IRON AND MOLYBDENUM CONTAINING COMPACTS

TECHNICAL FIELD

The present invention relates to a process for producing iron and molybdenum containing compacts. It also relates to and compacts produced by the process.

BACKGROUND

Ferromolybdenum is an iron molybdenum alloy normally having a molybdenum content of 60- 80 % by weight.

In most commercial applications ferromolybdenum is produced from molybdenum trioxide (Mo0 ₃ ) by a carbothermic reduction, an aluminothermic reduction, or a silicothermic reduction. The carbothermic process produces a high carbon ferromolybdenum, while the latter two produces a low carbon ferromolybdenum. Low carbon ferromolybdenum is more common than the high carbon alloy. Lumps of ferromolybdenum produced by these methods normally have densities around 9 g/cm ³ . Dissolving the lumps in the steel melt can be difficult due to the high melting point of the lumps, for instance the commercial grade FeMo70 has a melting point of 1950 °C, and since the temperature of the steel melt is considerably lower, dissolution of the ferromolybdenum is mainly affected by diffusion processes, which prolong the dissolution time of the ferromolybdenum. Another factor is the high cost of raw materials in the aluminothermic reduction and silicothermic reductions. Furthermore, around 2 % of the Mo can be lost in the slag in these processes.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a novel iron and molybdenum containing material suitable for molybdenum addition in melting industries e.g. steel, foundry and superalloy industry, and a process for producing such material in a comparably cost efficient manner.

A further object is to provide a novel iron and molybdenum containing material that has a comparably quick dissolving time in a steel melt, and a process for producing such material in a comparably cost efficient manner.

A further object is to provide a novel iron and molybdenum containing material low in carbon and high in Mo, and a process for producing such material in a comparably cost efficient manner. A further object is to provide a material that can be easily handled when added to the melt, and a process for producing such material in a comparably cost efficient manner. SUMMARY OF THE INVENTION

At least one of the above mentioned objects is at least to some extent achieved by a process for producing an iron and molybdenum containing compacts including the steps of:

a) mixing:

an iron containing powder,

a molybdenum oxide powder,

a carbonaceous powder,

a liquid, preferably water,

optionally a binder, and/or a lubricant and/or a slag former;

b) compacting to provide a plurality of green compacts.

Preferably, the green compacts have a geometric density in the range of 1.0-4.0 g/cm ³ . The non- reduced green compacts may be used as a substitute for traditionally manufactured

ferromolybdenum alloys or even as a substitute for molybdenum oxide, when alloying the melt in industrial production. The iron-and/or molybdenum containing green compacts can be produced at lower costs than standard grades of ferromolybdenum. Their porous structure facilitates quick dissolving time in a steel melt.

In the present application the term "green" is used for raw or non-reduced compacts. In the present applications, the term compacts includes briquettes, filter cakes, compacted sheets, and other shapes of compacted agglomerates.

Dry matter composition refers to the composition for a dried specimen, i.e. excluding any moisture present in the green compacts. The moisture content is defined as water present in the green compacts apart from water of crystallization. The moisture content can be determined by a LOD (loss on drying) analysis in accordance to ASTM D2216 - 10.

In some embodiments drying the green agglomerates to reduce the moisture content to less than 10 % by weight. The moisture content is defined as water present in the green pellets apart from water of crystallization. The moisture content can be determined by a LOD (loss on drying) analysis in accordance to ASTM D2216 - 10. By drying the green compacts to a moisture content less than 10% by weight, the risk of cracking due to quick vaporisation of the liquid, when heated at high temperatures, is minimised. Preferably the green agglomerates are dried to have a moisture content less than 5 % by weight, more preferably less than 3 % by weight.

Green compacts as defined by the pending claims may be produced by the suggested method.

Reduced compacts as defined by the pending claims may be produced by the suggested method.

The compacts can substitute for traditionally manufactured ferromolybdenum alloys, when alloying with molybdenum in melting practices. The iron- and/or molybdenum containing compacts can be produced at lower costs than standard grades of ferromolybdenum. The iron and molybdenum containing compacts dissolve quicker than standard grades of

ferromolybdenum. Depending on the reduction time, the relative amount of carbon in relation to the amount of reducible oxides, and the reduction temperature - the oxygen content in the compacts can be partially or fully reduced. The compacts can be easily transported on a conveying belt without the risk of rolling off.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Fig. 1 is a schematic overview of the process of producing iron and molybdenum containing briquettes according to the invention.

