Nippon Steel Corporation

Yoichi Mishima

Maremizu Ishibashi

Koji Yamasaki

Osamu Tanaka

Katsuro Kuroki

Yasunari Yoshitomi

Hiroaki Masui

Hotaka Honma

Tsutomu Haratani

Yoshio Nakamura

A grain oriented electrical steel sheet having no significant glass film and having a high magnetic flux density and an excellent iron loss property, comprising, in terms of by weight, 2.5 to 4.5% of Si, the steel sheet having, as oxides on its surface, a glass film comprising 0.6 g/m.sup.2 or less in total of forsterite and spinel composed of MgO, SiO.sub.2 and Al.sub.2 O.sub.3 and an insulating coating having a thickness of 6 .mu.m or less, the face tension imparted on the surface of the steel sheet by the coating being in the range of from 0.5 to 2.0 kg/mm.sup.2. In the final box annealing of the steel sheet after primary recrystallization annealing, use is made of an annealing separator comprising 100 parts by weight of MgO and, added thereto, 2 to 30 parts by weight of at least one member selected from the group consisting of chlorides, carbonates, nitrates, sulfates and sulfides of Li, K, Bi, Na, Ba, Ca, Mg, Zn, Fe, Zr, Sr, Sn, Al, etc., and the heating in the final box annealing is effected in an atmosphere comprising N.sub.2 and H.sub.2 with the nitrogen content being 30% or more at a heating rate of 20.degree. C./hr or less, and a seam or spotty flaw is imparted at an angle of 45.degree. to 90.degree. to the rolling direction of the steel sheet.

Grain oriented electrical steel sheet having high magnetic flux density

This invention is directed to improve magnetic properties and to stabilize the magnetic properties of a grain oriented electrical steel sheet used as a core of electric appliances. When producing a grain oriented electrical steel sheet by heating a slab containing C, Si, acid-soluble Al, N, not more than 0.014% of S+0.405 Se and 0.05 to 0.8% of Mn and the balance consisting of Fe and unavoidable impurities at a temperature of less than 1,280.degree. C., effecting hot rolling, applying cold rolling, decarbonization annealing and final finish annealing without annealing hot rolled sheet, the production method of the present invention controls the precipitation quantity of AlN in the hot rolled sheet, controls the mean grain size of the primary crystallization grains from completion of decarbonization annealing to the start of final finish annealing, applies nitriding treatment after hot rolling but before the start of secondary recrystallization at final finish annealing, controls the hot rolling condition in accordance with the quantities of acid-soluble Al and N of the slab, and further adds Sn.

Production method of grain oriented electrical steel sheet having

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Kitakyushu, Japan

Yoichi Mishima