steel sheet for hot-pressing is heated to a temperature equal to or higher than a transformation point Ac 3 ; and   a press-forming process in which the steel sheet for hot-pressing, which has been heated to the different temperatures at the various portions though the heating process, is subjected to press-forming to be formed into a prescribed shape, and the steel sheet for hot-pressing is rapidly cooled to be quench-hardened based on the temperatures to which the steel sheet for hot-pressing has been heated so that the tensile strength varies at different portions.   
     
     
         9 . A press-formed part in which tensile strength is varied at different portions by quench-hardening, the press-formed part being formed by heating a single steel sheet for hot-pressing to different temperatures at various portions such that at least part of the steel sheet for hot-pressing is heated to a temperature equal to or higher than a transformation point Ac 3 , and subsequently forming the steel sheet for hot-pressing into a prescribed shape through press-forming, and rapidly cooling the steel sheet for hot-pressing so that the part which has been heated to the temperature equal to or higher than the transformation point Ac 3  is quench-hardened,
 the steel sheet for hot-pressing being divided into three or more portions and the three or more portions being heated to different temperatures, two or more portions out of the three or more portions being heated to different temperatures that are equal to or higher than the transformation point Ac 3 , and the press-forming being subsequently performed, whereby three or more portions, which differ in tensile strength in three or more levels due to differences between the temperatures to which each of the three or more portions is heated, being formed in the press-formed part.