Method of producing a free-cutting steel

Abstract

A method of producing a free-cutting steel includes: rolling a rectangular cast steel at ≥1120° C. and an area reduction rate of ≥60% to obtain a billet; and hot working the billet at ≥1050° C. and an area reduction rate of ≥75%. The rectangular cast steel contains, in mass %: C: less than 0.09 %, Mn: 0.50% to 1.50%, S: 0.250% to 0.600%, 0: more than 0.010% and 0.050% or less, and Cr: 0.50% to 1.50%, with a balance consisting of Fe and inevitable impurities. An A value=2([Mn]+2[Cr])/[S] is 6.0 to 18.0, where [Mn], [Cr], and [S] respectively denote contents in mass % of elements Mn, Cr, and S. A side length of a cross section of the rectangular cast steel perpendicular to a longitudinal direction is ≥250 mm.

1 . A method of producing a free-cutting steel, the method comprising:
 rolling a rectangular cast steel at a heating temperature of 1120° C. or more and an area reduction rate of 60% or more to obtain a billet, the rectangular cast steel having a chemical composition that contains, in mass %,   C: less than 0.09%,   Mn: 0.50% to 1.50%,   S: 0.250% to 0.600%,   O: more than 0.010% and 0.050% or less, and   Cr: 0.50% to 1.50%   with a balance consisting of Fe and inevitable impurities, and in which a A value defined by the following formula (1) is 6.0 to 18.0,   
       
         
           
             
               
                 
                   
                     
                       A 
                       ⁢ 
                           
                       value 
                     
                     = 
                     
                       2 
                       ⁢ 
                       
                         ( 
                         
                           
                             [ 
                             Mn 
                             ] 
                           
                           + 
                           
                             2 
                             [ 
                             Cr 
                             ] 
                           
                         
                         ) 
                       
                       ⁢ 
                       
                         / 
                         [ 
                         S 
                         ] 
                       
                     
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
         where [Mn], [Cr], and [S] respectively denote contents in mass % of elements Mn, Cr, and S, and a side length of a cross section of the rectangular cast steel perpendicular to a longitudinal direction being 250 mm or more; and 
         hot working the billet at a heating temperature of 1050° C. or more and an area reduction rate of 75% or more. 
       
     
     
         2 . The method of producing a free-cutting steel according to  claim 1 , wherein the chemical composition further contains, in mass %, one or more selected from the group consisting of
 Si: 0.50% or less,   P: 0.10% or less,   Al: 0.010% or less, and   N: 0.0150% or less.   
     
     
         3 . The method of producing a free-cutting steel according to  claim 1 , wherein the chemical composition further contains, in mass %, one or more selected from the group consisting of
 Ca: 0.0010% or less,   Se: 0.30% or less,   Te: 0.15% or less,   Bi: 0.20% or less,   Sn: 0.020% or less,   Sb: 0.025% or less,   B: 0.010% or less,   Cu: 0.50% or less,   Ni: 0.50% or less,   Ti: 0.100% or less,   V: 0.20% or less,   Zr: 0.050% or less, and   Mg: 0.0050% or less.   
     
     
         4 . The method of producing a free-cutting steel according to  claim 2 , wherein the chemical composition further contains, in mass %, one or more selected from the group consisting of
 Ca: 0.0010% or less,   Se: 0.30% or less,   Te: 0.15% or less,   Bi: 0.20% or less,   Sn: 0.020% or less,   Sb: 0.025% or less,   B: 0.010% or less,   Cu: 0.50% or less,   Ni: 0.50% or less,   Ti: 0.100% or less,   V: 0.20% or less,   Zr: 0.050% or less, and   Mg: 0.0050% or less.