AND/OR NIOBIUM ALLOY, AND THE USE THEREOF

Technical field

The present invention relates to a ferrosilicon vanadium and/or niobium alloy, a method of production of a ferrosilicon vanadium and/or niobium alloy, and the use of such alloy. More specifically, the invention relates to a ferrosilicon vanadium and/or niobium alloy especially suitable as an additive in the manufacture of steels.

Background art

Vanadium metal and niobium metal are known as additives to improve qualities of steels, such as finer grain size giving higher strength, increased hardenability, and higher wear resistance through precipitation of carbides and nitrides or carbonitrides. Vanadium is conventionally added to liquid steel in the form of a ferrovanadium alloy, the most common is FeV80 (80 % vanadium). Niobium is conventionally added to liquid steel in the form of a ferroniobium alloy, the most common is FeNb with 60-70 weight % niobium. In addition to iron and vanadium for ferrovanadium alloys, and iron and niobium for ferroniobium alloys, such alloys normally include small amounts of silicon, aluminium, carbon, sulfur, phosphorous, titanium, chromium, arsenic, copper and manganese, and some of these are critical impurities to steelmaking. Ferrovanadium and ferroniobium alloys have a relatively high melting temperature and therefore long dissolution times when added to a steel melt, which may lead to valuable vanadium unit or niobium unit that go into the slag instead of the steel thereby reducing the yield (also known as recovery). The conventional ways to produce ferrovanadium alloys and ferroniobium alloys are by silicon reduction and by aluminium reduction. In both methods reduction is performed in a furnace, where vanadium oxide or niobium oxide is reduced either by reaction with silicon or with aluminium. The said production methods have the disadvantages of consumption of energy to run the reaction and a relatively low vanadium yield or niobium yield as a significant amount of the vanadium oxide or niobium oxide ends up in the slag during the processing.

Therefore, there is a desire for an improved vanadium and/or niobium additive for the production of steels. It is an object of the present invention to mitigate, alleviate or eliminate one or more of the above-identified disadvantages in the prior art. Summary of the invention

According to a first aspect there is provided a ferrosilicon vanadium and/or niobium (FeSi V and/or Nb) alloy comprising 35 - 75 wt % Si; 3 - 35 wt % V and/or Nb; up to 2 wt % Al; up to 25 wt % Mn; up to 25 wt% Cr; up to 0.15 wt % Ca; up to 0.10 wt % Ti; up to 0.10 wt % C; up to 0.02 wt % Cu; up to 0.05 wt % P; up to 0.02 wt % S; balance Fe and incidental impurities.

According to a first embodiment of the first aspect, the FeSi V and/or Nb alloy comprises from 35 - 60 wt % Si; from 16 - 35 wt % V and/or Nb; up to 2 wt % Al; up to 25 wt % Mn; up to 25 wt % Cr; up to 0.15 wt % Ca; up to 0.10 wt % Ti; up to 0.10 wt % C; up to 0.02 wt % Cu; up to 0.05 wt % P; up to 0.02 wt % S; balance Fe and incidental impurities. According to a second embodiment of the first aspect, the FeSi V and/or Nb alloy comprises from 51 - 75 wt % Si; from 3 - 35 wt % V and/or Nb; up to 2 wt % Al; up to 25 wt % Mn; up to 25 wt% Cr; up to 0.15 wt % Ca; up to 0.10 wt % Ti; up to 0.10 wt % C; up to 0.02 wt % Cu; up to 0.05 wt % P; up to 0.02 wt % S; balance Fe and incidental impurities.

In an embodiment of the said second embodiment of the first aspect, the FeSi V and/or Nb alloy comprises 5 - 25 wt % V and/or Nb.

In an embodiment of the said second embodiment of the first aspect, the FeSi V and/or Nb comprises 60 - 72 wt % Si.

The following embodiments are compatible with any of the first or second embodiments of the first aspect: According to some embodiments, the FeSi V and/or Nb comprises up to 0.5 wt % Al.

According to some embodiments, the FeSi V and/or Nb comprises up to 0.025 wt % Ti.

According to some embodiments, the FeSi V and/or Nb comprises up to 0.3 wt % Mn.

According to some embodiments, the FeSi V and/or Nb comprises 0.3 - 25 wt % Mn.

According to some embodiments, the FeSi V and/or Nb comprises up to 0.3 wt % Cr. According to some embodiments, the FeSi V and/or Nb comprises 0.3 - 25 wt % Cr.

According to some embodiments, the FeSi V and/or Nb alloy has a melting temperature range from 1250 to 1650 ^° C. According to some embodiments, the FeSi V and/or Nb alloy is in the form of particles or lumps having a sizing of between 3-80 mm or in the form of cored wire or in the form of briquettes.

According to some embodiments, the FeSi V and/or Nb alloy is an additive for use in production of steels.

According to a second aspect there is provided a method for preparing a ferrosilicon vanadium and/or niobium (FeSi V and/or Nb) alloy according to the first aspect, and any of the embodiments of the first aspect, the method comprises: providing a ferrosilicon alloy in liquid state in a vessel; adding vanadium oxide containing raw material and/or niobium oxide containing raw material to the liquid ferrosilicon alloy; mixing and reacting the liquid ferrosilicon alloy and vanadium oxide from the vanadium oxide containing raw material and/or niobium oxide from the niobium oxide containing raw material, thereby forming a melt of FeSi V and/or Nb alloy and slag; separating the slag from the said melt; and solidifying or casting the liquid FeSi V and/or Nb alloy.

