CA2148972A1 - Amorphous iron based alloy and method of manufacture - Google Patents

Abstract

Disclosed are an amorphous iron based alloy having excellent magnetic characteristics as well as bendability and a method of manufacturing the amorphous iron based alloy.
The amorphous iron based alloy has a mean centerline Ra surface roughness of about 0.8 µm or less and the formula FexBySiZMna in approximate proportions wherein:
75 X 82 at%
7 Y 15 at%, 7 Z 17 at%, and 0.2 a 0.5 at%.
The method of manufacturing the amorphous iron based alloy comprises quenching and solidifying a molten alloy having the formula FexBySiZMna in approximate proportions wherein:
75 X 82 at%
7 Y 15 at%, 7 Z 17 at%, and 0.2 a 0.5 at%, and effecting the quenching and solidifying steps in a CO2 atmosphere containing H2 in an amount of about 1- 4% by volume.

Description

2I4~972 R~cR~ouND OF THE INVENTION
Field of the Invention The present invention relates to an amorphous iron based alloy having excellent magnetic characteristics as well as resistance to brittleness. The invention further relates to a method of manufacturing the amorphous iron based alloy.

Description of the Related Art As disclosed in Japanese Patent Unexamined Publications No. 54-148122 (1979), No. 55-9460 (1980) and No.57-137451 ( 1982), when a molten alloy composed of Fe-B-Si or the like is ejected onto the surface of a cooling roll rotating at high speed, using the single roll method or the like, and is quenched and solidified at a cooling speed of about 10 _ 106 C/sec., a so-called amorphous alloy sheet can be produced with a thickness of about several dozens of microns and wherein the atoms are disposed in a disorderly arrangement.
Such an amorphous alloy sheet has low iron loss and high magnetic flux density and has excellent so-called soft magnetic characteristics when attempted to be put into practical use as a core material of a transformer.
Nevertheless, such a sheet composed of the Fe-B-Si ternary amorphous alloy has disadvantages. Although the sheet can achieve an iron loss value which is low to some degree, the improvement of iron loss is limited. A further reduced iron loss cannot be expected from a ternary alloy.

To cope with this problem, attempts have been made to add various elements to the ternary amorphous alloy as a fourth ~component.
For example, Japanese Patent Examined Publication No.
1-54422 (1989) proposed an amorphous iron based alloy obtained by the addition of Mn, Ni and the like to an Fe-B-Si alloy in an amount of 0.5 - 3 at% (atomic percent) and the thus obtained amorphous iron based alloy had a low iron loss and excellent insulating film processing properties.
However, when Mn is added in an amount of 0.5 at% or more, the material becomes brittle. Further, reduction of magnetic flux density becomes a problem in practical use.
Japanese Patent Unex~mined Publication No. 62-192560 (1987) proposed an amorphous alloy obtained by adding one element or two or more selected from Cr, Mo, Ta, Mn, Ni, Co, V, Nb and W to a Fe-B-Si alloy, in an amount of 0.05 -5 at%, and further subjecting the resulting alloy to a process such as rolling or the like for adjustment of surface roughness of the alloy.
However, Japanese Patent Unexamined Publication No.
62-192560 (1987) does not take brittleness into consideration. Further, even if the surface roughness of the alloy made into a sheet is adjusted by rolling or the like, such a process is doubtfully effective for reduction of brittleness. In addition, adjustment of surface roughness is industrially very ineffective and also disadvantageous as to manufacturing cost.
The present invention is directed to overcoming the 21~8972 aforesaid problems advantageously, and relates to an amorphous iron based alloy having excellent magnetic characteristics as well as resistance to brittleness. It is further directed to a method of manufacturing such a superior amorphous iron based alloy.

