A non-oriented electrical steel sheet with lower iron loss than conventional non-oriented electrical steel sheets is provided. The non-oriented electrical steel sheet has a chemical composition containing, in mass %: C: 0.05% or less; Si: 0.1% or more and 7.0% or less; Al: 0.1% or more and 3.0% or less; Mn: 0.03% or more and 3.0% or less; P: 0.2% or less; S: 0.005% or less; N: 0.005% or less; and O: 0.01% or less, and further optionally containing a predetermined amount of one or more of Sn, Sb, Ca, Mg, REM, Cr, Ti, Nb, V, and Zr, with the balance consisting of Fe and incidental impurities, wherein a sheet thickness is less than 0.30 mm, and arithmetic mean roughness Ra of a steel substrate surface at cutoff wavelength λc=20 μm is 0.2 μm or less.

A non-oriented electrical steel sheet with lower iron loss than conventional non-oriented electrical steel sheets is provided. The non-oriented electrical steel sheet has a chemical composition containing, in mass %: C: 0.05% or less; Si: 0.1% or more and 7.0% or less; Al: 0.1% or more and 3.0% or less; Mn: 0.03% or more and 3.0% or less; P: 0.2% or less; S: 0.005% or less; N: 0.005% or less; and O: 0.01% or less, and further optionally containing a predetermined amount of one or more of Sn, Sb, Ca, Mg, REM, Cr, Ti, Nb, V, and Zr, with the balance consisting of Fe and incidental impurities, wherein a sheet thickness is less than 0.30 mm, and arithmetic mean roughness Ra of a steel substrate surface at cutoff wavelength λc=20 μm is 0.2 μm or less.

There is provided a steel for solid oxide fuel cells which contains Zr and has a composition balance which allows a thin plate to stably obtain excellent oxidation resistance. The steel for solid oxide fuel cells 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 mass % 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 Zr and has a composition balance which allows a thin plate to stably obtain excellent oxidation resistance. The steel for solid oxide fuel cells 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 mass % 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))

In a method of producing a grain-oriented electrical steel sheet comprising subjecting a steel slab containing no inhibitor-forming components to hot rolling, cold rolling, primary recrystallization annealing working also as decarburization and to final annealing causing secondary recrystallization after applying an annealing separator on the surface, the final cold rolling for cold rolling the steel sheet to the final thickness uses a warm rolling with a tandem rolling mill at a total rolling reduction of not less than 80% at 150 to 280° C. and is performed by extending a pass line length of the steel sheet between the stands so that T satisfies T≥1.3×L/V, where an distance between the stands is defined as L(m), a speed of the steel sheet passing between the stands is defined as V (mpm), and a pass time during which the steel sheet passes between the stands is defined as T(min).

Disclosed is a method for manufacturing a grain-oriented electrical steel sheet using an inhibitor-less technique, in which cold rolling includes final cold rolling with a total cold rolling reduction being set to 85% or more and a rolling reduction per pass being set to 32% or more. The final cold rolling includes one or more passes and a final pass succeeding the one or more passes and uses work rolls having a surface roughness Ra of 0.25 μm or less in at least one of the one or more passes other than the final pass. According to this method, it is possible to stably manufacture a grain-oriented electrical steel sheet exhibiting excellent magnetic properties at low cost.

A method of manufacturing a grain oriented electrical steel sheet includes subjecting a steel slab to a rolling process including cold rolling to obtain a steel sheet with a final sheet thickness, the steel slab containing by mass % C: 0.01% to 0.20%, Si: 2.0% to 5.0%, Mn: 0.03% to 0.20%, sol. Al: 0.010% to 0.05%, N: 0.0010% to 0.020%, at least one element selected from S and Se in a total of 0.005% to 0.040%, and the balance including Fe and incidental impurities; forming, by a chemical process, a linear groove extending in a direction forming an angle of 45° or less with a direction orthogonal to a rolling direction of the steel sheet; subjecting the steel sheet to decarburization annealing; applying an annealing separator thereon mainly composed of MgO; and subjecting the steel sheet to final annealing to manufacture a grain oriented electrical steel sheet.

A method of manufacturing a grain oriented electrical steel sheet includes subjecting a steel slab to a rolling process including cold rolling to obtain a steel sheet with a final sheet thickness, the steel slab containing by mass % C: 0.01% to 0.20%, Si: 2.0% to 5.0%, Mn: 0.03% to 0.20%, sol. Al: 0.010% to 0.05%, N: 0.0010% to 0.020%, at least one element selected from S and Se in a total of 0.005% to 0.040%, and the balance including Fe and incidental impurities; forming, by a chemical process, a linear groove extending in a direction forming an angle of 45° or less with a direction orthogonal to a rolling direction of the steel sheet; subjecting the steel sheet to decarburization annealing; applying an annealing separator thereon mainly composed of MgO; and subjecting the steel sheet to final annealing to manufacture a grain oriented electrical steel sheet.

Provided is a hot-rolled steel sheet having a composition containing 0.04 mass percent to 0.20 mass percent C, 0.7 mass percent to 2.3 mass percent Si, 0.8 mass percent to 2.8 mass percent Mn, 0.1 mass percent or less P, 0.01 mass percent or less S, 0.1 mass percent or less Al, and 0.008 mass percent or less N, the remainder being Fe and inevitable impurities. Internal oxides containing one or more selected from the group consisting of Si, Mn, and Fe are present at grain boundaries and in grains in a base metal. The internal oxides present at the grain boundaries in the base metal are located within 5 μm from the surface of the base metal. The difference between the depths at which the internal oxides are formed in the cross direction of the steel sheet is 2 μm or less.

Provided is a hot-rolled steel sheet having a composition containing 0.04 mass percent to 0.20 mass percent C, 0.7 mass percent to 2.3 mass percent Si, 0.8 mass percent to 2.8 mass percent Mn, 0.1 mass percent or less P, 0.01 mass percent or less S, 0.1 mass percent or less Al, and 0.008 mass percent or less N, the remainder being Fe and inevitable impurities. Internal oxides containing one or more selected from the group consisting of Si, Mn, and Fe are present at grain boundaries and in grains in a base metal. The internal oxides present at the grain boundaries in the base metal are located within 5 μm from the surface of the base metal. The difference between the depths at which the internal oxides are formed in the cross direction of the steel sheet is 2 μm or less.