A METHOD FOR THE MANUFACTURE OF AN EFFICIENT STEEL DEOXIDIZER ALUMINUM MATRIX COMPOSITE MATERIAL

Abstract

A method of manufacture to provide an efficient and economical steel deoxidizer aluminum matrix composite material that is near fully dense, free of brittle intermetallic compounds and allows for deep penetration of aluminum into molten steel thus cutting unnecessary losses of this valuable metal to parasitic oxidation reactions with slag and atmosphere.

Claims

1. A method for the manufacture of a steel deoxidizer aluminum matrix composite material comprising the steps of: forming a porous free-standing preform, wherein the free-standing preform is comprised of aluminum and an iron-rich component; applying a quantity of heat to the free-standing preform to raise the temperature of the free-standing preform above the melting point of aluminum and below the melting point of the iron-rich component; and applying a quantity of pressure to densify the free-standing preform to a near full density and to allow for the aluminum in the free-standing preform to solidify.

2. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 1, wherein the iron-rich component is steel.

3. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 1, wherein aluminum is present in the range of ten to fifty percent of the composite material by weight.

4. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 3, wherein aluminum is thirty percent of the composite material by weight.

5. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 1, wherein the free-standing preform is formed by a process selected from the group consisting of: mechanical pressing, briquetting, a container, an inorganic binder, and any combination thereof.

6. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 1, wherein the quantity of heat applied to the free-standing preform is sufficient to raise its temperature over six hundred sixty one degrees Celsius.

7. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 1, wherein the quantity of heat applied to the free-standing preform is through a process selected from the group consisting of: induction heating, electrical resistance furnace heating, and organic fuel burner furnace heating, and any combination thereof.

8. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 1, wherein the quantity of external pressure applied to the free-standing preform is sufficient for a molten aluminum component to fill porosity and gaps between the iron-rich components.

9. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 1, wherein the quantity of external pressure to densify the preform is applied by means of pressing in a closed die.

10. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 1, wherein the iron-rich component is selected from the group consisting of: ferromanganese, and a mixture of steel and ferromanganese.

11. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 10, wherein the free-standing preform is bound and supported by a process selected from the group consisting of: mechanical pressing, inorganic binder, a steel container, and any combination thereof.

12. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 11, wherein the quantity of heat to the free-standing preform applied is through a process selected from the group consisting of: induction heating, electrical resistance furnace heating, and organic fuel burner furnace heating, and any combination thereof.

13. A method for the manufacture of a steel deoxidizer and inclusion modifier aluminum matrix composite material comprising the steps of: forming a porous free-standing preform, wherein the free-standing preform is comprised of a plurality of fines of aluminum and a plurality of fines selected from the group consisting of: steel, ferromanganese, silicocalcium, calcium carbide, rare earth metals, any ferroalloy other than ferromanganese, and any combination thereof; applying a quantity of heat to the free-standing preform to raise the temperature of the free-standing preform above the melting point of aluminum and below the melting point of other components of the free-standing preform; and applying a quantity of pressure to densify the free-standing preform to a near full density and to allow for the aluminum in the free-standing preform to solidify.

14. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 13, wherein aluminum is present in the range of ten to fifty percent of the composite material by weight.

15. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 13, wherein aluminum is thirty percent of the composite material by weight.

16. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 13, wherein the free-standing preform is formed by a process selected from the group consisting of: mechanical pressing, briquetting, a container, an inorganic binder, and any combination thereof.

17. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 13, wherein the quantity of heat applied to the free-standing preform is sufficient to raise its temperature over six hundred sixty one degrees Celsius.

18. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 13, wherein the quantity of heat to the free-standing preform applied is through a process selected from the group consisting of: induction heating, electrical resistance furnace heating, and organic fuel burner furnace heating, and any combination thereof.

19. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 13, wherein the quantity of external pressure applied to the free-standing preform is sufficient for a molten aluminum component to fill porosity and gaps between the iron-rich components.

20. The method for the manufacture of a steel deoxidizer aluminum matrix composite material of claim 13, wherein the quantity of external pressure to densify the preform is applied by means of pressing in a closed die.

