Forming method, heat treatment system, and formed product

Abstract

In heating step S101, a steel sheet is heated and made in an austenite state. In heating step S101, the whole region of the steel sheet is evenly heated, and the whole region of the steel sheet is made in the austenite state. In cooling step S102, only a first region set on the steel sheet in the austenite state is forcibly cooled (rapidly cooled) within a temperature range of a range where martensitic transformation does not occur. In cooling step S102, a second region other than the first region is cooled by natural cooling to maintain a state in which a temperature is higher than in the first region.

1 .- 13 . (canceled) 
     
     
         14 . A forming method comprising:
 a heating step of heating a steel sheet to make the steel sheet in an austenite state;   a cooling step of, outside a heating furnace in which the heating step is performed, forcibly cooling only a first region set on the steel sheet in the austenite state within a temperature range where martensitic transformation does not occur to a temperature at which a ferrite/pearlite phase is generated, and naturally cooling a second region other than the first region to a temperature lower than a temperature at which transformation to austenite starts; and   a forming step of hot-press-forming the steel sheet including the first region that is not in the austenite state and the second region in the austenite state;   wherein the forming method further comprises a reheating step of, immediately after the cooling step, heating the steel sheet to make the second region in the austenite state and maintain a state in which the first region is rapidly cooled for a predetermined time to grow the ferrite/pearlite phase, and   the forming step is performed after the reheating step.   
     
     
         15 . The forming method according to  claim 14 , wherein
 the heating step includes heating a whole region of the steel sheet evenly.   
     
     
         16 . The forming method according to  claim 14 , wherein
 in the cooling step, the second region is cooled by natural cooling to maintain a state in which the temperature is higher than in the first region,   in the reheating step, the steel sheet is heated under a condition of such a range that the first region is not made in the austenite state, and   in the forming step, only the second region is transformed to martensite.   
     
     
         17 . A heat treatment system configured to form, on a steel sheet, a first region that is not in an austenite state, and a second region other than the first region to form a region to be partially plastically deformed by hot press forming of the steel sheet, comprising:
 a heat treatment apparatus configured to heat the steel sheet and make the steel sheet in the austenite state;   a cooling processing apparatus configured to forcibly cool only the first region set on the steel sheet in the austenite state within a temperature range where martensitic transformation does not occur; and   a reheat treatment apparatus configured to heat the steel sheet processed by the cooling processing apparatus under such a condition that the diffusion layer does not grow to make the second region in the austenite state or maintain the austenite state of the second region,   wherein the reheat treatment apparatus comprises:   a heat source configured to irradiate the steel sheet with infrared rays; and   a cover configured to cover the first region of the steel sheet, and   in the cover, a plurality of through holes are formed in a surface irradiated with the infrared rays.   
     
     
         18 . The heat treatment system according to  claim 17 , wherein
 the heat treatment system is a heat treatment system configured to form the first region and the second region to form the region to be partially plastically deformed by hot-press-forming the steel sheet for which a plating layer of aluminum added with silicon is formed on a surface, and   the heat treatment apparatus heats the steel sheet and makes the steel sheet in the austenite state, alloys a whole of the plating layer, to have a composition ratio of iron which is not less than a composition ratio of iron of an γ-phase alloy of iron, aluminum and silicon, and set a thickness of a diffusion layer formed on the side of the steel sheet on which the plating layer is formed not more than 10 μm.   
     
     
         19 . The heat treatment system according to  claim 17 , wherein
 the cover is formed as a box body opening on a steel sheet side.