GB2173216A - Method of producing a ferro-alloy - Google Patents

Abstract

A method of making a molten ferro-alloy product in a melting furnace by charging a briquet consisting essentially of metallized iron, granulated alloy metal oxide, a carbon source such as coke breeze, and a binder such as a mixture of calcium hydroxide and molasses, to the melting furnace, burning solid carbonaceous material to reduce the alloy metal oxide to metallized form and to heat the charge to form a molten ferro-alloy product. Fluxes and slag formers are also charged to the furnace as required.

Description

SPECIFICATION Method of Producing a Ferro-alloy This invention relates to a method of making a ferro-alloy having a metallic iron content for use in the manufacture of iron and steel.

In the manufacture of iron and steel, it is customary to make certain additions to the rnelting furnace such as various metalliferous products in the form of alloys such as ferrosilicon, ferronickel, ferrochrome, ferromanganese, and the like. Such ferroalloys normally contain a substantial amount of carbon.

According to the present invention there is provided a method of producing a ferro-alloy including forming compacts consisting essentially of a mixture of metallized iron, solid carbonaceous material, and an oxide of at least one of silicon, nickel, molybdenum, manganese, magnesium, titanium, vanadium, chromium, and cobalt, charging said compacts and slag formers into a melting furnace, and burning said solid carbonaceous material to reduce the oxides in said compacts, to melt the constituents, and to form a high alloy melt.

Thus metallised iron, the alloy element in oxide form, and carbon are formed into a compact or briquet, then charged into a shaft furnace along with additional carbonaceous material such as coke, if necessary, and reduced to form a molten ferroalloy product of high value for foundry practice and other iron and steelmaking uses.

The briquet to be charged to the shaft furnace preferably employs metallized iron fines as the basic ingredient in its composition. Previously known briquets employ iron oxide fines. The presence of metallized fines reduces the energy requirement for the method of the invention. Since the iron fines are in the metallized condition, the energy normally required for reducing iron oxide to iron is not a requirement in this process. Since the iron in the briquet need not be reduced before melting, the energy requirement is reduced.

Known prior art patents include Rehder U.S. Patent 4,179,283, Merkert U.S. Patent 4,395,284, and Strange U.S. Patent 4,369,062.

Rehderteachesthe briquetting of metal oxides only and has no direct reduced iron in his briquet charge. He utilizes two sources of carbon, a high reactivity and a low reactivity carbon.

Merkertteaches that iron and a binder are optional and are not essential ingredients. He prepares porous compacts for use as a feed material to an electric furnace, the material having an apparent low density and high internal porosity. Merkert states that up to about 15% of the silica weight can be iron particles, however, this is identified as mill scale, which is generally in oxide form.

Strange teaches production of a briquetfrom reclaimed materials, such as iron fines and mill scale up to 41%. A study has shown that he has insufficient carbon in his briquet to reduce the mill scale. He also requires an additional source of energy to provide heat during the melt.

The method of the present invention differs from each of these prior art teachings in that the charged briquets contain the desired alloy oxide, carbon and iron which preferably is over 60% metallized, and a binder such as sodium silicate or a mixture of calcium hydroxide and molasses.

It is the general aim of this invention to provide a method for making a ferroalloy more economically than is presently possible, for various steelmaking and foundry practices.

A briquet of from 85 to 99 parts of a mixture of finely divided material consisting essentially of, by weight, 10 to 90 percent metallized iron, 7 to 65 percent alloy oxide, and 5 to 26 percent carbon, is blended with 1 to 15 parts of binder. The optimum briquet contains 92 parts of finely divided material and 8 parts of binder. The briquet is charged into a shaft furnace along with additional carbonaceous material, which is burned to heat and reduce the alloy oxide to metallized form, melt the iron and alloying element, and form a ferroalloy melt in the furnace.

The method of the invention utilizes as a charge material an iron bearing briquet consisting essentially of, by weight, from 10 to 90% metallized iron, from 7 to 65% alloy in metal oxide form, and from 5 to 26% carbon. The iron in the composition can be in the form of turnings, chips or metallized iron fines, but are preferably the latter. Metallized iron fines are preferably made by direct reduction of iron oxide and are at least 60% metallized, but usually more than 80% metallized.

