An object of the invention is to provide: a two-phase alloy as a metal material that can be preferably utilized under circumstances of a temperature range and a high corrosion as in an oil well, the two-phase alloy having a high corrosion resistance and good mechanical properties that are equivalent or more than those of conventional ones, and saving a cost; a product of the two-phase alloy; and a method for producing the product. There is provided a two-phase alloy containing Cr as a major component and including two phases of an austenite phase and a ferrite phase in a mixed state. The alloy has a chemical composition containing: 34-70 mass % of Cr; 17-45 mass % of Ni; 10-35 mass % of Fe; 0.1-2 mass % of Mn; 0.1-1 mass % of Si; and impurities. The total content of the Ni and the Fe is 30-65 mass %.

Proposed is a non-oriented electrical steel sheet being low in iron loss and excellent in tensile strength and fatigue strength, which has a chemical composition comprising C: not more than 0.005 mass %, Si: 3 to 5 mass %, Mn: not more than 5 mass %, P: not more than 0.1 mass %, S: not more than 0.01 mass %, Al: not more than 3 mass %, N: not more than 0.005 mass %, Zn: 0.0005 mass % to 0.003 mass %, and the remainder being Fe and inevitable impurities, an average crystal grain size being not more than 40 μm, the number of the inclusions having a diameter of not less than 5 μm being not more than 5/mm.sup.2, a tensile strength being not less than 600 MPa, and the fatigue strength being not less than 450 MPa.

A non-oriented electrical steel sheet according to an embodiment of the present invention includes: in wt %, C at 0.004 wt % or less (excluding 0 wt %), Si at 2.5 to 4.0 wt %, P at 0.1 wt % or less (excluding 0 wt %), Al at 0.3 to 2.0 wt %, N at 0.003 wt % or less (excluding 0 wt %), S at 0.003 wt % or less (excluding 0 wt %), Mn at 0.15 to 2.5 wt %, Cr at 0.5 wt % (excluding 0 wt %), and the balance including Fe and other impurities unavoidably added thereto; satisfies the following Equation 1; and has an average grain size of 20 μm or less.

[Mn]≥1450×[S]−0.8  [Equation 1]

(In Equation 1, [Mn] and [S] represent a content (wt %) of Mn and S, respectively.)

A process for producing grain-oriented electrical steel strip by means of thin slab continuous casting and which includes continuously casting the smelt by thin slab continuous casting, subjecting the thin slabs to homogenization annealing at a maximum temperature of 1250° C. and heating to a temperature between 1350° C. and 1380° C., and continuously hot rolling the thin slabs to form a hot-rolled strip, with cooling and reeling the hot-rolled strip to form a coil and cold rolling the hot-rolled strip to a nominal thickness, with subjecting the cold-rolled strip to recrystallization, decarburization and nitridation annealing, which includes a decarburization annealing phase and a subsequent nitridation annealing phase, with an intermediate reduction annealing phase being interposed between the decarburization annealing phase and the nitridation annealing phase, whereby a cold-rolled strip is obtained, which primary recrystallized grains have a circle equivalent mean size (diameter) between 22 μm and 25 μm.

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.

An embodiment of the present invention provides a grain-oriented electrical steel sheet, including a groove including a bottom portion and a side portion positioned on a surface of the electrical steel sheet, a metal oxide layer positioned on the groove, and an insulating layer positioned on the metal oxide layer, wherein the steel sheet includes a normal groove in which thicknesses of the metal oxide layer positioned on the bottom portion and the side portion exceed 0.5 μm, and a defective groove in which thicknesses of the metal oxide layer positioned on the bottom portion and the side portion are 0.5 μm or less, the insulating layer positioned on the normal groove has a thickness of 0.5 μm to 1.5 μm, and the insulating layer positioned on the defective groove has a thickness of 1.5 to 10 μm.

Provided is a manufacturing method of a grain-oriented electrical steel sheet including preparing a hot-rolled sheet by hot-rolling a slab; removing some of scales formed on the hot-rolled sheet and leaving a scale layer having a thickness of 10 nm or more to prepare a hot-rolled sheet on which the scale layer remains; preparing a cold-rolled sheet by cold-rolling the hot-rolled sheet on which the scale layer remains; preparing the decarburization annealed cold-rolled sheet by decarburization annealing the cold-rolled sheet; coating an annealing separator on the decarburization annealed cold-rolled sheet to form a metal oxide layer; and final annealing the steel sheet on which the metal oxide layer is formed, wherein the annealing separator includes magnesium oxide (MgO) or magnesium hydroxide (MgOH) and fluoride.

Further lower iron loss can be achieved in a grain-oriented electrical steel sheet including: a predetermined film mainly composed of forsterite on a front and back surfaces thereof; and a plurality of grooves on the front surface thereof, in which the plurality of grooves have an average depth of 6% or more of a thickness of the steel sheet and are spaced a distance of 1 mm to 15 mm from respective adjacent grooves, the steel sheet has a specific magnetic permeability μr.sub.15/50 of 35000 or more when subjected to alternating current magnetization at a frequency of 50 Hz and a maximum magnetic flux density of 1.5 T, and the steel sheet includes isolated parts having a presence frequency of 0.3/μm or less, the isolated parts being separated from a continuous part of the film in an interface between the steel sheet and the film in a cross section orthogonal to the rolling direction of the steel sheet.

A double oriented electrical steel sheet according to an embodiment of the present invention includes: in wt %, Si at 2.0 to 4.0 wt %, Al at 0.01 to 0.04 wt %, S at 0.0004 to 0.002 at %, Mn at 0.05 to 0.3 wt %, N at 0.008 wt % or less (excluding 0 wt %), C at 0.005 wt % or less (excluding 0 wt %), P at 0.005 to 0.15 wt %, Ca at 0.0001 to 0.005 wt %, Mg at 0.0001 to 0.005 wt %, and the balance including Fe and other impurities unavoidably added thereto.