Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1997-05-17
1998-11-24
Sheehan, John
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148113, H01F 118
Patent
active
058401318
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for producing a grain-oriented electrical steel sheet having excellent magnetic properties in which process an extremely uniform glass film having an excellent high tensile strength is formed over the entire surface of the coil in the final finish annealing step.
BACKGROUND ART
Usually in the production of a grain-oriented electrical steel sheet, a steel slab containing from 2.5 to 4.0% of Si is hot rolled, annealed, and cold rolled once or twice with intermediate annealing to give a steel sheet having a final thickness. Then, the steel sheet is subjected to decarburization annealing in a continuous annealing furnace in an atmosphere of H.sub.2 or H.sub.2 and N.sub.2 while the PH.sub.2 O/PH.sub.2 ratio is being controlled to achieve decarburization, primary recrystallization and formation of an oxide film mainly containing SiO.sub.2. The steel sheet is subsequently coated with a slurry of an annealing separator mainly containing MgO with a coating roll, etc., dried, coiled, subjected to final finish annealing, and usually subjected to insulating coating treatment and heat flattening to give a final product.
Since (110)<001> crystal grains each having a <001> axis preferentially grow in the grain-oriented electrical steel sheet in secondary recrystallization at high temperature and migrate other crystals the growth of which is inhibited by AlN, MnS, etc. dispersed in the steel as inhibitors, the (110)<001> crystal grains are thought to grow preferentially.
In order to obtain a grain-oriented electrical steel sheet having excellent magnetic properties, therefore, the dispersion state of the inhibitors in the steel and stabilized control of them before secondary recrystallization during finish annealing are important. In particular, since the inhibitors are influenced by the stage of forming the glass film, and the thickness and the uniformity of the glass film in final finish annealing, the oxide film formed in decarburization annealing, the annealing separator, and the heat cycle and the atmosphere gas conditions in finish annealing are important.
The reaction for forming a glass film in finish annealing is a reaction for forming a forsterite film usually termed a glass film through a reaction of MgO in the annealing separator with an oxide film formed in decarburization annealing containing SiO.sub.2 mainly (2MgO+SiO.sub.2 .fwdarw.Mg.sub.2 SiO.sub.4). Moreover, when AlN is used as an inhibitor in the steel during the glass film formation, a film having a spinel structure is formed from Al.sub.2 O.sub.3, MgO, SiO.sub.2, etc. directly under the forsterite film. In the reaction for forming the glass film, in the pure system of MgO and SiO.sub.2, the reaction does not take place unless the temperature is as high as near 1,600.degree. C. Accordingly, important factors of the glass film formation reaction are the properties of the annealing separator such as the impurities, particle size, particle shape and activity of the main component MgO and additives as the reaction accelerators in addition to the properties of the oxide film (components, formation state), the conditions of finish annealing (heat cycle, atmosphere gas). How the glass film is formed uniformly from a low temperature in finish annealing becomes an important key to obtain an excellent glass film and good magnetic properties.
As described above, since production conditions up to decarburization annealing and finish annealing of the grain-oriented electrical steel sheet significantly influence the glass film and magnetic properties which are important in deciding the commodity value thereof, developing such production conditions matching the steel components has become an important problem in the production thereof.
As described above, MgO used in the step of forming a glass film is suspended in water to form a slurry together with a small amount of opotional additives incorporated as reaction accelerators, and applied to the steel sheet. The additives are usually ox
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Honma Hotaka
Ishibashi Maremizu
Kumano Tomoji
Kuroki Katsuro
Sakaida Akira
Nippon Steel Corporation
Sheehan John
LandOfFree
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