Field of the Invention

[0001] The present invention is related to Fe-based amorphous alloy materials, in particular to alloy compositions suitable for producing soft magnetic glassy alloy materials and to products made thereof.

State of the art.

[0002] Fe-based amorphous /glas sy alloys comprising C, Si, B, P and Mo are known in the art. For example CN1936059 and CN101148743A describe such alloys. In WO2010/135415, an alloy is described which may further comprise Al . In most of these publications, production processes are described wherein the alloy is produced from pure starting materials, melted into a master alloy which is subsequently further melted and solidified to form a final product. Melting of the starting products and of the master alloy usually takes place under vacuum.

[0003] It is not economically advantageous to start from pure materials, nor is it always technically possible. For example, pure Phosphor is often problematic due to its high reactivity. Non-pure starting materials on the other hand have the disadvantage of containing an undefined number of impurities whose influence on the glass forming ability of the alloy is unknown so that the quality of the final product in terms of glass forming ability may vary between broad limits.

[0004] Also, melting under air is economically advantageous compared to vacuum melting, but again, the influence of oxygen on the product quality is not very well known, which leads to a further uncertainty.

[0005] As it is widely described in the scientific literature, the glass-forming ability (GFA) can be theoretically characterized by several measurable physical parameters, as the extension of the supercooled region (the difference between glass transition temperature and crystallization temperature) or the reduced glass transition temperature (the ratio between glass transition temperature and melting temperature) . In fact it represents the ability of a metallic alloy to become amorphous, i.e. to "freeze" its liquid-state structure. At a macroscopic level the glass-forming ability can be easily understood by considering the maximum achievable geometrical dimensions or geometrical complexity when the alloy is continuously cooled from its molten state.

Summary of the invention

[0006] The invention is related to an Fe based alloy material, suitable for producing a soft magnetic glassy alloy product, a product produced thereof and a method for producing such a product as disclosed in the appended claims. The product can be a master alloy product obtained after a first melting step starting from suitably selected starting materials, or it can be a final soft magnetic glassy alloy product obtained after a further step of melting the master alloy. According to a preferred embodiment, the product is a bulk Fe-based alloy product, e.g. a product shaped as a cylindrical rod with a diameter between 2mm and 5mm.

[0007] The soft magnetic glassy alloy product is amorphous in the sense that no long range atomic order appears, leading to the absence of Bragg peaks in X-Ray diffraction spectra. The term ^x amorphous' does not exclude the presence of crystalline phases in the amorphous matrix, e.g. crystalline particles of a few nm in size. The term 'glassy' refers to the fact that the amorphous material goes through a glass transition phase defined by a glass transition temperature Tg and a crystallization temperature Tx (Tx higher than Tg) upon heating.

[0008] The invention is thus related to an Fe-based alloy material, suitable for producing a soft magnetic glassy Fe-based alloy product, said material comprising :

· C between 1.4wt% and 2.2wt%,

Si between 0.9wt% and 1.35wt%,

B between 0.43wt% and 0.65wt%,

P between 5wt% and 7.5wt%,

Mo between 0.9wt% and 9.2wt%,

· Mn between 0.05wt% and 0.6wt%,

0 up to 0.3wt%,

Al up to 0.1wt%,

S up to 0.05wt%,

Ti up to 0.45wt%,

· Cr up to 0.3wt%

Cu up to 0,25wt%, or Cu between 0.25wt% and 0.8wt%, the balance being Fe and incidental impurities.

[0009] In the above and anywhere else in this specification, the wording 'up to' means that these elements are present between 0 and the given maximum value. Also, whenever it is stated that an alloy or product 'comprises or consists of a list of element ranges, 'the balance being Fe and incidental impurities', this is the same as stating that the alloy or product definition is 100% closed, in other words the alloy or product consists of said elements in the given ranges, of Fe and of incidental impurities. [0010] The invention is thus related to two distinct

Fe-based alloy materials :

The first Fe-based alloy material consists of :

C between 1.4wt% and 2.2wt%,

Si between 0.9wt% and 1.35wt%,

B between 0.43wt% and 0.65wt%,

P between 5wt% and 7.5wt%,

Mo between 0.9wt% and 9.2wt%,

Mn between 0.05wt% and 0.6wt%,

· Cu between 0.25wt% and 0.8wt%

0 up to 0.3wt%,

Al up to 0.1wt%,

S up to 0.05wt%,

Ti up to 0.45wt%,

· Cr up to 0.3wt%,

the balance being Fe and incidental impurities.

