Ferrite-based stainless steel plate, steel pipe, and production method therefor

Abstract

A ferritic stainless steel sheet and a steel pipe as a material suitable for a heat-resistant component that is required to have especially excellent formability are provided. The ferritic stainless steel sheet contains 10 to 20 mass % of Cr and a predetermined amount of C, Si, Mn, P, S, Al and one or both of Ti and Nb, a {111}-orientation intensity being 5 or more and {411}-orientation intensity being less than 3 at a portion in the vicinity of a sheet-thickness central portion of the ferritic stainless steel sheet. Further, with similar composition and by setting {111}<110>-orientation intensity at 4.0 or more and {311}<136>-orientation intensity at less than 3.0, a relationship r m ≧−1.0t+3.0 (t (mm): sheet thickness, r m : average r-value) is satisfied, thereby providing a ferritic stainless steel sheet and a steel pipe with excellent formability.

1 . A ferritic stainless steel sheet with excellent formability, comprising:
 0.001 to 0.03 mass % of C;
 0.01 to 0.9 mass % of Si; 
 0.01 to 1.0 mass % of Mn; 
 0.01 to 0.05 mass % of P; 
 0.0003 to 0.01 mass % of S; 
 10 to 20 mass % of Cr; 
 0.001 to 0.03 mass % of N; 
 0.05 to 1.0 mass % of one or both of Ti and Nb; 
 and a residual amount of Fe and inevitable impurities, wherein 
 {111}-orientation intensity of a portion in a vicinity of a sheet-thickness central portion is 5 or more and {411}-orientation intensity of the portion in the vicinity of the sheet-thickness central portion is less than 3. 
   
     
     
         2 . The ferritic stainless steel sheet with excellent formability according to  claim 1 , wherein a Cr content in the ferritic stainless steel sheet is 10.5 mass % or more and less than 14 mass %. 
     
     
         3 . The ferritic stainless steel sheet with excellent formability according to  claim 1  or  2 , further comprising one or more of elements selected from the group consisting of: 0.0002 to 0.0030 mass % of B; 0.005 to 0.3 mass % of Al, 0.1 to 1.0 mass % of Ni, 2.0 mass % or less of Mo, 0.1 to 3.0 mass % of Cu, 0.05 to 1.0 mass % of V, 0.0002 to 0.0030 mass % of Ca, 0.0002 to 0.0030 mass % of Mg, 0.01 to 0.3 mass % of Zr, 0.01 to 3.0 mass % of W, 0.01 to 0.3 mass % of Co, 0.003 to 0.50 mass % of Sn, 0.005 to 0.50 mass % of Sb, 0.001 to 0.20 mass % of REM, 0.0002 to 0.3 mass % of Ga, 0.001 to 1.0 mass % of Ta, and 0.001 to 1.0 mass % of Hf. 
     
     
         4 . The ferritic stainless steel sheet with excellent formability according to  claim 3 , wherein a Mo content in the ferritic stainless steel sheet is less than 0.5 mass %. 
     
     
         5 . The ferritic stainless steel sheet with excellent formability according to  claim 1  or  2 , wherein a grain size number is 5.5 or more. 
     
     
         6 . A manufacturing method of a ferritic stainless steel sheet with excellent formability, the method comprising:
 hot-rolling a stainless steel slab of a composition according to  claim 1  at a slab heating temperature in a range from 1100 to 1200 degrees C., the hot-rolling being a continuous rolling comprising rough rolling steps performed for (n) pass numbers and a finish rolling, at least (n−2) numbers of the rough rolling steps being performed under a 30% or more of rolling reduction and at a rough rolling end temperature of 1000 degrees C. or more, finishing temperature of the finish rolling being 900 degrees C. or less;   winding the stainless steel slab at a temperature of 700 degrees C. or less; and   without performing a annealing of hot-rolled sheet, subjecting the stainless steel slab to:
 intermediate cold rolling in which the stainless steel slab is cold-rolled at least once using a roller with a diameter of 400 mm or more and at a rolling reduction of 40% or more; 
 intermediate annealing in which the stainless steel slab is heated at a temperature in a range from 820 to 880 degrees C.; 
 finish cold rolling; and 
 finish annealing in which the stainless steel slab is heated at a temperature in a range from 880 to 950 degrees C. 
   
     
     
         7 . The manufacturing method of ferritic stainless steel sheet with excellent formability according to  claim 6 , wherein, in the intermediate annealing, a grain size number is made to be 6 or more and a {111}-orientation intensity at a portion in the vicinity of the sheet-thickness center layer is made to be 3 or more. 
     
     
         8 . The manufacturing method of ferritic stainless steel sheet with excellent formability according to  claim 6 , wherein, in the final annealing, a grain size number is made to be 5.5 or more. 
     
     
         9 . A ferritic stainless steel pipe with excellent formability, wherein the ferritic stainless steel pipe is made from a material in a form of the stainless steel sheet according to  claim 1  or  2 . 
     
     
         10 . A ferritic stainless steel sheet for an automobile exhaust component, wherein the ferritic stainless steel sheet for an automobile exhaust component is made from a material in a form of the stainless steel sheet according to  claim 1  or  2 . 
     
