Ferritic free-cutting stainless steel excellent in surface roughness and outgass resistance

Abstract

A ferritic free-cutting stainless steel excellent in surface roughness and outgass resistance is disclosed which comprises in weight percentage, 0.06% or less of C, 0.05 to 1.0% of Si, 2.0% or less of Mn, 0.050% or less of P, 0.05 to 0.50% of S, 2.0% or less of Cu, 2.0% or less of Ni, 9.0 to 25.0% of Cr, 4.0% or less of Mo, 0.065 to 2.0% of Ti, 0.0150% or less of 0, 0.020% or less of N, 0.001 to 0.100% of Al, and Fe and inevitable impurity in the rest portion, wherein the steel satisfies Equations (1) and (2) of the equations, [Ti]≧1.3×[S]  Equation (1) [Mn]/[Ti]≦3  Equation (2) (WTi+WCr) >2×WMn  Equation (3) where the amount of Ti contained in the steel is represented by [Ti], that of S is represented by [S] and that of Mn is represented by [Mn], and wherein the steel satisfies Equation (3) where the amount of Ti contained in sulfide produced in the texture of the steel is represented by WTi, that of Cr is represented by WCr and that of Mn is represented by WMn.

1 . A ferritic free-cutting stainless steel excellent in surface roughness and outgass resistance, comprising: 
 in weight percentage, 0.06% or less of C, 0.05 to 1.0% of Si, 2.0% or less of Mn, 0.050% or less of P, 0.05 to 0.50% of S, 2.0% or less of Cu, 2.0% or less of Ni, 9.0 to 25.0% of Cr, 4.0% or less of Mo, 0.065 to 2.0% of Ti, 0.0150% or less of O, 0.020% or less of N, 0.001 to 0.100% of Al, and Fe and inevitable impurity in the rest portion, wherein    the steel satisfies Equations (1) and (2) of the equations,      [Ti]≧1.3×[S]  Equation (1)  [Mn]/[Ti]≦3  Equation (2)  (WTi+WCr)>2×WMn  Equation (3)    where the amount of Ti contained in the steel is represented by [Ti], that of S is represented by [S] and that of Mn is represented by [Mn], and wherein    the steel satisfies Equation (3) where the amount of Ti contained in sulfide produced in the texture of the steel is represented by WTi, that of Cr is represented by WCr and that of Mn is represented by WMn.    
     
     
         2 . A ferritic free-cutting stainless steel excellent in surface roughness and outgass resistance, wherein 
 in addition to the components as claimed in  claim 1 , the steel contains in weight percentage any one or more selected from the group consisting of 0.01 to 0.30% of Pb, 0.01 to 0.30% of Se, 0.10% or less of Te and 0.01 to 0.30% or less of Bi.    
     
     
         3 . A ferritic free-cutting stainless steel excellent in surface roughness and outgass resistance, wherein 
 in addition to the components as claimed in  claim 1 , the steel contains in weight percentage any one or more selected from the group consisting of 0.05% or less of Ca, 0.02% or less of Mg, 0.02% or less of B, 0.02% or less of REM, 0.50% or less of V, 0.50% or less of Nb, 2.0% or less of W and 0.50% or less of Ta.    
     
     
         4 . A ferritic free-cutting stainless steel excellent in surface roughness and outgass resistance, wherein 
 in addition to the components as claimed in  claim 2 , the steel contains in weight percentage any one or more selected from the group consisting of 0.05% or less of Ca, 0.02% or less of Mg, 0.02% or less of B, 0.02% or less of REM, 0.50% or less of V, 0.50% or less of Nb, 2.0% or less of W and 0.50% or less of Ta.