[0011] In the first alloy, the elements 0, Al, S, Ti, Cr may be referred to also as incidental impurities of the alloy, in which case the balance is Fe and further incidental impurities.

[0012] The second Fe-based alloy material consists of :

C between 1.4wt% and 2.2wt%,

Si between 0.9wt% and 1.35wt%,

· B between 0.43wt% and 0.65wt%,

P between 5wt% and 7.5wt%,

Mo between 0.9wt% and 9.2wt%,

Mn between 0.05wt% and 0.6wt%,

0 up to 0.3wt%,

· Al up to 0.1wt%,

S up to 0.05wt%, • Ti up to 0.45wt%,

• Cr up to 0.3wt%

• Cu up to 0,25wt%,

the balance being Fe and incidental impurities.

[0013] In the second alloy, the elements 0, Al, S,

Ti, Cr and Cu may be referred to also as incidental impurities of the alloy, in which case the balance is Fe and further incidental impurities.

[0014] The invention is further related to a soft magnetic glassy Fe-based alloy product made from a material according to the invention.

[0015] The product of the invention preferably has coercivity He lower than 30m/a, more preferably lower than 15A/m.

[0016] The invention is furthermore related to a method for producing soft magnetic glassy Fe-based alloy product, the method comprising the steps of :

• selecting a set of starting materials, said set comprising at least the elements Fe, Mo, C, Si, B, P and Mn,

• Melting said starting materials at a temperature above the melting temperature of said materials,

• Keeping the materials in a molten state,

• Introducing the molten materials into a mould,

· Cooling the molten material, to obtain one or more master alloy products, said master alloy comprising :

- C between 1.4wt% and 2.2wt%

- Si between 0.9wt% and 1.35wt%

- B between 0.43wt% and 0.65wt%

- P between 5wt% and 7.5wt%

- Mo between 0. wt% and 9.2wt%

- Mn between 0.05wt% and 0.6wt%, - 0 up to 0.3wt%,

- Al up to 0.1wt%,

- S up to 0.05wt%,

- Ti up to 0.45wt%,

- Cr up to 0.3wt%

- Cu up to 0,25wt% or Cu between 0.25wt% and 0.8wt%,

the balance being Fe and incidental impurities,

• Introducing the master alloy product (s) in a melting device,

• Heating up the master alloy to a temperature above its melting temperature,

• Introducing the molten material into a mould,

• Cooling the molten material, to obtain the soft magnetic glassy Fe-based product.

[0017] As with regard to the Fe-based alloy, the invention is thus related to two methods, one where Cu is present up to 0.25wt% and one where Cu is present between 0.25wt% and 0.8wt% in the master alloy.

[0018] In the method, the elements 0, Al, S, Ti, Cr and Cu (the latter only in the case where Cu is present up to 0.25wt%) may also be referred to as incidental impurity elements of the master alloy, in which case the balance is Fe and further incidental impurities.

[0019] In a preferred embodiment of the method according to the invention, at least one of said starting materials comprises impurity elements, the remainder of said starting materials being pure grade materials. Said at least one starting material comprising impurity elements may be chosen from the group consisting of : electrolytic Fe, AK steel, standard raw grades of FeMo, FeP, FeB, FeSi, FeC. [0020] Mn may be present as an impurity element in at least one starting material.

[0021] According to an embodiment, said at least one starting material is standard raw grade FeP, wherein Mn is present in said FeP up to a level of 1.8wt%.

[0022] According to an embodiment of the method according to the invention, the starting materials are graphite, pure Fe and/or electrolytic Fe, pure Mn, pure Si, pure P, pure Mo and pure B.