Description

DETAILED DESCRIPTION OF THE SEVERAL EMBODIMENTS

[0027] The new steel deoxidizer material provided in the present method of manufacture may be best described as aluminum matrix composite. Composite materials are usually defined as comprising of discrete reinforcement or filler particles or fibers that are contained in, or surrounded by, continuous matrix material. Unlike conventional metallic alloys comprised of different metallic phases whose interactions are governed by thermodynamic equilibrium laws, metal matrix composites are often referred to as engineered materials. Composites reinforcement and matrix are joined together through an engineered manufacturing process and generally speaking do not find themselves in thermodynamic equilibrium, in many cases being chemically inert to each other—for example refractory ceramic particles in aluminum matrix composite.

[0028] From an engineering point of view, there is a compelling reason for adding composite materials to an already wide arsenal of previously available metals and alloys. This is because composites allow to engineer materials, with microstructures and properties not achievable using established methods of melting, casting, heat treating, cold and hot-working that rely on physicochemical processes and reactions in metallic systems. For example, to make a deoxidizer material heavier than aluminum, one could use smelting of aluminum with iron at a high temperature resulting in metallurgical ferroaluminum alloy described earlier in the text. Ferroaluminum is heavier than aluminum, but contains large amounts of brittle and corrosion-prone intermetallic phases that make it crumble in storage or when it is charged into molten steel. However, if steel particles could be joined with aluminum matrix into engineered near fully dense composite material using manufacturing method other than high temperature smelting, the resulting material will be much denser than aluminum, but at the same time, free of brittle intermetallic phases that reduce ferroaluminum deoxidizer efficiency due to crumbling.

[0029] There are many technological methods for the manufacturing of metal matrix composite materials well known to those skilled in the art. For example, casting is where reinforcement particles are first pre-mixed with molten metal and then the mixture is cast into a mold. Another example, powder metallurgy methods occur when solid reinforcement and matrix particles are mixed, pressed into a shape and then sintered in solid state at high temperature. Another well-known widely applied method may be generally described as pressure infiltration technology. In its custom implementation, a dry preform of reinforcement particles is first made, heated up, placed into a die, and then molten matrix metal is poured over the die and infiltrated into the dry preform under external pressure applied to the matrix metal, usually via hydraulic press punch. Drawbacks of custom pressure infiltration technology are that it requires a complex tooling, precise control over manufacturing parameters of each individual briquette. Also, the most critical shortcoming is the necessity to melt and hold large batches of matrix metal, which in the case of aluminum, leads to high losses of aluminum to dross.

[0030] New deoxidizer aluminum matrix composite material described herein is manufactured using a pressure infiltration technology that is radically improved compared to a custom one to make the technology economical to implement and minimize losses of valuable aluminum. Unlike custom technology, the new technology aluminum matrix infiltrant does not have to travel from one boundary of a dry preform made of steel particles through a bulk of the preform and all the way to the opposite boundary in order to infiltrate the preform completely. Such long travel of molten aluminum necessitates complex and precisely machined dies to avoid aluminum bursting out under pressure, and also carries risk of premature aluminum cool down and incomplete preform infiltration as a result. Instead, in the new technology, liquid aluminum has to travel only a short distance to fill gaps between steel particles in the preform. This is because aluminum is pre-mixed with the steel particles at the stage of preform manufacturing—a step, which also automatically guarantees precise aluminum to steel weight ratio in the new composite deoxidizer. The pre-mixed aluminum transitions to liquid state during preform heat-up and only travels distances comparable to average steel particle size to fill gaps around them when the preform is squeezed in a hydraulic press die. Such technology may be called in-situ pressure infiltration technology, because aluminum infiltrant is in-situ present in the preform that is being infiltrated.

[0031] In a preferred embodiment, first, a porous free-standing preform shape is formed from crushed turnings, shavings, borings or other substantially small pieces of aluminum mixed with crushed turnings, shavings, borings or other substantially small pieces of steel, wherein the preferred weight fraction of aluminum is close to 30%. Formation of the shape is a manufacturing operation that will be known to those skilled in the art, and preferably achieved by mechanical pressing or briquetting. Alternatively, the preform shape may be formed using a container, inorganic binder (i.e. sodium silicate), or both to make it free-standing. Geometry of the preform shape might vary. In a preferred embodiment, the geometry may be a cylinder between 20 and 200 millimeters in diameter and between 20 to 200 millimeters in height, and having diameter to height ratio of 1 to 1 or close to it.

[0032] Next, the preform shape is heated to a temperature that is over melting temperature of aluminum, but below melting temperature of steel and for a sufficient time for aluminum component to transition to liquid state. Exact heating temperature value might vary. In a preferred embodiment, the temperature range may be between 661 and 800 degrees Celsius. Possible techniques used to heat up the preform shape will be known to those skilled in the art. In a preferred embodiment, the technique may be induction heating, since it is extremely efficient at heating materials that contain ferromagnetic components, specifically carbon steel.