SUMMARY OF THE lNV~:NlION
To improve the iron loss of an Fe-B-Si amorphous iron based alloy, it is effective in some ways to add a slight amount of Mn to the alloy, as described above. However, this is disadvantageous because it is accompanied by reduction of magnetic flux density and increase of brittleness of the material.
As a result of a zealous examination for overcoming the above disadvantage, the inventors have obtained the following knowledge:
(1) when a Mn content is 0.2 at% or more to less than 0.5 at~, iron loss can improved without so much reducing magnetic flux density;

(2)when molten alloy is quenched and solidified in a reducing atmosphere, in particular, in a CO2 atmosphere cont~ining a small amount of H2, the surface roughness of the sheet is greatly improved as compared with molten alloy quenched and solidified in the atmosphere and thus the cooling speed of the alloy is increased as well as the oxidized state of the sheet surface is also improved, and as result, cracks are difficult to be produced and material can be effectively ductile;

21~972 (3) when the surface roughness is improved, since a demagnetizing field due to magnetic poles which is caused by irregular surface is reduced, magnetic flux density is improved; and (4) when the surface property of the sheet is improved by effecting a quenching and solidifying process in the (H2 + CO2) atmosphere, the disadvantage such as the reduction of magnetic flux density and/or the embrittlement which are caused by the addition of Mn can be completely overcome.
More specifically, the present invention relates to an amorphous iron based alloy having excellent magnetic characteristics as well as resistance to brittleness, and is composed of a component represented by the following chemical formula and having a surface roughness of about 0.8 ~m or less in terms of a mean roughness along the centerline Ra. The formula is FexBySizMna, where about 75 S X S 82 at%
7 S Y ~ 15 at%
7 S Z S 17 at%
0.2 S a < 0.5 at%
The amorphous iron based alloy can effectively be bent in intimate contact in a critical bending test.
Further, the present invention relates to a method of manufacturing an amorphous iron based alloy having excellent magnetic characteristics as well as resistance to brittleness, comprising the step of quenching and solidifying a molten alloy composed of a component represented by the following chemical formula, wherein the 21~972 quenching and solidifying process is effected in a CO2 atmosphere cont~ining H2 in an amount of about 1 - 4% by volume.
The formula is FexBySizMna, where about 75 ~ X ~ 82 at%
7 ~ Y ~ 15 at%
7 ~ Z ~ 17 at%
0.2 ~ a < 0.5 at%.

BRIEF DESCRIPTION OF THE DRAWINGS
Results of actual test work giving examples how the present invention is achieved will be described below, and in the drawings, wherein:
Fig. 1 is a chart showing determined relationships between iron loss W13/so and Mn content in an amorphous iron based alloy composed of Fe78aB13Si~na.
Fig. 2 is a chart showing determined relationships between magnetic flux density B1o and Mn content in an amorphous iron based alloy composed of Fe78aB13SigMna.
Fig. 3 is a chart showing determined relationships between iron loss W13/50 and Mn contents in an amorphous iron based alloy composed of Fe81aB12Si7Mna.
Fig. 4 is a chart showing determined relationships between magnetic flux density B1o and Mn contents in an amorphous iron based alloy composed of Fe81aB12Si7Mna.
Fig. 5 is a chart showing determined relationships between magnetic flux density B1o and mean centerline roughness Ra both in an amorphous iron based alloy composed of Fe~.7B12Si7MnO.3 and in an amorphous iron based alloy composed of Fe77.7B13SigMnO3.
Fig. 6 is a chart showing relation between an amount of Mn content and the bending limit heights in an various atmosphere at the time of rapid solidification of an amorphous iron based alloy with a sheet thic~ness of 30 ~m composed of Fe81aB12Si7Mna.
Fig. 7 is a chart showing relation between an amount of Mn content and the bending limit heights in an various atmosphere at the time of rapid solidification of an amorphous iron based alloy with a sheet thickness of 20 ~m composed of Fe81aBl2Si7Mna.
Fig. 8 is a chart showing relation between a mean roughness Ra and the bending limit heights of at different sheet thicknesses each in an amorphous iron based alloy composed of Fe~.7Bl2Si7MnO3.

Fig. 1 shows a result of actual tests on the relationship between amount of Mn and iron loss W13/50 (iron loss value when the frequency was 50 Hz and the magnetic flux density was 1.3T) of an amorphous iron based alloy composed of Fe~aB13SigMna.
The molten alloy was quenched and solidified in air, in air and CO2, and in a CO2 atmosphere containing H2 up to 4%. The resulting amorphous iron based alloy was 25 ~m thick and 20 mm wide and was annealed at 400C for one hour in a magnetic field. The resulting samples were investigated.