DESCRIPTION OF THE INVENTION

The invention will now be described in more detail and with reference to the figures. The invention is described in relation to the production of briquettes. However, other kinds of compacts can be produced by the process by substituting the briquetting machine to a machine that can compact powders in other forms such as filter cakes or sheets.

Fig. 1 is a schematic overview of the process of producing iron and molybdenum containing briquettes according to the invention. In the mixing station 30, a powder mixture is prepared by mixing an iron containing powder, a carbonaceous powder, a molybdenum oxide powder, and water. The mixing in the mixing station 30 can be executed batchwise or continuously.

Before being added to the mixing station 30, the molybdenum oxide powder may be milled in the rod mill 10. Of course other mills, grinders, or crushers may be used to disintegrate the molybdenum oxide into smaller particles. Furthermore, the iron containing powder and/or the carbonaceous powder may also be disintegrated into smaller particles by grinding and/or milling and/or crushing.

The ground and/or milled and/or crushed molybdenum oxide particles may be sieved in a sieve 20 to provide a desired particle distribution. Naturally, sieving can also be applied to the iron containing powder and/or the carbonaceous powder.

In one embodiment the molybdenum oxide powder and the carbonaceous powder are mixed and ground together and thereafter the iron containing powder is added and mixed with the molybdenum oxide powder and the carbonaceous powder. However, any combination of mixing order may be executed. The molybdenum oxide powder, iron containing powder, and the carbonaceous powder are each described under separate headline below. The amount of added powders are described under the headline Iron and molybdenum containing green compacts.

Optionally, lubricants and/or binders and/or slag formers can be added when mixing. The optional binders may be organic or inorganic binders. The binders may e.g. be a carbon containing binders partially replacing the carbonaceous powder. Other binders may e.g. be bentonite and/or dextrin and/or sodium silicate and/or lime. Gelatin may also be used. The optional slag former may be limestone, dolomite, and/or olivine. The total amount of optional lubricants and/or binders and/or optional slag formers can be 0.1-10 % by weight of the dry matter content of the mixture, more preferably less than 5 wt%. It may be in the range of 1-10 % by weight. The binders are optional since the green briquettes by the water and iron addition becomes sufficiently strong to be reduced in the reduction furnace without severely cracking. If added the lubricant is preferably added in amounts of 0.1-2 % of the the dry matter content of the mixture, e.g. about 0.5-1 % by weight. The lubricant can e.g. be zinc stearate. However, other lubricants that are used in powder metallurgy may be added. Preferably neither binder, nor lubricant nor slag former are used. The iron containing powder when mixed in wet condition strengthens the briquettes, making the use of a binder unnecessary. Thereby the amount of impurities can be reduced.

Liquid, preferably water, is preferably added in amounts of 1-10 % by weight of the dry matter content of the mixture, preferably 2-7 % by weight. In some embodiments 2-5 % by weight. From the mixing station 30 the prepared powder mixture is transferred to a briquetting machine 40. In briquetting machine 40 the powder mixture is briquetted to provide a plurality of green briquettes. Preferably the briquetting machine 40 is a roller press. However, other kinds of briquetting machines 40 can be used including but not limited to: mechanical piston presses, hydraulic presses, screw presses, briquette extruders. Furthermore the briquetting machine 4 may be substituted for other machines capable of compacting the mixture. For instance but not limited to; filter cakes may be produced in a filter press, flakes or sheets may be produced between two counter rotating rollers.

In one embodiment the powder mixture is compacted at a comparably low pressure. The lower limit of the compacting pressure may be as low as 20 kg/cm ² , but is typically at least 50 kg/cm ² . Preferably the compacting pressure is in the range of 80-1000 kg/cm ² , more preferably 100-500 kg/cm ² . The low compacting pressure has been found out to improve the quality of the produced green compacts.

In one embodiment a briquetting machines operates at higher pressures, e.g. 1000-10000 kg/cm ² . Higher pressure can be used to increase the geometric density of green briquettes.

The green briquettes produced from the powder mixture are preferably reduced in a reduction furnace 60. Alternatively the non-reduced green briquettes can be used as alloying additive in iron and steel making. Optionally the green briquettes are dried in a dryer 50 before being transferred to the reduction furnace 60. Many different kinds of industrial dryers can be used. The briquettes may also be dried without active heating, e.g. in ambient air temperature. In a dryer vapour may be removed by a gas steam or by vacuum. The green briquettes can be dried until desired moisture content has been reached. The green briquettes may be dried to moisture content less than 10 % by weight, more preferably less than 5 % by weight, most preferably less than 3 % by weight. The green briquettes may be dried at a temperature in the range of 50-250 °C, more preferably 80- 200 °C, most preferably 100-150 °C. For improved process economy, drying time is preferably in the range of 10- 120 minutes, more preferably 20-60 minutes. But longer drying times are of course viable. The moisture content is defined as water present in the green briquettes apart from water of crystallization. The moisture content can be determined by a LOD (loss on drying) analysis in accordance to ASTM D2216 - 10.