The preferred binders are three parts lime and five parts molasses. Lime for the binder is in the form of hydrated lime, which is calcium hydroxide.

All of these components should be in the finely divided form, preferably less than 3 millimeters.

Silica, manganese oxide, chromite, molybdenum oxide, nickel oxide, cobalt oxide, magnesium oxide, vanadium oxide, or other desired alloy oxide is present in fine or granulated form. Such oxides are herein given the formula MO for ease of notation in equations.

The metallized iron fines within the briquet melt to form discreet iron droplets which are saturated with carbon. The carbon is preferably a component of a solid fuel, such as coal or coke, or alternatively could be pitch or tar. The briquet should include additional carbon beyond the stoichiometric requirements in order to have a pbrtion act as fuel to provide the heat of reaction for reduction and supply the necessary energy to heat and melt the reduced iron and silicon to tapping temperature (about 2700"F or 150000).The function of carbon in the briquet is: 1) to supply the energy required for the heat of reaction to reduce the alloy metal oxide species, the reaction being; MOP+~ heat M (5)+CO 2) to supply the energy required to dissolve the carbon into the molten iron, the reaction being; C(s, heat C 3) to provide the energy required to satisfy the enthalpy requirement in heating the iron and metallized oxide species (after reduction) to tapping temperature; and 4) to provide the energy to dissolve the reduced metal species into the molten iron, the reaction being; M(s) heat M Preferably, the particle size of all components is less than 25 millimeters, but most advantageously the particles size of all components will be less than 1 millimeters prior to briquetting.

A more advantageous range of components in the briquet is, by weight, from 20 to 70% metallized iron, from 15 to 60% alloy oxide and from 9 to 23% carbon. The optimum composition is, by weight, from 40 to 55% metallized iron, from 20 to 40% alloy oxide, and from 13 to 21 % carbon.

The mixture set forth above can be briquetted by hot briquetting at a temperature of at least 6000C and a pressure of at least 6.895 N/mm (1,000 pounds per square inch) to form a hot iron-bearing briquet.

The preferred binder is a mixture of calcium hydroxide and molasses in roughly equal parts, with an optimum composition of 3 parts lime to 5 parts molasses. However, each can be present in the amount of from 30 to 70% of the binder. Alternative binders are sodium silicate, pitch, and tars, other organic or chemical binders, and cements.

In carrying outthe method of the invention, the ferroalloy briquet is charged into a shaft furnace melter, such as a cupola or other melting furnace. A substantial portion of the alloy oxide in the briquet will be reduced during the melting process, and the metallic alloy elements will become available to the molten product as an alloying element. Thus it is seen that the ferroalloy briquets can be substituted for the more expensive ferro-silicon or other ferroalloy.

In a cupola furnace, which is a melting furnace and not a reduction furnace, a loss in melting productivity results when reduction of both alloy oxide and iron oxide must be performed in the furnace.

When only the alloy oxide must be reduced, that is if the oxide has already been reduced to the metallized iron form, the loss in melting productivity is minimized.

Oxygen for combustion in the cupola is provided by preheated air, with optional oxygen enrichment.

The cupola could be a conventional coke cupla, or a cokeless cupola, or any desired melting furnace, which could be fired by oxy-fuel burners, oxygen enriched air/natural gas burners, plasma torches, or electrodes such as carbon arc electrodes in an electric arc furnace.

The briquet charged preferably consists essentially of metallized iron fines, fine or granulated alloy in oxide form, a carbon source such as coke breeze or coal fines, and a binder such as a mixture of calcium hydroxide and molasses. After the mixture is compressed into a briquet, the briquet can be dried or cured at low temperature such as from 150 to 200or (about 300 to 4000F) in order to remove any moisture and to improve the green strength.

Stainless steel, alloy chips, borings or turnings, or non-ferrous oxides such as ilmenite, chromite, titania concentrates, nickel laterites or oxides, and even alloy mill scale could be included in the briquets.

Sufficient additional carbon, in the form of solid carbonaceous material such as coke, is charged to the melting furnace in such quantity that it will satisfy the enthalpy and heat of fusion requirements to melt the solid iron, solid iron alloy, and slag formers that have been charged to the melter, as well as provide carbon to the extent of being partially oxidized to form a non-oxidizing atmosphere in the melting zone of the melter to protect the iron and any reduced alloy specie against oxidation.

