Ferromagnetic amorphous alloy strip and method for manufacturing sameTechnical Field
The present invention relates to ferromagnetic amorphous alloy ribbons for use in transformer cores, rotating machinery, electrical chokes (chokes), magnetic sensors and pulse power equipment, and to a method of making the ribbons.
Background
The iron-based amorphous alloy ribbon exhibits excellent soft magnetic properties including: low magnetic loss under AC excitation; can be applied to energy-efficient magnetic devices (energyefficientmagnetics) such as transformers, motors, generators, energy management devices (which include pulsed power generators and magnetic sensors). In these devices, ferromagnetic materials with high saturation induction and high thermal stability are preferred. Moreover, in large-scale industrial applications, the ease of manufacture of the materials and the cost of their raw materials are both important factors. Alloys based on amorphous Fe-B-Si meet these requirements. However, the saturation induction of these amorphous alloys is lower than that of crystalline silicon steel (crystalloid silicon steel) conventionally used in devices such as transformers, which results in a device based on amorphous alloys having a larger size to some extent. Accordingly, various efforts have been made to develop amorphous ferromagnetic alloys having higher saturation induction. One approach is to increase the iron content in the Fe-based amorphous alloy. However, this is not straightforward, as the thermal stability of such alloys decreases with increasing Fe content. To alleviate this problem, elements such as Sn, S, C, and P have been added. For example, U.S. Pat. No.5,456,770 (referred to as the' 770 patent) discloses amorphous Fe-Si-B-C-Sn alloys in which the addition of Sn increases the formability of such alloys and their saturation induction. It is disclosed in U.S. Pat. No.6,416,879 (referred to as the' 879 patent) to add P to an amorphous Fe-Si-B-C-P system and increase the saturation induction with increased Fe content. However, the addition of elements such as Sn, S, and C in the Fe-Si-B based amorphous alloy reduces the ductility (yield) of the as-cast strip, which results in difficulty in manufacturing a wide strip. Furthermore, if P is added to Fe-Si-B-C based alloys as disclosed in the' 879 patent, it results in a loss of long-term thermal stability, which in turn results in an increase in core loss of several tens of percent over several years. Thus, the amorphous alloys disclosed in the '770 patent and the' 879 patent have not been actually produced by casting from their molten state.
In addition to the high saturation induction required in magnetic devices such as transformers, inductors, and the like, a high B-H squareness ratio (B-Hsquare) and a low coercivity HcIt is also desirable wherein B and H are the magnetic induction and the excitation magnetic field, respectively. The reason for this is that: such magnetic materials have a high magnetic softness, meaning that they are easily magnetized. This therefore results in low magnetic losses in magnetic devices using these materials. With these factors in mind, the inventors of the present application found that: these desirable magnetic properties, in addition to high strip ductility, are achieved by selecting the ratio of Si to C at a certain level in the amorphous Fe-Si-B-C system as described in U.S. patent No.7,425,239 to maintain a thickness of the C precipitate layer on the surface of the strip. Also, in japanese patent laid-open No.2009052064, an amorphous alloy ribbon of high saturation induction is proposed, which controls the height of the C precipitate layer by adding Cr and Mn to the alloy system, whereby the ribbon exhibits improved thermal stability, i.e., thermal stability for up to 150 years in the case where the apparatus is operated at 150 ℃. However, the produced strip shows many surface defects: such as scratches, facelines (facelines) and cracks(s) formed for example along the length of the strip and on the surface of the strip facing the casting atmosphere side opposite to the surface of the strip in contact with the surface of the casting cooling bodyplitline), and the like. Fig. 1 shows an example of a crack line and an upper line. The basic arrangement of casting nozzles, cooling body surfaces on a rotating wheel and the resulting cast strip are illustrated in U.S. Pat. No.4,142,571.
