Hot shear method with grain refining in surface layer and work piece obtained by hot shear with grain refining in surface layer

摘要

A method of hot shearing with grain refinement in surface layer comprising: heating and maintaining a steel sheet having a carbon content of 0.15% or more in mass in a temperature range of Ac3 at 1400 ° C to austenizing the steel sheet; subsequently shearing the steel sheet in a state in which the steel sheet is placed on a die; and quenching by rapidly cooling the sheared steel sheet, where an initial shear temperature is set to be a temperature (° C) obtained by adding a temperature of 30 ° C to 140 ° C to an Ar3 previously measured from the sheet metal. steel; or where an initial shear temperature is set to be a temperature (° C) obtained by adding a value, which is calculated by multiplying an amount of equivalent plastic deformation of a surface layer in a sheared part by a coefficient of 40 to 60, to an Ar3 previously measured from the steel sheet, wherein the amount of equivalent plastic deformation of the surface layer in the sheared part is calculated as the average value of an amount of plastic deformation equivalent to a region in a range of 5% 20% of a thickness of the steel sheet from a shear plane of the sheared part to an interior of the steel sheet in a direction normal to the shear plane and in a range of 20% to 50% of the thickness of the steel sheet in a thickness direction of the steel sheet from a lower part on a burr side of the sheared part, and where the amount of plastic deformation equivalent to the c Surface shear at the sheared part is calculated by a shear simulation by analysis using a finite element method (FEM) that is performed on the basis of a strain diagram at a sheet steel temperature of 500 ° C to 800 ° C , integrating an increase in the equivalent plastic deformation "dε-P" by a Mises voltage function that is represented by the following Formula (1) when a material coordinate system is defined as x, y, yz: ** Formula **