Ferritic stainless steel sheet and production method thereof, and ferritic stainless member

1. A ferritic stainless steel sheet, comprising a chemical composition consisting of, in mass %,

C: 0.001 to 0.020%,

Si: 0.02 to 1.50%,

Mn: 0.02 to 1.50%,

P: 0.01 to 0.05%,

S: 0.0001 to 0.01%,

Cr: 10.0 to 25.0%,

Ti: 0.01 to 0.30%,

N: 0.001 to 0.030%,

Nb: 0 to less than 0.10%,

Sn: 0 to 0.500%,

Mg: 0 to 0.0100%,

B: 0 to 0.0050%,

V: 0 to 1.0%,

Mo: 0 to 3.0%,

W: 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%, and

the balance: Fe and unavoidable impurities,

wherein:

a grain size number is 6.0 or more,

the ferritic stainless steel sheet satisfies formula (i), formula (ii) and formula (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;

A+B≥ 12.0/ t   (i)

X+Y≥ 12.0/( t− 0.3)  (ii)

( X+Y )−( A+B )≤5.0  (iii)

where, each symbol in the above formulas is defined as follows:

t: sheet thickness in mm

A: a {111}<112> crystal orientation intensity at a center portion of sheet thickness

B: a {111}<112> crystal orientation intensity at a ¼ portion of the sheet thickness

X: a {322}<236> crystal orientation intensity at a center portion of sheet thickness

Y: a {322}<236> crystal orientation intensity at a ¼ portion of the sheet thickness.

2. The ferritic stainless steel sheet according to claim 1 , wherein a mean r-value calculated by formula (iv) described hereunder and a minimum r-value satisfy formula (v) and formula (vi) described hereunder:

r m =( r 0 +2 r 45 +r 90 )/4  (iv)

r m ≥2.0/ t   (v)

r min ≥2.0/( t+ 0.3)  (vi)

where, each symbol in the above formulas is defined as follows:

r m : mean r-value

r min : minimum r-value

t: sheet thickness in mm

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.

3. The ferritic stainless steel sheet according to claim 1 , wherein the chemical composition has, in mass %, one or more elements selected from:

Nb: more than 0.005% to less than 0.10%,

Sn: 0.01 to 0.500%,

Mg: 0.0002 to 0.0100%,

B: 0.0002 to 0.0050%,

V: 0.05 to 1.0%,

Mo: 0.2 to 3.0%,

W: 0.1 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%.

4. The ferritic stainless steel sheet according to claim 1 , wherein the ferritic stainless steel sheet is used for an exhaust system component.

5. A ferritic stainless member for an exhaust system component of an automobile or a motorcycle, comprising the ferritic stainless steel sheet according to claim 1 .

6. The ferritic stainless steel sheet according to claim 2 , wherein the chemical composition has, in mass %, one or more elements selected from:

Nb: more than 0.005% to less than 0.10%,

Sn: 0.01 to 0.500%,

Mg: 0.0002 to 0.0100%,

B: 0.0002 to 0.0050%,

V: 0.05 to 1.0%,

Mo: 0.2 to 3.0%,

W: 0.1 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%.

7. The ferritic stainless steel sheet according to claim 2 , wherein the ferritic stainless steel sheet is used for an exhaust system component.

8. A ferritic stainless member for an exhaust system component of an automobile or a motorcycle, comprising the ferritic stainless steel sheet according to claim 2 .

9. The ferritic stainless steel sheet according to claim 3 , wherein the ferritic stainless steel sheet is used for an exhaust system component.

10. A ferritic stainless member for an exhaust system component of an automobile or a motorcycle, comprising the ferritic stainless steel sheet according to claim 3 .

11. The ferritic stainless steel sheet according to claim 6 , wherein the ferritic stainless steel sheet is used for an exhaust system component.

12. A ferritic stainless member for an exhaust system component of an automobile or a motorcycle, comprising the ferritic stainless steel sheet according to claim 6 .

13. 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 a chemical composition, and hot-rolling the slab to form a hot-rolled steel sheet;

(b) a hot-rolled steel sheet pickling process of pickling the hot-rolled steel sheet without subjecting the hot-rolled steel sheet to 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 until reaching the annealing temperature Tf (° C.) 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)

Ts (° C.)=700+(1− X/ 100)×130  (viii)

where, a symbol in the above formula is defined as follows:

X: rolling reduction in cold rolling (%);

wherein the chemical composition of the slab consists of, in mass %,

C: 0.001 to 0.020%,

Si: 0.02 to 1.50%,

Mn: 0.02 to 1.50%,

P: 0.01 to 0.05%,

S: 0.0001 to 0.01%,

Cr: 10.0 to 25.0%,

Ti: 0.01 to 0.30%,

N: 0.001 to 0.030%,

Nb: 0 to less than 0.10%,

Sn: 0 to 0.500%,

Mg: 0 to 0.0100%,

B: 0 to 0.0050%,

V: 0 to 1.0%,

Mo: 0 to 3.0%,

W: 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%, and

the balance: Fe and unavoidable impurities.

14. A method for producing the ferritic stainless steel sheet according to claim 3 , comprising executing in sequence:

(a) a process of heating a slab having a chemical composition, and hot-rolling the slab to form a hot-rolled steel sheet;

(b) a hot-rolled steel sheet pickling process of pickling the hot-rolled steel sheet without subjecting the hot-rolled steel sheet to 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 until reaching the annealing temperature Tf (° C.) 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)

Ts (° C.)=700+(1− X/ 100)×130  (viii)

where, a symbol in the above formula is defined as follows:

X: rolling reduction in cold rolling (%);

wherein the chemical composition of the slab consists of, in mass %,

C: 0.001 to 0.020%,

Si: 0.02 to 1.50%,

Mn: 0.02 to 1.50%,

P: 0.01 to 0.05%,

S: 0.0001 to 0.01%,

Cr: 10.0 to 25.0%,

Ti: 0.01 to 0.30%,

N: 0.001 to 0.030%,

one or more elements selected from:

Nb: more than 0.005% to less than 0.10%,

Sn: 0.01 to 0.500%,

Mg: 0.0002 to 0.0100%,

B: 0.0002 to 0.0050%,

V: 0.05 to 1.0%,

Mo: 0.2 to 3.0%,

W: 0.1 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%, and

the balance: Fe and unavoidable impurities.