Ferritic stainless steel

A ferritic stainless steel comprising a composition consisting of, in mass %,

• C:
• 0.003 to 0.020%,
• Si:
• 0.05 to 0.60%,
• Mn:
• 0.05 to 0.50%,
• P:
• 0.04% or less,
• S:
• 0.02% or less,
• Cr:
• 17.0 to 24.0%,
• Ni:
• 0.20 to 0.80%,
• Cu:
• 0.01 to 0.80%,
• Mo:
• 1.32 to 2.50%,
• Al:
• 0.001 to 0.015%,
• Nb:
• 0.25 to 0.60%,
• N:
• 0.020% or less,
• optionally one or more of:
• Co:
• 0.01 to 0.50%,
• Ti:
• 0.01 to 0.10%,
• V:
• 0.01 to 0.20%,
• Zr:
• 0.01 to 0.10%,
• Mg:
• 0.0005 to 0.0050%,
• Ca:
• 0.0003 to 0.0030%,
• B:
• 0.0003 to 0.0030%,
• one or more REMs (rare earth metals):
• 0.001 to 0.100% and,
• Sb:
• 0.001 to 0.100%,
• with the balance of Fe and incidental impurities, satisfying formula (1) below and formula (2) below,
• Cu+Mo≥0.30% (1)
• 4Ni−(Si+Mn)≥0% (2)
• wherein Cu and Mo in formula (1) and Ni, Si, and Mn in formula (2) each represent a content, in mass %, of a corresponding element,
• wherein when a steel sheet formed from the ferritic stainless steel has a Ni-containing brazing filler metal applied to a surface that is heated in a nitrogen carrier gas atmosphere at 1200° C. with 1 Torr for 10 minutes and then cooled to room temperature, a ratio of an equivalent circular diameter of the brazing filler metal after the heating to an equivalent circular diameter of the brazing filler metal before the heating is 150% or greater, and
• wherein when a test piece of 20 mm square is cut from a portion of the steel sheet formed from the ferritic stainless steel free of the brazing filler metal after brazing, and when the test piece, except for a measurement surface of 11 mm square, is covered with a sealing material, and this covered test piece is immersed in a 3.5% NaCl solution at 30° C., a pitting potential is 150 mV or greater.

A ferritic stainless steel comprising a composition containing, in mass %,

• C:
• 0.003 to 0.020%,
• Si:
• 0.05 to 0.60%,
• Mn:
• 0.05 to 0.50%,
• P:
• 0.04% or less,
• S:
• 0.02% or less,
• Cr:
• 17.0 to 24.0%,
• Ni:
• 0.20 to 0.80%,
• Cu:
• 0.01 to 0.80%,
• Mo:
• 1.32 to 2.50%,
• Al:
• 0.001 to 0.015%,
• Nb:
• 0.25 to 0.60%,
• W:
• 0.01 to 0.50%, and
• N:
• 0.020% or less, with a balance of Fe and incidental impurities, the composition excluding Sn and satisfying formula (1) below and formula (2) below,
• Cu+Mo≥0.30% (1)
• 4Ni−(Si+Mn)≥0% (2)
• wherein Cu and Mo in formula (1) and Ni, Si, and Mn in formula (2) each represent a content, in mass %, of a corresponding element,
• wherein when a steel sheet formed from the ferritic stainless steel has a Ni-containing brazing filler metal applied to a surface that is heated in a nitrogen carrier gas atmosphere at 1200° C. with 1 Torr for 10 minutes and then cooled to room temperature, a ratio of an equivalent circular diameter of the brazing filler metal after the heating to an equivalent circular diameter of the brazing filler metal before the heating is 150% or greater, and
• wherein when a test piece of 20 mm square is cut from a portion of the steel sheet formed from the ferritic stainless steel free of the brazing filler metal after brazing, and when the test piece, except for a measurement surface of 11 mm square, is covered with a sealing material, and this covered test piece is immersed in a 3.5% NaCl solution at 30° C., a pitting potential is 150 mV or greater.