There is provided a steel for solid oxide fuel cells which contains more than 0 and not more than 0.05 mass % of C, 0.05 mass % or less of N, 0.01 mass % or less of O, 0.2 mass % or less of Al, 0.15 mass % or less of Si, 0.1 to 1.0 mass % of Mn, 20.0 to 25.0 mass % of Cr, more than 0 mass % and not more than 1.0 mass % of Ni, 0.02 to 0.12 mass % of La, 0.1 to 0.5 mass % of Zr, 0.15 to 0.5 mass % of La+Zr, and Fe and impurities as a remainder. The following relational formula is satisfied, and an Fe and Zr-containing intermetallic compound viewed in a ferrite matrix is 1.1 % or less in terms of a visual field area ratio
5(7C+6N)/(7−4(7C+6N))≤Zr≤41(7C+6N)/(7+66(7C+6N)).

There is provided a steel for solid oxide fuel cells which contains more than 0 and not more than 0.05 mass % of C, 0.05 mass % or less of N, 0.01 mass % or less of O, 0.2 mass % or less of Al, 0.15 mass % or less of Si, 0.1 to 1.0 mass % of Mn, 20.0 to 25.0 mass % of Cr, more than 0 mass % and not more than 1.0 mass % of Ni, 0.02 to 0.12 mass % of La, 0.1 to 0.5 mass % of Zr, 0.15 to 0.5 mass % of La+Zr, and Fe and impurities as a remainder. The following relational formula is satisfied, and an Fe and Zr-containing intermetallic compound viewed in a ferrite matrix is 1.1 % or less in terms of a visual field area ratio
5(7C+6N)/(7−4(7C+6N))≤Zr≤41(7C+6N)/(7+66(7C+6N)).

A metal strip is provided having a casting-wheel side that has been solidified on an outer surface of a heat sink, an opposing, air side and a microstructure. The microstructure is at least 80 vol. % amorphous or has at least 80 vol. % nanocrystalline grains and a residual amorphous matrix in which at least 80% of the nanocrystalline grains have an average grain size of less than 50 nm and a random orientation. The air side of the metal strip has a surface crystallisation proportion of less than 23%.

A metal strip is provided having a casting-wheel side that has been solidified on an outer surface of a heat sink, an opposing, air side and a microstructure. The microstructure is at least 80 vol. % amorphous or has at least 80 vol. % nanocrystalline grains and a residual amorphous matrix in which at least 80% of the nanocrystalline grains have an average grain size of less than 50 nm and a random orientation. The air side of the metal strip has a surface crystallisation proportion of less than 23%.

An aspect of the present invention relates to a cold-rolled steel plate for hot forming, which is excellent in corrosion-resistance and spot-weldability, contains, by weight %, C: 0.1-0.4%, Si: 0.5-2.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001-0.02%, Cr: 0.5% to less than 3.0%, N: 0.001-0.02%, and a balance of Fe and inevitable impurities, satisfying formula (1) below, and includes an Si amorphous oxidation layer continuously or discontinuously formed at a thickness of 1 nm-100 nm on the surface thereof. Formula (1): 1.40.4*Cr+Si3.2 (wherein element symbols denote measurements of respective element contents by weight %).

An aspect of the present invention relates to a cold-rolled steel plate for hot forming, which is excellent in corrosion-resistance and spot-weldability, contains, by weight %, C: 0.1-0.4%, Si: 0.5-2.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001-0.02%, Cr: 0.5% to less than 3.0%, N: 0.001-0.02%, and a balance of Fe and inevitable impurities, satisfying formula (1) below, and includes an Si amorphous oxidation layer continuously or discontinuously formed at a thickness of 1 nm-100 nm on the surface thereof. Formula (1): 1.40.4*Cr+Si3.2 (wherein element symbols denote measurements of respective element contents by weight %).

A hot-pressed member has a predetermined chemical composition. In the hot-pressed member, a steel sheet has a microstructure in which a prior austenite average grain diameter is 8 m or less, and martensite is present in a volume fraction of 95% or greater in a region within 30 m of a surface; a Ni diffusion region having a thickness of 0.5 m or greater exists in a surface layer; a standard deviation of Vickers hardness values is 35 or less; Mndif (mass %) in a sheet thickness direction 0.20, where Mndif (mass %) is a degree of Mn segregation; and a tensile strength is 1780 MPa or greater.

A hot-pressed member has a predetermined chemical composition. In the hot-pressed member, a steel sheet has a microstructure in which a prior austenite average grain diameter is 8 m or less, and martensite is present in a volume fraction of 95% or greater in a region within 30 m of a surface; a Ni diffusion region having a thickness of 0.5 m or greater exists in a surface layer; a standard deviation of Vickers hardness values is 35 or less; Mndif (mass %) in a sheet thickness direction 0.20, where Mndif (mass %) is a degree of Mn segregation; and a tensile strength is 1780 MPa or greater.

Disclosed is a duplex stainless clad steel plate in which a duplex stainless steel plate as a cladding metal is bonded or joined to one or both surfaces of a base steel plate, in which the base steel plate comprises a predetermined chemical composition such that Nb/N is 3.0 or more and Ceq is 0.35 to 0.45, and the duplex stainless steel plate comprises: a predetermined chemical composition such that PI is 33.0 to 38.0; and a microstructure containing a ferrite phase in an area fraction of 35% to 65%, and in the microstructure, an amount of precipitated Cr is 1.00% or less and an amount of precipitated Mo is 0.50% or less.

Disclosed is a duplex stainless clad steel plate in which a duplex stainless steel plate as a cladding metal is bonded or joined to one or both surfaces of a base steel plate, in which the base steel plate comprises a predetermined chemical composition such that Nb/N is 3.0 or more and Ceq is 0.35 to 0.45, and the duplex stainless steel plate comprises: a predetermined chemical composition such that PI is 34.0 to 43.0; and a microstructure containing a ferrite phase in an area fraction of 35% to 65%, and in the microstructure, an amount of precipitated Cr is 2.00% or less and an amount of precipitated Mo is 0.50% or less.