[0023] The alloy of the invention can be characterized by expressing the ranges for the various element levels by atomic percentages, in stead of weight percentages. The relevant limits in at% equivalent to the wt% limits given above and in the claims are given hereafter :

• C between 6at% and 9at%,

• Si between 1.6at% and 2.4at%,

• B between 2at% and 3at%,

• P between 8at% and 12at%,

· Mo between 0.46at% and 4.8at%,

• Mn between 0.07at% and 0.6at%,

• 0 : up to lat%,

• Al : up to 0.1at%,

• S : up to 0.08at%,

· Ti : up to 0.5at%,

• Cr : up to 0.3at%,

• Cu : up to 0.2at% or Cu between 0.2at% and 0.7at%,

Detailed description of the invention

[0024] The alloy of the invention is defined by ranges for the elements C , S i , B , P , M o a n d characteristically for the invention : manganese. It was found that the presence of Mn between 0.05wt% and 0.6wt% is crucial - in combination with the other element ranges - for obtaining good glass forming ability. Optionally, Cu can be added to the alloy between 0.25wt% and 0.8wt%. Added in this range, Cu improves the mechanical properties of the amorphous product while maintaining good glass forming ability. If not added within this range, Cu may be present as an impurity element up to a specific level. The remainder of the alloy consists of Fe and incidental impurities. A more preferred range for Mn is between 0.05wt% and 0.5wt% (i.e. 0.07at% - 0.49at%); an even more preferred range for Mn is between 0.05wt% and 0.4wt% (i.e. 0.07at% - 0.39at%) .

[0025] The alloy of the invention is thus characterized by the presence of the ferromagnetic metal Fe, metalloids C/Si/P/B and transition metals Mo and M . Molybdenum is known to have a significant influence on the glass forming ability of amorphous /glassy Fe-based alloys. Higher Mo-levels allow good GFA up to higher diameters of the final product when that product is a cylindrical rod. The present invention reveals that in the presence of Mn, this influence is still observed but only with Mn between the limits of 0.05wt% and 0.6wt%. At Mn-levels lower and higher than this range, no good GFA is obtained, even at high Mo-levels and low diameters of the final rod-shaped product. The invention therefore teaches that when Mn is added to a Fe/Mo/B/Si/P/B-based amorphous/glassy alloy, it must be added between specific limits in order to maintain good GFA-properties .

[0026] The soft magnetic glassy alloy product according to the invention may be produced from non-pure starting materials (although pure starting materials can be used as well) . Mn is often present as an impurity in materials such as standard raw grade FeB or FeP (see further) . The product of the invention can thus be obtained by selecting non-pure starting materials with a suitable Mn-content.

[0027] A master alloy or a final product according to the invention may comprise 0, Al , S, Cr, Cu and Ti up to specific levels. These elements may be present as impurity elements in some of the preferred non-pure starting materials used for the production of a product according to the invention (see further) . Oxygen can further enter the alloy composition during processing, as said processing does not need to take place under vacuum conditions. Other impurity elements (e.g. V, Nb, Ni) are preferably present at levels not higher than 0.2wt%, more preferably at levels not higher than 0.1wt% in the master alloy and final product.

[0028] The soft magnetic properties of a product of the invention may be expressed by the coercivity He (expressed in A/m) of the material. The coercivity value is mainly determined by the presence of features which hinder the movement of the magnetic domain walls (Bloch walls), as there are grain boundaries, precipitates, secondary phase, etc. The absence of them in amorphous/glassy materials makes them magnetically extremely soft. The measurement of He is a technique which can only be used for soft magnetic amorphous materials. It is very sensitive to the local structure, therefore very efficient and at the same time nondestructive and fast. Values of coercivity of a soft magnetic glassy alloy product according to this invention are lower than 30A/m and preferably lower than 15A/m. If the coercivity value increases, this indicates that there are crystals present of sufficient size to hinder the movement of the walls of the magnetic domains. He is thus also a measure for expressing whether or not the material can be regarded as amorphous in the sense described above.

