Stainless steel and manufacturing method therefor, and stainless steel product and manufacturing method therefor

Abstract

Provided are a stainless steel having excellent cold workability and a manufacturing method therefor; and a stainless steel product for which surface hardness is sufficiently high and for which corrosion resistance against acids, particularly non-oxidative acids, is excellent and a manufacturing method therefor.Provided are the stainless steel and the manufacturing method therefor, said steel having a component composition, in terms of % by mass, 0.18-0.25% of C, 0.1-1.5% of Si, 0.35-1.5% of Mn, 0.04% or less of P, 0.01% or less of S, 0.05-0.20% of Ni, 12.5-14.6% of Cr, 1.5-3.0% of one or both of Mo and W according to the relational expression (Mo+½W), 1.0-3.0% of Cu, and 0.03-0.10% of N, the remainder being Fe and impurities. Further provided are the stainless steel product and the manufacturing method therefor, said stainless steel product being obtained by quenching and tempering the foregoing stainless steel.

What is claimed is: 
     
         1 . A stainless steel, having a component composition: in terms of % by mass, 0.18% to 0.25% of C, 0.1% to 1.5% of Si, 0.35% to 1.5% of Mn, 0.04% or less of P, 0.01% or less of S, 0.05% to 0.20% of Ni, 12.5% to 14.6% of Cr, 1.5% to 3.0% of one or both of Mo and W according to a relational expression of (Mo+½W), 1.0% to 3.0% of Cu, and 0.03% to 0.10% of N, remainders being Fe and impurities. 
     
     
         2 . The stainless steel as claimed in  claim 1 , wherein an area ratio of a Cu phase having an equivalent circle diameter of 0.03 μm or more in a cross-sectional structure is 2.4% or more. 
     
     
         3 . A manufacturing method for a stainless steel, the manufacturing method comprising: performing, on a stainless steel material having a component composition: in terms of % by mass, 0.18% to 0.25% of C, 0.1% to 1.5% of Si, 0.35% to 1.5% of Mn, 0.04% or less of P, 0.01% or less of S, 0.05% to 0.20% of Ni, 12.5% to 14.6% of Cr, 1.5% to 3.0% of one or both of Mo and W according to a relational expression of (Mo+½W), 1.0% to 3.0% of Cu, and 0.03% to 0.10% of N, remainders being Fe and impurities, hot working after performing a heat treatment that holds at 850° C. to 1090° C. for 60 minutes or more, and then performing annealing at 760° C. to 780° C. for four hours or more. 
     
     
         4 . A stainless steel product, having a nitride layer on a surface of a stainless steel having a component composition: in terms of % by mass, 0.18% to 0.25% of C, 0.1% to 1.5% of Si, 0.35% to 1.5% of Mn, 0.04% or less of P, 0.01% or less of S, 0.05% to 0.20% of Ni, 12.5% to 14.6% of Cr, 1.5% to 3.0% of one or both of Mo and W according to a relational expression of (Mo+½W), 1.0% to 3.0% of Cu, and 0.03% to 0.10% of N, remainders being Fe and impurities,
 wherein a hardness of a center of the stainless steel product is 480 HV or more and less than 630 HV, and a hardness of a surface of the stainless steel product is 630 HV or more. 
 
     
     
         5 . A manufacturing method for a stainless steel product, the manufacturing method comprising: performing, on a stainless steel having a component composition: in terms of % by mass, 0.18% to 0.25% of C, 0.1% to 1.5% of Si, 0.35% to 1.5% of Mn, 0.04% or less of P, 0.01% or less of S, 0.05% to 0.20% of Ni, 12.5% to 14.6% of Cr, 1.5% to 3.0% of one or both of Mo and W according to a relational expression of (Mo+½W), 1.0% to 3.0% of Cu, and 0.03% to 0.10% of N, remainders being Fe and impurities, quenching that sets a quenching temperature at 1000° C. to 1090° C. in a nitrogen atmosphere, performing, following the quenching, a sub-zero treatment that sets a treatment temperature at −50° C. or lower, and then performing tempering that sets a tempering temperature at 150° C. to 470° C. 
     
     
         6 . The manufacturing method for the stainless steel product as  claim 5 , wherein the tempering temperature is set at 150° C. to 400° C.