Ferritic Stainless Steel for Use as Conduit Members for Emission of Automotive Exhaust Gas

Abstract

A ferritic stainless steel useful as conduit members for emission of automotive exhaust gas consists of C up to 0.03 mass %, Si up to 1.0 mass %, Mn up to 1.5 mass %, Ni up to 0.6 mass %, 10-20 mass % of Cr, Nb up to 0.50 mass %, 0.8-2.0 mass % of Cu, Al up to 0.03 mass %, 0.03-0.20 mass % of V, N up to 0.03 mass % and the balance being Fe except inevitable impurities with a provision that at least 90% of Cu contained is dissolved in a steel matrix and that Nb□8(C+N). The steel may further contain 0.05-0.30 mass % of Ti and/or 0.0005-0.02 mass % of B. Mo as an inevitable impurity is controlled to be less than 0.10 mass %. The steel has excellent formability, low-temperature toughness and weldability as well as the same heat-resistance as Nb, Mo-alloyed steel.

The invention claimed is: 
     
         1 . A ferritic stainless steel for use as a conduit member for emission of automotive exhaust gas, consisting essentially of C up to 0.03 mass %, Si up to 1.0 mass %, Mn up to 1.5 mass %, Ni up to 0.6 mass %, 10-20 mass % of Cr, 0.50 mass % or less of Nb, 0.8-2.0 mass % of Cu, Al up to 0.03 mass %, 0.03-0.20 mass % of V, N up to 0.03 mass % and the balance being Fe except inevitable impurities with a provision that at least 90% of Cu contained is dissolved in a steel matrix and that Nb≧8(C+N). 
     
     
         2 . The ferritic stainless steel defined by  claim 1 , wherein Mo as an inevitable impurity is controlled to be less than 0.10 mass %. 
     
     
         3 . The ferritic stainless steel defined by  claim 1 , which further contains 0.05-3.0 mass % of Ti. 
     
     
         4 . The ferritic stainless steel defined by  claim 1 , which further contains 0.0005-0.02 mass % of B. 
     
     
         5 . The ferritic stainless steel defined by  claim 2 , which further contains 0.05-3.0 mass % of Ti. 
     
     
         6 . The ferritic stainless steel defined by  claim 2 , which further contains 0.0005-0.02 mass of B. 
     
     
         7 . The ferritic stainless steel defined by  claim 3 , which further contains 0.0005-0.02 mass % of B. 
     
     
         8 . The ferritic stainless steel defined by  claim 5 , which further contains 0.0005-0.02 mass % of B. 
     
     
         9 . A method of manufacturing a ferritic stainless steel for use as a conduit member for emission of automotive exhaust gas, the method comprising:
 heating a steel consisting essentially of C up to 0.03 mass %, Si up to 1.0 mass %, Mn up to 1.5 mass %, Ni up to 0.6 mass %, 10-20 mass % of Cr, 0.50 mass % or less of Nb, 0.8-2.0 mass % of Cu, Al up to 0.03 mass %, 0.03-0.20 mass % of V, N up to 0.03 mass % and the balance being Fe except inevitable impurities with a provision that Nb≧8(C+N) to at least 900° C.; and   quenching the heated steel sheet such that at least 90% of Cu contained is dissolved in a steel matrix.