[0029] Embodiments of the method of the invention for producing an Fe-based soft magnetic glassy product according to the invention are described hereafter. First, a master alloy is prepared by performing the following steps :

[0030] Selection of suitable starting materials Starting materials are suitable for the method of the invention, when the set of starting materials selected comprises at least the elements Fe, Mo, C, Si, B, P and Mn . According to a preferred embodiment of the method, at least one of the starting materials comprises impurities, i.e. elements other than Fe, Mo, C, Si, B, P and Mn . Preferably one or more of the following standard raw grade materials is selected : AK steel (Aluminium killed steel), FeMo, FeP, FeB, FeSi, electrolytic Fe . With Standard raw grade' is meant : materials with a limited amount of impurities. Table 1 shows preferred maximum impurity levels (in wt%) in standard raw grade FeB, FeP, FeMo, FeSi, electrolytic Fe and AK steel usable as starting materials for the product according to the invention. Table 2 shows typical compositions for the same materials. According to the embodiment wherein standard raw grade FeB and/or FeP is used as a starting material, Mn is thus added as an impurity element in one or both of said starting materials. The source of carbon in the starting materials is preferably graphite, which consists essentially of pure carbon although it may contain small levels of impurities. Otherwise, FeC can also be used as a starting material. Electrolytic Fe ( ^X el-Fe' ) is included in table 1 as a non- pure starting material, but in practice it is usually approaching pure Fe with very low amounts of impurities, as seen in table 2. The typical el-Fe composition of table 2 is equivalent to pure Fe for the purposes of this invention. Electrolytic Fe is preferably used in combination with a non-pure Fe-source such as FeB or FeSi, as illustrated in the examples. It must be noted that the values in wt% given in tables 1 and 2 are to be regarded with respect to each starting material separately, and not with respect to the master alloy or final product produced from one or more of said starting materials.

[0031] When not all of the alloy elements Fe, C, Si,

B, P, Mo, Mn are present in the non-pure starting materials, said one or more non-pure materials are combined with one or more pure grades. Preferably, one or more of the following pure grades are then used : pure Fe and/or electrolytic Fe (in a composition similar to table 2), pure Mo, pure P, pure B, pure Si, pure Mn . As pure P is too reactive, it is preferably added in the form of Fe ₂ P or Fe3P, obtainable by a known process starting from pure P and pure Fe . According to a specific embodiment, all the starting materials are non-pure materials. According to another embodiment, all the starting materials are pure materials .

[0032] Preparing the necessary amounts of the various starting materials

In a second step, the necessary amounts of the selected materials are weighed to approximate the aimed composition, taking into account that the exact amounts of the alloy elements (C, Si, B, P, Mo and Mn) are not known due to the presence of impurity elements.

[0033] Melting the raw materials

The first melting step can be done by induction melting or another melting technique, e.g. levitation melting. The mixture of materials is heated up to a temperature higher than the melting temperature, preferably 100°C higher than the melting point, to assure homogenization . The melting step can be done under air, under a protective gas like Ar (atmospheric pressure or under pressure) or under vacuum. The material is kept in the molten state during 500 to 3000s .

[0034] Introducing the molten material into a mould to form the master alloy

The molten materials are introduced, e.g. poured into a mould. Then the melt is cooled down to form the master alloy. It is preferred to use an adequate size/shape of the master alloy piece (s) which are beneficial for an easy manipulation in later steps. Sizes of 50g to 500 g are the most convenient, but higher sizes up to 1kg or even 100kg are possible.

[0035] Then the levels of C, Si, B, P, Mo and Mn in the master alloy are measured. Preferably also the levels of 0, Al, S, Ti, Cu and Cr are measured. If all levels are within the ranges of the invention, the following steps are performed :

1) Collecting the right amount of the master alloy to cast the desired product by weighing and selecting pieces of master alloy,

2) Heating the selected amount of master alloy by induction melting or by another melting technique to a temperature higher than its melting point. It is desirable to reach a temperature at least 50°C above its melting point,

3) Holding the master alloy at this temperature for at least 5 seconds, 4) Introducing the master alloy into a mould having the desired shape. It is favourable to force the molten metal to enter the mould as fast as possible to increase the cooling rate. This can be done for example by gas injection casting or by die casting techniques known as such in the art .

