FIELD OF THE INVENTION
This invention relates to a process for production of an Fe-based amorphous alloy at low cost. DESCRIPTION OF THE RELATED ART
Amorphous alloy ribbons whose base component system is Fe-B-Si have excellent properties as electromagnetic materials. When used as an iron core material in an electric power transformer, such an amorphous alloy ribbon is said to lower core loss to about 1/3 that when using conventional grain-oriented Si-steel sheet. However, progress in implementing mass production of Fe-B-Si amorphous alloy ribbons has been slow.
The main reason for this is that the cost of the amorphous alloy ribbons is much higher than that of Si-steel sheet. Most of the cost is accounted for by the Fe-B or other main raw material.
As a method for inexpensive production of amorphous alloy, Japanese Patent Publication (A) No. S58-77509 teaches a process for smelting reduction of boron oxide or boric acid and iron oxide using a carbon-based solid reducing agent such as coke. However, owing to the use of a carbon reducing agent, this method has a problem in that when it is attempted to directly produce the amorphous alloy to optimum B and Si contents for obtaining a steel with good electromagnetic properties, the C content comes to exceed the optimum range.
For overcoming this problem, Japanese Patent Publication (A) No. S59-38353 teaches a method of once producing a matrix alloy with high B and Si contents so that a C content in the optimum range can be obtained and thereafter diluting the B and Si with a separately produced molten steel. However, owing to the fact that the product is obtained via the matrix alloy with a high B content, this method shortens the service life of the
melting furnace refractory and increases raw material consumption per unit product because B reduction yield is lowered. Japanese Patent Publication (A) No. S62-287040 further teaches a method for overcoming these problems by adjusting the composition of the matrix alloy to a somewhat low B content and high Si content. However, the foregoing methods all reduce B, Si and Fe oxides with carbon. They are therefore fundamentally flawed in the point of requiring great reductive energy and also in the point that they increase refractory cost tremendously because the reductive energy is obtained by using a hot air blast to burn the carbon, thus producing a high temperature that forms a molten slag that readily causes fusion damage of the refractory made of B, Si and Fe oxides.
On the other hand, other general methods for producing Fe-B as a B raw material include methods that perform refining by the aluminum thermite reaction or the electric furnace method. However, the electric furnace method consumes much electric power, resulting in high power costs and increasing the cost of amorphous alloy production. Although the aluminum thermite method is low in production cost, the resulting Fe-B includes Al and Ti, and an amorphous alloy produced using the Fe-B is therefore increased in Ti concentration and Al concentration. As increased Ti and Al concentration is known to degrade magnetic properties, Fe-B produced by the aluminum thermite reaction cannot be used to produce amorphous alloys until cheap removal of Ti and Al becomes possible.
Although it is also conceivable to lower production cost by using scrap Si-steel sheet or the like as the starting material containing Fe and Si, such scrap is difficult to use for amorphous alloy because the Al contamination of the scrap similarly increases the Al concentration of the amorphous alloy.
SUMMARY OF THE INVENTION
In view of the forgoing problems of the prior art, the present invention is directed to providing a process for production of an Fe-based amorphous alloy ribbon at low cost by efficiently removing magnetic-property-degrading Al and Ti when using inexpensive Fe-B or scrap as an amorphous alloy raw material.
The essence of the present invention for overcoming the problems is as set out in the following.
(1) A process for production of an Fe-based
amorphous alloy comprising, by mass, 2 to 4% of B, 1 to
6% of Si, and a balance of Fe and unavoidable materials,
which method comprises:
determining whether a molten alloy obtained by melting a main raw material has a Ti concentration or Al concentration of 0.005 mass% or greater, and when it does,
adding thereto an iron oxide source having an iron content of 55 mass% or greater to reduce both Ti and Al to less than 0.005 mass% by oxidative removal.
(2) A process for production of an Fe-based
amorphous alloy comprising, by mass, 2 to 4% of B, 1 to
6% of Si, and a balance of Fe and unavoidable materials,
which method comprises:
determining whether a main raw material has a composition whose Ti concentration or Al concentration is 0.005 mass% or greater, and when it does,
precharging an iron oxide source having an iron content of 55 mass% or greater into a melting vessel together with the main raw material.
(3) A process for production of an Fe-based amorphous alloy according to (1) or (2), further comprising, by mass, one or both of 0.001 to 3% of C and 0.008 to 0.15% of P.
