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The present invention relates to a process for the preparation of Fe-based ultrasoft nanocrystallme ferromagnetic alloys.
The present invention particularly relates to a process for preparation of Fe-Nb-Cu-Al-Mn-Si-B based ferromagnetic alloys and preparation of ultrasoft nanocrystalline ferromagnetic ribbons by using the same alloys.
The present invention will be useful for the preparation of low cost ferromagnetic alloys used in magnetic cores for sensor applications. It will be used for high frequency transformers, magnetic heads, saturable reactors, choke coils etc.
Conventional materials used in various magnetic parts of power supplies and magnetic head are mainly permalloy, Fe-Al-Si alloy, Silicon steels, ferrite and the like. In view of increasing demand for miniaturization, higher frequency electronic equipment and appliances, the above materials are not suitable.
There are various metallic magnetic alloys which have good soft magnetic properties. These alloys are electrical grade silicon steel, Fe-Si-Al alloys, Ni-based permalloy etc. These materials are prepared by melting, casting and very controlled rolling and heat-treatment to generate texture as descnbed in the book 'Ferromagnetism' by Richard M.Bozorth, Bell Telephone Laboratories, Murray Hill, N.J.,1993. The process of generating texture is expensive. In this process of preparation the magnetocrystalline anisotropy, which is detrimental for achieving superior soft magnetic properties, cannot be eliminated. Moreover the brittleness of the alloy like Fe-Si-Al prevents the production of thin sheets for winding as a transformer core or for other applications. Some alloys like Ni-base permalloy are mechanically soft and very sensitive to plastic deformations and special care is needed to handle it.
Reference may be made to European Patent No.: 87114568.6 and 88111364.1 entitled "Fe-based soft magnetic alloy and method of producing same" and "Magnetic core an method of producing the same" respectively, wherein the addition of Cu and at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo to a Fe-based alloy having an essential composition of Fe-Si-B and a proper heat treatment exhibited excellait soft magnetic properties. The alloy was initially made in the form of amorphous material and then by proper heat treatment gave nanocrystalline particles and thus having good soft magnetic properties. However, it uses the pure metals which are expensive and not cost-effective for industrial scale production Moreover, the properties are still unsatisfactory, as there is scope of further improvement of properties like core loss, coercivity and permeability.
Reference may be made to Japanese Patent No.320504 wherein Fe-based soft magnetic alloys having precipitated super fine crystal grains and soft magnetic properties comparable to those of Co-based amorphous alloys have been proposed. The disadvantages of these Fe-based alloys is that their magnetic properties have large dependence on the heat-treatment temperatures during their production process. When the heat treatment temperature exceeds the prescribed range, coarse crystals are liable to be precipitated and the above excellent soft magnetic properties cannot be obtained.
Reference may be made to U.S Patent No.5522948 entitled "Fe-based soft magnetic alloy, method of producing same and magnetic core made of same". Here super fine grains necessary for soft magnetic properties have been generated using a ceramic fusible material like CuO, Cu2O, SnO> etc as nucleation centres in Fe-based alloys This process bear a disadvantage of using powder technique were consolidation into magnetic cores may lead to porosity which deteriorates the magnetic properties.
The main object of the present invention is to provide a process for preparation of Fe based ferromagnetic alloys.
Another object of the present invention is to provide a process for preparation of Fe-Nb-Cu-Al-Mn-Si-B based ultrasoft nanocrystallme ferromagnetic alloys using commercial grade raw matenals and thereby reducing the cost of production.
Still another object of the present invention is to provide a process for preparation of Fe-Nb-Cu-Al-Mn-Si-B based ultrasoft nanocrystallme magnetic ribbons.