Thus, what is needed is a ferromagnetic amorphous alloy ribbon as follows: which exhibits high saturation induction, low core loss, high B-H squareness ratio, high mechanical ductility, high long-term thermal stability, and reduced strip surface defects at high levels of strip manufacturability. This is a main aspect of the present invention. More specifically, through a thorough study of the surface quality of the cast strip during casting, the following findings were obtained: surface defects begin early in the casting and when the length of the defect along the length of the strip exceeds about 200mm or the depth of the defect exceeds about 40% of the thickness of the strip, the strip breaks at the location of the defect, which results in a sudden termination of the casting. Due to such strip breakage, the rate of casting termination within 30 minutes after casting start-up amounted to about 20%. On the other hand, for a strip having a saturation induction of less than 1.6T, the rate of casting termination within 30 minutes is about 3%. In addition, on these strips, the defect length was less than 200mm and the defect depth was less than 40% of the strip thickness, with a defect incidence of 1 or 2 per 1.5m length along the length of the strip. Thus, there is a clear need to reduce surface defects formed in the length direction of the strip in strips having saturation induction exceeding 1.6T to achieve continuous casting. This is another aspect of the invention.
Disclosure of Invention
According to various aspects of the present invention, a ferromagnetic amorphous alloy ribbon is based on an alloy of: the alloy consists of FeaSibBcCdAnd has incidental impurities, wherein 80.5. ltoreq. a.ltoreq.83 atom%, 0.5. ltoreq. b.ltoreq.6 atom%, 12. ltoreq. c.ltoreq.16.5 atom%, 0.01. ltoreq. d.ltoreq.1 atom%, and a + b + c + d 100. The strip material has a strip material length, a strip material thickness,The strip width and the strip surface facing the casting atmosphere side. The strip has strip surface defects formed on the surface of the strip facing the casting atmosphere side. The strip surface defects are measured in terms of defect length, defect depth and frequency of occurrence of defects. The defect length along the length of the strip is between 5mm and 200mm, the defect depth is less than 0.4 x t μm, and the frequency of occurrence of defects is less than 0.05 x w times within 1.5m of the strip length, where t is the strip thickness and w is the strip width. In the annealed state and straight strip (straigrip) form of the strip, the strip has a saturation induction in excess of 1.60T and exhibits a core loss of less than 0.14W/kg when measured at 60Hz and 1.3T induction levels.
According to one aspect of the invention, in the composition of the strip, the content B of Si and the content C of B are related to the content a of Fe and the content d of C according to the following relations: b is more than or equal to 166.5 (100-d)/100-2a and c is more than or equal to a-66.5 (100-d)/100.
According to another aspect of the invention, the strip is cast from the alloy in a molten state, the alloy in the molten state having a molten alloy surface tension of 1.1N/m or greater.
According to another aspect of the invention, the strip further comprises a trace element, the trace element being at least one of Cu, Mn and Cr, which advantageously reduces strip surface defects. In an alternative embodiment, the Cu content is between 0.005 and 0.20 wt%. In another alternative example, the content of Mn may be between 0.05 and 0.30 wt%, and the content of Cr is between 0.01 and 0.2 wt%.
According to another aspect of the invention, up to 20 atomic% of the Fe is optionally replaced by Co and less than 10 atomic% of the Fe is optionally replaced by Ni in the strip, and surface defects of the strip are reduced by controlling the molten metal surface tension during casting.
According to another aspect of the invention, the casting of the strip is carried out at a melting temperature comprised between 1250 ℃ and 1400 ℃ and the surface tension of the molten metal is comprised in the range 1.1N/m to 1.6N/m.
According to another aspect of the invention, the casting of the strip is carried out in an ambient atmosphere of: the ambient atmosphere comprises less than 5% by volume of oxygen at the molten alloy-strip interface.
According to yet another aspect of the invention, a method for manufacturing a ferromagnetic amorphous alloy ribbon comprises: selecting a material having a composition consisting of FeaSibBcCdAn alloy of the composition represented and having incidental impurities, where 80.5. ltoreq. a.ltoreq.83 atomic%, 0.5. ltoreq. b.ltoreq.6 atomic%, 12. ltoreq. c.ltoreq.16.5 atomic%, 0.01. ltoreq. d.ltoreq.1 atomic%, and a + b + c + d 100; casting from said alloy in the molten state; and obtaining the strip. The strip is cast out with surface defects formed on the surface of the strip facing the casting atmosphere side. The length of the defect along the length of the strip is between 5mm and 200mm, the depth of the defect is less than 0.4 x t μm, and the frequency of occurrence of defects within 1.5m of the strip length is less than 0.05 x w times, where t is the thickness of the strip and w is the width of the strip. In the annealed state and straight strip form of the strip, the strip has a saturation induction in excess of 1.60T and exhibits a core loss of less than 0.14W/kg when measured at 60Hz and 1.3T induction levels.