According to some embodiments of the method, the liquid ferrosilicon alloy is provided directly from a reduction furnace, wherein ferrosilicon is as-produced from raw materials according to conventional methods.

According to some embodiments of the method, the liquid ferrosilicon alloy is provided by re melting a charge of ferrosilicon alloy.

According to some embodiments of the method, the vanadium oxide containing raw material and/or niobium oxide containing raw material is added in an amount (by weight) providing essentially the target amount of elemental vanadium and/or niobium (by weight) in the FeSi V and/or Nb alloy.

According to some embodiments of the method, the vanadium oxide containing raw material is one or more vanadium oxide phases selected from vanadium (II) oxide, vanadium (III) oxide, vanadium (IV) oxide, vanadium (V) oxide, and/or other non-principal oxides of vanadium.

According to some embodiments of the method, the niobium oxide containing raw material is one or more niobium oxide phases selected from niobium (II) oxide, niobium (III) oxide, niobium (IV) oxide, niobium (V) oxide, and/or other non-principal oxides of niobium.

According to some embodiments of the method, the vanadium oxide phase is vanadium (V) oxide, V2O5 and/or vanadium (III) oxide, V2O3. According to some embodiments of the method, the niobium oxide phase is niobium (V) oxide, Nb ₂ 0 ₅ and/or niobium (III) oxide, Nb203.

According to some embodiments of the method, the vanadium oxide containing raw material further comprises industrial waste material or ore comprising elemental vanadium or vanadium oxide. According to some embodiments of the method, the niobium oxide containing raw material further comprises industrial waste material or ore comprising elemental niobium or niobium oxide.

According to some embodiments of the method, a slag modifying compound is added to the liquid ferrosilicon alloy in an amount of 0.5 - 30 wt %, based on the total amount of ferrosilicon alloy.

According to some embodiments of the method, the slag modifying compound is at least one of CaO and MgO.

According to some embodiments of the method, the liquid ferrosilicon alloy has a general composition;

45 - 90 wt % Si; up to 0.5 wt % C; up to 2 wt % AI; up to 1.5 wt% Ca; up to 0.1 wt % Ti; up to 26 wt % Mn; up to 26 wt % Cr; up to 0.02 wt % P; up to 0.005 wt % S; the balance being Fe and incidental impurities

According to some embodiments of the method, the method further comprises adding aluminium to the ferrosilicon melt, prior to, simultaneously, or after the addition of the vanadium oxide containing raw material and/or the niobium oxide containing raw material, in an amount of up to about 10 wt %, based on the total amount of ferrosilicon and vanadium oxide and/or niobium oxide.

According to some embodiments of the method, the liquid ferrosilicon alloy and the vanadium oxide containing raw material and/or the niobium oxide containing raw material, and any added aluminium and/or slag modifying compound, are mixed by mechanical stirring or gas stirring. According to some embodiments of the method, the slag is separated before or during casting of the liquid FeSi V and/or Nb alloy. According to some embodiments of the method, the solidified or casted FeSi V and/or Nb alloy is crushed and optionally graded in size fractions.

According to a third aspect, there is provided a use of a FeSi V and/or Nb alloy, according to the first aspect, and any embodiments of the first aspect, as an additive in the manufacture of vanadium and/or niobium containing steels.

According to some embodiments of the third aspect, the vanadium and/or niobium containing steels are chosen among, but not limited to, spring steels, tool steels, forging steels, rail steels, rebar steels, heavy plate steels, microalloyed automotive steels and aircraft steels.

The present invention will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the invention by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the invention as defined in the appended claims.

Hence, it is to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

The term "incidental impurities" should be understood to denote minor amounts of impurity elements present in the FeSi V and/ or Nb alloy or the ferrosilicon alloy, according to the normal interpretation of such term.

The term "ferrosilicon alloy" (may also be denoted "ferrosilicon", "FeSi alloy" or simply "FeSi") in the present context should be understood to be a silicon based alloy containing iron, and optionally manganese and/or chromium above impurity levels, which are conventionally produced in an submerged arc furnace (SAF) by carbothermic reduction of silica or sand with coke (or any other carbonaceous reduction agent) in the presence of iron or an iron source. Common FeSi formulations on the market are ferrosilicons with 15%, 45%, 65%, 75% and 90% (by weight) silicon. As-produced ferrosilicon alloys typically comprises about 2 wt% other elements, mainly aluminium and calcium, however, minor amounts of carbon, titanium, copper, manganese, phosphorous and sulphur are also common. The ferrosilicon alloy in the present context may also comprise manganese and/or chromium as alloying elements. Such alloys may also be denoted FeSiMn, FeSiCr and FeSiMnCr alloys. In the present context, all such possible alloys will for simplicity be referred to as ferro silicon alloys (or "ferrosilicon" "FeSi alloy" or simply "FeSi) as indicated above.

The term "ferrosilicon vanadium and/or niobium alloy" (may also be denoted "FeSi V and/or Nb alloy" or simply "FeSi V and/or Nb") in the present context should be understood to be a ferrosilicon alloy comprising vanadium or niobium or comprising both niobium and vanadium. In addition to vanadium and/or niobium, the other elements as defined in the first aspect may also be present in the alloy.

The term "up to" when used in the indication of an amount of an element in the present context should be understood to mean that the element may be present in a range from 0 wt % and up to the indicated wt % value.