The matenals which can be magnetised and demagnetised easily are considered to be the soft magnetic alloys. Thus the Fe-based alloys which have been prepared in the form of rod was considered to be the soft magnetic matenals However, their magnetic softness are restricted by the magnetocrystalline and magnetoelastic anisotropies. The melt spinning process where the melt is quenched by the rapidly rotating drum to bye pass the crystallisation process has been adopted in the present work to reduce the effect of magnetocrystalline amsotropy. Hence the process which involved the preparation of amorphous ribbons by rapid quenching technique eliminate the magnetocrystalline anisotropy and the materials became magnetically softer. However, after this process the matenals were having magneto-elastic anisotropy. So there was scope for further processing of the materials to reduce magnetoelastic anisotropy to get ultrasoft magnetic matenals. This was done by heat-treatment process. After the heat-treatment process nanoparticles, which have negative magnetostriction value, embedded in positive magnetostrictive amorphous matnx. Hence the overall
magnetostriction value was minimum after the heat-treatment process. Thus after entire process the materials have ultrasoft magnetic properties
In the process of present invention Fe - based soft magnetic alloy matrix is prepared by mixing commercial grade low carbon iron, ferro-niobium, ferro-silicon, ferro-boron and elctrolytic grade copper and have the general formula:
Accordingly the present invention provides a process for preparation of Fe-based ultrasoft nanocrystallme ferromagnetic alloys which comprises:
i) melting low carbon iron in the temperature of 1 600K - 1 700K,
ii) adding ferro-niobium, ferro-boron to the melt and raising the temperature to 1 900K - 2000K,
lii) adding ferro-silicon & copper to the said melt,
iv) casting the melt of alloy matrix in the form of cylindrical ingot,
v) melting the cast of alloy matrix in a crucible in the temperature 1400-1500K and ejecting on a
rapidly rotating quenching wheel to get ribbon, vi) heating the ribbon for 1 5-20 minutes in inert gas atmosphere in the temperature 600-900K to
get nanocrystallme state.
In the present invention heat treatment in an optimum temperature, a-Fe(Al,Si) nanocrystallme particles are embedded in amorphous matrix and hence ultrasoft magnetic properties are acheived.
In an embodiment of the present investigation the matenals used to prepare Fe-based alloy matrix may be selected from the commercial grade low carbon iron, ferro-niobium, ferro-silicon, ferro-boron and electrolytic grade copper and may have composition range:
Low Carbon iron (Wt %)
Fe : «8-Q«
C : 0.0 1 -0.04
Mn 0.02-0.06
Si : 0.0-0.2
Al 0.001-0006
Ferro-Niobium (Wt %)
Fe : 50-70
Nb ; 30-50
Al : 6-8
Mn :3-6
Ferro-Silicon (Wt %)
Fe : 15-20
Si : 70-90
Fe : 40-60
B : 30-50
In another embodiment of the present invention Fe-based alloy matrix may have the general formula Feioo-x-y-/.a-iH;NbxCuyAlzMn,SibBc which may satisfy the following equation:
3
0.5
0.5
12.5
7.5
20
5
In another embodiment of the present invention the separation between the quenching wheel and the nozzle of die crucible may be 0.4 - 0.6 mm and nozzle diameter may be 1.2 -1.8mm.
In yet another embodiment of the present invention the quenching wheel velocity may be 32 - 42 mitre/second
In still another embodiment of. the present invention the Fe-based alloy matrix may be heat-treated in die temperature 725 - 825K to obtain nanocrystalline structure.
The novelty of the present invention is the use of commercial grade low carbon iron, ferro-niobium, ferro-silicon, ferro-boron materials for preparation of Fe-based alloy matrix and thereby reducing the cost of production. In the preparation of Fe-based alloy ribbon the crucible position and heat temperature schedule are the important novel features of the invention.
The following examples are given by way of illustration and should not be construed to limit the scope of the invention:
Example-1
3kg of the alloy having composition Fevo.gNb.vTCuiAh.vMno.TSii.^By.fi was prepared in air induction furnace using the following materials
low carbon (
Ferroniobium = 0.43 kg
Ferrosilicon =0.34 kg
Ferroboron = 0.44 kg
Cu = 0.04 kg
The required amount of Al and Mn came from their presence in ferroalloys and iron. The melting of the alloy was done in a air-induction heating furnace. When the temperature of the low carbon iron was 1675K, terroniobium was added to it. Subsequently, ferro-boron and ferro-silicon were added. The temperature of the melt was allowed to nse up to 1925K when copper was added. The melt was poured in a sand mould and cast in the form of rod.