[0036] The step of measuring the composition of the master alloy can be omitted when the starting materials are all pure materials. In that case, the amounts of the starting materials can be determined to lead to a predefined master alloy composition. Also when the composition of non-pure starting materials is very well known in advance, the step of measuring the master alloy composition can be omitted.

[0037] While the invention has been illustrated and described in detail in the foregoing description, such description is to be considered illustrative or exemplary and not restrictive. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0038] The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated.

Examples - Experimental results

[0039] A number of test samples was produced by the above described method. Soft magnetic glassy Fe-alloy rods were produced of various diameter : 2mm, 2.5mm, 3mm, 3.5mm and 4mm. The starting materials were melted by induction melting or levitation melting to obtain master alloy pieces. These were further melted in a quartz tube by induction melting under vacuum (between 10 ^~2 and 10 ^_1 bar) or air. After this, the final product was obtained by injection casting, at a temperature between 1100°C and 1350°C, at an overpressure of between 200mbar and 500mbar under an Ar-atmosphere .

[0040] Table 3 shows the composition of 22 master alloy samples. For each sample the coercivity of the final product (i.e. after further melting to form rods of the given diameter) is given. The composition of the final product in terms of Fe, Mo, Si, P, C, B and Mn does not substantially differ from the master alloy composition.

[0041] From the examples, it is clear that there is a correlation between the Mn level and the coercivity in the final product, which leads to the conclusion that the range for Mn as claimed is significant in terms of obtaining good glass forming ability. It is to be noted that within the inventive range for Mn of 0.05-0.6wt%, the effect of Mo on the obtainable diameter is as known in the art : the higher Mo-levels allow to obtain good GFA for diameters up to 4mm. However, when the Mn is lower than 0.05wt% or higher than 0.6wt%, GFA deteriorates, even for high Mo levels and low product diameters. [0042] The starting materials used for the production of these samples are given in table 4. The Mn- levels of all samples are obtained due to the presence of Mn as an impurity element in FeP. For samples 17 to 19, no raw grade FeP was used, leading to very low Mn-levels in the master alloy. For samples 20 to 22, FeP was used with Mn at levels between 2 and 3wt%, i.e. above the maximum level shown in table 1. This was the reason for the high Mn level in the master alloy which led to too high He values. Table 3 shows that both these low and high Mn- levels are correlated to Hc-values above 30A/m, i.e. the product can no longer be regarded as amorphous in the sense described above. Mn can also be included in pure form as a starting material.

[0043] For sample 13, copper was deliberately added to the starting materials, leading to a higher Cu-level in the master alloy compared to the other samples. Sample 19 exhibits a rather high S-level despite the use of pure starting materials. This could be because of a higher than normal S-level in the starting materials electrolytic Fe and/or graphite.

[0044] Table 5 shows measurements of a number of element levels in the final products obtained from four of the master alloy samples. The slight increase measured for some elements is due to measurement errors. It can be concluded therefore that most of the elements levels in the final product remain unchanged, except for 0 which decreases significantly. El-Fe AK

steel FeB FeP FeSi FeMo

Cr 0,08 0,1 2

Mn 0,2 0,5 0,7 1,8

S 0,05 0,01 0,01 0,03 0, 02 0,1

Si 0,1 0,3 0,75 2,5 1,5

Ti 0,1 0,1 1 0,1

V 1,8

Al 0,2 0,4 0,8 1,5

C 0,1 0,11 0,5 0, 02 0,2

P 0,03 0,1 0,05 0,03 0,05

Cu 0,08 0,1 0,5

Nb 0,1 0,1

Ni 0,08 0,1

0 0,1 0,1

N 0,01 0,02

B 0,001 0,001

Mo 0,05 0,1

Table 1: max. levels (wt%) of impurity elements in various non-pure starting materials

Table 2 : typical composition of various non-pure starting materials

Table 3 : master alloy compositions of 22 product samples (all element levels in wt%)- 'na' = not analysed - ^Λ <' = value under detection limit

Table 4 : starting materials for 22 product samples

element levels measured on final products (all values in wt% - nm means