EP0059864B1 - Process for manufacturing amorphous metal alloys based on iron, phosphorus, carbon and chromium - Google Patents

Description

The present invention relates to a process for the preparation of amorphous, or vitreous, metallic alloys based on iron, phosphorus, carbon and chromium.

We know, since the work directed in 1958 by Pol Duwez at the California Institute of Technology, amorphous metal alloys, which are obtained by very rapid cooling of a liquid phase, thus allowing to keep its disordered structure, or not crystalline. Indeed, the material is thus brought directly to a temperature below a certain threshold, called the vitrification temperature, itself located at a temperature much lower than that of solidification at which crystallization begins.

A technique for manufacturing amorphous metal alloys, called hyperhardening, involves sending a jet of molten metal onto the surface of a rotating disc or cylinder, the temperature of which is maintained. less than or equal to room temperature. The liquid then spreads over the disc in a thick film of only a few microns. As the film is extremely thin and in close contact with a heat sink of much larger volume and the metals have a high thermal conductivity, the metal cools and solidifies very quickly, at a speed of the order of 10 ⁶ ° C / second.

In one particular embodiment, the jet of molten metal strikes the internal surface of a rapidly rotating hollow cylinder (POND and MADDIN, Trans of Met. Soc., AIME, Vol. 245, p. 2475, 1969).

The films or ribbons thus prepared have remarkable properties, both mechanically and magnetically. Thus, the alloys have a very high tensile strength and their ductility is characterized by excellent resistance to bending, making it possible to achieve curvatures around a radius of the order of the thickness of the strip; they also have properties of soft magnetism, that is to say that they are magnetized and demagnetized with a very weak field.

The first compositions of amorphous alloys were binary, based on gold and silicon; many metallic compositions have been tried since, but those likely to lead to an amorphous alloy by hyper quenching generally consist of a metal or an alloy of transition metals (iron, cobalt, nickel) or a noble metal ( gold, palladium, platinum) and a metalloid with a small atomic radius (boron, silicon, phosphorus, carbon).

FR-A-2 211 536 describes a composition of the MYZ type, in which M is a metal chosen from iron, nickel, chromium, cobalt or vanadium or a mixture of these elements, Y is a metalloid chosen from phosphorus, carbon or boron and Z is an element chosen from the group consisting of aluminum, silicon, tin, antimony, germanium, indium or beryllium. However, the various iron-based compositions are made from elements of high purity. Similarly, the iron-phosphorus-carbon alloy developed according to the technique described in Journal of non-crist. Solid. No. 5.1970, p. 1, by Pol DUWEZ, is obtained by melting an iron powder with 99.99% purity, pure red phosphorus, graphite-quality carbon powder electrode, this mixture undergoing sintering to form ingots . Finally, document FR-A-2257700 describes the production of amorphous alloys of the Fe-Cr-C-P type, but containing only these four elements, to the exclusion of all others.

The processes for preparing these amorphous metal alloys are therefore expensive since they require the use of the elemental metals constituting the alloy in the pure state.

The document Métal Science and Heat Treatment, May 1981, pages 900 and 901, indicates, in its last paragraph, that liquid cast iron could be used to obtain amorphous metals, by drawing of microfilaments, but the only process described consists in performing on an alloy of very precise composition, a laser treatment which affects only the surface layer.

The Applicant has found that, surprisingly, an amorphous metal alloy can be prepared from extremely common materials.

The subject of the invention is therefore a process for the preparation of amorphous metal alloys based on iron, phosphorus, carbon and chromium, of the type according to which a metal alloy is cooled very quickly in the liquid phase so as to obtain a glassy structure, characterized in that the liquid phase is prepared from cast iron, phosphorus and chromium, the cast iron used having a carbon content of 2 to 4.5%, of sulfur less than 0.45% , in silicon lower than 5%, in manganese lower than 4% and possibly being able to be alloyed with chromium up to a content of 14%.

According to a first embodiment of the process of the present invention, the liquid phase is obtained by adding phosphorus, at a rate of 3.8 to 11.5% by weight and chromium, up to 12% by weight, to cast iron in liquid state, the above percentages being counted in relation to cast iron.

Unless otherwise indicated, the percentages given in the remainder of this specification for the proportions of the various elements are by weight.

According to a first variant, it is possible to carry out a simultaneous addition of phosphorus and chromium.

According to a second preferred variant, the phosphorus is first added to the liquid cast iron, the resulting cast iron mixture is scoured and then the chromium is added.

In a third variant, the chromium is first added to the liquid iron, then the phosphorus is then added.

