Metal deforming – With cleaning – descaling – or lubrication of work or product
Patent
1994-08-25
1996-11-12
Larson, Lowell A.
Metal deforming
With cleaning, descaling, or lubrication of work or product
72200, 723652, 148111, 148504, B21B 126
Patent
active
055728928
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of producing silicon steel hot rolled sheets, and more particularly to a method of producing silicon steel hot rolled sheets having excellent surface properties.
BACKGROUND ART
Grain-oriented magnetic steel sheets are used as a material for iron core in transformers and other electrical machinery and apparatus and required to have a high magnetic flux density and a low iron loss. These magnetic properties are attained by providing secondary recrystallized structure with a texture having {110} face in parallel to a rolling face and <001> axis along a rolling direction or having so-called Goss orientation as a main direction.
For this purpose, various components including silicon are added to the grain-oriented magnetic silicon steel sheet. However, it is known that the workability lowers and particularly surface cracks and surface defects are apt to be considerably produced through hot rolling. If the degree of the surface defects is conspicuous, not only the appearance is poor, but also the degradation of the properties such as lowering of lamination factor, lowering of interlaminar insulation property and the like is caused. Therefore, it is an important matter how to prevent such surface cracks and surface defects in view of the production step.
As a method of decreasing cracks at the hot rolling step for the grain-oriented silicon steel sheet, there have hitherto been proposed a method of controlling intergranular oxidation by the addition of Mo or the like as described in JP-A-61-9521, a method of decreasing cracks by refining the structure through recrystallization as described in JP-A-2-182832, JP-A-3-115526 and JP-A-62-149815, and the like. However, these methods are not involved in drastic settlements.
Furthermore, JP-A-63-295044 proposes a method of controlling generation of slag by setting an existing time in a high-temperature furnace during the heating of slab to a certain upper limit, which brings about the restriction of operation to lower the productivity.
As mentioned above, the conventional techniques for preventing cracks of silicon steel sheet in the hot rolling do not yet provide satisfactory results.
DISCLOSURE OF INVENTION
It is an object of the invention to provide a method capable of producing silicon steel hot rolled sheets having good surface properties while effectively preventing generation of surface cracks from a new viewpoint that stress condition in the rolling deformation is improved to prevent generation of surface cracks by controlling a temperature distribution in the thickness direction.
The inventors have detailedly investigated a relationship between a temperature distribution in the thickness direction of a steel sheet and a state of surface cracks generated every a stand in rough and finish rolling at hot rolling step and found that the temperature distribution in the thickness direction of the steel sheet at the first stand of rough rolling and/or finish rolling has particularly a specific relation to the generating frequency of surface cracks and the temperature distribution in the thickness direction of the steel sheet is rendered into a particular range in accordance with thicknesses at entrance and delivery sides of said stands, and as a result the invention has been accomplished.
The feature and construction of the invention are as follows.
A method of producing silicon steel hot rolled sheets having excellent surface properties by subjecting a slab of silicon steel containing Si: 2.0-4.5 wt % to a rough hot rolling and then subjecting to a finish hot rolling is characterized in that rolling at the first stand of the rough hot rolling is carried out so that a relation of thickness at entrance side of the stand t.sub.R1 (mm), thickness at delivery side thereof t.sub.R2 (mm), surface temperature of the steel sheet at gripping T.sub.R0 (.degree. C.) and temperature at the depth of (t.sub.R1 -t.sub.R2)/2 (mm) from the surface of the steel sheet at gripping T.sub.R1 satisfies the following equation (fi
REFERENCES:
patent: 4231818 (1980-11-01), Henke
patent: 5129965 (1992-07-01), Kobayashi et al.
patent: 5296050 (1994-03-01), Takamiya et al.
Koseki Satoshi
Muraki Mineo
Takamiya Toshito
Kawasaki Steel Corporation
Larson Lowell A.
Miller Austin R.
Schoeffler Thomas C.
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