According to still another aspect of the present invention, an energy efficiency apparatus includes: ferromagnetic amorphous alloy ribbon having a composition consisting of FeaSibBcCdAn alloy of the composition indicated and having incidental impurities, where 80.5. ltoreq. a.ltoreq.83 atomic%, 0.5. ltoreq. b.ltoreq.6 atomic%, 12. ltoreq. c.ltoreq.16.5 atomic%, 0.01. ltoreq. d.ltoreq.1 atomic% and a + b + c + d is 100, and the energy efficient device is a transformer, a rotating machinery device, an electric choke, a magnetic sensor or a pulse power supply device. The strip is cast out with surface defects formed on the surface of the strip facing the casting atmosphere side. Defect length along the length of the stripBetween 5mm and 200mm, the defect depth is less than 0.4 x t μm and the frequency of defect occurrences is less than 0.05 x w times within a strip length of 1.5m, where t is the strip thickness and w is the strip width. The strip material has a saturation induction in excess of 1.60T in an annealed state and in straight strip form of the strip material and exhibits a core loss of less than 0.14W/kg when measured at 60Hz and 1.3T induction levels.
According to another aspect of the invention, a method for manufacturing an energy efficient device comprises: selecting a material having a composition consisting of FeaSibBcCdAn alloy of the composition represented and having incidental impurities, where 80.5. ltoreq. a.ltoreq.83 atomic%, 0.5. ltoreq. b.ltoreq.6 atomic%, 12. ltoreq. c.ltoreq.16.5 atomic%, 0.01. ltoreq. d.ltoreq.1 atomic%, and a + b + c + d 100; casting from said alloy in the molten state; and obtaining a ribbon and incorporating the ribbon as part of the energy efficient device, which may be a transformer, a rotating machinery, an electrical choke, a magnetic sensor, or a pulsed power supply device. The strip is cast out with surface defects formed on the surface of the strip facing the casting atmosphere side. The length of the defect along the length of the strip is between 5mm and 200mm, the depth of the defect is less than 0.4 x t μm, and the frequency of occurrence of defects within 1.5m of the strip length is less than 0.05 x w times, where t is the thickness of the strip and w is the width of the strip. Moreover, in the annealed state and straight strip form of the strip, the strip has a saturation induction in excess of 1.60T and exhibits a core loss of less than 0.14W/kg when measured at 60Hz and 1.3T induction levels.
Drawings
The present invention will be understood more fully and other advantages will become more apparent, by reference to the following detailed description of the preferred embodiments and the accompanying drawings. In these drawings:
fig. 1 is a picture illustrating an example of a crack line and an upper line formed along the length direction of a strip and on the surface of the strip.
FIG. 2 is a graph showing the surface tension of a molten alloy on an Fe-Si-B phase diagram, where the numbers shown are the surface tension of the molten alloy in N/m.
Fig. 3 is a picture illustrating a wave pattern observed on the surface of the as-cast strip, and the wavelength of the wave pattern on the surface of the strip is represented by a length λ.
FIG. 4 is a graph showing the relationship between the surface tension of a molten alloy and the oxygen concentration in the vicinity of the molten alloy-strip interface.
Detailed Description
As disclosed in U.S. patent No.4,142,571, amorphous alloy ribbons can be prepared by spraying molten alloy through a slot nozzle onto a rotating cooling body surface. The surface of the strip facing the surface of the cooling body appears matt, but the opposite surface facing the atmosphere is shiny and reflects the liquid properties of the molten alloy. In the following description, this side is also referred to as the "shiny side" of the cast strip. It has been found that: a small amount of molten alloy splashes to adhere to the nozzle surface and rapidly solidifies when the surface tension of the molten alloy is low, which results in surface defects such as face lines, crack lines, and scratch-like lines formed along the length of the strip. Fig. 1 shows an example of a crack line and an upper line. An upper line and a scratch-like line are formed on the surface of the strip facing the atmosphere side, which is the opposite side of the strip surface facing the surface of the cooling body. This deteriorates the soft magnetic characteristics of the strip material. Further damage is: the cast strip is prone to cracking or breaking at the location of the defect, resulting in termination of the strip casting.