(4) A process for production of an Fe-based amorphous alloy according to any of (1) to (3), wherein, by mass, Fe is partially replaced by one or more of Co
plus Ni of not greater than 20% of Fe content and Cr of not greater than 6% of Fe content.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing time-course changes in molten alloy Ti concentration when iron oxide sources were added to molten alloy of an amorphous alloy raw material.
FIG. 2 is a diagram showing time-course changes in molten alloy Al concentration when iron oxide sources were added to molten alloy of an amorphous alloy raw material.
DETAILED DESCRIPTION OF THE INVENTION
The inventors learned from experiments conducted using a small melting furnace that addition of iron oxide to an Fe-based amorphous alloy raw material during melting enables efficient oxidative removal of Ti and Al. Ti and Al are oxidized preferentially relative to B or Si constituting the main components of the amorphous alloy and can therefore be oxidatively removed without much reducing B or Si yield.
In one embodiment of the invention, a main raw material mixed with the required B and Si components is melted in a melting furnace, and when a molten alloy has been formed, Ti and Al are oxidatively removed by adding an iron oxide source containing at least 55 mass% of iron.
In a small-scale experiment, an amorphous alloy raw material containing B: 3.2 mass% and Si: 1.8 mass% was produced in a melting furnace, the temperature of the
molten alloy was raised to 1,500 °C, and an iron oxide source was added at the rate of, by mass, 50 kg per ton of molten alloy. The experiment was conducted using various iron oxide sources. The time-course changes in the concentrations of Ti and Al in the molten alloy are shown in FIG. 1. It can be seen that in the case of all
iron oxide sources having an iron content of at least 55%, Ti and Al were reduced to less than 0.005 mass%, a level at which no effect on magnetic properties is observed. However, the speed of Ti and Al oxidative removal decreased in proportion as the iron oxide source was lower in iron content and higher in content of gangue constituents other than iron oxide. On the other hand, when steelmaking dust of an iron concentration of less than 55% was used as the iron oxide source, the Ti and Al oxidative removal speed was very slow and Ti was not reduced to less than 0.005 mass%. A production cost analysis was carried out taking into account the amount of added iron oxide source required, refining time, slag treatment expense owing to increase in generated slag volume from gangue and the like, and other factors. The results showed that the effect is small unless the iron concentration is 55% or greater.
The holding time after iron oxide source refining depends on the amount of iron oxide source used but is preferably 15 min or longer.
In another embodiment of the invention, an iron oxide source containing at least 55 mass% of iron is precharged into a melting furnace together with a main raw material prepared to include the required B and Si contents, whereafter melting is conducted to produce an amorphous alloy ribbon. When the dust collection capability of the melting furnace is low, this embodiment is preferably adopted because the preceding embodiment in which the iron oxide source is added after producing the molten alloy generates dust at the time of the addition.
Table 1 shows the Ti and Al concentrations of the molten alloy when, in the small-scale experiment discussed earlier, the various iron oxide sources were precharged into the melting furnace at the rate of, by mass, 50 kg per ton of molten alloy and melted together with the main raw material. The temperature at 10 min after meltdown was 1,370 to 1,380 °C. If Ti and Al had not
been removed, their concentrations would have stayed the same as the initial values in FIG. 1. However, in every case where an iron oxide source having an iron concentration of at least 55% was used, the Ti and Al concentrations were less than 0.005 mass%, demonstrating that Ti and Al were oxidatively removed at the melting stage. Since Ti and Al are oxidatively removed at the melting stage, refining is completed within the time the material melts and rises to the temperature required for tapping. In contrast, when an iron oxide source having an iron concentration of less than 55% was used, the Ti concentration was 0.005 mass% or greater.
The constituents of the invention Fe-based amorphous alloy and their content ranges will be explained. Unless specifically indicated, all content ranges are expressed in mass%.
B effectively improves amorphous phase forming ability and thermal stability. It is added in an amount suitable in light of the property requirements. When B content is less than 2%, amorphous phase cannot be obtained stably, and when it exceeds 4%, the melting point rises to make amorphous phase formation difficult.
Si also effectively improves amorphous phase forming ability and thermal stability. It is added in an amount suitable in light of the property requirements. When Si content is less than 1%, amorphous phase cannot be obtained stably, and when it exceeds 6%, its effect of improving thermal stability saturates.
