Ferritic stainless steel sheet, production method thereof, and ferritic stainless member
A ferritic stainless steel sheet is provided that has a predetermined chemical composition, wherein: a grain size number is 6.0 or more; the ferritic stainless steel sheet satisfies the formulas [A+B≥9.0] and [X+Y≥9.0] with respect to crystal orientation intensities of a ferrite phase obtained by X-ray diffraction; and the sheet thickness is 1.0 mm or more. A represents a {111}<112> crystal orientation intensity at a center portion of sheet thickness, B represents a {111}<112> crystal orientation intensity at a ⅛ portion of the sheet thickness, X represents a {322}<236> crystal orientation intensity at a center portion of sheet thickness, and Y represents a {322}<236> crystal orientation intensity at a ⅛ portion of the sheet thickness.
1. A ferritic stainless steel sheet having a chemical composition comprising, in mass %,
C: 0.001 to 0.020%,
Si: 0.02 to 1.5%,
Mn: 0.02 to 1.5%,
P: 0.01 to 0.05%,
S: 0.0001 to 0.01%,
Cr: 13.0 to 20.0%,
N: 0.001 to 0.030%,
Nb: 0.005% or more and less than 0.10%,
Ti: 0 to 0.30%,
W: 0 to 2.0%,
Sn: 0 to 0.50%,
Mg: 0 to 0.0100%,
B: 0 to 0.005%,
V: 0 to 1.0%,
Mo: 0 to 3.0%,
Al: 0 to 0.5%,
Cu: 0 to 2.0%,
Zr: 0 to 0.30%,
Co: 0 to 0.50%,
Sb: 0 to 0.50%,
REM: 0 to 0.05%,
Ni: 0 to 2.0%,
Ca: 0 to 0.0030%,
Ta: 0 to 0.10%,
Ga: 0 to 0.1%,
balance: Fe and unavoidable impurities,
wherein:
the chemical composition satisfies formula (i) described hereunder,
a grain size number is 6.0 or more,
the ferritic stainless steel sheet satisfies formula (ii) and (iii) described hereunder with respect to crystal orientation intensities of a ferrite phase obtained by X-ray diffraction,
and a sheet thickness is 1.0 mm or more;
Ti≥4(C+N) (i)
A+B≥ 9.0 (ii)
X+Y≥ 9.0 (iii)
where, each symbol of an element in the above formula (i) represents a content (mass %) of the corresponding element that is contained in the steel, with a value of a symbol being taken as zero if the corresponding element is not contained, and each symbol in the above formulas (ii) and (iii) is defined as follows:
A: a {111}<112> crystal orientation intensity at a center portion of the sheet thickness
B: a {111}<112> crystal orientation intensity at a ⅛ portion of the sheet thickness
X: a {322}<236> crystal orientation intensity at a center portion of the sheet thickness
Y: a {322}<236> crystal orientation intensity at a ⅛ portion of the sheet thickness.
2. The ferritic stainless steel sheet according to claim 1 , wherein the chemical composition contains, in mass %, one or more elements selected from:
W: 0.0005 to 2.0%,
Sn: 0.01 to 0.50%,
Mg: 0.0002 to 0.0100%,
B: 0.0002 to 0.005%,
V: 0.05 to 1.0%,
Mo: 0.2 to 3.0%,
Al: 0.003 to 0.5%,
Cu: 0.1 to 2.0%,
Zr: 0.05 to 0.30%,
Co: 0.05 to 0.50%,
Sb: 0.01 to 0.50%,
REM: 0.001 to 0.05%,
Ni: 0.1 to 2.0%,
Ca: 0.0001 to 0.0030%,
Ta: 0.01 to 0.10%, and
Ga: 0.0002 to 0.1%.
3. The ferritic stainless steel sheet according to claim 1 , wherein the ferritic steel sheet satisfies the formula (v) and formula (vi) described hereunder when a mean r-value is calculated by formula (iv) described hereunder:
r m =( r 0 +2 r 45 +r 90 )/4 (iv)
r m ≥1.50 (v)
r 45 ≥1.30 (vi)
where, each symbol in the above formulas is defined as follows:
r 0 : r-value in a rolling direction
r 45 : r-value in 45° direction with respect to the rolling direction
r 90 : r-value in 90° direction with respect to the rolling direction.
