Ferritic stainless steel for exhaust system member having excellent corrosion resistance after heating

Abstract

A ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating includes: 0.015 mass % or less of C; 0.02 mass % or less of N; 0.03 mass % to 1.0 mass of Si; 1.0 mass of Mn; 0.04 mass of P; 0.01 mass of S; 10.5 mass % to 22.5 mass of Cr; 0.02 mass % to 0.5 mass of Sn; 0.003 mass % to 0.2 mass of Al; one or both of 0.03 mass % to 0.35 mass of Ti and 0.03 mass % to 0.6 mass of Nb; and a remnant comprising Fe and inevitable impurities, wherein a grain size number on a surface of the ferritic stainless steel is 6 to 2 to 15 nm of a layer containing Sn at a concentration twice or more of Sn content in the base material is formed on the ferritic stainless steel.

1 - 13 . (canceled) 
     
     
         14 . A ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating, the ferritic stainless steel comprising:
 0.015 mass % or less of C;   0.02 mass % or less of N;   0.03 mass % to 1.0 mass % of Si;   1.0 mass % or less of Mn;   0.04 mass % or less of P;   0.01 mass % or less of S;   10.5 mass % to 22.5 mass % of Cr;   0.02 mass % to 0.5 mass % of Sn;   0.003 mass % to 0.2 mass % of Al;   one or both of 0.03 mass % to 0.35 mass % of Ti and 0.03 mass % to 0.6 mass % of Nb; and   a remnant comprising Fe and inevitable impurities, wherein   a grain size number on a surface of the ferritic stainless steel is 6 or more, and   2 to 15 nm of a layer containing Sn at a concentration twice or more of a Sn concentration in a base material is formed on the ferritic stainless steel when the ferritic stainless steel is heated at 673 K for 24 hours in the atmosphere.   
     
     
         15 . A ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating, the ferritic stainless steel comprising:
 0.015 mass % or less of C;   0.02 mass % or less of N;   0.03 mass % to 1.0 mass % of Si;   1.0 mass % or less of Mn;   0.04 mass % or less of P;   0.01 mass % or less of S;   10.5 mass % to 22.5 mass % of Cr;   0.02 mass % to 0.5 mass % of Sn;   0. 003 mass % to 0.2 mass % of Al;   one or both of 0.03 mass % to 0.35 mass % of Ti and 0.03 mass % to 0.6 mass % of Nb; and   a remnant comprising Fe and inevitable impurities, wherein   a grain size number on a surface of the ferritic stainless steel is 6 or more, and   2 to 15 nm of a layer containing Sn at a concentration twice or more of a Sn concentration in a base material is formed on the ferritic stainless steel.   
     
     
         16 . The ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating according to  claim 14  or  15 , further comprising at least one of a first group and a second group, the first group consisting of one or more of 0.05 mass % to 1.5 mass % of Cu, 0.1 mass % to 1.2 mass % of Ni, 0.03 mass % to 3 mass % of Mo, 0.03 mass % to 1 mass % of W, 0.05 mass % to 0.5 mass % of V and 0.01 mass % to 0.5 mass % of Sb, the second group consisting of one or more of 0.03 mass % to 0.5 mass % of Zr, 0.02 mass % to 0.2 mass % of Co, 0.0002 mass % to 0.002 mass % of Ca, 0.0002 mass % to 0.002 mass % of Mg, 0.0002 mass % to 0.005 mass % of B, 0.001 mass % to 0.01 mass % of REM, 0.0002 mass % to 0.01 mass % of Ga and 0.01 mass % to 0.5 mass % of Ta. 
     
     
         17 . The ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating according to  claim 14  or  15 , wherein the Sn content is 0.02 mass % or more and less than 0.05 mass % and/or 0.07 mass % or more and 0.3 mass % or less. 
     
     
         18 . The ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating according to  claim 16 , wherein the Ni content is 0.1 mass % or more and less than 0.5 mass %. 
     
     
         19 . An exhaust system component excellent in corrosion resistance after heating, the exhaust system component being made from a ferritic stainless steel, the ferritic stainless steel comprising:
 0.015 mass % or less of C;   0. 02 mass % or less of N;   0.03 mass % to 1.0 mass % of Si;   1.0 mass % or less of Mn;   0.04 mass % or less of P;   0.01 mass % or less of S;   10.5 mass % to 22.5 mass % of Cr;   0.02 mass % to 0.5 mass % of Sn;   0.003 mass % to 0.2 mass % of Al;   one or both of 0.03 mass % to 0.35 mass % of Ti and 0.03 mass % to 0.6 mass % of Nb; and   a remnant comprising Fe and inevitable impurities, wherein   a grain size number on a surface of the ferritic stainless steel is 6 or more, and   2 to 15 nm of a layer containing Sn at a concentration twice or more of a Sn concentration in a base material is formed on the ferritic stainless steel.   
     