2l~8972 Fig. 2 shows results of tests on the relationship between Mn content and magnetic flux density B1o (magnetic flux density in a magnetic field of 1000 A/m) of an amorphous iron based alloy having the same components. The band-shaped dispersion of the magnetic flux density to the Mn content in Fig. 2 is caused by dispersion of surface roughness of the samples.
It is found from FIGS. 1 and 2 that a low iron loss can be obtained and the reduction of a magnetic flux density can be also suppressed by the addition of a small amount of Mn to Fe-B-Si ternary alloy.
Figs. 3 and 4 show the relationship between Mn content and iron loss W13/so and the relationship between Mn content and magnetic flux density B1o of an amorphous iron based alloy composed of Fe81aB12Si7Mna, respectively in the same way as in Figs. 1 and 2.
A sheet made of an amorphous iron based alloy composed of Fe81aB12Si7Mna was annealed at 360C for one hour in a magnetic field. The band-shaped dispersion of the magnetic flux density to the Mn content in Fig. 4 is caused by dispersion of surface roughness of the samples.
As apparent from FIGS. 3 and 4, a low iron loss can be obtained and the reduction of a magnetic flux density can be also suppressed by the addition of a small amount of Mn also in this case.
Further, in particular, when a large amount of Fe exceeding 80~ is contained as the case of this alloy composition, there is also an advantage that the effect of 21~8972 reducing an iron loss resulting from the addition of Mn is more remarkably increased.
Fig. 5 shows the relationship between mean roughness along the centerline Ra and magnetic flux density when a is controlled to be 0.3 at% in the amorphous iron based alloys composed of Fe78aB13SigMna and Fe81aB12Si7Mna.
The Ra is an average value obtained by measuring the surface contacted to a quench roll three times at the center part of the sheet in a sheet width direction according to JIS B0601.
It is shown in Fig. 5 that when the average roughness on the centerline Ra is reduced, the magnetic flux density can be greatly improved.
When an amorphous iron based alloy with a sheet thickness of 30 ~m composed of Fe81aB12Si7Mna was quenched and solidified in air, the bending limit height was increased as the Mn content was increased as shown by the dotted line in Fig. 6.
The bending limit height is an index for indicating degree of brittleness of a material. It is represented by the distance between the inner surfaces of a sheet 150 mm long just before the sheet is broken when it is being bent with the surface thereof in contact with a roll directed to the outside. When the bending limit height is 0, the sheet can be bent upon itself in intimate contact.
On the other hand, when the same amorphous iron based alloy was quenched and solidified in a CO2 atmosphere cont~in;ng 3% H2, the resulting bending limit height of the alloy was greatly reduced. This is shown by the solid line of Fig. 6.
Further, FIG. 7 shows the case that a sheet having the same composition, is 20 ~m thick in the same way. When the molten alloy was quenched and solidified in the CO2 atmosphere cont~ining 3% H2 in the same way as FIG. 6, it is found that the bending limit height of the amorphous alloy is reduced and brittleness is improved.
A difference of characteristics of the sheet may be caused by a difference of the atmosphere in which the sheet is processed. This affects the condition of the surface of the sheet. We have found that when the sheet was made in air, the sheet had a surface roughness of about 0.8 - 1.2 ~m, expressed as Ra, on the surface of the sheet in contact with a roll, whereas when the sheet was made in a CO2 atmosphere cont~ining 3% H2, the sheet had a surface roughness of about 0.4 - 0.8 ~m and less irregularity.
FIG. 8 shows the relationship between Ra and brittleness. It can be found that when the Ra is reduced, the sheet become less brittle. The number of irregular portions from which cracks start, when the sheet is bent, is very small and the sheet is difficult to be cracked accordingly.
Further, when the Ra is reduced, since heat is effectively transmitted from the alloy to a cooling roll when the alloy is quenched and solidified, a cooling speed is increased so that the alloy reaches the ideal amorphous state.