The following tables compare the chemical analyses of various ferrosilicon compositions with equivalentferrosilica briquets, as used in the present invention.

TABLE I Ferrosilicon Analysis Ferrosilicon Designation FeSi 1 FeSi 5 FeSi 10 FeSi 25 FeSi 50 FeSi 75 Fe 98.5% 94.5% 89.5% 74.5% 49.5% 24.5% Si 1.0 5.0 10.0 25.0 50.0 75.0 C 0.5 0.5 0.5 0.5 0.5 0.5 TABLE II Ferrosilica Briquet Composition Ferrosilicon Equivalent FeSi 1 FeSi 5 FeSi 10 FeSi 25 FeSi 50 FeSi 75 Metallized 96.6% 86.7% 75.9% 51.6% 26.2% 10.5% Iron Fines SiO2 0.5 7.8 15.7 33.5 52.1 63.5 C 2.9 5.5 8.4 14.9 21.7 25.9 TABLE Ill Ferrosilica Briquet Analysis FeSi 1 FeSi 5 FeSi 10 FeSi 25 FeSi 50 FeSi 75 Fe 81.9% 73.5% 64.4% 43.7% 22.2% 8.9% FeO 9.3 8.3 7.3 4.9 2.5 1.0 C 4.3 6.8 9.5 15.7 22.1 26.0 SiO2 1.9 9.1 16.8 34.3 52.5 63.8 CaO 0.9 0.8 0.7 0.5 0.3 0.1 Other 1.6 1.5 1.3 0.9 0.4 0.2 "Metallized", as used throughout this specification does not mean coated with metal, but means nearly completely reduced to the metallic state, i.e., always in excess of 60% metal, and usually in excess of 80% metal in the material. Such metallized iron in many forms, including pellets, is well suited as feed material to steelmaking furnaces such as an electric arc furnace.

Alternative binders of the matrix type such as coal-tar pitch, or of the film type such as sodium silicate, or of the chemical type such as hydrated lime and carbon dioxide, are all envisioned to be suitable binders for this application.

The charge to the cupola could be a mixture of briquets, hot briquetted iron, plain carbon steel scrap, alloy steel scrap, reclaimed cast iron, and coke.

Flux additions such as limestone, burned lime, dolomitic lime, spar, and the like would be utilized to form a suitable slag for either desulfurization, dephosphorization, or both, or just to flux impurities from the melt to the slag.

The molten ferroalloy product could be granulated, or cast into pigs or small ingots.

Claims (11)

1. A method of producing a ferro-alloy including forming compacts consisting essentially of a mixture of metallized iron, solid carbonaceous material, and an oxide of at least one of silicon, nickel, molybdenum, manganese, magnesium, titanium, vanadium, chromium, and cobalt, charging said compacts and slag formers into a melting furnace, and burning said solid carbonaceous material to reduce the oxides in said compacts, to melt the constituents, and to form a high alloy melt.

2. A method according to claim 1, including adding one or more of carbon, metallic aluminium and metallic magnesium to said compact prior to charging it into the furnace.

3. A method according to claim 1, including charging additional solid carbonaceous material to said furnace to provide additional heat and reactive carbon.

4. A method according to claim 1, including charging solid iron, iron alloy, hot briquetted iron, carbon steel scrap, alloy steel scrap, reclaimed cast iron, or a mixture thereof to said melting furnace.

5. A method according to any one of claims 1 to 4, including injecting oxygen into said furnace to aid combustion.

6. A method according to claim 5, wherein said oxygen is present in the form of preheated air.

7. A method according to any one of claims 1 to 6 including providing heat to said furnace by oxy-fuel burners, oxygen enriched air/natural gas burners, plasma torches, or electrodes.

8. A method according to claim 1, comprising including in said compact at least one of stainless steel, alloy chips, borings, turnings, ilmenite, chromite, titania concentrates, nickel laterites, nickel oxides, and alloy mill scale.

9. A method according to claim 1, in which the compacts used include additional carbon beyond the stoichiometric requirement.

10. A method of producing a ferm-alloy substantially as hereinbefore described.

11. A ferro-alloy made according to the method of any one of claims 1 to 10.