Patent ID: 11913088
Assignee: KOBE STEEL, LTD.
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  B | IPC B  C

Claim 0:
1. A high-strength steel sheet, comprising:
0.10% to 0.35% of C;
0.5% to 3.0% of Si+Al;
1.0% to 3.0% of Mn;
more than 0% and 0.05% or less of P; and
more than 0% and 0.01% or less of S, in terms of mass percentage,
wherein the high-strength steel sheet has a metallographic microstructure having a ferrite fraction of 0% to 10%, a Fresh-Martensite/Retained-Austenite (MA) fraction in a range of from 0% to 30%, a hard phase other than ferrite and MA in a range of from 70% to 100% in terms of area proportion, and
a retained austenite fraction in a range of from 5% to 30% in terms of volume proportion, and
wherein a skewness of image quality (IQ) as analyzed by an Electron Back Scatter Diffraction (EBSD) method is in a range of from −1.2 to −0.3, when the skewness is expressed by Formula (1) in a case where crystal grains having a bcc structure and a bet structure are regarded as an aggregation of regions having an area of 0.05 μm2:, n
       
        
         (
         
          n
          -
          1
         
         )
        
        ⁢
        
         (
         
          n
          -
          2
         
         )
        
       
      
      ⁢
      
       ∑
       
        
         (
         
          
           
            x
            i
           
           -
           
            x
            ave
           
          
          s
         
         )
        
        3
       
      
     
     ,
    
   
   
    
     (
     1
     )
    
   
  
 

wherein, in Formula (1),
n is total number of regions having a bcc structure and a bct structure and an area of 0.05 μm2,
s is standard deviation of the IQ in a region having an area of 0.05 μm2,
xi is the IQ of a region i having an area of 0.05 μm2, and
xave is an average IQ of regions having a bee structure and a bet structure and an area of 0.05 μm2.