Ferritic steel sheet concurrently improved in formability, high-temperature strength, high-temperature oxidation resistance, and low-temperature toughness

Abstract

A low-cost ferritic steel sheet possessing not only formability enabling application to complexly configured automobile exhaust gas passage components but also high-temperature strength, high-temperature oxidation resistance and low-temperature toughness as good as or superior to existing ferritic steels, which ferritic steel sheet comprises, in mass percent, C: not more than 0.02%, Si: 0.7-1.1%, Mn: not more than 0.8%, Ni: not more than 0.5%, Cr: 8.0 to less than 11.0%, N: not more than 0.02%, Nb: 0.10-0.50%, Ti: 0.07-0.25%, Cu: 0.02-0.5%, B: 0.0005-0.02%, V: 0 (no addition)-0.20%, one or both of Ca and Mg: 0 (no addition)-0.01% in total, one or more elements among Y and rare earth elements: 0 (no addition)-0.20% in total, and the balance of Fe and unavoidable impurities, and satisfies 3Cr+40Si≧61, Cr+10Si≦21, and 420C−11.5Si+7Mn+23Ni−11.5Cr−12Mo+9Cu−49Ti−25(Nb+V)−52Al+470N+189≦70.

What is claimed is:  
     
         1 . A ferritic steel sheet concurrently improved in formability, high-temperature oxidation resistance, high-temperature strength, and low-temperature toughness comprising, in mass percent 
 C: not more than 0.02%,    Si: 0.7-1.1%,    Mn: not more than 0.8%,    Ni: not more than 0.5%,    Cr: 8.0 to less than 11.0%,    N: not more than 0.02%,    Nb: 0.10-0.50%,    Ti: 0.07-0.25%,    Cu: 0.02-0.5%,    B: 0.0005-0.02%,    V: 0 (no addition)-0.20%,    one or both of Ca and Mg: 0 (no addition)-0.01% in total,    one or more elements among Y and rare earth elements: 0 (no addition)-0.20% in total, and    the balance of Fe and unavoidable impurities,    and having a chemical composition satisfying all of Equations (1)-(3):    3Cr+40Si≧61  (1) Cr+10Si≦21  (2) 420C−11.5Si+7Mn+23Ni−11.5Cr−12Mo+9Cu−49Ti−25(Nb+V)−52Al+470N+189≦70  (3).    
     
     
         2 . A steel sheet according to  claim 1 , wherein the content of V is 0.01-0.20%.  
     
     
         3 . A steel sheet according to  claim 1 , wherein the content of one or both of Ca and Mg is 0.0003-0.01% in total.  
     
     
         4 . A steel sheet according to  claim 1 , wherein the content of one or more elements among Y and rare earth elements is 0.01-0.20% in total.  
     
     
         5 . A steel sheet according to  claim 1 , further including 
 Mo: not more than 0.50% and    Al: not more than 0.10%.    
     
     
         6 . A steel sheet according to any of  claims 1  to  5 , which has a metallic structure obtained by cold rolling and annealing a partially recrystallized hot-rolled sheet.  
     
     
         7 . A steel sheet according to any of  claims 1  to  5 , which has a metallic structure obtained by cold rolling and annealing a totally recrystallized hot-rolled sheet  
     
     
         8 . A steel sheet according to any of  claims 1  to  7 , which is used as fabricated into an automobile engine exhaust gas passage component.