Ferritic Stainless steel material for automobile exhaust gas passage components

Abstract

To provide a ferritic stainless steel material for automobile exhaust gas passage components usable in a high-temperature range over 900° C. and even over 950° C. The ferritic stainless steel material has excellent heat resistance and low-temperature toughness and has a composition comprising, in terms of % by mass, at most 0.03% of C, at most 1% of Si, from 0.6 to 2% of Mn, at most 3% of Ni, from 10 to 25% of Cr, from 0.3 to 0.7% of Nb, from more than 1 to 2% of Cu, from 1 to 2.5% of Mo, from 1 to 2.5% of W, at most 0.15% of Al, from 0.03 to 0.2% of V, and at most 0.03% of N, and optionally containing any of B, Co, W, Ti, Zr, REM and Ca with a balance of Fe and inevitable impurities, and the composition satisfies restrictive formulae 1.2Nb+5Mo+6Cu≧11.5 and 15Nb+2Mo+0.5Cu≧10.5. The steel material has a texture where the total amount of Nb and Mo existing as a precipitation phase is at most 0.2% by mass.

1 . A ferritic stainless steel material having excellent heat resistance and low-temperature toughness for automobile exhaust gas passage components, which has a composition comprising, in terms of % by mass, at most 0.03% of C, at most 1% of Si, from 0.6 to 2% of Mn, at most 3% of Ni, from 10to 25% of Cr, from 0.3 to 0.7% of Nb, from more than 1 to 2% of Cu, from 1 to 2.5% of Mo, from 1 to 2.5% of W, at most 0.15% of Al, from 0.03 to 0.2% of V, and at most 0.03% of N, with a balance of Fe and inevitable impurities, and satisfying the following formulae (1) and (2), and which has a texture where the total amount of Nb and Mo existing as a precipitation phase is at most 0.2% by mass:
   2Nb+5Mo+6Cu≧11.5   (1),     15Nb+2Mo+0.5Cu≧10.5   (2).   
   
   
       2 . The steel material as claimed in  claim 1 , wherein the composition further contains at least one of Ti and Zr in an amount of less than 1% in total. 
   
   
       3 . The steel material as claimed in  claim 1 , wherein the composition further contains at least one of B in an amount of at most 0.02% and Co in an amount of at most 2%. 
   
   
       4 . The steel material as claimed in  claim 1 , wherein the composition further contains at least one of REM (rare earth element) and Ca in an amount of at most 0.1% in total. 
   
   
       5 . The steel material as claimed in  claim 1 , which is used for exhaust gas components of which the material temperature is in a temperature range over 900° C. 
   
   
       6 . The steel material as claimed in  claim 2 , wherein the composition further contains at least one of B in an amount of at most 0.02% and Co in an amount of at most 2%. 
   
   
       7 . The steel material as claimed in  claim 2 , wherein the composition further contains at least one of REM (rare earth element) and Ca in an amount of at most 0.1% in total. 
   
   
       8 . The steel material as claimed in  claim 3 , wherein the composition further contains at least one of REM (rare earth element) and Ca in an amount of at most 0.1% in total. 
   
   
       9 . The steel material as claimed in  claim 2 , which is used for exhaust gas components of which the material temperature is in a temperature range over 900° C. 
   
   
       10 . The steel material as claimed in  claim 3 , which is used for exhaust gas components of which the material temperature is in a temperature range over 900° C. 
   
   
       11 . The steel material as claimed in  claim 4 , which is used for exhaust gas components of which the material temperature is in a temperature range over 900° C.