[0033] It should be noted, that though some oxidation of aluminum during heating of the preform will take place, it will be drastically minimized compared to melting and holding of large aluminum batches in open air furnaces because of brevity of the process and restricted air paths in the preform.

[0034] Then, the heated preform shape is squeezed in an adequately tight volume at a pressure sufficient for in-situ molten aluminum component in the shape to fill practically all porosity and gaps between steel particles, so that the composite becomes near fully dense with a density at least higher than 90 percent of theoretical and preferably higher than 95 percent of theoretical. Pressure on the preform should be maintained until the moment where the molten aluminum solidifies. Squeezing operation may be performed using wide variety of techniques known to those skilled in the art. In a preferred embodiment, the technique may be pressing in a closed die mounted on a hydraulic press. The die suitable for squeezing operation may be much less complex compared to dies used in custom pressure infiltration technology. This is because in custom pressure infiltration hydraulic press punch has to drive a relatively large volume of liquid metal under high pressure for a considerable distance until it fully infiltrates dry preform. Hot liquid metal under pressure may burst out of a die if it finds even a tiny gap between the punch and die wall. To avoid bursting, precise machining of the die and punch to minimize the gap is necessary, which in turn, makes it difficult to extract the punch from the die once infiltration is complete.

[0035] Difficulties with punch extraction often lead to further complexities in die design. For example, use of a split die may be necessary for extraction, instead of unitary cylindrical die. In the case of in-situ pressure infiltration, the punch has to travel only a short distance to densify the preform, and material being pressed by the punch is semi-solid, not fully liquid like aluminum in the case of custom pressure infiltration technology. This allows for much less tighter gaps between the punch and die walls and relieves punch extraction problem, so that a simple cylindrical unitary die may be used.

[0036] In alternative embodiments of the method of manufacture, weight fractions of aluminum in the free-standing porous shape may vary between 10% and 50%.

[0037] In another alternative embodiment of the method of manufacture, the porous free-standing preform shape is formed from crushed turnings, shavings, borings or other substantially small pieces of aluminum mixed with substantially small pieces of ferromanganese, wherein the weight fraction of aluminum is close to 25%. The rest of the process steps, including shape heating and heated shape squeezing are substantially the same. A rational for substituting steel with ferromanganese, is that on one hand, it is known to those skilled in the art that combined effect of aluminum and manganese as deoxidizers is stronger than of either element separately. On the other hand, ferromanganese may serve the same functions as steel as far as making aluminum-containing deoxidizer heavier and providing efficient induction coupling during induction heating of the porous free-standing preform shape.

[0038] In other alternative embodiments of the method of manufacture, some of the steel and aluminum in the free-standing porous preform shape may be replaced by additions useful in the steelmaking process, such as silicocalcium, calcium carbide, rare earth metals and other useful additions. Such additions may help deoxidize steel even better than aluminum alone, or modify shape and size of oxides and other non-metallic particles suspended in molten steel, making them smaller and more compact, thus improving appearance and mechanical properties of a final flat rolled steel product.

[0039] In a preferred embodiment, the new steel deoxidizer aluminum matrix composite material manufactured as described in the preferred embodiment above is used to deoxidize steel at the stage of EAF or BOF tapping into a ladle as direct replacement of aluminum ingot or cone. Not to be held to a particular theory, weight ratio of the deoxidizer composite material to weight of aluminum ingot or cone it replaces may be estimated as 1.66 to 1 based on the following considerations. It is known from past industrial practice that non-crumbled ferroaluminum containing close to 30% aluminum by weight saves about 50% of aluminum compared to deoxidation using ingot or cone. Therefore, each kilogram of aluminum ingot or cone may be replaced by 0.5 kilogram of aluminum contained in ferroaluminum, or in case of the present method of manufacture in deoxidizer aluminum matrix composite. For a preferred weight ratio of aluminum to steel of 30 to 70, one may calculate the total weight of new deoxidizer replacing one kilogram of aluminum ingot or cone as 0.5 kilogram multiplied by 100 and divided by 30, which equals 1.66 kilogram.

[0040] While the above description contains many specificities, these should not be construed as limitations on the scope of the method of manufacture, but rather as an exemplification of preferred embodiments thereof. Many other variations are possible. Accordingly, the scope of the method of manufacture should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.