The green briquettes are preferably reduced in a reduction furnace 60. The reduction furnace is preferably a continuous furnace but may also be a batch furnace. The continuous furnace 6 having an inlet 7 and outlet 8, and the briquettes are conveyed during reduction from the inlet 7 to the outlet 8. In a preferred embodiment a belt furnace is used. Of course other furnace types may be used, for instance a walking beam furnace.

The green briquettes are reduced at a temperature in the range of 800-1500 °C, preferably 800- 1350 °C. In some embodiments 1000-1200 °C. The reduction time at least 10 minutes, preferably reducing during at least 20 minutes. In some embodiments during at least 30 minutes. By monitoring the formation of CO/C0 ₂ it can be determined when the reduction process is finished. Preferably the reduction time is at most 10 hours, preferably at most 2 hours, more preferably at most 1 hour. Depending on the reduction time, the reduction temperature, and the relation between carbon and reducible oxides in the briquettes; the reducible oxides of the briquettes can be partially or fully reduced.

Optionally the green briquettes are heat treated at a lower temperature before reduction. The green briquettes may be heat treated at a temperature in the range of 200-800 °C, more preferably 400-700 °C. Preferably, the optional heat treating at lower temperature is performed from 10 minutes to less than 2 hours, preferably less than 1 hour. By heat-treating at lower temperatures the optional lubricant can be burned off in a controlled manner. In addition molybdenum trioxide may be reduced to molybdenum dioxide. This may be employed as a prereduction step prior to the reduction described in the previous paragraph or when producing partially reduced briquettes. The optional heat treating at 200-800 °C, can be performed in the same furnace as the reduction. The optional heat treating and optional drying may also be combined.

Unexpectedly it has been found that briquettes can be reduced at high temperatures without noticeable sublimation losses of Mo0 ₃ . Accordingly the claimed process results in a simplified process resulting in improved yield and higher Mo content in the end product. I.e. there is no need to perform a pre-reduction in regards to sublimation losses of Mo0 ₃ .

During the reduction CO and C0 ₂ can form from reactions with the carbon source and the reducible oxides in the briquettes. Additionally remaining moisture may vaporise. The reduction time can be optimised by measuring the formation of CO and C0 ₂ ; in particular CO since C0 ₂ is mainly formed during the first minutes of reduction where after CO formation is dominating until the carbon source is consumed or all reducible oxides have been reduced.

The reduction reactions are endothermic and require heat. Preferably heat is generated by heating means not affecting the atmosphere within the furnace, more preferably the heat is generated by electrical heating.

The atmosphere within the furnace 60 is preferably controlled by supplying an inert or a reducing gas, preferably a weakly reducing gas, at one end of the furnace and evacuating gases (e.g. reaction gases (e.g. CO, C0 _2j and H ₂ 0) and the supplied gas) at the opposite end, more preferably, supplying the inert or reducing gas counter current at an outlet side 80 of the furnace 60, and evacuating gases at an inlet side 70 of the furnace 60. I.e. the inert or reducing gas is preferably supplied counter flow. The gas supplied may include argon, N _2j H _2> CO, C02 or any mixture of them. For instance H2/N2 having relations such as 5:95, 20:80, 40:60, 80:20, and 95:5 by vol. . In one embodiment the atmosphere comprises 20-60 vol % of H ₂ and balance N ₂ . Such atmosphere may reduce N ₂ uptake, compared to e.g. H ₂ /N ₂ (5:95), and it may increase the density of the reduced pellets. The atmosphere may also be supplied with CO, e.g. from burning natural gas. Of course, other gas mixes being inert or reducing may be supplied to the furnace.

Preferably the furnace operates at pressure in the range of 0.1-5 atm, preferably 0.8-2 atm, more preferably at a pressure in the range of 1.0-1.5 atm, most preferably 1.05-1.2 atm.

