Method of manufacturing a nonoriented electromagnetic steel sheet

Abstract

A method for manufacturing a non-oriented electrical steel sheet including hot-rolling a steel slab containing 0-0.010% of C; at least one of Si and Al in a total amount of 0.03% to 0.5%; 0.5% or less of Mn; 0.10% or more to 0.26% or less of P; 0.015% or less of S; and 0.010% or less of N, on a mass percentage basis, the remainder being Fe and unavailable impurities, under conditions of a heating temperature in a single-phase austenite region and a coiling temperature of 650° C. or less; descaling the hot-rolled sheet to cold-roll the descaled sheet once or twice or more with an intermediate annealing sub-step therebetween; and then finish-annealing the cold-rolled sheet at a temperature of 700° C. or more in the single-phase ferrite region.

Description

TECHNICAL FIELD [0001] The present invention relates to non-oriented electrical steel sheets used for iron core materials for electric apparatus. In particular, the present invention relates to a non-oriented electrical steel sheet suitable for an iron core material for reluctance motors, IPM-type DC brushless motors, and the like, and relates to a method for manufacturing the non-oriented electrical steel sheet, wherein the reluctance and DC brushless motors need to have high dimensional accuracy in punching together with high magnetic flux density, and the DC brushless motors further need to have high strength. BACKGROUND ART [0002] The non-oriented electrical steel sheet is of a soft magnetic material mainly used for iron cores of electric apparatus such as motors and transformers. In order to improve the efficiency and in order to miniaturize the electric apparatus, the non-oriented electrical steel sheet needs to have a small core loss and a high magnetic flux density. In the f...

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Benefits of technology

[0012] As described above, high magnetic flux density and low core loss are characteristics that are commonly preferred for all the applications of non-oriented electrical steel sheets, such as various motors and transformers. Among the characteristics, for a non-oriented electrical steel sheet used for reluctance motors, the high magnetic flux density and high dimensional accuracy are particularly important from the point of view of the operating principle.

[0013] However, a non-oriented electrical steel sheet having the following characteristics has not been found: excellent magnetic characteristics such as high magnetic flux density and low core loss, and superior punching properties that is, particularly high dimensional accuracy. In addition to these characteristics, another non-oriented electrical steel sheet further having the following characteristic has also not been found: high strength required for the interior permanent magnet-type DC brushless motor and the like.

[0016] a non-oriented electrical steel sheet having superior magnetic characteristics, that is, high magnetic flux density together with low core loss more than ever, which are preferred for iron core materials, used for reluctance motors and the like, that need to have particularly high magnetic flux density and dimensional accuracy and further having high dimensional accuracy punching; and

[0017] another non-oriented electrical steel sheet having high magnetic flux density and strength that is important to obtain high-speed rotation and to prevent interior permanent magnets from being detached and further having high dimensional accuracy in punching.

[0020] As a result of the intensive research conducted in order to obtain the above objects, the inventors have found that not only excellent magnetic characteristics such as high magnetic flux density and low core loss can be obtained but also dimensional accuracy in punching is significantly improved when steel having a small Si and Al content the same as that of low-Si steel and thus essentially having high magnetic flux density is manufactured to adjust the average crystal grain diameter within a predetermined range and to add P to the resulting steel in an appropriate amount. The inventors have also found that the addition of P in an appropriate amount in addition to the adjustment of the total Si and Al content within a range of more than 0.05% by mass to about 2.5% by mass provides a greatly increased strength without reducing the magnetic flux density, that is, unprecedented well-balanced magnetic and strength characteristics can be obtained, in addition to high dimensional accuracy in punching.

[0035] 4. In the above item 1, 2, or 3, the non-oriented electrical steel sheet having excellent magnetic properties and dimensional accuracy in punching further having a thickness of 0.35 mm or less.

Problems solved by technology

However, when the Si content is increased, the core loss is lowered but the magnetic flux density is caused to decrease simultaneously.

However, there is a problem in that the core loss is large.

However, in the grain growth of such low-Si steel, since a decrease in strength arises, shear drop part and burr height of a punched sheet become large at a punching step.

Therefore, there is a problem in that the punching properties such as the dimensional accuracy are significantly lowered.

However, among the above techniques, the technique for improving the punching properties by adding P is focused on reducing the burrs by adjusting the hardness but does not make any consideration for the dimensional accuracy in punching.

Thus, it is conventionally difficult to obtain high strength together with high magnetic flux density.

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