Ferritic stainless steel and martensitic stainless steel having excellent machinability

摘要

A ferritic stainless steel containing, in mass %, 0.01 to 1 % of C, 1.0 % or less of Si, 1.0 % or less of Mn, 15 to 30 % of Cr, 0.60 % or less of Ni, and 0.5 to 6.0 % of Cu, or a martensitic stainless steel containing, in mass %, 0.01 to 0.5 % of C, 1.0 % or less of Si, 1.0 % or less of Mn, 10 to 15 % of Cr, 0.60 % or less of Ni, and 0.5 to 6.0 % of Cu, in which a Cu-rich phase having a C concentration of 0.1 mass % or more or a concentration of Sn and/or In of 10 mass % or more is dispersed in the matrix thereof in a proportion of 0.2 vol % or more. The Cu-rich phase is dispersed and precipitated in the matrix by subjecting the steel one or more times to an aging treatment of holding it at a temperature ranging 500 to 900 ° C for 1 hr or more. The above types of stainless steel allow the improvement of machinability of a ferritic stainless steel and a martensitic stainless steel without detriment to formability, corrosion resistance, the environment and the like, through the dispersion and deposition of a Cu-rich phase in place of the addition of an element imparting machinability such as S or Pb.