Brief descriptions of the drawings

Figure 1 is a diagram showing a comparison of dissolution time of a FeSiVIO alloy and a FeSiV20 alloy according to an embodiment of the present invention, and a standard FeV80 alloy in a steel melt.

Detailed description

The present ferrosilicon vanadium and/or niobium (FeSi V and/or Nb) alloy is especially suitable for use as an additive in steel production for the production of vanadium and/or niobium containing steels. According to the first aspect of the present invention, it is provided a FeSi V and/or Nb alloy comprising 35 - 75 wt % Silicon (Si); 3 - 35 wt % Vanadium (V) and/or Niobium (Nb); up to 2 wt % Aluminium (Al); up to 25 wt % Manganese (Mn); up to 25 wt % Chromium (Cr); up to 0.15 wt % Calcium (Ca); up to 0.10 wt % Titanium (Ti); up to 0.10 wt % Carbon (C); up to 0.02 wt % Copper (Cu); up to 0.05 wt % Phosphorous (P); up to 0.02 wt % Sulfur (S); balance iron (Fe) and incidental impurities.

The present FeSi V and/or Nb alloy is especially suitable as an additive in steel manufacturing for several reasons, e.g. that the FeSi V and/or Nb alloy is low in impurities. A low aluminium content in the FeSi V and/or Nb alloy is advantageous as aluminium may cause formation of inclusions, such as for example AI2O3 inclusions, when added to liquid steels. These types of inclusion can be detrimental in several steels such as but not limited to spring steels and rail steels.

Further, the FeSi V and/or Nb alloy according to the present invention has a lower melting temperature and a different assimilation route in liquid steel compared with conventional FeV alloys and conventional FeNb alloys. The lower melting temperature and different assimilation route leads to significantly higher dissolution rates in liquid steel, compared to FeV and FeNb. The lower melting temperature and higher dissolution rate can lead to reduced energy consumption when added to liquid steel and may result in better distribution of vanadium and/or niobium in the melt.

Furthermore, a higher dissolution rate means that the ferrosilicon vanadium and/or niobium additive alloy can be added later in the steel manufacturing process, which may lead to less oxidizing of the vanadium and/or niobium in the steel melt. In addition, the higher dissolution rate of the alloy may prevent added lumps from resurfacing. Resurfacing enables contact between alloy and atmosphere or slag at high temperatures and can lower the yield of alloy element into steel melt. For FeSi V and/or Nb less superheat may be required for melting and dissolving into steel compared with FeV and/or FeNb which are endothermic and consume a significant amount of heat by adding into steel. Another advantage is the option to save up to two addition steps in the alloying process with the FeSi V and/or Nb alloys. This can reduce the required time in the steelmaking process and the required equipment like silos/hoppers for each alloy in the steel plant. When microalloys like FeV and/or FeNb are handled by hand due to their high cost per kilogram this effort may be saved with the usage of the lower cost per kilogram FeSi V and/or Nb alloy.

Silicon is a common additive in the manufacture of steels. Silicon is an alloying element in steel, known to increase strength, wear resistance, elasticity and scale resistance. Further, Si lowers electrical conductivity and magnetorestriction in steels. Si is also used as a treatment additive in steelmaking as a deoxidizer and slag reduction agent, commonly added as a ferrosilicon alloy. The silicon protection in FeSi V and/or Nb may be especially relevant in semi-killed steels like FISLA rebar or SBQ forging steels grades to increase the V and/or Nb yield. Further, silicon protection may allow to reduce the vacuum degassing effort for some steel grades. Lower V and/or Nb content compared to FeV and FeNb alloys together with oxidation protection by silicon may allow for less complex transportation and packing compared to prior art. Essentially, FeSi V and/or Nb may be handled in the same manner as FeSi. The amount of Si in the present FeSi V and/or Nb alloy is between 35 and 75 wt %. In an embodiment, the amount of Si is at least 40 wt %, at least 45 wt %, at least 47 wt %; or at least 51 wt %; such as at least 55 wt % or at least 58 wt %. In an embodiment, the amount of Si is up to 72 wt %; such as up to 70 wt %; or up to 68 wt %; or up to 60 wt %.

The present FeSi V and/or Nb alloy comprises between 3 and 35 wt % V and/or Nb. This means that if only V is present it may be present in the range 3 - 35 wt %. If only Nb is present it may be present in the range 3 -35 wt %. If both V and Nb are present, the total amount of V and Nb in the alloy is in the range 3 - 35 wt %. If both V and Nb are present, they may be present in any ratio of V to Nb within the given range. Vanadium and/or niobium forms stable nitrides and/or carbides and/or carbonitrides, resulting in a significant increase in the strength of steels. Steels comprising vanadium and/or niobium are such as, but not limited to, spring steels, tool steels, forging steels, rail steels, rebar steels, heavy plate steels, microalloyed automotive steels and aircraft steels. Depending on the required amounts of vanadium and/or niobium that should be added in different steel application, the content of vanadium and/or niobium in the FeSi V and/or Nb alloy may in some embodiments be in the range 5 - 30 wt %. In some embodiments, the content of vanadium and/or niobium in the FeSi V and/or Nb alloy may be at least 5 wt %, or at least 9 wt %, or at least 10 wt %; such as at least 16 wt %. In some embodiments the content of vanadium and/or niobium in the FeSi V and/or Nb alloy may be up to 25 wt%, or up to 20 wt %, or up to 15 wt %, or up to 10 wt %.

