CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry of PCT/US2019/040519, filed on Jul. 3, 2019, which claims the benefit of priority of Brazilian Patent Application No. BR 10 2018 013644 5 filed on Jul. 3, 2018, the contents of which are incorporated herein by reference in their entirety for all purposes.

Technical Field

The products and processes described below can be applied in the steel industry, more specifically in the production of steels and other alloys.

Background

The steel production process can be summarized in two basic steps: alloy formation and refining thereof, which are carried out in succession. The steel is formed by the addition of various metal alloys and is then refined by various techniques.

The refining step may include desulfurization, modification and removal of nonmetallic inclusions, such as globular inclusions, in addition to degassing, i.e. reduction of the oxygen, nitrogen and hydrogen content.

The desulphurization and modification and removal of non-metallic inclusions are fundamental for obtaining a quality steel, since inclusions can affect the mechanical characteristics of the product. Nonmetallic inclusions are impurities present in steels that alter their properties to a greater or lesser degree, depending on the quantity, size, morphology and chemical composition of the same. In the majority they can be considered deleterious to the product. For example, inclusions of iron sulfide (FeS) have a very low melting point, relative to that of steel (FeS melts at around 1000° C.), so that their presence in the processes of hot mechanical forming, carried out usually above 1000° C., gives the steel the so-called “hot brittleness”.

For these reasons, the steel industry has sought to reduce and control the level of non-metallic inclusions in steels in order to produce “cleaner steels” and consequently more homogeneous and with better mechanical properties.

Non-metallic inclusions, in general, originate from reactions during the manufacturing process, from precipitation during cooling or are also the result of mechanical incorporation of materials with which the liquid steel comes in contact. These inclusions may be modified morphologically or eliminated by treatment with calcium, silicon and aluminum alloys, for example.

Metal alloys used in steel refining comprising calcium, silicon and aluminum are widely known in the art and are produced and commercialized on a large scale by dozens of manufacturers and suppliers around the world.

Such alloys include, for example, calcium-silicon (CaSi), iron-sodium-manganese (FeSiMn) and calcium alum inate alloys, the former being a deoxidizer and morphological controller of inclusions, the latter a complex deoxidizer and third increases refining efficiency and has other possible uses.

Although the aforementioned existing alloys are relatively useful in their respective purposes, for example, for the elimination of non-metallic inclusions, deoxidation and desulphurization of steel in intermediate stages of production, there is a need to develop new cheaper and more efficient products that meet better the production requirements of steels, for example with higher quality, better physical properties and durability, as well as improved processes for obtaining them.

Based on the above, it can be deduced that a Calcium-Silicon-Aluminum alloy is, in theory, a highly efficient deoxidizer because it counts on the simultaneous action of silicon and aluminum, with a high utilization of calcium in the control of inclusions, for example.

However, in the case of a purely physical mixture of Ca, Al and Si, each element has an independent behavior per se. Thus, in the environment of an oxidized steel bath, the preferential deoxidation reaction will be that with the most reactive element.

Thus, in the case of a physical mixture of Ca, Al and Si, the main deoxidizer would be calcium, which deviates it from its main purpose, which is the control of inclusions. Furthermore, since the components are isolated, the respective equilibrium points will be reached prematurely, reducing the extent of the desired reactions.

SUMMARY

In the attempt to develop a new metal alloy that meets market needs and overcome the shortcomings cited above, the inventors have found that steel refining results using Ca, Al and Si alloys are optimized when the Ca, Al, and Si elements of the alloys are chemically interconnected, in relation to alloys in which the elements are physically connected.

The calcium, aluminum and silicon alloy (CaAlSi) described and claimed below is formed by the chemical bonding between these three elements and as a result is an excellent deoxidizer because of the synergistic effect of the combined action of aluminum and silicon, which preserve the calcium when chemically bound thereto, leaving it fully available to act on the oxidation products (silicates and aluminates), transforming them into liquid globular inclusions, easily removable by flotation of the metal bath, for example.

In addition, extensive deoxidation and the presence of elemental calcium create an environment conducive to the removal of residual sulfur by means of calcium itself.

It can therefore be said that the inventors have found that there is a synergistic effect between calcium, aluminum and silicon for the modification and elimination of non-metallic inclusions during the steel refining when such elements are chemically bonded. This fact is explained by the thermodynamic conditions of the system. In fact, the simultaneous action of two or more components generating complex products is more extensive than that of each of the components acting alone.

Better explaining, deoxidation reactions by silicon and aluminum, i.e.:
Si+O2→SiO2
2Al+1.5O2→Al2O3
they reach equilibrium, that is, they are less extensive than the simultaneous reaction of the two components, namely:
SiAl2+2.5O2→SiO2.Al2O3

However, during the development of the CaAlSi alloys as proposed herein, where all three elements are chemically bonded, the inventors have encountered several difficulties. For example, the stability of Si, Al and Ca oxides is increasing in this order (Si<Al<Ca), so the tendency is for preferential reduction of Si at temperatures below those of reduction of the others, as well as Ca slagification and Al.

Moreover, the formation of carbides is preferential to the formation of molecules formed only by the elements Ca, Al or Si, precisely because of the excess of carbon not used in the reduction of Al and Ca. Thus, there will be formation of carbides until saturation. In the case of silicon carbide, this can cause the furnace to become crushed, since such a compound is refractory.

The process described and claimed herein has been developed in order to obtain the CaAlSi alloy with the improved features described above, at the same time eliminating the difficulties set forth above.

Therefore one of the objects of the product and process described and claimed herein is to provide a metal alloy of Ca, Al and Si where the elements C, Al and Si are chemically bonded.

It is also one of the objectives to provide an alloy of Ca, Al and Si that has a synergistic effect on the control of nonmetallic inclusions, deoxidation and desulfurization.

In addition, one of the objectives is to provide a metallic alloy with the same characteristics mentioned above and also comprising other elements such as Iron (Fe), Titanium (Ti), Manganese (Mn), among other metals.

It is another object of the process described herein and claimed to produce metal alloys as described above, comprising a simultaneous carbothermal melting-reduction step of the three metals from their sources.