2I~8972 Further, a reason why the CO2 + H2 atmosphere is effective to the improvement of brittleness is that an effect of improving the oxidized state of sheet surface is also obtained by the reducing atmosphere, in addition to the effect of improving the Ra.
Next, reasons why the components of the novel alloy are limited to the above ranges will be described below.

Fe: about 75 - 82 at% (hereinafter, atomic percentages are simply shown as %) Fe is an important element for determining magnetic properties. When the Fe content is less than about 75%, the magnetic flux density of the alloy is too low, whereas when the Fe content exceeds about 82%, iron loss is increased and thermal stability deteriorates. Thus, the Fe content is limited to a range of about 75 - 82%. A more preferable range is about 80 to 82%.

B: about 7 - 15%
Although B is useful to make the material amorphous, when B is less than about 7%, it is difficult to make the material amorphous, whereas when the B content exceeds about 15%, magnetic flux density is reduced and the Curie temperature is also reduced. Thus, the B content is limited to a range of about 7 - 15%. A more preferable range of the content is about 9 - 13%.

Si: about 7 - 17%

21~8972 Although Si promotes making the material amorphous and achieves thermal stability, when the Si content is less than about 7%, the Curie temperature is low and not practically usable, whereas when the Si content exceeds about 17%, iron loss is increased. Thus, the Si content is limited to a range of about 7 - 17%. A more preferable range of the content is about 7 - 10%.

Mn: about 0.2% or more to less than about 0.5%
Although Mn is effective to reduce iron loss, when Mn is less than about 0.2%, there is little effect upon iron loss. When the Mn content is about 0.5% or more, magnetic flux density is reduced as the Mn content is increased and the material becomes more brittle. Thus, the Mn content is limited to a range of from about 0.2% or more to less than about 0.5%.

When a material is quenched and solidified in air, the material becomes more brittle as shown in Figs. 6 and 7.
When, for example, a transformer winding is made, difficulties such as breaking of the sheet are likely to be caused by the brittleness of the material.
The bending limit height should be as small as possible to prevent these difficulties. A sheet that is capable of being bent upon itself in intimate contact is most effective.
When a material can be bent in intimate contact, no breaking of the sheet is caused when winding a transformer.

21~8972 More specifically, when the bending limit height is about 0.10 mm, this defect occurs at a rate of 0.2%, whereas when the bending limit height is about 0.25 mm, defects occur at a rate of 0.8%.
Thus, the present invention effectively controls and limits the brittleness of a material by keeping its surface roughness to about 0.8 ~m or less (Ra) as well as reducing the oxidation of the surface of a sheet by effecting quenching and solidifying in a CO2 atmosphere containing H2 in a range of about 1 - 4%.
The atmosphere used in quenching and solidification is m~ i n ly composed of CO2 because the gas is inactive and available at low cost and has a high radiation capability because it is a ternary gas and has a high specific gravity. Thus, the gas effectively acts to reduce surface roughness by entrapment of the gas.
It is important to maintain the H2 gas content of the CO2 gas to a range of about 1 - 4%. When the H2 gas content is less than about 1%, surface roughness (Ra) cannot be kept to about 0.8 ~m or less. Also the reduction of surface oxidation is not sufficient because a sufficient reducing atmosphere cannot be obtained. In sharp distinction, when the H2 gas content exceeds about 4%, the handling of the gas becomes a serious problem because there is danger of explosion. Further, when the H2 gas content is further increased the gas invades the sheet surface and makes the sheet brittle.

