Metal treatment – Stock – Magnetic
Reexamination Certificate
2001-04-06
2002-11-12
Sheehan, John P (Department: 1742)
Metal treatment
Stock
Magnetic
C148S307000, C148S111000, C148S112000, C148S120000, C148S121000
Reexamination Certificate
active
06478892
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-oriented electrical steel sheet excellent in workability and iron loss property which can be used as iron core material for electric apparatuses and a method for producing the same.
2. Description of the Related Art
An improvement in the efficiency of electric apparatuses has been desired intensely under the trend toward worldwide electricity and energy saving and global environmental conservation. In particular, most recently, a material with better magnetic property, i.e. better iron loss property, than that presently available has been required for a non-oriented electrical steel sheet used for rotors or stators while the efficiency upgrading of rotating machines is developing.
As a means to reduce the iron loss of a non-oriented electrical steel sheet, a method to reduce eddy current loss by increasing the content of alloying elements such as Si, Al and Mn, etc. and increasing electric resistance is widely and generally used. Further, after determining a component, it is important to attempt to optimize iron loss by adjusting the crystal grain diameter of a product sheet to about 100 to 150 &mgr;m.
With regard to workability, it has been proven recently that the problems of rough ridges and burrs, etc. occur during the punching of a motor core if the crystal grain diameter of a product sheet is too large. On the other hand, the iron loss of a core deteriorates if the crystal grain diameter of a product sheet is too small. To cope with those problems, means for reducing a crystal grain diameter during the punching of a core and of growing crystal grains to some extent during the stress relief annealing of the core have been required.
It is well-known that the most harmful precipitate as an impurity for preventing crystal grain growth markedly is MnS having a relatively low solution temperature. Though the reduction of S amount itself may reduce the precipitate in a process for refining steel, there is a limitation in industrial application. To cope with this, disclosed are methods to suppress the precipitation of fine MnS by a means to fix S in steel as precipitates with a high solution temperature using rare earth elements (REM) such as Ce and La, etc. (Japanese Unexamined Patent Publication No. S51-62115) and by a means to fix S using Ca (Japanese Unexamined Patent Publication No. S59-74213).
However, the precipitates of REM and S, for example, actually have complicated forms including oxygen and therefore, dissolve partially since they are compound precipitates even though the solution temperature is high as single substance, and precipitate again as fine precipitates with Mn. In these cases, if the precipitates of REM and Ca become the precipitation nuclei of MnS, above problem will be avoided. However, CaS which is a precipitate of Ca and S, for example, has poor lattice coherence with MnS and its performance as precipitation nucleus is poor when S is contained to some extent or more and the formation of MnS cannot be avoided.
SUMMARY OF THE INVENTION
The present invention provides a low iron loss non-oriented electrical steel sheet having a small crystal grain diameter and excellent workability during the punching of a motor core and also having a sufficiently grown large crystal grain diameter and excellent workability after stress relief annealing by a user, and a method for producing the same.
The gist of the present invention is as follows:
(1) a low iron loss non-oriented electrical steel sheet excellent in workability, characterized by containing, in weight %, 0.010% or less of C, 0.1 to 1.5% of Mn, 0.1 to 4% of Si, 0.1 to 4% of Al, wherein the latter three elements satisfy the formula Si+Mn+Al≦5.0%, 0.0005 to 0.0200% of Mg, and the remainder consisting of Fe and unavoidable impurities,
(2) a low iron loss non-oriented electrical steel sheet excellent in workability, containing, in weight %, 0.010% or less of C, 0.1 to 1.5% of Mn, 0.1 to 4% of Si, 0.1 to 4% of Al, wherein the latter three elements satisfy the formula Si+Mn+Al≦5.0%, 0.0005% or more of Mg, 0.0005% or more of Ca, wherein the total amount of Mg and Ca is 0.0200% or less, and the remainder consisting of Fe and unavoidable impurities,
(3) a low iron loss non-oriented electrical steel sheet excellent in workability, containing, in weight %, 0.010% or less of C, 0.1 to 1.5% of Mn, 0.1 to 4% of Si, 0.1 to 4% of Al, wherein the latter three elements satisfy the formula Si+Mn+Al≦5.0%, 0.0005% or more of Mg, 0.0005% or more of REM, wherein the total amount of Mg and REM is 0.0200% or less, and the remainder consisting of Fe and unavoidable impurities,
(4) a low iron loss non-oriented electrical steel sheet excellent in workability, containing, in weight %, 0.010% or less of C, 0.1 to 1.5% of Mn, 0.1 to 4% of Si, 0.1 to 4% of Al, wherein the latter three elements satisfy the formula Si+Mn+Al≦5.0%, 0.0005% or more of Mg, 0.0005% or more of Ca and 0.0005% or more of REM, wherein the total amount of Mg, Ca and REM is 0.0200% or less, and the remainder consisting of Fe and unavoidable impurities,
(5) a low iron loss non-oriented electrical steel sheet excellent in workability according to item (1) or (2), characterized by the amount of S contained in said steel sheet not exceeding 0.010% in weight %,
(6) a method for producing a low iron loss non-oriented electrical steel sheet excellent in workability, characterized by deoxidizing molten steel with Al and then adding Mg source therein when refining the steel containing, in weight %, 0.010% or less of C, 0.1 to 1.5% of Mn, 0.1 to 4% of Si, 0.1 to 4% of Al, 0.0005 to 0.0200% of Mg, and the remainder consisting of Fe and unavoidable impurities,
(7) a method for producing a low iron loss non-oriented electrical steel sheet excellent in workability, characterized by adding at least one or more of Mg source, Ca source and REM source in molten steel after deoxidizing the molten steel with Al when refining the steel containing, in weight %, 0.010% or less of C, 0.1 to 1.5% of Mn, 0.1 to 4% of Si, 0.1 to 4% of Al, 0.0005% or more of Mg, 0.0005% or more of Ca, 0.0005% or more REM, wherein the total amount of Mg, Ca and REM is 0.0200% or less, and the remainder consisting of Fe and unavoidable impurities,
(8) a method for producing a low iron loss non-oriented electrical steel sheet excellent in workability according to item (6) or (7), characterized by reheating a slab containing said component, hot-rolling the slab, pickling the hot-rolled sheet after hot rolling or after hot rolling and then annealing, producing the steel sheet with a product thickness by single cold-rolling or two or more cold-rolling while rendering intermediate annealing in between, and then finish-annealing the steel sheet at a temperature of 700 to 1,100° C. in a continuous annealing line,
(9) a method for producing a low iron loss non-oriented electrical steel sheet excellent in workability according to any one of items (6) to (8), characterized by the amount of S contained in said steel sheet not exceeding 0.010% by weight.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will be explained in detail hereunder.
The present inventors have selected elements to be added to a steel sheet considering the following points as a guideline to produce a material with excellent grain growth property. That is, the present inventors, so as not to precipitate fine MnS, have selected elements (1) whose S compounds commence to precipitate at a temperature higher than the temperature at which MnS commences to precipitate and (2) whose S compounds or oxides can act as the precipitation nuclei of MnS even though MnS precipitates.
As a candidate of (1), the present invention has selected Mg in contrast to Ce employed in Japanese Unexamined Patent Publication No. S51-62115 and Ca employed in Japanese Unexamined Patent Publication No. S59-74213. Though the data on the precipitation of MgS are not well known, it is estimated that MgS commences precipitation at a
Kanao Shinichi
Kawamata Ryutaro
Kubota Takeshi
Kumano Tomoji
Morohoshi Takashi
Kenyon & Kenyon
Nippon Steel Corporation
Sheehan John P
LandOfFree
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