Further observations indicate the following facts: during casting, the number of surface defects, as well as their length and depth, increases with casting time. For such defect development, it has been found that: this development is slow when the defect length is between 5mm and 200mm, the depth of the defect is less than 0.4 x t μm, and the number of defects along the length of the strip is less than 0.05 x w (where t and w represent the thickness and width, respectively, of the cast strip). Thus, the incidence of ribbon breakage is also low. On the other hand, when the number of defects in the length direction of the strip is greater than 0.05 × w, the size of the defects increases, thereby causing the strip to break. This indicates that: for continuous casting without strip breakage, it is desirable to minimize the incidence of molten alloy splatter onto the nozzle surface. After a plurality of experimental tests, the inventor of the invention finds that: maintaining the surface tension of the molten alloy at a high level is critical to reducing splashing of the molten alloy.
For example, in the case of a chemical composition of Fe81.4Si2B16C0.6A molten alloy having a surface tension of 1.0N/m and a melting temperature of 1350 ℃ and a chemical component of Fe81.7Si4B14C0.3The effect of the surface tension of the molten alloy was compared between the molten alloys having a surface tension of 1.3N/m and a melting temperature of 1350 ℃. With Fe81.4Si2B16C0.6Molten alloy ratio of composition Fe81.7Si4B14C0.3The alloy exhibits more splashing on the nozzle surface, thereby resulting in shorter casting times. Based on Fe when the surface of the strip is evaluated81.4Si2B16C0.6A strip of alloy has more than a few defects within 1.5m of the strip. On the other hand, in the presence of Fe81.7Si4B14C0.3No such defects were observed on the strip of alloy. Many other alloys have also been evaluated with respect to the effect of surface tension of molten alloys and thus found: splashing of the molten alloy occurs frequently and the number of defects in a 1.5m strip length is greater than 0.05 xw at a molten alloy surface tension below 1.1N/m. Note that: attempts to treat the nozzle surface by surface coating and polishing (polising) to minimize the solidified molten alloy splattering onto the nozzle surface have been unsuccessful. Accordingly, the inventors of the present invention proposeA method of varying the surface tension of a molten alloy at an interface between the molten alloy and a strip by controlling the oxygen concentration near the interface is presented.
The next step taken by the inventors of the present invention is to find the chemical composition range of the as-cast amorphous ribbon with saturation induction exceeding 1.60T, which is one aspect of the present invention. It has been found that the alloy composition meeting the above requirements consists of FeaSibBcCdHere, 80.5. ltoreq. a.ltoreq.83 atomic%, 0.5. ltoreq. b.ltoreq.6 atomic%, 12. ltoreq. c.ltoreq.16.5 atomic%, 0.01. ltoreq. d.ltoreq.1 atomic% and a + B + c + d 100, the alloy composition also having incidental impurities (inclusion) which are generally found in commercial raw materials such as iron (Fe), ferrosilicon (Fe-Si) and ferroboron (Fe-B).
With respect to the Si content and the B content, it has been found that the following chemical constraints are more favorable for achieving the goal of increasing the surface tension of the molten alloy: b is more than or equal to 166.5 (100-d)/100-2a and c is more than or equal to a-66.5 (100-d)/100. In addition, for incidental impurities and intentionally added trace elements (traceelements), it has been found to be advantageous to have the following elements in the given content ranges: 0.05 to 0.30 wt% of Mn, 0.01 to 0.2 wt% of Cr, and 0.005 to 0.20 wt% of Cu.