The V and/or Nb to Si range in the FeSi V and/or Nb alloy may depend on the amount of Si in the starting ferrosilicon alloy from which the FeSi V and/or Nb alloy is produced, e.g. a FeSi65 alloy might provide a higher V and/or Nb to Si range compared to when starting from e.g. a FeSi75 alloy.

In some embodiments, the FeSi V and/or Nb alloy may comprise 35-60 wt % Si and 16-35 wt % V and/or Nb, such as 16-30 wt % V and/or Nb, or such as 16-25 wt % V and/or Nb, with the other elements as defined above according to the first aspect (up to 2 wt % Al; up to 25 wt % Mn; up to 25 wt % Cr; up to 0.15 wt % Ca; up to 0.10 wt % Ti; up to 0.10 wt % C; up to 0.02 wt % Cu; up to 0.05 wt % P; up to 0.02 wt % S; balance Fe and incidental impurities).

In other embodiments, the FeSi V and/or Nb alloy may comprise from 51 to 75 wt % Si, such as 55 - 75 wt % Si, or 58 - 72 wt % Si, or 60 - 72 wt % Si, and from 3-35 wt % V and/or Nb, such as 5 to 30 wt % V and/or Nb, such as 5 - 25 wt % V and/or Nb, or 9 - 25 wt % V and/or Nb, or 10-20 wt % V and/or Nb, with the other elements as defined above according to the first aspect (up to 2 wt % Al; up to 25 wt % Mn; up to 25 wt % Cr, up to 0.15 wt % Ca; up to 0.10 wt % Ti; up to 0.10 wt % C; up to 0.02 wt % Cu; up to 0.05 wt % P; up to 0.02 wt % S; balance Fe and incidental impurities).

It should be understood that several V and/or Nb to Si ranges can be realized within the above defined alloy compositions.

The following disclosure relating to the amounts of further elements Al, Mn, Cr, Ca, Ti, C, Cu, P, S, balance Fe and incidental impurities applies to each of the above mentioned embodiments, unless otherwise stated.

The FeSi V and/or Nb alloy comprises up to 2 wt % Al, or up to 1 wt % Al, or up to 0.5 wt % Al, e.g., from 0.001 to 0.4 wt % Al, or from 0.01 to 0.35 wt% Al, or up to 0.2 wt % Al. In steels such as spring steels and rail steels, Al causes detrimental inclusions, such as for example AI2O3 inclusions. Therefore, the content of Al in the FeSi V and/or Nb alloy is preferably kept low. During the production of FeSi V and/or Nb Al in the liquid ferrosilicon will react with the oxygen of the added vanadium oxide and/or niobium oxide, resulting in a low level of Al. In alloys according to the invention, the Al content can in some embodiments be very low, for example up to only 0.04 wt %.

The FeSi V and/or Nb alloy comprises up to 25 wt % Mn. Manganese is typically an impurity in the production of ferrosilicon based alloys, and the present FeSi V and/or Nb alloy may comprise up to 0.3 wt % Mn, typically in the range 0.02 - 0.3 wt % Mn. Mn may be present as an alloying element in the starting ferrosilicon alloy when it is required as an alloying element in steel. Thus, the present FeSi V and/or Nb alloy may contain manganese in the range 0.3 - 25 wt %. Other suitable Mn ranges are 0.5-20 wt %, or 1-15 wt %, 2-12 wt % or also 3-10 wt %.

The FeSi V and/or Nb alloy comprises up to 25 wt % Cr. Chromium may be present as an impurity in the production of ferrosilicon based alloys, and the present FeSi V and/or Nb alloy may comprise up to 0.3 wt % Cr, typically in the range 0.02 - 0.3 wt % Cr. Cr may be present as an alloying element in the starting ferrosilicon alloy when it is required as an alloying element in steel. Thus, the present FeSi V and/or Nb alloy may contain chromium in the range 0.3 to 25 %. Other possible Cr ranges are 0.5-20 wt %, or 1-15 wt %, 2-12 wt % or also 3-10 wt %.

The FeSi V and/or Nb alloy comprises up to 0.15 wt % Ca, e.g., from 0.01 to 0.15 wt %. Calcium is also a common element in as-produced ferrosilicon. During the production of FeSi V and/or Nb some of the Ca in the liquid ferrosilicon will react with the oxygen of the added vanadium oxide and/or niobium oxide, resulting in a level of Ca up to about 0.15 wt %.

The FeSi V and/or Nb alloy comprises up to 0.10 wt % Ti, e.g., from 0.003 to 0.10 wt %.

Titanium is normally present in low amounts in the starting ferrosilicon alloy. Titanium may also come from the vanadium oxide raw material and/or niobium oxide raw material added during the production of the FeSi V and/or Nb alloy. Titanium is harmful in some steel grades as it can form hard carbides and nitrides that lead to brittleness and reduced fatigue stress. Therefore, the content of Ti in FeSi V and/or Nb alloy is preferably as low as possible, such as below 0.025 wt %.

