Ferrite-austenite stainless steel sheet excellent in ridging resistance and workability and process for manufacturing the same

1. A ferrite-austenite stainless steel sheet having excellent ridging resistance and workability, the steel sheet comprising: in terms of mass %,

C: 0.1% or less;

Cr: 17 to 25%;

Si: 1% or less;

Mn: 3.7% or less;

N: 0.06% to less than 0.15%, and

a balance of Fe and unavoidable impurities;

wherein the steel sheet has a two-phase structure consisting of a ferrite phase and an austenite phase,

a volume fraction of the austenite phase is in a range of 15 to 70%, and

in a sheet plane (ND) of a center of a sheet thickness, grains of the ferrite phase having a crystal orientation satisfying ND//{111}±10° and grains of the ferrite phase having a crystal orientation satisfying ND//{101}±10° are present in a total amount of 10% by area or more.

2. A ferrite-austenite stainless steel sheet having excellent ridging resistance and workability, the steel sheet comprising: in terms of mass %,

C: 0.1% or less;

Cr: 17 to 25%;

Si: 1% or less;

Mn: 3.7% or less;

Ni: 0.6 to 3%;

Cu: 0.1 to 3%;

N: 0.06% to less than 0.15%, and

a balance of Fe and unavoidable impurities,

wherein the steel sheet has a two-phase structure consisting of a ferrite phase and an austenite phase,

a volume fraction of the austenite phase is in a range of 15 to 70%, and

in a sheet plane (ND) of a center of a sheet thickness, grains of the ferrite phase having a crystal orientation satisfying ND//{111}±10° and grains of the ferrite phase having a crystal orientation satisfying ND//{101}±10° are present in a total amount of 10% by area or more.

3. The ferrite-austenite stainless steel sheet having excellent ridging resistance and workability according to claim 2 ,

the steel sheet further comprising, in terms of mass %, one or more elements selected from the group consisting of Al: 0.2% or less, Mo: 1% or less, Ti: 0.5% or less, Nb: 0.5% or less, B: 0.01% or less, Ca: 0.01% or less, Mg: 0.01% or less, and rare-earth elements: 0.5% or less.

4. The ferrite-austenite stainless steel sheet having excellent ridging resistance and workability according to any one of claims 1 to 3 ,

wherein a uniform elongation measured by a tensile testing is in a range of 30% or more.

5. A process for manufacturing a ferrite-austenite stainless steel sheet having excellent ridging resistance and workability, the process comprising:

heating a stainless steel slab at a temperature within a range of 1150 to 1300° C., the stainless steel slab comprising C: 0.1% or less; Cr: 17 to 25%; Si: 1% or less; Mn: 3.7% or less; N: 0.06% to less than 0.15%, and a balance of Fe and unavoidable impurities,

optionally further comprising Ni: 0.6 to 3% and Cu: 0.1 to 3%, and

optionally further comprising one or more elements selected from the group consisting of Al: 0.2% or less, Mo: 1% or less, Ti: 0.5% or less, Nb: 0.5% or less, B: 0.01% or less, Ca: 0.01% or less, Mg: 0.01% or less, and rare-earth elements: 0.5% or less;

subjecting the heated stainless steel slab to a hot rolling including a hot rough rolling and a hot finish rolling after the hot rough rolling to form a hot-rolled steel sheet; and

annealing the hot-rolled steel sheet,

wherein, in the hot rough rolling, a multi-pass rolling is carried out under conditions where a rolling start temperature is in a range of 1150° C. or higher, a rolling end temperature is in a range of 1050° C. or higher, and a pass interval is in a range of 2 seconds or more to 60 seconds or less, and

thereby providing a steel sheet having a two-phase structure consisting of a ferrite phase and an austenite phase, in which a volume fraction of the austenite phase is in a range of 15 to 70%, and in a sheet plane (ND) of a center of a sheet thickness, grains of the ferrite phase having a crystal orientation satisfying ND//{111}±10° and grains of the ferrite phase having a crystal orientation satisfying ND//{101}±10° are present in a total amount of 10% by area or more.

6. The process for manufacturing a ferrite-austenite stainless steel sheet having excellent ridging resistance and workability according to claim 5 ,

wherein, in the hot rough rolling, a number of passes having a rolling reduction rate of 20% or more is ½ or more of a total number of passes, and

a rolling reduction rate of a pass having a highest rolling reduction rate is in a range of 50% or more, or a total of rolling reduction rates of two passes having high rolling reduction rates is in a range of 50% or more.

7. The process for manufacturing a ferrite-austenite stainless steel sheet having excellent ridging resistance and workability according to claim 5 ,

wherein an end temperature of the hot finish rolling is set to be in a range of 900° C. or higher.

8. The process for manufacturing a ferrite-austenite stainless steel sheet having excellent ridging resistance and workability according to claim 5 , the process further comprising:

subjecting the annealed hot-rolled steel sheet to one pass of a cold rolling at a rolling reduction rate of 50% or more, or two or more passes of a cold rolling with an intermediate annealing therebetween under conditions where a total of rolling reduction rates is in a range of 50% or more, thereby forming a cold-rolled steel sheet; and

subjecting the cold-rolled steel sheet to a finish annealing at a temperature within a range of 900 to 1200° C.

9. The process for manufacturing a ferrite-austenite stainless steel sheet having excellent ridging resistance and workability according to claim 6 ,

wherein an end temperature of the hot finish rolling is set to be in a range of 900° C. or higher.

10. The process for manufacturing a ferrite-austenite stainless steel sheet having excellent ridging resistance and workability according to claim 6 , the process further comprising:

subjecting the annealed hot-rolled steel sheet to one pass of a cold rolling at a rolling reduction rate of 50% or more, or two or more passes of a cold rolling with an intermediate annealing therebetween under conditions where a total of rolling reduction rates is in a range of 50% or more, thereby forming a cold-rolled steel sheet; and

subjecting the cold-rolled steel sheet to a finish annealing at a temperature within a range of 900 to 1200° C.

11. The process for manufacturing a ferrite-austenite stainless steel sheet having excellent ridging resistance and workability according to claim 7 , the process further comprising:

subjecting the annealed hot-rolled steel sheet to one pass of a cold rolling at a rolling reduction rate of 50% or more, or two or more passes of a cold rolling with an intermediate annealing therebetween under conditions where a total of rolling reduction rates is in a range of 50% or more, thereby forming a cold-rolled steel sheet; and

subjecting the cold-rolled steel sheet to a finish annealing at a temperature within a range of 900 to 1200° C.