C effectively enhances the magnetic flux density of amorphous alloy ribbon and improves amorphous phase forming ability (improves castability). Its content is decided as a suitable; amount in light of the property requirements. The wettability between the molten alloy and the cooling substrate can be improved to form a good amorphous alloy ribbon by making the C content 0.001% or greater and preferably 0.003% or greater. In addition, C content is preferably made 0.01% or greater, because an
effect of improving amorphous phase forming ability is obtained. When C content exceeds 3%, the effect of enhancing magnetic flux density declines.
P effectively improves core loss property and amorphous phase forming ability. It is included in an amount suitable in light of the property requirements. Although presence of P improves core loss property and amorphous phase forming ability, and increases the allowable content of impurity elements, the effects of amorphous phase forming ability improvement and core loss property improvement are not observed at a P content of less than 0.008%. In addition, the effect of increasing the allowable content of the impurity elements Mn and S is not exhibited. With increasing amount of P addition, cracks more readily propagate in the amorphous alloy ribbon, thereby degrading workability. Therefore, to avoid this problem, C content is preferably 0.15% or less.
Moreover, it was found that the effect of the present invention is not particularly impaired, when for the purpose of improving magnetic flux density, corrosion resistance property, annealing conditions and the like, the Fe of the composition of the invention Fe-based amorphous alloy is partially replaced by one or more among Co plus Ni of not greater than 20% of the Fe content and Cr of not greater than 6% of the Fe content. Although Co and Ni effectively improve magnetic flux density, they are expensive, so that from the viewpoint of raw material cost, the replacement of Fe thereby is preferably held to 10% or less and more preferably to 5% or less of the Fe content.
Moreover, the effect of the present invention is in no way impaired by including in the composition of the invention Fe-based amorphous alloy as constituent elements not only Fe, B, Si, C, P, Ni, Co and Cr but also known constituents such as N, Ti, Zr, V, Nb, Mo, and Cu.
Table 1

(Table Removed)
A study on the effect of the molten alloy temperature showed that Ti and Al decline to less than 0.005 mass% insofar as the temperature is equal to or higher than the matrix melting point but that the higher the temperature, the better is the Ti and Al oxidation efficiency, the lower is the final Ti and Al concentration, and the better are the B and Si yields. However, the higher the temperature, the greater is the amount of electric power needed for melting and the greater is the melting furnace refractory cost. The molten alloy temperature is therefore preferably lowered to the level at which the required amount of Ti and Al oxidative removal can be achieved.
EXAMPLES
The invention is concretely explained based on specific examples in the following. First Set of Examples
Amorphous alloy ribbons produced using a 3-ton class high-frequency melting furnace were subjected to Ti and Al oxidative refining. As main raw material was used low-cost magnetic steel scrap and Fe-B of the compositions shown in Table 2. Some amount of Fe-Si was used for Si

concentration adjustment. The amounts of the raw
materials per unit mass are also shown in Table 2.
Table 2(Mass%)

(Table Removed)
The main raw materials were melted and the molten alloy was then heated to 1,500 °C. In the Invention Examples, as shown in Table 3, the same iron oxide sources as used in the small-scale experiment, namely, iron ore (Mount Newman: iron content of 65 mass%), steelmaking dust (dust occurring during decarburization treatment: iron content of 64 mass%), and sintered ore (iron content of 58 mass%), were each added in an amount of 150 kg (50 kg/t) and the melt was tapped 20 min thereafter. In some Invention Examples, C, P, Co, Ni and Cr were added to the main raw material for property improvement. Specifically, the molten composition after melting was made to contain one or both of C: 0.001 to 3% and P: 0.008 to 0.15%, and/or the Fe thereof was partially replaced by one or more among Co plus Ni of not greater than 20% of the Fe content and Cr of not greater than 6% of the Fe content. A refining operation was also similarly conducted. In the Comparative Examples, the same method was used except that the refining treatment was conducted with addition of iron oxide sources having an iron content of less than 55 mass%, namely of 150 kg of steelmaking dust (dust occurring during hot metal pretreatment: iron content of 53 mass%) or mixed steelmaking dust and slag.