The FeSi V and/or Nb alloy may comprise minor amounts of C, Cu, P and S. The said elements can be normally present in small amounts in as-produced ferrosilicon or be added via the vanadium oxide raw material and/or niobium oxide raw material and/or slag modifying compound added during the production of the FeSi V and/or Nb alloy. The said elements in the indicated amounts will typically not be harmful for steel production. The FeSi V and/or Nb alloy may comprise up to 0.10 wt % C, e.g., from 0.003 to 0.10 wt % C. The FeSi V and/or Nb alloy may comprise up to 0.02 wt % Cu, e.g., 0.001 to 0.02 wt % Cu, or 0.001 to 0.01 wt %. The FeSi V and/or Nb alloy may comprise up to 0.05 wt % P, e.g., 0.001 to 0.05 wt % P. The FeSi V and/or Nb alloy may comprise up to 0.02 wt % S, e.g., 0.001 to 0.02 wt % S.

The FeSi V and/or Nb alloy, according to any of the above said embodiments, is advantageously in the form of lumps. In the present context, the term "lumps" denotes particles or pieces of the FeSi V and/or Nb alloy, e.g. of crushed FeSi V and/or Nb alloy particles. The FeSi V and/or Nb alloy lumps may be produced in different size grades. Common sizings used within steelmaking are from about 3 mm to about 80 mm. The term sizing refers to the size of the holes in a sieve that a lump fits through. It should be understood that smaller and larger sizes of the FeSi V and/or Nb lumps are possible depending on applications. Thus, the sizing may be from about 3 mm, such as from 5 mm, such as from about 10 mm, such as from about 20 mm up to about 80 mm, or up to about 50, or up to about 30 mm, or up to about 20 mm, or up to about 10 mm. Since FeSi V and/or Nb lumps are less tough than FeV and/or FeNb they may be crushed in regular FeSi crushers giving the option to produce different sizings conveniently. The FeSi V and/or Nb alloy, according to any of the above said embodiments, may also be in the form of cored wire or briquettes.

The FeSi V and/or Nb alloy, according to any of the above said embodiments, has a melting temperature range from about 1250 to about 1650 ^° C. The relatively low melting temperature and the assimilation route of the present FeSi V and/or Nb alloy in a steel melt has the effect that the FeSi V and/or Nb added to a steel melt dissolves relatively rapid. Tests performed by the inventors have for example shown that lumps of the FeSi V alloy according to the invention having a sizing of about 25 mm melt in about 20 seconds compared to FeV lumps dissolving only after about 60 seconds.

The method for preparing the FeSi V and/or Nb alloy according to any of the above embodiments comprises: providing a ferrosilicon alloy in liquid state in a vessel; adding a vanadium oxide containing raw material and/or a niobium oxide containing raw material to the liquid ferrosilicon alloy; mixing and reacting the liquid ferrosilicon alloy and vanadium oxide from the vanadium oxide containing raw material and/or niobium oxide from the niobium oxide containing raw material, thereby forming a melt of FeSi V and/or Nb alloy and slag; separating the slag from the said melt of FeSi V and/or Nb alloy; and solidifying or casting the liquid FeSi V and/or Nb alloy.

The reaction between the liquid ferrosilicon alloy and the vanadium oxide and/or the niobium oxide is fast allowing high productivity rate. The FeSi V and/or Nb alloy can be produced in e.g. a ladle, or a similar vessel such as a crucible or a melting pot including any kind of furnaces. As liquid FeSi in a ladle occurs in any ferrosilicon production processes there is no need of heating by supplying external energy such as using a furnace, thus allowing for economic and ecological savings over the prior art of obtaining vanadium- and/or niobium ferroalloy. The energy released from the exothermic reaction will give additional economic benefit to the FeSi production. Aluminium and calcium, which are normally present in ferrosilicon alloys (as-produced), are consumed during the reaction with vanadium oxide and/or niobium oxide, leading to a FeSi V and/or Nb alloy with very low aluminium and calcium content. Furthermore, the present method for producing the FeSi V and/or Nb alloy also leads to a high V and/or Nb-yield from the vanadium oxide and/or the niobium oxide (e.g. vanadium pentoxide and/or niobium pentoxide) added into the FeSi alloy, compared with conventional methods for producing ferrovanadium alloys, FeV and/or ferroniobium alloys, FeNb. Therefore, compared to conventional FeV and FeNb production, the present method is elegant, cost efficient, and more environmentally friendly.

The following detailed description of the method of producing FeSi V and/or Nb alloy applies to any of the above-described embodiments of the FeSi V and/or Nb alloy according to the present invention.

The liquid ferrosilicon alloy can be provided directly from a reduction furnace, typically a submerged arc furnace (SAF) wherein the ferrosilicon alloy is produced according to a conventional method. Alternatively, the liquid ferrosilicon alloy can be provided by remelting a charge of ferrosilicon, possibly refined, or a combination of as-produced ferrosilicon alloy and a solidified ferrosilicon that is brought into liquid state by any suitable heating means.

The method for preparing the FeSi V and/or Nb alloy can be performed in a ladle, or in any suitable vessel such as a crucible or a melting pot including any kind of furnaces, to hold the liquid ferrosilicon. The temperature of the ferrosilicon melt before addition of the vanadium oxide containing raw material and/or the niobium oxide containing raw material ranges ideally from about 1400 to about 1700 ^° C.

According to the method, the vanadium oxide containing raw material, e.g. V O , and/or niobium oxide containing raw material, e.g. Nb ₂ 0 ₅ , is added to the liquid ferrosilicon alloy. The vanadium oxide containing raw material and/or the niobium oxide containing raw material may be added in an amount (by weight) providing essentially the target amount of elemental vanadium and/or niobium (by weight) in the FeSi V and/or Nb alloy. The method for adding the vanadium oxide containing raw material and/or the niobium oxide containing raw material may be performed in any convenient manner that ensures contact between vanadium oxide and/or niobium oxide and liquid ferrosilicon.

