Method for processing member having excellent chemical conversion treatability

Abstract

In a method for processing a high-strength member having a high Si content of more than 0.7% by mass, a high-strength steel material containing, on the basis of mass percent, 0.05% or more C, more than 0.7% Si, and 0.8% or more Mn is subjected to processing controlled such that the sum total of absolute surface strains in a predetermined direction each applied in individual process steps of the processing is 5% or more as nominal strain to form a member having a predetermined shape. The member, even containing more than 0.7% Si, can have markedly improved chemical conversion treatability without mechanical grinding or chemical pickling treatment.

1 . A method for processing a member having excellent chemical conversion treatability, the method comprising:
 processing a high-strength steel material having a composition containing, on the basis of mass percent,   0.05% or more C,   more than 0.7% Si, and   0.8% or more Mn   
       to form the member, and
 controlling the processing such that the sum total of absolute surface strains in a predetermined direction each applied in individual process steps of the processing is 5% or more as nominal strain. 
 
     
     
         2 . The method for processing a member according to  claim 1 , wherein the sum total of absolute surface strains in a predetermined direction is the sum total of absolute surface strains applied in two directions intersecting at right angles. 
     
     
         3 . The method for processing a member according to  claim 1 , wherein conditions for the processing are controlled such that the sum total of absolute surface strains in a predetermined direction each applied in individual process steps of the processing in combination with the sum total of absolute surface strains applied in the manufacture of the high-strength steel material is 5% or more as nominal strain. 
     
     
         4 . The method for processing a member according to  claim 1 , wherein the high-strength steel material is a hot-rolled material or a cold-rolled material. 
     
     
         5 . The method for processing a member according to  claim 1 , wherein the composition contains, on the basis of mass percent,
 0.05% or more C,   1% or more Si, and   1.5% or more Mn.   
     
     
         6 . The method for processing a member according to  claim 1 , wherein the sum total of absolute surface strains in a predetermined direction each applied in individual process steps of the processing is 7% or more as nominal strain.