Method for improving delayed fracture characteristics of metal sheet, method for producing blank, method for producing press-formed article, and press-formed article

Abstract

A method for improving the delayed fracture characteristics of a metal sheet made of a high-strength steel sheet to suppress delayed fracture from a sheared end face after forming by a simple method. A method for improving delayed fracture characteristics of a metal sheet, the metal sheet having a sheared end face on at least a part of a sheet end portion and being made of a high-strength steel sheet. Plastic deformation is imparted to at least a part of the sheared end face of the metal sheet.

1 . A method for improving delayed fracture characteristics of a metal sheet, the metal sheet having a sheared end face on at least a part of a sheet end portion and being made of a high-strength steel sheet,
 wherein plastic deformation is imparted to at least a part of the sheared end face of the metal sheet.   
     
     
         2 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 1 ,
 wherein the plastic deformation imparts plastic strain greater than 0 in a direction along an extending direction of the end face to at least a part of the sheared end face.   
     
     
         3 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 1 ,
 wherein the plastic deformation is imparted by bending and unbending.   
     
     
         4 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 3 ,
 wherein each bending angle in the bending and unbending is set to less than 90 degrees.   
     
     
         5 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 3 ,
 wherein the bending and unbending is performed by bending by press forming.   
     
     
         6 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 3 ,
 wherein the bending and unbending is performed by leveling using a plurality of rolls.   
     
     
         7 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 3 ,
 wherein a final bend in the bending and unbending is set such that an outside of the bend is on a burr side of the sheared end face.   
     
     
         8 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 1 ,
 wherein the metal sheet is a steel sheet having a tensile strength of 980 MPa or more.   
     
     
         9 . A method for producing a blank for press forming, comprising:
 performing shearing on a metal sheet; and   imparting plastic deformation to a sheared end face by the method for improving delayed fracture characteristics according to  claim 1 , which is a step after the performing of shearing.   
     
     
         10 . A method for producing a press-formed article by press-forming a metal sheet made of a high-strength steel sheet, comprising:
 performing shearing on the metal sheet; and   imparting plastic deformation to a sheared end face by the method for improving delayed fracture characteristics according to  claim 1 , which is a step after the performing of shearing.   
     
     
         11 . A press-formed article having a sheared end face on at least a part of a sheet end portion and being obtained by processing a metal sheet made of a high-strength steel sheet,
 wherein plastic strain greater than 0 in a direction along an extending direction of the end face is imparted to at least a part of the sheared end face.   
     
     
         12 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 2 ,
 wherein the plastic deformation is imparted by bending and unbending.   
     
     
         13 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 12 ,
 wherein each bending angle in the bending and unbending is set to less than 90 degrees.   
     
     
         14 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 4 ,
 wherein the bending and unbending is performed by bending by press forming.   
     
     
         15 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 12 ,
 wherein the bending and unbending is performed by bending by press forming.   
     
     
         16 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 13 ,
 wherein the bending and unbending is performed by bending by press forming.   
     
     
         17 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 4 ,
 wherein the bending and unbending is performed by leveling using a plurality of rolls.   
     
     
         18 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 12 ,
 wherein the bending and unbending is performed by leveling using a plurality of rolls.   
     
     
         19 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 13 ,
 wherein the bending and unbending is performed by leveling using a plurality of rolls.   
     
     
         20 . The method for improving delayed fracture characteristics of a metal sheet according to  claim 14 ,
 wherein the bending and unbending is performed by leveling using a plurality of rolls.