4. The ferritic stainless steel sheet according to claim 1 , wherein the ferritic stainless steel sheet is used for exhaust system parts.
5. A ferritic stainless steel member for exhaust system parts of an automobile or a motorcycle, comprising a ferritic stainless steel sheet according to claim 1 .
6. A method for producing the ferritic stainless steel sheet according to claim 1 comprising executing in sequence:
(a) a process of heating a slab having the chemical composition, and hot-rolling the slab to form a hot-rolled steel sheet under the condition that the finish rolling temperature is 900° C. or lower;
(b) a hot-rolled steel sheet pickling process of pickling the hot-rolled steel sheet without annealing, to obtain a pickled steel sheet;
(c) a cold rolling process of using a rolling mill having a roll diameter of 400 mm or more to subject the pickled steel sheet to cold rolling with a rolling reduction of 60% or more to obtain a cold-rolled steel sheet; and
(d) a process of annealing the cold-rolled steel sheet at an annealing temperature Tf (° C.) that satisfies formula (vii) described hereunder;
wherein:
in the process of (d), an average heating rate is:
set to 15° C./s or more in a temperature region from a starting temperature of heating to a starting temperature of recrystallization Ts (° C.) calculated by formula (viii) described hereunder, and
set to 10° C./s or less in a temperature region from the starting temperature of recrystallization Ts (° C.) to the annealing temperature Tf (° C.);
800≤ Tf (° C.)≤950 (vii)
700≤ Ts (° C.)≤ Tf (° C.)−100 (viii).
7. The ferritic stainless steel sheet according to claim 2 , wherein the ferritic steel sheet satisfies the formula (v) and formula (vi) described hereunder when a mean r-value is calculated by formula (iv) described hereunder:
r m =( r 0 +2 r 45 +r 90 )/4 (iv)
r m ≥1.50 (v)
r 45 ≥1.30 (vi)
where, each symbol in the above formulas is defined as follows:
r 0 : r-value in a rolling direction
r 45 : r-value in 45° direction with respect to the rolling direction
r 90 : r-value in 90° direction with respect to the rolling direction.
8. The ferritic stainless steel sheet according to claim 2 , wherein the ferritic stainless steel sheet is used for exhaust system parts.
9. The ferritic stainless steel sheet according to claim 3 , wherein the ferritic stainless steel sheet is used for exhaust system parts.
10. The ferritic stainless steel sheet according to claim 7 , wherein the ferritic stainless steel sheet is used for exhaust system parts.
11. A ferritic stainless steel member for exhaust system parts of an automobile or a motorcycle, comprising a ferritic stainless steel sheet according to claim 2 .
12. A ferritic stainless steel member for exhaust system parts of an automobile or a motorcycle, comprising a ferritic stainless steel sheet according to claim 3 .
13. A ferritic stainless steel member for exhaust system parts of an automobile or a motorcycle, comprising a ferritic stainless steel sheet according to claim 7 .
14. A method for producing the ferritic stainless steel sheet according to claim 2 comprising executing in sequence:
(a) a process of heating a slab having the chemical composition and hot-rolling the slab to form a hot-rolled steel sheet under the condition that the finish rolling temperature is 900° C. or lower;
(b) a hot-rolled steel sheet pickling process of pickling the hot-rolled steel sheet without annealing, to obtain a pickled steel sheet;
(c) a cold rolling process of using a rolling mill having a roll diameter of 400 mm or more to subject the pickled steel sheet to cold rolling with a rolling reduction of 60% or more to obtain a cold-rolled steel sheet; and
(d) a process of annealing the cold-rolled steel sheet at an annealing temperature Tf (° C.) that satisfies formula (vii) described hereunder;
wherein:
in the process of (d), an average heating rate is:
set to 15° C./s or more in a temperature region from a starting temperature of heating to a starting temperature of recrystallization Ts (° C.) calculated by formula (viii) described hereunder, and
set to 10° C./s or less in a temperature region from the starting temperature of recrystallization Ts (° C.) to the annealing temperature Tf (° C.);
800≤ Tf (° C.)≤950 (vii)
700≤ Ts (° C.)≤ Tf (° C.)−100 (viii).