Wiredrawn product and method for manufacturing wiredrawn product

Abstract

Provided is a wiredrawn product drawn from a heat-treated steel containing: 0.38 to 1.05% by mass of C; 0.0 to 1.0% by mass of Mn; 0.0 to 0.50% by mass of Cr; and 0.0 to 1.5% by mass of Si, with the remainder being Fe and unavoidable impurities, wherein a GOS value/average crystal grain size is greater than or equal to −0.6×GAM value+1.5 at a grain boundary setting angle of 2° and a step number of 0.07 μm.

1 . A wiredrawn product drawn from a heat-treated steel containing: 0.38 to 1.05% by mass of C; 0.0 to 1.0% by mass of Mn; 0.0 to 0.50% by mass of Cr; and 0.0 to 1.5% by mass of Si, with the remainder being Fe and unavoidable impurities, characterized in that:
 a GOS value/average crystal grain size at a grain boundary setting angle of 2° and a step number of 0.07 μm is greater than or equal to −0.6×GAM value+1.5.   
     
     
         2 . A wiredrawn product drawn from a heat-treated steel containing: 0.38 to 1.05% by mass of C; 0.0 to 1.0% by mass of Mn; 0.0 to 0.50% by mass of Cr; and 0.0 to 1.5% by mass of Si, with the remainder being Fe and unavoidable impurities, characterized in that:
 a GOS value/average crystal grain size at a grain boundary setting angle of 2° is greater than or equal to −0.18×average crystal grain size+2.25.   
     
     
         3 . A wiredrawn product drawn from a heat-treated steel containing: 0.38 to 1.05% by mass of C; 0.0 to 1.0% by mass of Mn; 0.0 to 0.50% by mass of Cr; and 0.0 to 1.5% by mass of Si, with the remainder being Fe and unavoidable impurities, characterized in that:
 a GOS value/average crystal grain size at a grain boundary setting angle of 2° is greater than or equal to 0.06×degree of integration in a longitudinal direction [101]+1.45.   
     
     
         4 . A wiredrawn product drawn from a heat-treated steel containing: 0.38 to 1.05% by mass of C; 0.0 to 1.0% by mass of Mn; 0.0 to 0.50% by mass of Cr; and 0.0 to 1.5% by mass of Si, with the remainder being Fe and unavoidable impurities, characterized in that:
 within a range where a torsional fracture surface is normal in a torsion test, a relationship between tensile strength (TS) and hardness is as follows, and the relationship between tensile strength and hardness is adjustable according to a heating condition and an isothermal transformation temperature during patenting.
   0.16TS+90≤hardness≤0.16TS+290
 
   
     
     
         5 . A wiredrawn product drawn from a heat-treated steel containing: 0.38 to 1.05% by mass of C; 0.0 to 1.0% by mass of Mn; 0.0 to 0.50% by mass of Cr; and 0.0 to 1.5% by mass of Si, with the remainder being Fe and unavoidable impurities, characterized in that:
 when a structure of the heat-treated steel before wire drawing is observed with a backscattered electron (BSE) image, in a two-phase structure of ferrite and iron carbide, an area fraction of bent, curved, or branched iron carbide is 9% or more in the field of view.   
     
     
         6 . A method for producing a wiredrawn product, characterized by comprising the steps of:
 preparing a steel containing 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities;   causing the steel itself to generate heat to directly heat the steel;   passing the heated steel through a bath in which a cooling medium capable of isothermal transformation is stored to cool the steel; and   drawing the cooled steel, wherein   a temperature gradient is the largest in a final stage of heating of the heating step, and the heated steel is allowed to enter the cooling medium immediately after the steel reaches a predetermined maximum heating temperature in the final stage of heating of the heating step to start cooling without maintaining the predetermined maximum heating temperature.   
     
     
         7 . A method for producing a wiredrawn product, comprising:
 heating a steel from room temperature to 800° C. or more within a few seconds, the steel containing 0.38 to 1.05% by mass of C, 0.0 to 1.0% by mass of Mn, 0.0 to 0.50% by mass of Cr, and 0.0 to 1.5% by mass of Si with the remainder being Fe and unavoidable impurities;   cooling the heated steel to 620° C. or less within a few seconds without maintaining a maximum heating temperature; and   drawing the cooled steel.