Ferritic stainless steel and component for exhaust gas

Abstract

This ferritic stainless steel has a predetermined chemical composition, at least one type of oxides of oxides containing 5 mass % or more of Al and oxides containing 5 mass % or more of Si are present on the surface, and, among the oxides present on the surface, the number of oxides having a diameter D of 0.1 μm or more and 2.0 μm or less is 10 or more per 93 μm 2 , the diameter D being represented by D=(Dmax+Dmin)/2 where Dmax is the maximum diameter of the oxide on the surface and Dmin is the minimum diameter of the oxide on the surface.

1 . A ferritic stainless steel comprising, as a chemical composition:
 0.05 mass % or more and 2.50 mass % or less of Si;   0.05 mass % or more and 1.50 mass % or less of Mn;   0.025 mass % or less of C;   0.040 mass % or less of P;   0.003 mass % or less of S;   0.025 mass % or less of N;   0.01 mass % or more and 0.50 mass % or less of Ni;   10.50 mass % or more and 25.00 mass % or less of Cr;   0.01 mass % or more and 1.80 mass % or less of Cu;   0.002 mass % or more and 0.200 mass % or less of Al;   0.001 mass % or more and 1.00 mass % or less of Nb;   0 mass % or more and 2.5 mass % or less of W;   0 mass % or more and 3.00 mass % or less of Mo;   0 mass % or more and 0.500 mass % or less of Ti;   0 mass % or more and 0.0100 mass % or less of B;   0 mass % or more and 0.0030 mass % or less of Ca;   0 mass % or more and 0.50 mass % or less of Hf;   0 mass % or more and 0.40 mass % or less of Zr;   0 mass % or more and 0.50 mass % or less of Sb;   0 mass % or more and 0.30 mass % or less of Co;   0 mass % or more and 1.0 mass % or less of Ta;   0 mass % or more and 1.00 mass % or less of Sn;   0 mass % or more and 0.30 mass % or less of Ga;   0 mass % or more and 0.50 mass % or less of V;   0 mass % or more and 0.003 mass % or less of Mg;   0 mass % or more and 0.20 mass % or less of REM; and   a remainder including Fe and an impurity,   wherein at least one type of oxides of oxides containing 5 mass % or more of Al and oxides containing 5 mass % or more of Si are present on a surface, and, among the oxides present on the surface, the number of oxides having a diameter D of 0.1 μm or more and 2.0 μm or less is 10 or more per 93 μm 2 , the diameter D being represented by the following formula (1)
     D =( D max+ D min)/2  (1)
 
   in the formula (1), Dmax is a maximum diameter of the oxide on the surface, and Dmin is a minimum diameter of the oxide on the surface.   
     
     
         2 . The ferritic stainless steel according to  claim 1 ,
 wherein, regarding the surface, CIE1976 luminosity L* that is measured using a D65 light source in a diffuse lighting mode by receiving light in a direction at 8° with respect to a normal line to the surface at a visual field angle of 10° visual field for a measurement time of one second is 60 or more.   
     
     
         3 . The ferritic stainless steel according to  claim 1 ,
 wherein the chemical composition contains one or more of:   0.01 mass % or more and 2.5 mass % or less of W;   0.01 mass % or more and 3.00 mass % or less of Mo;   0.001 mass % or more and 0.500 mass % or less of Ti;   0.0002 mass % or more and 0.0100 mass % or less of B;   0.0002 mass % or more and 0.0030 mass % or less of Ca;   0.001 mass % or more and 0.50 mass % or less of Hf;   0.01 mass % or more and 0.40 mass % or less of Zr;   0.005 mass % or more and 0.50 mass % or less of Sb;   0.01 mass % or more and 0.30 mass % or less of Co;   0.001 mass % or more and 1.0 mass % or less of Ta;   0.002 mass % or more and 1.00 mass % or less of Sn;   0.0002 mass % or more and 0.30 mass % or less of Ga;   0.01 mass % or more and 0.50 mass % or less of V;   0.0003 mass % or more and 0.003 mass % or less of Mg; and   0.001 mass % or more and 0.20 mass % or less of REM.   
     
     
         4 . The ferritic stainless steel according to  claim 1 ,
 wherein, in a range from the surface to 1.0 μm after the ferritic stainless steel is held in an atmosphere of 300° C. to 900° C. for 100 hours or longer, when a Cr content is represented by [Cr], a Si content is represented by [Si] and an Al content is represented by [Al] by unit mass %, the following formula (2) is satisfied,
   [Cr]+[Si]+[Al]≥18.0  (2).
 
   
     
     
         5 . A ferritic stainless steel,
 wherein, in a range from a surface to 1.0 μm, when a Cr content is represented by [Cr], a Si content is represented by [Si] and an Al content is represented by [Al] by unit mass %, the following formula (2) is satisfied,
   [Cr]+[Si]+[Al]≥18.0  (2).
 
   
     
     
         6 . A component for exhaust gas comprising:
 the ferritic stainless steel according to  claim 1 .   
     
     
         7 . The ferritic stainless steel according to  claim 2 ,
 wherein, in a range from the surface to 1.0 μm after the ferritic stainless steel is held in an atmosphere of 300° C. to 900° C. for 100 hours or longer, when a Cr content is represented by [Cr], a Si content is represented by [Si] and an Al content is represented by [Al] by unit mass %, the following formula (2) is satisfied,
   [Cr]+[Si]+[Al]≥18.0  (2).
 
   
     
     
         8 . The ferritic stainless steel according to  claim 3 ,
 wherein, in a range from the surface to 1.0 μm after the ferritic stainless steel is held in an atmosphere of 300° C. to 900° C. for 100 hours or longer, when a Cr content is represented by [Cr], a Si content is represented by [Si] and an Al content is represented by [Al] by unit mass %, the following formula (2) is satisfied,
   [Cr]+[Si]+[Al]≥18.0  (2).
 
   
     
     
         9 . A component for exhaust gas comprising:
 the ferritic stainless steel according to  claim 2 .   
     
     
         10 . A component for exhaust gas comprising:
 the ferritic stainless steel according to  claim 3 .   
     
     
         11 . A component for exhaust gas comprising:
 the ferritic stainless steel according to  claim 4 .   
     
     
         12 . A component for exhaust gas comprising:
 the ferritic stainless steel according to  claim 5 .   
     
     
         13 . A component for exhaust gas comprising:
 the ferritic stainless steel according to  claim 7 .   
     
     
         14 . A component for exhaust gas comprising:
 the ferritic stainless steel according to  claim 8 .