Metal treatment – Stock – Magnetic
Patent
1997-09-30
1999-03-02
Sheehan, John
Metal treatment
Stock
Magnetic
148111, 420117, H01F 114, H01F 1147
Patent
active
058765204
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a semiprocessed nonoriented magnetic steel sheet having excellent magnetic characteristics and a method for making the same. In particular, the magnetic characteristics are effectively improved by a modification of a cold rolling step.
BACKGROUND ART
Nonoriented magnetic steel sheets have been primarily used in iron cores of motors and transformers. For improving the energy efficiency of motors and transformers it is essential to increase the magnetic flux density and simultaneously to decrease the iron loss of the nonoriented magnetic steel sheet used in the iron core. In particular, semiprocessed nonoriented magnetic steel sheets are products rolled at rolling reduction rate of 2 to 18% after final annealing in manufacture's plants. Stress relief annealing by users after processing causes coarsening of crystal grains and assures desired magnetic characteristics.
Many ideas have been disclosed for improving magnetic characteristic, that is, increasing the magnetic flux density and decreasing the iron loss. Improvement in second cold rolling processes is disclosed in, for example, Japanese Patent Publication No. 4-34614, in which second cold rolling is performed at a rolling reduction rate of 2 to 18% and a controlled rolling speed of 500 to 2,000 mpm in order to improve magnetic characteristics in a low magnetic field. High-rate rolling of 500 mpm or more, however, increases cost. Further, magnetic characteristics do not reach the severe levels recently required.
Japanese Patent Laid-Open No. 58-9927 discloses a method for adding B so that the B/N ratio is 0.65 to 1.5, and Japanese Patent Laid-Open No. 60-39121 discloses a method for annealing hot-rolled sheets after an addition of 0.01 to 0.30 wt% of Sb. These methods, however, increase cost due to the addition of B or Sb and the annealing of hot-rolled steel sheets. Further, magnetic characteristics do not reach the severe levels recently required.
It is an object of the present invention to effectively solve the above-mentioned problems and to provide a semiprocessed nonoriented magnetic steel sheet having excellent magnetic characteristics and a method for making the same.
The present inventors have conducted intensive research to achieve the above-mentioned object. As a result, it has been discovered that a strain value applied to the steel sheet and the ratio of the strain value applied to the surface section to the strain value applied to the central section have a great influence on magnetic characteristics after stress relief annealing.
The experimental results which have been conducted in respect of the present invention will now be described.
A steel having a composition shown in Table 1 was prepared by a melting process and subjected to continuous casting to form slabs which were subjected to hot rolling to a thickness of 2.2 mm then first cold rolling to an intermediate thickness of 0.526 mm. After intermediate annealing at 800.degree. C. for 20 seconds, second cold rolling with a rolling reduction of 5% was performed under conditions represented by X and Y in Table 2 to prepare a second cold rolled sheet having a final thickness of 0.50 mm.
Epstein test pieces of 280 mm by 30 mm were prepared from a second cold rolled steel sheet so that the long sides of 8 pieces among them agree with the rolling direction and the long sides of the residual 8 pieces agree with the direction perpendicular to the rolling direction. These test pieces were subjected to strain-relief annealing at 750.degree. C. for 2 hours to measure magnetic characteristics.
At the same time, strain values of the second cold rolled steel sheet were determined at a surface layer, at an inner layer corresponding to one fifth of the thickness from the surface (hereinafter referred to as one-fifth layer) and at the central layer. Each strain value was calculated from the width (integral width) of the {222} X-ray diffraction profile of the test piece prepared as follows. ______________________________________ Component C Si Mn Al
REFERENCES:
patent: 4946519 (1990-08-01), Honda et al.
patent: 5259892 (1993-11-01), Kubota et al.
patent: 5413640 (1995-05-01), Manabe et al.
Fujita Akio
Kawano Masaki
Sato Keiji
Takashima Minoru
Kawasaki Steel Corporation
Miller Austin R.
Sheehan John
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