21~72 DET~TT~n DESCRIPTION OF PREFERRED EMBODIMENT
Example 1 Molten alloys containing Fe in an amount exceeding 80 at% and various components shown in Table 1 were injected onto the surface of a Cu roll rotating at high speed in a vessel of a CO2 atmosphere containing 3%H2 and made to amorphous alloy sheets of 25 ~m thick and 20 mm wide and then the sheets were annealed at 340 - 420C for an hour in a magnetic field.
Annealing in a magnetic field is a well-known method of annealing a sheet while a magnetic field is applied to the sheet in a direction toward which the sheet is desired to be magnetized so that the soft magnetic properties of the sheet are improved.
Table 1 shows the result of measurements of iron loss values, magnetic flux density and surface roughness of the surface in contact with the roll of the resulting amorphous iron based alloy sheets.
As is apparent from Table 1, the amorphous alloy sheets obtained by the present invention had low iron losses and magnetic flux densities excellently adapted to be used for transformers.
Further, the sheets could easily be bent upon themselves in intimate contact in critical bending tests, and had excellent resistance to brittleness.
Whereas, although the comparative examples could be subjected to an intimate contact bending, all of them had high iron loss or low magnetic flux density.

Table 1 Sample C~ lt~- (at%)~13/50 Blo Surface P-ug' -99 Critlcsl BendLng HeLght Reference No. (W/kg) (T) Ra (~m) (mm) 1 ~egl.6 Bll SL7 Mn0A 0-109 1.550 0.7 LntLmate bendLng possLble Example of the Present LnventLon 2 ~e8155 Bll SL8 MnO.45 0.087 1.546 0.8 - dLtto - - dLtto 3 Pegl.7 BlO SL3 Mno.3 0.104 1.547 0.6 - dLtto - - dLtto 4 Pegl.6 Blo SL8 Mn0A 0.091 1.542 0.7 - dLtto - - dLtto Ee80~8 B12 SL7 Mn0.2 0-095 1.538 0.6 - dLtto - - dLtto 6 ~ego.6 B12 SL7 Mno.4 0.084 1.530 0.7 - dLtto - - dLtto 7 ~e81.0 B12 SL7 0.213 1.545 0.7 - dLtto - C~ t~ve Example 8 Pe8l.9 Bll MnO.l 0.162 1.540 0.7 - ditto - - ditto 9 Ee80.3 B12 Si7 Mno.7 0.082 1.515 0 7 - ditto - - ditto ~80.1 Bl2 Si7 Mno.g 0.081 1.493 0.7 - ditto - - ditto CD

214897~

Example 2 Molten alloys containing Fe in an amount 80 at% or less and various components shown in Table 2 were evaluated in the same way as the embodiment 1 and the result of the evaluation is shown in Table 2.
As apparent from Table 2, all of the amorphous alloy sheets obtained according to the present invention had low iron loss and excellent bendability.
Whereas, the comparative examples had high iron loss or low magnetic flux density although they could be subjected to intimate contact bending.
According to the present invention, the iron loss of an Fe-B-Si amorphous iron based alloy can be reduced and its magnetic flux density can be increased.
Further, according to the present invention, the brittleness of a material after addition of Mn can be effectively reduced and sheet breakage in manufacture of winding transformers can be prevented by effecting the quenching and solidifying process in a CO2 atmosphere contA; n ing a slight amount of H2.

