Ferritic stainless steel sheet with excellent thermal fatigue properties, and automotive exhaust-gas path member

Abstract

Disclosed is a ferritic stainless steel sheet with excellent thermal fatigue properties, including, by mass %, 0.03% or less of C, 1.0% or less of Si, 1.5% or less of Mn, 0.6% or less of Ni, 10˜20% of Cr, 0.05˜0.30% of Ti, 0.51˜0.65% of Nb, 0˜less than 0.10% of Mo, 0.8˜2.0% of Cu, 0˜0.10% of Al, 0.0005˜0.02% of B, 0˜0.20% of V, and 0.03% or less of N, with the balance being Fe and inevitable impurities, having a composition satisfying the following equations (1) and (2) and having a structure in which ε-Cu phase grains each having a long diameter of 0.5 μm or more are present in a density of 10 or less per 25 μm 2 : Nb−8(C+N)≧0 . . . (1), 10 Si+20 Mo+30 Cu+20(Ti+V)+160 Nb−(Mn+Ni)≧100 . . . (2). The ferritic stainless steel sheet, having a relatively inexpensive component composition, has excellent thermal fatigue properties, and is suitable for use in an automotive exhaust-gas path member, including an exhaust manifold, a catalyst converter, a front pipe, or a center pipe.

1 . A ferritic stainless steel sheet with excellent thermal fatigue properties, which comprises, by mass %, 0.03% or less of C, 1.0% or less of Si, 1.5% or less of Mn, 0.6% or less of Ni, 10˜20% of Cr, 0.05˜0.30% of Ti, 0.51˜0.65% of Nb, 0˜less than 0.10% of Mo, 0.8˜2.0% of Cu, 0˜0.10% of Al, 0.0005˜0.02% of B, 0˜0.20% of V, and 0.03% or less of N, with a balance being Fe and inevitable impurities, has a composition satisfying equations (1) and (2) represented below, and has a structure in which ε-Cu phase grains, each having a long diameter of 0.5 μm or more, are present in a density of 10 or less per 25 μm 2 :
   Nb−8(C+N)≧0   (1)     10 Si+20 Mo+30 Cu+20(Ti+V)+160 Nb−(Mn+Ni)≧100   (2)   
     
     
         2 . The ferritic stainless steel sheet according to  claim 1 , wherein the steel sheet is a steel plate. 
     
     
         3 . An automotive exhaust-gas path member, using the steel sheet of  claim 1 . 
     
     
         4 . The automotive exhaust-gas path member according to  claim 3 , wherein the member is an exhaust manifold, a catalyst converter, a front pipe, or a center pipe. 
     
     
         5 . The automotive exhaust-gas path member according to  claim 3  or  claim 4 , wherein the member is heated to a temperature of 700° C. or higher when an engine is running, and is then cooled to 400° C. from the increased temperature at an average cooling rate of 0.1˜30° C./sec after the engine is stopped.