Ferritic-austenitic duplex stainless steel sheet

A ferritic-austenitic duplex stainless steel sheet having a chemical composition comprising, in mass %,

• C:
• 0.10% or less,
• Si:
• 1.0% or less,
• Mn:
• 2.0 to 7.0%,
• P:
• 0.07% or less,
• S:
• 0.030% or less,
• Cr:
• 18.0 to 24.0%,
• Ni:
• 0.1 to 3.0%,
• Mo:
• 0.1 to 1.0%,
• Cu:
• 0.1 to 3.0%,
• Al:
• 0.003 to 0.10%,
• Zr:
• 0.03 to 0.50%, and
• N:
• 0.15 to 0.30%, with the balance being Fe and incidental impurities, the chemical composition satisfying formula (1) below and formula (2) below,
• N—Zr/6.5≥0.15% (1)
• N—Zr/6.5≤0.23% (2)
• where, in formula (1) and formula (2), N represents a content (mass %) of the corresponding chemical element N and Zr represents a content (mass %) of the corresponding chemical element Zr and,
• wherein when a machined edge face of each of two ferritic-austenitic duplex steel sheets, each having a thickness of 4.0 mm, are butt-welded together, along a groove, by TIG welding, and then entire cross sections of thea weld metal zone and thea weld heat affected zone (HAZ) are examined, no blowholes 3 μm or greater in diameter are present,
• where the groove is an I-type groove and,
• where the welding conditions are as follows:
• current, 220 A;
• voltage, 15 V;
• welding speed, 200 mm/min;
• welding wire, none;
• shielding gas, Ar;
• gas flow rate, 15 1/min for both front and back sides.