Steel sheet
A steel sheet has a predetermined chemical composition, and a surface exhibits an absorption peak at which a reflectance is not less than 50% nor more than 85% in a range of wave numbers of 1200 cm −1 to 1300 cm −1 by a Fourier transform-infrared spectroscopy analysis by a reflection absorption spectrometry method, and does not exhibit an absorption peak in a range of wave numbers of 1000 cm −1 to 1100 cm −1 , or exhibits an absorption peak at which a reflectance is 85% or more in the range of wave numbers of 1000 cm −1 to 1100 cm −1 , wherein Ni of 3 mg/m 2 to 100 mg/m 2 adheres to the surface.
1. A steel sheet comprising
a chemical composition represented by, in mass %,
C: 0.050% to 0.400%,
Si: 0.10% to 2.50%,
Mn: 1.20% to 3.50%,
P: 0.100% or less,
Al: 1.200% or less,
N: 0.0100% or less,
Cr, Mo, Ni and Cu: 0.00% to 1.20% in total,
Nb, Ti and V: 0.000% to 0.200% in total,
B: 0.0000% to 0.0075%,
Ca, Mg, Hf, Zr, Sb and REM: 0.0000% to 0.1000% in total, and
the balance: Fe and impurities, in which
a surface
exhibits an absorption peak at which a reflectance is not less than 50% nor more than 85% in a range of wave numbers of 1200 cm −1 to 1300 cm −1 by a Fourier transform-infrared spectroscopy analysis by a reflection absorption spectrometry method, and
exhibits an absorption peak at which a reflectance is either 0% or 85% or more in the range of wave numbers of 1000 cm −1 to 1100 cm −1 , wherein
Ni of 40 mg/m 2 to 100 mg/m 2 adheres to the surface, and
a thickness of a decarburized layer is 3 μm or less.
2. The steel sheet according to claim 1 , wherein the surface exhibits an absorption peak at which a reflectance is not less than 60% nor more than 85% in the range of wave numbers of 1200 cm −1 to 1300 cm −1 by the Fourier transform-infrared spectroscopy analysis by the reflection absorption spectrometry method.