Table 4 shows the compositions of the molten alloys sampled just before iron oxide source addition and the
compositions of the molten alloys just before tapping. The Invention Examples, which used iron oxide sources having iron content of 55 mass% or greater, had their concentrations of both Ti and Al lowered to less than 0.005 mass%, a level at which no effect on magnetic properties is observed. They were also found to be low in B and Si oxidative loss and have yields of 95% or greater relative to the initial mixing proportions. Moreover, in cases where the composition contained one or both of C: 0.001 to 3% and P: 0.008 to 0.15%, and the case where the Fe thereof was partially replaced by one or more among Co plus Ni of not greater than 20% of the Fe content and Cr of not greater than 6% of the Fe content, these effects were not impaired. In contrast, in the Comparative Examples, which used iron oxide sources having iron content of less than 55 mass?;, the B and Si yields were on the same level but Ti concentration or Al concentration was 0.005 mass% or greater.
Table
(Table Removed)
Second Set of Examples
Raw material of the same kind in the same amount as used in Example 1 was charged into a 3-ton class high-frequency melting furnace together with an iron oxide source that, as shown in FIG. 5, had an iron content of more than 55 mass% before melting, whereafter melting was conducted. When about. 10 min had passed following raw material meltdown, the temperature was measured and the molten alloy was sampled. After the temperature had risen to 1,500 °C, the molten alloy was sampled and then tapped. In some Invention Examples, C, P, Co, Ni and Cr were added to the main raw material for property improvement. Specifically, the amorphous alloy composition after melting was made to contain one or both of C: 0.001 to 3% and P: 0.008 to 0.15%, and/or the Fe thereof was partially replaced by one or more among Co plus Ni of not greater than 20% of the Fe content and Cr of not greater than 6% of the Fe content. A refining operation was also similarly conducted. In the Comparative Examples, the same method was used except that, as shown in Table 4, melting was conducted using iron oxide sources having an iron content of less than 55 mass%.
Table 6 shows the compositions of the molten alloys after meltdown and also their compositions just before tapping. The Invention Examples, which used iron oxide sources having iron content of 55 mass% or greater, had their concentrations of both Ti and Al lowered to less than 0.005 mass%, a level at which no effect on magnetic properties is observed, from the stage in which the material melted down, and the Ti and Al concentrations decreased still further at the tapping stage after temperature increase. They were also found to be low in B and Si oxidative loss and have yields of 92% or greater relative to the mixing proportions before tapping. Moreover, in case where the composition contained one or both of C: 0.001 to 3% and P: 0.008 to 0.15%, and the case where the Fe thereof was partially replaced by one
or more among Co plus Ni of not greater than 20% of the Fe content and Cr of not greater than 6% of the Fe content, these effects were not impaired. In contrast, in the Comparative Examples, which used iron oxide sources having iron content of less than 55 mass%, the B and Si yields were on the same level but Ti concentration or Al concentration was 0.005 mass% or greater.
Table 5
(Table Removed)
Industrial Applicability
The present invention provides a process for production of an amorphous alloy at low cost by efficiently removing magnetic-property-degrading Al and Ti when using inexpensive Fe-B or scrap as an amorphous alloy raw material.

What is claimed is:
1. A process for production of an Fe-based
amorphous alloy comprising, by mass, 2 to 4% of B, 1 to
6% of Si, and a balance of Fe and unavoidable materials,
which method comprises:
determining whether an iron melt obtained by melting a main raw material has a Ti concentration or Al concentration of 0.005 mass% or greater, and when it does;
adding thereto an iron oxide source having an iron content of 55 mass% or greater to reduce both Ti and Al to less than 0.005 mass% by oxidative removal.
2. A process for production of an Fe-based
amorphous alloy comprising, by mass, 2 to 4% of B, 1 to
6% of Si, and a balance of Fe and unavoidable materials,
which method comprises:
determining whether a main raw material has a composition whose Ti concentration or Al concentration is 0.005 mass% or greater, and when it does;
precharging an iron oxide source having an iron content of 55 mass% or greater into a melting vessel together with the main raw material.
3. A process for production of an Fe-based amorphous alloy according to claim 1 or 2, further comprising, by mass, one or both of 0.001 to 3% of C and 0.008 to 0.15% of P.
4. A process for production of an Fe-based amorphous alloy according to any of claims 1 to 3 wherein, by mass, Fe is partially replaced by one or more of Co plus Ni of not greater than 20% of Fe content and Cr of not greater than 6% of Fe content.