Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1992-08-04
1994-03-22
Dean, R.
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148112, 148504, C21D 946
Patent
active
052960501
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of producing grain oriented silicon steel sheets having improved magnetic properties.
1. Background of the Invention
As is well-known, grain oriented silicon steel sheets are mainly used as a material for iron core in transformers and other electrical machinery and equipment and are comprised of secondary recrystallized grains aligned {110} face to plate face and <001> axis to rolling direction. In order to develop the secondary recrystallized grains having such a crystal orientation, it is required that precipitates such as MnS, MnSe, AlN and the like called as an inhibitor are uniformly and finely dispersed in steel to effectively suppress growth of crystal grains in an orientation other than {110}<001> orientation during the final annealing at a high temperature. Therefore, the control of the inhibitor dispersed state is carried out by solid-soluting these precipitates in the slab heating prior to hot rolling at once and then subjecting to a hot rolling having a proper cooling pattern.
Here, an important role of the hot rolling lies in that the solid-soluted inhibitor components are finely and uniformly precipitated as an inhibitor.
2. Description of the Prior Art
For example, Japanese Patent laid open No. 53-39852 has reported that a proper dispersion phase of MnSe is obtained by holding the steel sheet within a temperature range of not lower than 850.degree. C. but not higher than 1200.degree. C. for 60-360 seconds. In this method, however, the inhibitor is ununiform and coarsely precipitated in a fair frequency. Particularly, it is experientially known that the inhibitor becomes considerably coarse when being held at about 1100.degree. C. for a long period of time. Therefore, this method is difficult to provide a complete secondary recrystallized structure because the inhibiting force of the inhibitor decreases.
Furthermore, Japanese Patent Application Publication No. 58-13606 has proposed a method wherein the steel sheet is cooled at a cooling rate of not less than 3.degree. C./s while being continuously subjected to a hot rolling within a temperature range of 950.degree.-1200.degree. C. at a draft of not less than 10%. In this method, however, the inhibitor is not always finely precipitated, and the coarse or nonuniform precipitation of the inhibitor is caused in accordance with the size of crystal grains. Particularly, the dispersion in a direction of sheet thickness is apt to become nonuniform. As a cause, there is mentioned a nonuniformity of strain inherent to high temperature deformation.
In these conventional methods, the dispersed state of the inhibitor can not completely be rendered into a fine and uniform state, and the normal growth of primary crystal grains can not effectively be controlled at a secondary recrystallization annealing step in final finish annealing, so that the complete secondary recrystallization structure can not be obtained.
Another important role of the hot rolling lies in that the slab cast structure is made fine by recrystallization to form a structure most suitable for secondary recrystallization. Moreover, such a treatment for increasing the fineness of the crystal structure has hitherto been carried out apart from the solid solution treatment of the inhibitor.
As to the solid solution of the inhibitor, it has hitherto been reported, for example, in Japanese Patent laid open No. 63-10911 that grain oriented silicon steel sheets having less surface defect and good properties are obtained by raising the slab surface temperature above 1320.degree. C. to a temperature of 1420.degree.-1495.degree. C. at a temperature rising rate of not less than 8.degree. C./min when holding the slab surface temperature within a range of 1420.degree.-1495.degree. C. for 5-60 minutes. According to this method, the complete solid solution of the inhibitor has certainly be achieved and also the coarsening of the slab surface grains can be suppressed in principle to improve the surface properties, but it is actually difficult t
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Iida Yoshiaki
Manabe Masahiko
Obara Takashi
Takamiya Toshito
Takeuchi Fumihiko
Dean R.
Ip Sikyin
Kawasaki Steel Corporation
Miller Austin R.
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