Less than 20 atomic% of the Fe is optionally replaced with Co, and less than 10 atomic% of the Fe is optionally replaced with Ni. The reasons for selecting the ranges of ingredients given in the two paragraphs above are as follows: an Fe content "a" of less than 80.5 at% results in a saturation induction level of less than 1.60T, while an "a" of more than 83 at% reduces the thermal stability and strip formability of the alloy. It is advantageous to replace Fe by up to 20 at% Co and/or up to 10 at% Ni to achieve saturation induction in excess of 1.60T. Si exceeds 0.5 atomic%, Si improves strip formability and enhances its thermal stability, and Si is below 6 atomic% to achieve the envisaged saturation induction level and high B-H squareness ratio. B contributes favorably to the strip formability of the alloy and its saturation induction level, and B exceeds 12 atomic% and is less than 16.5 atomic%, because its advantageous effect is reduced above the above-mentioned concentration. These findings are summarized in the phase diagram of fig. 2, and region 1 where the surface tension of the molten alloy is at or above 1.1N/m and region 2 where the surface tension of the molten alloy exceeds 1.3N/m are clearly shown in fig. 2, with region 2 being more preferable. In terms of chemical composition, region 1 in FIG. 2 is composed of Fe as followsaSibBcCdTo define: where a is 80.5-83 atom%, b is 0.5-6 atom%, c is 12-16.5 atom%, d is 0.01-1 atom%, and a + b + c + d is 100; region 2 is composed of FeaSibBcCdTo define: where 80.5. ltoreq. a.ltoreq.83 atom%, 0.5. ltoreq. b.ltoreq.6 atom%, 12. ltoreq. c.ltoreq.16.5 atom%, 0.01. ltoreq. d.ltoreq.1 atom% and a + b + c + d 100 and b. ltoreq.166.5X (100-d)/100-2a and c. ltoreq.a-66.5X (100-d)/100. In fig. 2, the eutectic composition (eutecticcoomposion) is represented by a thick dotted line, which indicates that: the molten alloy surface tension is low near the eutectic composition of the alloy system.
C of more than 0.01 atomic% is effective for achieving a high B-H squareness ratio and a high saturation induction, but C of more than 1 atomic% causes a reduction in the surface tension of the molten alloy, and C of less than 0.5 atomic% is preferable. Among incidental impurities and intentionally added trace elements, Mn reduces the surface tension of the molten alloy and the allowable concentration limit is Mn < 0.3 wt.%. More preferably, Mn < 0.2 wt.%. The coexistence of Mn and C in the Fe-based amorphous alloy improves the thermal stability of the alloy, and (Mn + C) > 0.05 wt% is effective. Cr also improves thermal stability and Cr > 0.01 wt% is effective, but the saturation induction of the alloy decreases at Cr > 0.2 wt%. Cu is insoluble in Fe and tends to precipitate on the strip surface, and it helps to increase the surface tension of the molten alloy; cu > 0.005 wt.% is effective, and Cu > 0.02 wt.% is more advantageous, but C > 0.2 wt.% results in brittle strip. It has been found that one or more elements from the group consisting of Mo, Zr, Hf and Nb with 0.01 to 5.0 wt.% are permissible.
The alloy according to embodiments of the present invention has a melting temperature preferably between 1250 ℃ and 1400 ℃ and in this temperature range the surface tension of the molten alloy is in the range 1.1N/m to 1.6N/m. When lower than 1250 ℃, the casting nozzle tends to be frequently clogged, and when higher than 1400 ℃, the surface tension of the molten alloy is reduced. More preferably the melting point is 1280 ℃ to 1360 ℃.
The surface tension σ of the molten alloy is determined by the formula which can be found in "Metallurgical materials transformations, vol.37B, pp.445-456(published Springer 2006)" (Metallurgical and materials journal, volume 37B, pages 445-456, published by Schleminger, 2006).
σ＝U2G3ρ/3.6λ2
Here, U, G, ρ and λ are the velocity of the surface of the cooling body, the gap between the nozzle and the surface of the cooling body, the mass density of the alloy, and the wavelength of the wavy pattern observed on the shiny side of the strip surface as shown in fig. 3, respectively. The measured wavelength lambda is in the range of 0.5mm to 2.5 mm.
The inventors of the present invention have found that surface defects can be further reduced by providing oxygen at a concentration of at most 5 volume% at the interface between the molten alloy and the cast strip directly below the casting nozzle. Based on the surface tension of the molten alloy relative to O as shown in FIG. 42Data on concentration to determine O2Upper limit of gas, the figure shows: when the oxygen concentration exceeds 5 vol%, the surface tension of the molten alloy becomes less than 1.1N/m.
