A grain oriented electrical steel sheet comprising a grain oriented electrical steel sheet having a surface and a forsterite film formed on the surface of the steel sheet, wherein a total area percentage of defective parts scattered on the forsterite film is less than 1.5% relative to a surface area of the forsterite film when viewed from above the surface, and methods for evaluating a grain oriented electrical steel sheet comprising a grain oriented electrical steel sheet having a surface and a forsterite film formed on the surface of the steel sheet.

A steel slab having a composition not containing an inhibitor component further contains, in mass %, at least one selected from: Sn: 0.010% to 0.200%; Sb: 0.010% to 0.200%; Mo: 0.010% to 0.150%; and P: 0.010% to 0.150%, and annealing that satisfies a relationship Td≧Tf is performed, where Td (° C.) is a highest temperature at which the steel sheet is annealed in decarburization annealing and Tf (° C.) is a highest temperature before secondary recrystallization of the steel sheet starts in final annealing. Thus, a grain-oriented electrical steel sheet with significantly reduced magnetic property scattering in a coil is obtained without using an inhibitor component.

A pre-coating agent composition for a grain-oriednted electrical steel sheet, a grain-oriednted electrical steel sheet including the same, and a manufacturing method thereof are provided. Particularly, a pre-coating agent composition for a grain-oriednted electrical steel sheet including an acid containing boron (B); and a solvent, a grain-oriednted electrical steel sheet including the same, and a manufacturing method thereof are provided.

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).

Provided is a method of producing a hot-rolled steel sheet for a grain-oriented electrical steel sheet. The method comprising: preparing a steel slab having a chemical composition containing, by mass %, C: 0.002% or more and 0.080% or less, Si: 2.00% or more and 8.00% or less, Mn: 0.02% or more and 0.50% or less, acid-soluble Al: 0.003% or more and less than 0.010%, and at least one of S or Se: 0.001% or more and 0.010% or less in total, with N limited to less than 0.006%, and the balance being Fe and inevitable impurities; heating the steel slab to 1300° C. or lower; and subjecting the steel slab to hot rolling, wherein a friction coefficient in final pass of the hot rolling is 0.35 or less.

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 are an oriented electrical steel sheet and a manufacturing method thereof. An exemplary embodiment of the present invention provides a method of manufacturing an oriented electrical steel sheet, including: providing a slab including Si at 1.0 to 4.0 wt %, C at 0.1 to 0.4 wt %, and the remaining portion including Fe and other inevitably incorporated impurities; reheating the slab; producing a hot rolled steel sheet by hot rolling the slab; performing annealing of the hot rolled steel sheet; cold rolling the annealed hot rolled steel sheet; decarburizing and annealing the cold rolled steel sheet; cold rolling the decarburized and annealed steel sheet; and final annealing the cold rolled steel sheet.

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.

When a steel material is processed to produce a grain-oriented electrical steel sheet, conditions of a decarburization annealing process and conditions of a process before the decarburization annealing are adjusted so that a difference in concentration of O, Si, Al, Mn and P between the front and back surfaces of the steel sheet after the decarburization annealing is within a given range with respect to an average concentration between the front and back surfaces, and hence the difference in concentration of each of O, Si and Mg between the front and back surfaces of the product sheet is within ±5%, the difference in concentration of one or more of Al, Mn and P between the front and back surfaces is within ±15% and the difference in the concentration of one or more of Ca and Ti between the front and back surfaces is within ±20%.

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises: a step for hot-rolling a slab to produce a hot-rolled sheet; a step for cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; a step for subjecting the cold-rolled sheet to primary recrystallization annealing; and a step for subjecting the primary recrystallization annealing-completed cold-rolled sheet to secondary recrystallization annealing, wherein the primary recrystallization annealing step includes a preceding step and a subsequent step, and the amount (A) of nitriding gas introduced in the preceding step with respect to the total amount (B) of nitriding gas introduced in the primary recrystallization annealing step satisfies expression 1 below.

0.05≤[A]/[B]≤[t]  [Expression 1]

(In expression 1, the amount of nitriding gas introduced is in units of Nm.sup.3/hr, and [t] represents the thickness (mm) of a cold-rolled sheet.)