     
         20 . The exhaust system component excellent in corrosion resistance after heating and being made from the ferritic stainless steel according to  claim 19 , wherein the ferritic stainless steel further comprises at least one of a first group and a second group, the first group consisting of one or more of 0.05 mass % to 1.5 mass % of Cu, 0.1 mass % to 1.2 mass % of Ni, 0.03 mass % to 3 mass % of Mo, 0.03 mass % to 1 mass % of W, 0.05 mass % to 0.5 mass % of V and 0.01 mass % to 0.5 mass % of Sb, the second group consisting of one or more of 0.03 mass % to 0.5 mass % of Zr, 0.02 mass % to 0.2 mass % of Co, 0.0002 mass % to 0.002 mass % of Ca, 0.0002 mass % to 0.002 mass % of Mg, 0.0002 mass % to 0.005 mass % of B, 0.001 mass % to 0.01 mass % of REM, 0.0002 mass % to 0.01 mass % of Ga and 0.01 mass % to 0.5 mass % of Ta. 
     
     
         21 . The exhaust system component excellent in corrosion resistance after heating and being made from the ferritic stainless steel according to  claim 19  or  20 , wherein the Sn content is 0.02 mass % or more and less than 0.05 mass % and/or 0.07 mass % or more and 0.3 mass % or less. 
     
     
         22 . The exhaust system component excellent in corrosion resistance after heating and being made from the ferritic stainless steel according to  claim 20 , wherein the Ni content is 0.1 mass % or more and less than 0.5 mass %. 
     
     
         23 . A manufacturing method of the ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating according to  claim 14  or  15 , wherein
 when the ferritic stainless steel is manufactured, a finish annealing temperature in a cold rolling step is 1030 degrees C. or less, and 
 when the ferritic stainless steel is cooled from a cold-rolled-sheet annealing temperature, a cooling rate in a temperature range from 800 to 600 degrees C. is less than 20 degrees C./s. 
 
     
     
         24 . A manufacturing method of the ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating according to  claim 14  or  15 , wherein
 when the ferritic stainless steel is manufactured, a finish annealing temperature in a cold rolling step is 1030 degrees C. or less, and 
 when the ferritic stainless steel is cooled from a cold-rolled-sheet annealing temperature, a cooling rate in a temperature range from 800 to 600 degrees C. is less than 5 degrees C./s. 
 
     
     
         25 . A manufacturing method of the exhaust system component excellent in corrosion resistance after heating and being made from the ferritic stainless steel according to  claim 19  or  20 , wherein,
 when the ferritic stainless steel forming the exhaust system component is manufactured, a finish annealing temperature in a cold rolling step is 1030 degrees C. or less, and 
 when the ferritic stainless steel is cooled from a cold-rolled-sheet annealing temperature, a cooling rate in a temperature range from 800 to 600 degrees C. is less than 20 degrees C./s. 
 
     
     
         26 . A manufacturing method of the exhaust system component excellent in corrosion resistance after heating and being made from the ferritic stainless steel according to  claim 19  or  20 , wherein
 when the ferritic stainless steel forming the exhaust system component is manufactured, a finish annealing temperature in a cold rolling step is 1030 degrees C. or less, and 
 when the ferritic stainless steel is cooled from a cold-rolled-sheet annealing temperature, a cooling rate in a temperature range from 800 to 600 degrees C. is less than 5 degrees C./s. 
 
     
     
         27 . The ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating according to  claim 16 , wherein the Sn content is 0.02 mass % or more and less than 0.05 mass % and/or 0.07 mass % or more and 0.3 mass % or less. 
     
     
         28 . The ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating according to  claim 17 , wherein the Ni content is 0.1 mass % or more and less than 0.5 mass %. 
     
     
         29 . The ferritic stainless steel for exhaust system components excellent in corrosion resistance after heating according to  claim 27 , wherein the Ni content is 0.1 mass % or more and less than 0.5 mass %. 
     
     
         30 . The exhaust system component excellent in corrosion resistance after heating and being made from the ferritic stainless steel according to  claim 21 , wherein the Ni content is 0.1 mass % or more and less than 0.5 mass %.