The inventors of the present invention have further found that strip thicknesses of 10 μm to 50 μm are obtained in the strip manufacturing method according to embodiments of the present invention. It is difficult to form a tape having a thickness of less than 10 μm, and for a tape thickness of more than 50 μm, the magnetic characteristics of the tape may be deteriorated.
As demonstrated by example 4, the ribbon fabrication method according to embodiments of the present invention is applicable to a wider range of amorphous alloy ribbons.
To the surprise of the inventors of the present invention, the ferromagnetic amorphous alloy ribbon shows low core loss contrary to the expectation that core loss generally increases when the saturation induction of the core material increases. For example, the annealed straight strip of ferromagnetic amorphous alloy ribbon according to embodiments of the present invention exhibits a core loss of less than 0.14W/kg when measured at 60Hz and 1.3T induction.
Example 1
Ingots having chemical compositions according to examples of the invention were prepared and cast from molten metal at 1350 c on a rotating cooling body. The cast strip has a width of 100mm and a thickness in the range of 22 to 24 μm. Chemical analysis showed that the strip contained 0.10 wt.% Mn, 0.03 wt.% Cu and 0.05 wt.% Cr. CO 22A mixture of gas and oxygen is blown into the vicinity of the interface between the molten alloy and the cast strip. The oxygen concentration near the interface between the molten alloy and the cast strip was 3 vol%. The surface tension σ of the molten alloy is determined by using the formula σ ═ U2G3ρ/3.6λ2And is determined by measuring the wavelength of the wave pattern on the shiny side of the as-cast strip. The number of surface defects of the strip within 1.5m in the length direction of the strip was measured at 30 minutes after the start of casting, and the maximum number of surface defects N in the three samples is given in table 1. The strips cut from the strip were annealed at 300-400 c by applying a magnetic field of 1500A/m along the length of the strip and the magnetic properties of the heat treated strips were measured according to ASTM standard a-932. The results obtained are listed in table 1. For the surface tension σ of the molten alloy, the number of defects N per 1.5m of the cast strip, and the saturation induction strength BsAnd core loss W at 60Hz excitation and 1.3T induction1.3/60Samples No. 1 to 15 satisfy the requirements of the object of the present invention. Since the strip width is 100mm, the maximum number of N is5. Examples of failed tapes (samples No. 1-6) are given in table 2. For example, samples No. 1, 3 and 4 exhibited favorable magnetic properties, but resulted in a large number of surface defects in the strip due to the surface tension of the molten alloy being below 1.1N/m. Samples nos. 2,5 and 6 had a molten alloy surface tension higher than 1.1N/m, whereby N is 0, but B issBelow 1.60T.
TABLE 1
TABLE 2
Example 2
With Fe81.7Si3B15C0.3Amorphous alloy strip of composition was cast under similar casting conditions as in example 1, except that O2The gas concentration was changed from 0.1 vol% to 20 vol% (equivalent to air). The magnetic properties B obtained are listed in Table 3sAnd W1.3/60The molten alloy surface tension σ and the maximum number of surface defects N. These data demonstrate that: oxygen levels in excess of 5 vol% reduce the molten alloy surface tension, which increases the number of defects, resulting in shorter casting times.
TABLE 3
Example 3
A small amount of Cu was added to the alloy of example 2 and the ingot was cast as an amorphous alloy ribbon as in example 1. In Table 4, magnetic characteristics B are comparedsAnd W1.3/60Surface tension of molten alloy toAnd the maximum number of defects on the strip. The strip with 0.25 wt% Cu showed favorable magnetic properties, but was brittle. No increase in the surface tension of the molten alloy was observed in the strip with 0.001 wt% Cu.
TABLE 4
Example 4
With Fe81.7Si3B15C0.3The amorphous alloy ribbon of composition was cast under similar conditions as in example 1 except that the ribbon width was changed from 140mm to 254mm and the ribbon thickness was changed from 15um to 40 μm. Table 5 shows the magnetic properties B obtainedsAnd W1.3/60The surface tension σ of the molten alloy, and the number of surface defects N.
TABLE 5
Although embodiments of the present invention have been illustrated and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.