The vanadium oxide containing raw material can be one or more vanadium oxide phases, such as vanadium (II) oxide, vanadium (III) oxide, vanadium (IV) oxide, vanadium (V) oxide, and/or other non-principal oxides of vanadium. The vanadium oxide is preferably vanadium (V) oxide (V O ) and/or vanadium (III) oxide (V2O3). The vanadium oxide containing raw material may also comprise industrial waste materials or ores comprising elemental vanadium or vanadium oxide.

The niobium oxide containing raw material can be one or more niobium oxide phases, such as niobium (II) oxide, niobium (III) oxide, niobium (IV) oxide, niobium (V) oxide, and/or other non-principal oxides of niobium. The niobium oxide is preferably niobium (V) oxide (Nb20 ₅ ) and/or niobium (III) oxide (Nb203). The niobium oxide containing raw material may also comprise industrial waste materials or ores comprising elemental niobium or niobium oxide.

The reduction reaction of the vanadium oxide and/or the niobium oxide leads to the formation of oxide compounds, generally denoted slags. A slag modifying compound can be added to the ferrosilicon melt to modify the slag formed during the reaction. The slag modifying compound can be CaO and/or MgO, and can be added in an amount of about 0.5 - 30 wt % of the final alloy, based on the total amount of the initial ferrosilicon alloy. The necessary amount is based on the amount of vanadium oxide and/or niobium oxide to be added. The slag modifying compound can be added before or during the addition of the vanadium oxide containing raw material and/or the niobium oxide containing raw material. The slag composition is modified in a way to have a low viscosity and low melting slag to allow good slag/metal contact during the reduction reaction. Additionally, it can be modified for good metal/slag separation before casting. The slag, both produced during the reaction and added, will float on the melt, such that any formed waste and slag compounds formed during the reaction will accumulate in the layer of slag floating on the top of the melt.

The starting ferrosilicon alloy for the production of the FeSi V and/or Nb alloy should have a general composition of 45 - 90 wt % Si; up to 0.5 wt % C; up to 2 wt % Al; up to 1.5 wt % Ca; up to 0.1 wt % Ti; up to 26 wt % Mn; up to 26 wt % Cr; up to 0.02 wt % P; up to 0.005 wt % S; the balance being Fe and incidental impurities.

Examples of compositions of the starting ferrosilicon alloy are: 45 - 90 wt % Si; up to 0.5 wt % C; up to 2 wt % Al; up to 1.5 wt % Ca; up to 0.1 wt % Ti; up to 0.5 wt % Mn; up to 0.5 wt % Cr; up to 0.02 wt % P; up to 0.005 wt % S; the balance being Fe and incidental impurities;

45 - 90 wt % Si; up to 0.5 wt % C; up to 2 wt % Al; up to 1.5 wt% Ca; up to 0.1 wt % Ti; 0.5 - 26 wt % Mn; up to 0.5 wt % Cr; up to 0.02 wt % P; up to 0.005 wt % S; the balance being Fe and incidental impurities;

45 - 90 wt % Si; up to 0.5 wt % C; up to 2 wt % Al; up to 1.5 wt% Ca; up to 0.1 wt % Ti; up to 0.5 wt % Mn; 0.5 - 26 wt% Cr; up to 0.02 wt % P; up to 0.005 wt % S; the balance being Fe and incidental impurities; IB

45 - 90 wt % Si; up to 0.5 wt % C; up to 2 wt % Al; up to 1.5 wt% Ca; up to 0.1 wt % Ti; 0.5 - 26 wt % Mn; 0.5-26 wt% Cr; up to 0.02 wt % P; up to 0.005 wt % S; the balance being Fe and incidental impurities.

According to some embodiments of the method, the amount of Si in the starting ferrosilicon alloy is 70 - 80 wt %.

As-produced ferrosilicon alloys comprise small amounts of Al from the raw materials, typically in an amount of up to 1.5 wt %. The starting ferrosilicon alloy of the present invention may comprise up to 2 wt % Al; e.g., 0.01 - 2 wt % Al. When the vanadium oxide containing raw material and/or the niobium oxide containing raw material is added to the liquid ferrosilicon alloy, the metallic Al present in the liquid ferrosilicon reacts with the oxygen of the vanadium oxide and/or the niobium oxide reducing the vanadium and/or the niobium, resulting in pure V and/or Nb and heat while the oxidized Al will accumulate in the slag. Si in the liquid ferrosilicon alloy will also react with the oxygen of the vanadium oxide and/or the niobium oxide, resulting in reduction of vanadium oxide and/or niobium oxide to elemental V and/or Nb, while the oxidized Si will also accumulate in the slag phase. Si is less reactive than Al in the present mixture; therefore, essentially most of the Al present in the ferrosilicon alloy will react with the oxygen of the vanadium oxide and/or the niobium oxide, resulting in a very low amount of aluminium in the produced FeSi V and/or Nb alloy. Calcium is also a common element in ferrosilicon alloys, generally in an amount of up to about 1.5 wt %. Ca present in the liquid ferrosilicon alloy will also react with the oxygen of the vanadium oxide and/or the niobium oxide resulting in pure V and/or Nb and heat resulting in a low amount of Ca in the produced FeSi V and/or Nb alloy.