According to a second embodiment of the process of the present invention, the liquid phase is prepared by simultaneous remelting of cast iron in the solid state and up to 12% by weight of chromium in the solid state, relative to the cast iron, then from 3.8 to 11.5% by weight of phosphorus in the solid state is added, relative to the cast iron.

The phosphorus is preferably introduced in the form of an alloy such as ferrophosphorus, and the chromium also in the form of an alloy such as ferrochrome.

It is then possible to prepare an amorphous metal alloy from very conventional industrial products such as cast iron, without being forced to use pure elements or at least 99% purity, or to use production techniques. like that of vacuum production which avoids the formation of oxides, the dissolution of gases or the loss of volatile elements.

The alloy thus obtained is characterized both by its P / C ratio <1, and by the presence of Si.

According to the first embodiment; the process of the invention consists in adding to a pig iron maintained in the liquid state, ferrophosphorus and ferrochrome. By pig iron is meant pig iron which has not undergone any particular treatment, such as desulphurization or dephosphorization, but which is scoured, but it is also possible to use a pig iron which has undergone, in addition to scouring, prior desulphurization or dephosphorization. This cast iron can be, for example, a cast iron collected in a conventional manner during the casting of the blast furnace. Cast iron is used as a liquid directly from the blast furnace or a storage mixer, or can also be obtained by remelting ingots. Ferrophosphorus and ferrochrome are added in the form of commercial granules. The pig iron is kept liquid by any suitable means such as induction, oxygen blowing, etc., at a temperature between 1,250 and 1,450 ° C during the additions, the temperature is then reduced to a value between 1,250 and 1350 ° C to avoid excessive phosphorus losses. The yields of these additions vary between 80 and 97%, ie 90 to 97% for the ferrochrome and 80 to 97% for the ferrophosphorus.

• - de 3,8 à 11,5 % en poids en phosphore par rapport à la fonte, par exemple sous forme de 15 à 44 % en poids de ferrophosphore ayant une teneur d'environ 26 % en phosphore ;
• - de 0 à 12 % en poids de chrome par rapport à la fonte, par exemple sous forme de 0 à 17 % en poids de ferrochrome ayant une teneur d'environ 70 % en chrome ;
• - le reste étant de la fonte.

The additions are made in the following proportions:

• - from 3.8 to 11.5% by weight of phosphorus relative to the cast iron, for example in the form of 15 to 44% by weight of ferrophosphorus having a content of about 26% of phosphorus;
• - from 0 to 12% by weight of chromium relative to the cast iron, for example in the form of 0 to 17% by weight of ferrochrome having a content of approximately 70% in chromium;
• - the rest being cast iron.

When the second embodiment is implemented, one starts with a cast iron ingot having the same nature as the cast iron defined above, this ingot being remelted in the presence of ferrochrome in the form of commercial granules, in order to '' obtain a liquid mixing phase to which the ferrophosphorus is added.

The alloy thus obtained is either directly hyper-soaked or cooled and then hyper-soaked from remelted ingots at a temperature between 1,100 and 1,300 ° C, according to any known method, such as cooling on or in a roller, or even between two rolls when you want to get a ribbon.

As indicated above, the essential characteristic of the process is that the constituents of the starting mixture do not have a high purity.

Different types of pig iron have been used, the carbon content of which is between 2 and 4.5%, a higher content leading to deposits of free graphite on the amorphous ribbon obtained and a lower content unfavorable to the economic conditions of the process, because it it is then necessary to add ferrophosphorus in larger proportions. The sulfur content is preferably less than 0.45%, a value which already exceeds the levels usually encountered for standard pig iron which has not undergone any desulphurization treatment.

The amount of silicon ranges from trace amounts up to 5%, a limit beyond which obtaining a hyper-soaked product is very difficult, the ribbons obtained becoming more and more brittle. The amount of manganese goes up to 4%. Finally, the use of a very phosphorous cast iron as obtained from a phosphorous ore like that extracted from the mines of Lorraine is very suitable, this type of cast iron having a phosphorus content of up to 1.65%. It is also possible to use a chrome cast iron with a chromium content of up to 14%.

By way of illustration, elementary compositions will be given below for four fonts that have been used.
(See table on page 4)

The ferrophosphorus used as an addition element preferably has the best possible phosphorus content, compatible with commercial requirements, a minimum content of 15% being desirable. The ferrophosphorus preferably does not contain more than 2.5% of titanium, which is a conventional impurity because, beyond this value, the formation of titanium oxide disturbs the quenching. Examples of ferrophosphorus compositions are shown in the following table.

Ferrochrome, which is the other preferred addition element in the process of the present invention, is a commercial product preferably having a minimum chromium content of 50%, for example around 70% and which may contain impurities in the water. 'trace amounts such as manganese and magnesium, these impurities having no harmful consequences since they are already present in the initial melt.