Table 2 Sample Composition (at%)W13~50 B1o Surface P~ L ~ Critical Bending ~eight Reference No. (W/kg) (T)Ra (~m) (mm) 11 PeM,8 B13 Si9 Mn0.2 0.0891.515 0.6intLmate bending possible Exsmple of the Present invention 12~e77.7 B13 Si9 Mno.3 0.0821.512 0.7 - ditto - - ditto 13~e77,6 B13 Si9 Mno4 0.0801.508 0.7 - ditto - - ditto -14~e7755 B13 Si9 Mno.45 0.0801.505 0.7 - ditto - - ditto 15Pe7765 B13 Si9 Mno.35 0.0801.510 0.8 - ditto - - ditto 16Ee79,7 B12 Si8 Mno30.098 1.5200.7 - ditto - - ditto 17Ee796 B12 Sig Mno40.091 1.5180.7 - ditto - - ditto 18~e767 B9 Si14 Mno30.092 1.4930.6 - ditto - - ditto -19 Ee766 B9 Si14 Mno,4 0-0901.490 0.7 - ditto - - ditto -l?e78 B13 Si9 0.1151.520 0.6 - ditto - C~ tive Example 21 Ee779 B13 Si9 MnQl 0.1131.511 0.7 - ditto - - ditto -22 Pego Bl2 Sig 0.231 1.5350.6 - ditto - - ditto -23 ~eM Bg Si14 0.203 1.4950.7 - ditto - - ditto -24 ~eM 2 B13 Si9 Mn0.80.080 1. 463 0 . 6 - ditto - - ditto Example 3 Amorphous iron alloy sheets each composed of ' Fe80.6B12Si7MnO.4 (thickness: 30 ~m) were made by the same method as Example 1 except that the atmospheres used in quenching and solidification were variously changed as shown in Table 3.
Surface roughnesses of the surfaces in contact with the roll and bending limit heights of each of the thus obtained sheets were investigated. Table 3 shows the results of the investigation, together with iron loss and magnetic flux density.
As is apparent from Table 3, the surface roughnesses and the bending limit heights of the sheets were changed depending upon differences of the atmospheres used in quenching and solidification. When the sheets were made in atmospheres according to the present invention, the sheets had small mean roughnesses along centerlines Ra of 0.7 ~m and had excellent resistance to brittleness more than sufficient to enable intimate contact bending.
When an atmosphere contained H2 in an amount less than 1%, all of the mean centerline Ra surface roughnesses exceeded 0.8 ~m, and further, as the Ra increased, the limit bending height increased and brittleness proceeded.
Further, when an excessive amount of H2 was contained (Sample No. 28), although the Ra was 0.7 ~m, intimate contact bending could not be effected.

Table 3 SampleAtmosphere in Wl3/50 Blo RaCritical Bending Height Reference No.Quenching and (W/kg) (T) (~m) Solidification Air 0.085 1.524 1.2 0.25 Comparative Example 26 C02 0.085 1.529 0.9 0.13 Comparative Example 270.5%H2 + C02 0.084 1.530 0.9 0.10 Comparative Example 28 lOZH2 + C02 0.084 1.536 0.7 0.05 Comparative Example _O 29 1.0%H2 + C02 0.084 1.537 0.7 intimate contact Example of the Present bending achieved Invention 4-0%H2+ C02 0.084 1.537 0.7 intimate contact Example of the Present - bending achieved Invention 31 60%C02 + Air 0.085 1.525 1.1 0.20 Comparative Example 32 30ZC02 + Air 0.085 1.525 1.0 0.16 Comparative Example

Claims (7)

1. An amorphous iron based alloy having excellent magnetic characteristics as well as bendability, and having a mean centerline Ra surface roughness of about 0.8 µm or less, said alloy having the formula FeXBySiZMna in approximate proportions wherein:
75 X 82 at%, 7 Y 15 at%, 7 Z 17 at%, and 0.2 a < 0.5 at%.

2. An amorphous iron based alloy according to claim 1, which can be bent upon itself in intimate contact in a critical bending test.

3. A method of manufacturing an amorphous iron based alloy having excellent magnetic characteristics and bendability without breaking, comprising: quenching and solidifying a molten alloy having the formula FeXBySiZMna in approximate proportions wherein:
75 X 82 at%, 7 Y 15 at%, 7 Z 17 at%, and 0.2 a < 0.5 at%, and effecting said quenching and solidifying steps in a CO2 atmosphere containing H2 in an amount of about 1 - 4% by volume.

4. An amorphous iron based alloy according to claim 1, wherein the mean centerline Ra surface roughness is from about 0.4 to about 0.8 µm.

5. An amorphous iron kased alloy according to claim 1, 2 or 4, wherein a is from 0.2 to 0.45.

6. A method of manufacturing the amorphous iron based alloy according to claim 1, 2 or 4 in a sheet form, which comprises:
injecting a molten alloy having the formula FexBySiZMna (in which X, Y, Z and a are as defined in claim 1) onto a surface of a cooling roll rotating at a high speed in a vessel saturated with a CO2 atmosphere containing 1 - 4% by volume of H2, to quench and solidify the molten alloy in a sheet form, and annealing the sheet in a magnetic field.

7. A method according to claim 6, wherein the cooling roll is made of copper and the annealing is carried out at a temperature of 340 - 420°C.