Additional aluminium can be added to the liquid ferrosilicon alloy, to increase the amount of Al contained in the melt available for reducing the vanadium oxide and/or the niobium oxide. This may especially be relevant when producing FeSi V and/or Nb alloy with a high amount of vanadium and/or niobium, such as from FeSi V and/or Nb with a V and/or Nb amount of 20 wt % (FeSi V and/or Nb 20), up to FeSi V and/or Nb 25 or up to FeSi V and/or Nb 30, even up to FeSi V and/or Nb 35, while keeping the amount of silicon in the FeSi V and/or Nb alloy in the upper range. If additional aluminium is added to the ferrosilicon melt, the addition can be made before, during or after, preferably during or after, the addition of the vanadium oxide containing raw material and/or the niobium oxide containing raw material. Aluminium may be added in an amount of up to about 10 wt %, or up to about 5 wt %, or up to about 1 wt %, based on the total amount of ferrosilicon and vanadium oxide and/or niobium oxide.

The liquid ferrosilicon alloy is preferably stirred during the addition of the vanadium oxide containing raw material and/or the niobium oxide containing raw material, and any added aluminium and/or slag modifying compound, and during the reduction reaction in order to ensure contact of the V and/or Nb oxides and metal. The melt is conveniently stirred by mechanical stirring and/or gas stirring means generally known in the field.

The slag can be separated before or during casting of the liquid FeSi V and/or Nb alloy. Separating the slag from the FeSi V and/or Nb melt after the reactions are completed, results in a purified FeSi V and/or Nb alloy, very low in aluminium and calcium. The FeSi V and/or Nb alloy may be casted, or solidified according to generally known methods in the field. The solidified or casted metal may be crushed and graded in size fractions adapted for different applications areas.

The FeSi V and/or Nb alloy according to the present invention may be used as an additive in the production of steels, especially as an additive for the production of vanadium containing and/or niobium containing steels. The vanadium and/or niobium containing steels may be chosen among, but not limited to, spring steels, tool steels, forging steels, rail steels, rebar steels, heavy plate steels, microalloyed automotive steels and aircraft steels.

It was surprisingly found that FeSiV and FeSiNb have a higher vanadium-yield and niobium- yield than the respective ferroalloys (FeV and FeNb). This is especially advantageous as both vanadium and niobium are scarce alloys and relatively high priced. Further, it was surprisingly found that FeSiV and FeSiNb alloys have a fast dissolution compared to the prior art alloys (FeV and FeNb). This allows the alloy elements to integrate into the steel quickly and prevents further oxidation or entrapment of V and/or Nb into the slag.

A method for production of steels, such as spring steels, tool steels, forging steels, rail steels, rebar steels, heavy plate steels, microalloyed automotive steels and aircraft steels, comprises adding a FeSi V and/or Nb alloy comprising 35 - 75 wt % Silicon (Si); 3 - 35 wt % Vanadium (V) and/or Niobium (Nb); up to 2 wt % Aluminium (Al); up to 25 wt % Manganese (Mn); up to 25 wt% Chromium (Cr); up to 0.15 wt % Calcium (Ca); up to 0.10 wt % Titanium (Ti); up to 0.10 wt % Carbon (C); up to 0.02 wt % Copper (Cu); up to 0.05 wt % Phosphorous (P); up to 0.02 wt % Sulfur (S); balance iron (Fe) and incidental impurities. The said method for production of steels comprises adding a FeSi V and/or Nb alloy according to any of the above-described embodiments.

Examples

Example 1. Production of FeSiV alloys.

Five trials for the production of FeSiV alloys according to the present invention were prepared. The following table 1 shows raw material amounts of FeSi75 and V O for five test productions of FeSiV. Additionally, lime (CaO) amounts to modify the slag and the total Al in the system are given. The temperature (T) was set to be above the melting point of FeSiV alloy before V2O5 addition. The liquid ferrosilicon alloy was stirred during addition of V2O5, lime and any aluminium. The produced compositions are given in the right part of the table. During tapping, it is important for the purity of the produced FeSiV alloy to separate slag and metal. Table 1. Amounts FeSi, vanadium oxide, lime and aluminium and temperatures. Analyses of produced FeSiV alloy compositions.

The analyses show that each of the resulting FeSiV alloys produced by the present method have a comparably low amount of aluminium. Therefore, the FeSiV alloys are very suitable as an additive in the manufacture of steels where levels of aluminium should be kept low.

Starting from FeSi alloys comprising Mn and Cr as alloying elements with Mn or Cr content of 5 wt %, 14 wt % or 25 wt %, will result in FeSi V and/or Nb alloys comprising Mn and/or Cr. This is calculated for the case of FeSiV alloys with compositions as indicated in table 2 below.

Table 2: Amounts FeSiMn/FeSiCr, vanadium oxide, lime and resulting alloy compositions from adding V ₂ O ₅ into FeSiMn or FeSiCr.

Further trials for the production of FeSiV alloys according to the present invention using FeSiMn or FeSiCr as a raw material were prepared. The following table 3 shows raw material amounts of FeSiMn or FeSiCr and V ₂ O ₅ for two test productions of FeSiV. Additionally, lime (CaO) amounts to modify the slag and the total Al in the system are given. The liquid alloy was stirred during addition of V ₂ O ₅ , lime and any aluminium. The produced compositions are given in the right part of table 3. Table 3: Amounts of FeSiMn/FeSiCr, lime, aluminum, V2O ₅ . Analyses of produced alloy compositions.

