Ferrite-based stainless steel with high resistance to corrosiveness caused by exhaust gas and condensation and high brazing properties and method for manufacturing same

Abstract

This ferritic stainless steel contains, by mass %, C: 0.001% to 0.030%; Si: 0.01% to 1.00%, Mn: 0.01% to 2.00%, P: 0.050% or less, S: 0.0100% or less, Cr: 11.0% to 30.0%, Mo: 0.01% to 3.00%, Ti: 0.001% to 0.050%, Al: 0.001% to 0.030%, Nb: 0.010% to 1.000%, and N: 0.050% or less, with a remainder being Fe and inevitable impurities, wherein an amount of Al, an amount of Ti, and an amount of Si (mass %) satisfy Al/Ti≧8.4Si−0.78.

1 .- 10 . (canceled) 
     
     
         11 . A ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability, comprising, by mass %:
 C: 0.001% to 0.030%;   Si: 0.01% to 1.00%;   Mn: 0.01% to 2.00%;   P: 0.050% or less;   S: 0.0100% or less;   Cr: 11.0% to 30.0%;   Mo: 0.01% to 3.00%;   Ti: 0.001% to 0.050%;   Al: 0.001% to 0.015%;   Nb: 0.010% to 1.000%;   N: 0.050% or less; and   Sn: 0.005% to 0.500%,   with a remainder being Fe and inevitable impurities,   wherein an amount of Al, an amount of Ti, and an amount of Si (mass %) satisfy Al/Ti≧8.4Si−0.78.   
     
     
         12 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 11 , further comprising, by mass %, any one or more of:
 Ni: 0.01% to 0.25%;   Cu: 0.050% to 1.500%;   W: 0.010% to 1.000%;   V: 0.010% to 0.300%,   Sb: 0.0050% to 0.5000%, and   Mg: 0.0001% to 0.0030%.   
     
     
         13 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 11 , further comprising, by mass %, any one or more of:
 B: 0.0002% to 0.0030%;   Ca: 0.0002% to 0.0100%;   Zr: 0.010% to 0.300%;   Co: 0.010% to 0.300%,   Ga: 0.0001% to 0.0100%,   Ta: 0.0001% to 0.0100%, and   REM: 0.001% to 0.200%.   
     
     
         14 . A ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability, comprising, by mass %:
 C: 0.001% to 0.030%;   Si: 0.01% to 1.00%;   Mn: 0.01% to 2.00%;   P: 0.050% or less;   S: 0.0100% or less;   Cr: 11.0% to 30.0%;   Mo: 0.01% to 3.00%;   Ti: 0.001% to 0.050%;   Al: 0.001% to 0.030%;   Nb: 0.010% to 1.000%; and   N: 0.050% or less,   with a remainder being Fe and inevitable impurities,   wherein an amount of Al, an amount of Ti, and an amount of Si (mass %) satisfy Al/Ti≧8.4Si−0.78,   when a rolling direction is represented by an L direction, a direction perpendicular to the rolling direction is represented by a C direction, a direction inclined at 450 with respect to the rolling direction is represented by a V direction, and arithmetic average roughness values of a steel surface in the respective directions are respectively represented by Ra L , Ra C , and Ra V  (unit: μm), (Ra L +Ra C +2Ra V )/4≦0.50 and |(Ra L +Ra C −2Ra V )/2|≦0.10 are satisfied.   
     
     
         15 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 14 , further comprising, by mass %, any one or more of:
 Ni: 0.01% to 3.00%;   Cu: 0.050% to 1.500%;   W: 0.010% to 1.000%;   V: 0.010% to 0.300%,   Sn: 0.005% to 0.500%,   Sb: 0.0050% to 0.5000%, and   Mg: 0.0001% to 0.0030%.   
     
     
         16 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 14 , further comprising, by mass %, any one or more of:
 B: 0.0002% to 0.0030%;   Ca: 0.0002% to 0.0100%;   Zr: 0.010% to 0.300%;   Co: 0.010% to 0.300%,   Ga: 0.0001% to 0.0100%,   Ta: 0.0001% to 0.0100%, and   REM: 0.001% to 0.200%.   
     
     
         17 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 14 ,
 wherein an amount of change in grain size number (GSN) before and after a thermal treatment at 1,150° C. for 10 minutes in a vacuum atmosphere of 50 Pa or lower is 5.0 or less.   
     
     
         18 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 11  which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments. 
     
     
         19 . A method for manufacturing a ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability, the method comprising:
 a step of cold-rolling a steel having the chemical components according to  claim 14 ,   wherein, in the cold rolling step, in a final pass, the steel is rolled using a roll with a roll roughness of #60 or more under conditions where a rolling reduction in the final pass is set to 15.0% or less and a cold rolling speed in the final pass is set to 800 m/min or less.   
     
     
         20 . The method for manufacturing a ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 19 , the method further comprising:
 a step of annealing a cold-rolled steel sheet,   wherein the annealing step includes: a step of maintaining the steel sheet at a temperature of 650° C. to 950° C. for 5.0 s or longer; and a step of maintaining the steel sheet at a temperature of 950° C. to 1,050° C. for 80.0 s or shorter.   
     
     
         21 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 12 , further comprising, by mass %, any one or more of:
 B: 0.0002% to 0.0030%;   Ca: 0.0002% to 0.0100%;   Zr: 0.010% to 0.300%;   Co: 0.010% to 0.300%,   Ga: 0.0001% to 0.0100%,   Ta: 0.0001% to 0.0100%, and   REM: 0.001% to 0.200%.   
     
     
         22 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 15 , further comprising, by mass %, any one or more of:
 B: 0.0002% to 0.0030%;   Ca: 0.0002% to 0.0100%;   Zr: 0.010% to 0.300%;   Co: 0.010% to 0.300%,   Ga: 0.0001% to 0.0100%,   Ta: 0.0001% to 0.0100%, and   REM: 0.001% to 0.200%.   
     
     
         23 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 15 ,
 wherein an amount of change in grain size number (GSN) before and after a thermal treatment at 1,150° C. for 10 minutes in a vacuum atmosphere of 50 Pa or lower is 5.0 or less.   
     
     
         24 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 16 ,
 wherein an amount of change in grain size number (GSN) before and after a thermal treatment at 1,150° C. for 10 minutes in a vacuum atmosphere of 50 Pa or lower is 5.0 or less.   
     
     
         25 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 12  which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments. 
     
     
         26 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 13  which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments. 
     
     
         27 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 14  which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments. 
     
     
         28 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 15  which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments. 
     
     
         29 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 16  which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments. 
     
     
         30 . The ferritic stainless steel with high corrosion resistance against exhaust gas condensate water and high brazeability according to  claim 17  which is used in automobile mufflers, exhaust heat recovery devices, and EGR coolers that are automobile parts exposed to exhaust gas-condensate environments.