     
         11 . A ferritic stainless steel sheet with excellent formability, comprising:
 0.03 mass % or less of C;   0.03 mass % or less of N;   1.0 mass % or less of Si;   3.0 mass % or less of Mn;   0.04 mass % or less of P;   0.0003 to 0.0100 mass % of S;   10 to 30 mass % of Cr;   0.300 mass % or less of Al;   one or both of 0.05 to 0.30 mass % of Ti and 0.01 to 0.50 mass % of Nb, a sum of Ti and Nb being in a range from smaller one of 8(C+N) and 0.05 to 0.75 mass %   and a residual amount of Fe and inevitable impurities, wherein   {111}<110>-orientation intensity is 4.0 or more and {311}<136>-orientation intensity is less than 3.0.   
     
     
         12 . The ferritic stainless steel sheet with excellent formability according to  claim 11 , further comprising one or more of elements selected from the group consisting of: 0.0002 to 0.0030 mass % of B, 0.1 to 1.0 mass % of Ni, 0.1 to 2.0 mass % of Mo, 0.1 to 3.0 mass % of Cu, 0.05 to 1.00 mass % of V, 0.0002 to 0.0030 mass % of Ca, 0.0002 to 0.0030 mass % of Mg, 0.005 to 0.500 mass % of Sn, 0.01 to 0.30 mass % of Zr, 0.01 to 3.0 mass % of W, 0.01 to 0.30 mass % of Co, 0.005 to 0.500 mass % of Sb, 0.001 to 0.200 mass % of REM, 0.0002 to 0.3 mass % of Ga, 0.001 to 1.0 mass % of Ta, and 0.001 to 1.0 mass % of Hf. 
     
     
         13 . The ferritic stainless steel sheet with excellent formability according to  claim 11  or  12 , wherein a grain size number is 6 or more. 
     
     
         14 . The ferritic stainless steel sheet with excellent formability according to  claim 11  or  12 , wherein, when a plate thickness is represented by t (mm) and an average r-value is represented by r m , r m  satisfies a relationship of r m ≧−1.0t+3.0. 
     
     
         15 . The ferritic stainless steel sheet with excellent formability according to  claim 11  or  12 , wherein the ferritic stainless steel pipe is suitable for use in an automobile component or a motorcycle component. 
     
     
         16 . The ferritic stainless steel sheet with excellent formability according to  claim 11  or  12 , wherein the ferritic stainless steel pipe is suitable for use in an automobile exhaust pipe, fuel tank or a fuel pipe. 
     
     
         17 . A manufacturing method of a ferritic stainless steel sheet with excellent formability, the method comprising:
 hot-rolling a stainless steel slab of a composition according to  claim 11  or  12 , the hot-rolling comprising rough rolling and finish rolling, the rough rolling being performed at a slab heating temperature in a range from 1100 to 1200 degrees C., the finish rolling being performed at a start temperature of 900 degrees C. or more and an end temperature of 800 degrees C. or more so that a difference between the start temperature and the end temperature is 200 degrees C. or less;   winding the stainless steel slab at a temperature of 600 degrees C. or more; and   subsequently subjecting the stainless steel slab to intermediate cold rolling, intermediate annealing, finish cold rolling, and finish annealing without applying annealing of hot-rolled sheet, wherein   the cold rolling is at least once performed at 40% or more of rolling reduction using a roller having a diameter of 400 mm or more,   the stainless steel slab is heated to a temperature in a range from 800 to 880 degrees C. in the intermediate annealing,   the stainless steel slab is cold-rolled in the finish cold rolling at a rolling reduction of 60% or more, and   in the final annealing, the stainless steel slab is heated to a temperature in a range from 850 to 950 degrees C.   
     
     
         18 . The manufacturing method of ferritic stainless steel sheet with excellent formability according to  claim 17 , wherein a texture immediately before completion of recrystallization or a minute texture of a grain size number of 6 or more is obtained in the intermediate annealing. 
     
     
         19 . A ferritic stainless steel pipe with excellent formability, wherein the ferritic stainless steel pipe is made from a material in a form of the stainless steel sheet according to  claim 11  or  12 . 
     
     
         20 . The ferritic stainless steel sheet with excellent formability according to  claim 3 , wherein a grain size number is 5.5 or more. 
     
     
         21 . The ferritic stainless steel sheet with excellent formability according to  claim 4 , wherein a grain size number is 5.5 or more. 
     
     
         22 . A ferritic stainless steel pipe with excellent formability, wherein the ferritic stainless steel pipe is made from a material in a form of the stainless steel sheet according to  claim 3 . 
     
     
         23 . A ferritic stainless steel pipe with excellent formability, wherein the ferritic stainless steel pipe is made from a material in a form of the stainless steel sheet according to  claim 4 . 
     
     
         24 . A ferritic stainless steel sheet for an automobile exhaust component, wherein the ferritic stainless steel sheet for an automobile exhaust component is made from a material in a form of the stainless steel sheet according to  claim 3 . 
     
     
         25 . A ferritic stainless steel sheet for an automobile exhaust component, wherein the ferritic stainless steel sheet for an automobile exhaust component is made from a material in a form of the stainless steel sheet according to  claim 4 . 
     
     
         26 . The ferritic stainless steel sheet with excellent formability according to  claim 13 , wherein, when a plate thickness is represented by t (mm) and an average r-value is represented by r m , r m  satisfies a relationship of r m ≧−1.0t+3.0.