Example 2. Production of FeSiNb alloys. Three trials for the production of FeSiNb alloys according to the present invention were prepared. The following table 4 shows raw material amounts of FeSi75 and Nb ₂ 0 ₅ for three test productions of FeSiNb. Additionally, lime (CaO) amounts to modify the slag and the total Al in the system are given. The temperature (T) was set to be above the melting point of FeSiNb alloy before Nb ₂ 0 ₅ addition. The liquid ferrosilicon alloy was stirred during addition of Nb ₂ 0 ₅ , lime and any aluminium. The produced compositions are given in the right part of table 4. During tapping, it is important for the purity of the produced FeSiNb alloy to separate slag and metal.

Table 4. Amounts FeSi, niobium oxide, lime and aluminium and temperatures. Analyses of produced FeSiNb alloy compositions. Example 3. Comparison of dissolution behavior of FeSiV vs. FeV80

To prove the faster dissolution behavior of FeSi V according to the present invention compared to commercial alloys as an example the dissolution behavior of a FeSiVIO (FeSiV with about 10% V) and a FeSiV20 (FeSiV with about 20% V) alloy was compared to dissolution behavior of FeV80 in a bath of low alloyed steel with a temperature of 1600 °C. The dissolution time can be measured with different techniques known from literature. Examples would be connecting a load cell to the ferroalloy and measuring the loss in weight [Argyropoulus, 1983] or taking samples of the steel melt in fixed intervals and analyzing the element content [Gourtsoyannis et al., 1984]

Fig. 1 is a diagram showing dissolution time of the FeSiVIO alloy and FeSiV20 alloy according to the present invention, compared to the standard commercial FeV80 alloy in the low-alloyed steel melt at a temperature of about 1600 ^° C. The diagram shows dissolution time vs. different sizing of the FeSiVIO and FeSiV20 as well as FeV80 lumps. Fig. 1 shows that the measured dissolution time for FeV80 with size 25 mm was more than 3 times longer than dissolution time of FeSiVIO. The dissolution time of FeV80 alloy becomes significantly longer as the size of the lumps added to the steel melt increases, compared to the FeSiVIO and FeSiV20 alloy. A faster dissolution time shortens the steelmaking process time and thereby saves cost and increases flexibility compared to prior art solutions.

Example 4. Yield test FeSiVIO vs. FeV80

To prove the yield behavior and the effectiveness of the alloys according to the invention to produce steel a test of FeSiVIO against FeV80 was conducted. Six steel melts of the same composition (54SiCrV6 steel) were produced in a 100 kg induction furnace at 1600 °C. The steels were deoxidized using aluminum and alloyed with the necessary alloy elements except silicon and vanadium. Three melts were alloyed using case 1: addition of FeSi75 and FeV80 and three melts were alloyed using case 2: addition of FeSiVIO.

Samples of the steel melt were taken before and after the addition of the alloys and analyzed with the ICP (inductively coupled plasma) method. Additionally, solute oxygen, total oxygen, pre alloying sample and ladle samples were analyzed to detect any possible irregularities. A comparison of the vanadium and silicon added into the melt with the vanadium and silicon analyzed in the ICP analysis was used to calculate the yields. The results are shown in table 5 below. Table 5: Average yields obtained from a steelmaking test with six heats of 54SiCrV6 steel.

As can be seen from Table 5, it was found that the vanadium yield of FeSiVIO was on average 3.5 % higher as from FeV80. The average silicon yields are similar. This trial proves that the present invention is not only efficiently obtaining the respective alloy element from oxides but also improves a steelmaking process by higher yield of the respective alloy.

Example 5. Production of alloys comprising Vanadium and Niobium.

With the present invention, combined alloys of vanadium and niobium from oxides as described in table 6 can be produced. The alloys can be produced in a process of either one or two steps. The difference being that in a two-step process e.g. first FeSi V is produced from oxides with the respective ideal Al and lime addition. Then the slag is removed and the Nb is added as oxides to the liquid FeSiV with the respective ideal Al and lime additions. Subsequently the slag may be modified to help the deslagging before casting. In the same manner as described above, the alloys can be produced by starting with FeSi Nb and add V as oxides to liquid FeSiNb.

Table 6: Amounts FeSi, vanadium oxide, niobium oxide, lime, aluminum and resulting alloy compositions.

Example 6. Production of FeSiVNb alloys. A trial for the production of a FeSiVNb alloy according to the present invention was prepared.

The following table 7 shows raw material amounts of FeSi75, V2O5, and Nb ₂ 0 ₅ for a test production of FeSiVNb. Additionally, lime (CaO) amounts to modify the slag and the total Al in the system are given. The temperature (T) was set to be above the melting point of FeSiVNb alloy before any oxide addition. The liquid ferrosilicon alloy was stirred during addition of V2O5, Nb ₂ 0 ₅ , lime and any aluminium. The produced composition is given in the right part of table 7. During tapping, it is important for the purity of the produced FeSiVNb alloy to separate slag and metal. Table 7. Amounts FeSi, vanadium oxide, niobium oxide, lime and aluminium and temperature. Analyses of produced FeSiVNb alloy composition.

The person skilled in the art realizes that the present invention is not limited to the preferred embodiments described above. The person skilled in the art further realizes that modifications and variations are possible within the scope of the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the disclosure, and the appended claims.