Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1992-02-11
1993-11-09
Sheehan, John P.
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148120, H01F 104
Patent
active
052598926
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for producing a non-oriented electromagnetic steel sheet having excellent magnetic properties after stress relief annealing for use as an iron core material for electrical equipment, particularly to a process for producing a non-oriented electromagnetic steel sheet having excellent magnetic properties after stress relief annealing suitable as the so-called "semi-process type non-oriented electromagnetic steel sheet" which, in the production of the above-mentioned iron core, is subjected to stamping and then annealed to remove stamping strain and, at the same time, conducts recrystallization and crystal grain growth of the steel sheet to improve magnetic properties.
BACKGROUND ART
In recent years, there is a very strong demand for improvement in performance particularly in the field of a rotating machine, a medium or small size transformer, etc. For this reason, as described in, for example, Japanese Unexamined Patent Publication (Kokai) Nos. 54-76422, 55-82732 and 57-203718, in order to bring out magnetic properties of a non-oriented electromagnetic steel sheet as much as possible, a method wherein the stress relief annealing for removing stamping stress of a non-oriented electromagnetic steel sheet in the production of an iron core is utilized to simultaneously conduct the recrystallization and crystal grain growth of the steel sheet, thereby improving magnetic properties to attain substantially the same effect as that attained when use is made of a non-oriented electromagnetic steel sheet of higher grade, has widely been used in the art. For this purpose, a box or tunnel furnace wherein electricity or gas is used as a heating source has been generally used because the stress relief annealing should usually be conducted under conditions of a temperature in the range of from 700.degree. to 850.degree. C. and a soaking time of one hour or longer.
In the above-described conventional stress relief annealing method, however, the annealing including heating, soaking and cooling requires several hours or longer. Further, since the annealing is a batch process independent of a series of iron core manufacturing steps, it leads to an increase in the time necessary for the manufacturing process and an increase in the complexity of the manufacturing process, so that productivity is very poor.
In view of the above, an object of the present invention is to provide a process for producing a non-oriented electromagnetic steel sheet having excellent magnetic properties after stress relief annealing which can sufficiently attain an improvement in the desired magnetic properties even in stress relief annealing for a short period of time and improve productivity through a reduction in the time necessary for the manufacturing process and a simplification of the manufacturing process.
DISCLOSURE OF INVENTION
The present inventors have made extensive and intensive studies with focus of attention particularly on the relationship between the Si content and the crystal grain growing property with a view to improve the magnetic properties through the removal of stamping stress simultaneously with the recrystallization and crystal grain growth of the steel sheet in stress relief annealing for a short period of time by a combination of the above-mentioned relationship with manufacturing process conditions.
As a result, they have found that a proper combination of the selection of the Si content of the steel with skin pass rolling conditions allows for an improvement in the magnetic properties to be attained by stress relief annealing for a very short period of time, that is, 5 min or less, as opposed to the prior art wherein stress relief annealing for one hour or longer is necessary. The present invention has been made based on the above-described finding, and the subject matter thereof resides in that a steel comprising, on the weight basis, 0.010% or less of carbon and from 4.0% to 8.0% of silicon with the balance consisting of Fe and unavoidable impurity elements,
REFERENCES:
patent: 3770517 (1973-11-01), Gray et al.
Kubota Takeshi
Suga Yozo
Nippon Steel Corporation
Sheehan John P.
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