By hyperquenching the mixture defined above, an amorphous alloy is obtained, the composition of which has been given above and which comprises other elements in the form of impurities, in particular manganese.

Example 1

By operating according to the first embodiment of the method of the present invention, 70% by weight of liquid iron corresponding to sample 1 defined above was mixed with 23% of solid ferrophosphorus corresponding to sample 1 defined above. above, then the mixture was descaled and finally 7% solid ferrochrome with 70% chromium was added, the various percentages being given relative to the weight of the mixture. After hyper quenching, the resulting amorphous alloy has the following composition (in atomic%):

Example 2

Still operating according to the first embodiment of the process of the invention, 65% by weight of liquid pig iron with a composition corresponding to that of sample 2 defined above was mixed with 26.4% of solid ferrophosphorus corresponding to sample 2 defined above, the mixture was descaled, 8.6% solid ferrochrome with 70% chromium was added, the percentages being given by weight relative to the mixture. The alloy obtained has the following composition (in atomic%):

Example 3

By operating according to the second embodiment of the process of the present invention, 65% solid cast iron of composition corresponding to that of sample 2 defined above is remelted, with 8.6% solid ferrochrome containing 70% chromium. , then 26.4% of solid ferrophosphorus corresponding to sample 2 defined above is added to the liquid mixture, the percentages being given by weight relative to the mixture. The alloy obtained has the composition given in Example 2.

In its usual crystalline form, an alloy having a composition as defined above is very hard and brittle and its mechanical properties are obviously poor. The tensile strength at break is less than 200 MPa. On the other hand, the cost price of this material is very low since its production requires only a cast iron which can be untreated to which ferrophosphorus and ferrochrome are added in modest quantities.

When made amorphous, this same alloy makes it possible, for example, to obtain metal ribbons of theoretically unlimited length, of thickness less than 60 μm and of width between 0.2 and several millimeters, while remaining of a low cost, since it is obtained from the same raw materials.

correspondant au premier exemple de réalisation a été soumis à divers essais. Sa température de recristallisation est de l'ordre de 470 °C ; il subit, avant recristallisation, une perte de ductilité après un traitement de 6 heures à 220 °C.By way of comparison, an amorphous alloy (A) of the following composition (in atomic%):

corresponding to the first exemplary embodiment was subjected to various tests. Its recrystallization temperature is around 470 ° C; before recrystallization, it undergoes a loss of ductility after a treatment of 6 hours at 220 ° C.

A comparison of the mechanical characteristics of this alloy of composition (A) in its amorphous form and in its crystalline form is shown in the table below:

Claims (9)

1. Process for the manufacture of amorphous metal alloys based on iron, phosphorus, carbon and chromium, of the type according to which, with a view to obtaining a vitreous structure, a metal alloy in the liquid phase is cooled very quickly on a rotating cylinder, characterised in that the liquid phase is prepared from cast iron, phosphorus and chromium, the cast iron used having a content of 2 to 4.5 % by weight carbon, less than 0.45 % sulphur, less than 5 % silicon, less than 4 % manganese and possibly being able to be alloyed with chromium up to a content of 14 %.

2. Process according to claim 1, characterised in that the liquid phase is obtained by the addition of phosphorus, at the rate of from 3.8 to 11.5 % by weight and chromium up to 12 % by weight, to cast iron in the liquid state, the above percentages being given with respect to the cast iron.

3. Process according to claim 2, characterised in that the addition of phosphorus is firstly carried out, the mixture obtained is stirred and then the chromium is added.

4. Process according to claim 2, characterised in that the addition of chromium is firstly carried out, then the phosphorus is added.

5. Process according to claim 1, characterised in that the liquid phase is prepared by the simultaneous remelting of cast iron in the solid state and up to 12 % by weight chromium in the solid state, with respect to the cast iron, then one adds from 3.8 to 11.5 % by weight phosphorus in the solid state, with respect to the cast iron.

6. Process according to one of the preceding claims, characterised in that the cast iron used is a cast iron stirred directly, obtained at the time of blast furnace casting and which has not undergone any previous treatment or a cast iron which may possibly have undergone a previous treatment, in particular desulphurization and/or dephosphoration.

7. Process according to one of claims 1 to 6, characterised in that the phosphorus is added in the form of Ferro-phosphorus having a minimum content of phosphorus of 15 %.

8. Process according to one of claims 1 to 6, characterised in that the chromium is added in the form of Ferro-chromium, having a minimum content of chromium of 50 %.

9. Process according to one of the preceding claims, characterised in that the addition of Ferro-phosphorus and Ferro-chromium is effected in the cast iron kept at a temperature of 1 250 to 1 450 °C.