Example-2
3kg of the alloy having composition Fe^.sNb^UiAlo.sMno-iSiioBg.., (m at%) was prepared in air induction furnace using the following materials:
low carbon (
Ferroniobium = 0.58 kg
Ferrosihcon Ferroboron Cu
=0.38 kg = 0.45 kg = 0.04 kg
Hie required amount of Al and Mn came from their presence in ferroalloys and iron. The melting of the alloy was done in a air-mductjon heating furnace. When the temperature of the low carbon iron was 1675K, ferroniobium was added to it. Subsequently, ferro-boron and ferro-silicon were added. The temperature of the melt was allowed to rise up to 1925K when copper was added. The melt was poured in a sand mould and cast in the form of rod
Example-3
About 250 gins of the alloy of composition Fe7o.8TMb.v7CiiiAl2.7lvm0.7Sii3.
Table -1
(Table Removed)
Example-4
The processing of FeTdsNbijCuiAhjMno.TSiu.^B?,, alloy in the form of ribbon was done by keeping separation between the quenching wheel and the crucible nozzle end at 0.5mm and changing the quenching wheel velocity The wheel surface velocity was varied between 27m/sec and 42m/sec. The thickness as well as the fracture strain of the prepared ribbons changed with the quenching wheel velocity The magnetic properties of the materials was also dependent on the quenching wheel velocity
The results are shown in the table-2
Table - 2
(Table Removed)
Example-5
The ribbon of composition Fe7o.8Nb^CuiA1...7Mn0.7Sii:,.?B7.(, Was processed heat treated at different temperature in inert atmosphere for 15 minutes. The magnetic properties were evaluated for different heat treated materials and is shown in the table-3
Table - 3
(Table Removed)
Main advantages of the present invention are:
1 Processing of ultrasoft magnetic materials using low carbon iron, elctrolytic copper and commercial
grade ferroalloys of boron, niobium and silicon reduces the cost of preparation of the alloys.
2 Processing of the magnetic materials in the form continuous ribbons and hence no further rolling is
required for thinning down the ingot.
3 Processing of magnetic materials in the form of ribbon with coercivity as low as 0.32AAn by suitable
heat-treatment schedule.
We Claim:
1. A process for the preparation of Fe-based ultrasoft nanocrystalline ferromagnetic alloys which comprises:
I. melting low carbon iron at a temperature of 1600K - 1700K,
II. adding ferro-niobium, ferro-boron to the melt and raising the temperature to 1900K - 2000K,
III. adding ferro-silicon & copper to the above said melt,
IV. casting the melt of alloy matrix in the form of cylindrical ingot,
V. melting the cast of alloy matrix in a crucible at a temperature of 1400K - 1500K and ejecting on a rapidly rotating quenching wheel to get ribbon,
VI. characterized in that heating the ribbon for 15-20 minutes in inert gas atmosphere at a temperature of 600-900K to get nanocrystalline state.
2. A process as claimed in claim 1 wherein the materials used to prepare Fe-based alloy matrix are selected from the commercial grade low carbon iron, ferro-niobium, ferro-silicon, ferro-boron and electrolytic grade copper.
3. A process as claimed in claims 1-2 wherein the separation between the quenching wheel and the nozzle of the crucible is 0.4 - 0.6 mm and nozzle diameter is 1.2 - 1.8mm.
4. A process as claimed in claims 1-3 wherein the quenching wheel velocity is 32 - 42 metre/second.
5.A process for the preparation of Fe-based ultrasoft nanocrystalline ferromagnetic alloys substantially as herein described with reference to the examples.
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