At the outlet 80 of the reduction furnace the briquettes are transferred to a cooling section 90, for cooling the briquettes in a non-oxidising atmosphere (e.g. reducing or inert) to a temperature below 200 °C to avoid re-oxidation of the briquettes, more preferably below 150 °C in an inert atmosphere. The atmosphere may e.g. be argon, N _2j H ₂ , or any mixture of H ₂ /N ₂ (e.g. 5:95 by vol.). Other atmospheres may also be employed. If it is desirable to have very low levels of nitrogen in the briquettes, the briquettes may be cooled in a nitrogen free atmosphere such as for example an argon gas atmosphere.

Fig. 2 shows a method how to produce briquettes. In a mixing station 300 a powder mixture is prepared by mixing an iron containing powder, a carbonaceous powder, a molybdenum oxide powder, and water in a blender 300. A convening belt 110 conveys a tray 120 to the mixing station 300. In the mixing station 300 the tray 120 is filled with mixture from the blender 310. The tray 120 is thereafter conveyed to a briquetting station 40 and at the same time another tray 120 is conveyed to the mixing station 300 to be filled with mixture from the blender 310. In the briquetting station 400 the mixture on the tray is stamped by a meshed stamp 410 forming a set of green briquettes. The pattern seen is indicated by reference number 420. The tray 120 holding the green briquettes thereafter continues to a reduction furnace 600, here schematically shown as a belt furnace. Of course other furnace types may be used, for instance walking beam furnaces. Optionally a drying station may be positioned between the briquetting station and the reduction furnace 600.

Molybdenum oxide powder

The molybdenum oxide powder is preferably a molybdenum trioxide powder. The powder may also be a molybdenum dioxide powder or a mix of molybdenum trioxide powder and molybdenum dioxide powders.

The molybdenum powder should include 50-80 % of Mo, the remaining elements being oxygen and impurities. The purer the grade of molybdenum oxide is, the purer the iron and molybdenum containing compacts can be made. However, purer grades of Mo0 ₃ are on the other hand more expensive.

In a preferred embodiment technical grade Mo0 ₃ is used. Such powders are less costly than purer grades of Mo0 ₃ and may contain oxides that are difficult to reduce in solid state reduction with carbon. Examples of such oxides are e.g. A1 ₂ 0 ₃ , Si0 ₂ , and MgO. Fortunately these oxides can easily be removed to the slag phase when alloying in steel melts and they can therefore be allowed in the product. Preferably at least 90% by weight of the particles of the molybdenum oxide powder pass through a test sieve having nominal aperture sizes of 300 μπι and at least 50 % by weight of the particles of the molybdenum oxide powder pass through a test sieve having nominal aperture sizes of 125 μπι. More preferably at least 90% by weight of the particles of the molybdenum oxide powder pass through a test sieve having nominal aperture sizes of 125 μπι and at least 50 % by weight of the particles of the molybdenum oxide powder pass through a test sieve having nominal aperture sizes of 45 μπι. Nominal aperture sizes in the present application are in accordance with ISO 565: 1990 and which hereby is incorporated by reference. In one embodiment at least 90 % by weight, more preferably at least 99 % by weight, of the particles of the molybdenum oxide powder pass through a test having nominal aperture sizes of 250 μιη, more preferably 125 μιη, most preferably 45 μιη.

Iron containing powder

The iron containing powder is preferably an iron powder containing at least 80 wt% Fe, preferably at least 90 wt% Fe, more preferably at least 95 wt% Fe, most preferably at least 99 wt% Fe. The iron powder can be an iron sponge powder and/or a water atomised iron powder and/or a gas atomised iron powder and/or an iron filter dust and/or an iron sludge powder. For instance filter dust X-RFS40 from Hoganas AB, Sweden is a suitable powder.

The iron powder may partly or fully be replaced by an iron oxide powder, for instance but not limited to: powder consisting of one or more from the group of FeO, Fe ₂ 0 ₃ , Fe ₃ 0 ₄ , FeO(OH), (Fe ₂ O ₃ *H ₂ 0). The iron oxide powder may e.g. be mill scale. In one embodiment the iron containing powder contains at least 50 % be weight of metallic iron, more preferably at least 80 wt% metallic Fe, most preferably at least 90 wt% metallic Fe.

Preferably at least 90% by weight of the particles of the iron containing powder pass through a test sieve having nominal aperture sizes of 125 μιη and at least 50 % by weight of the particles of the iron containing powder pass through a test sieve having nominal aperture sizes of 45 μιη.

In one embodiment at least 90 % by weight, more preferably at least 99 % by weight, of the particles of the iron containing powder pass through a test sieve having nominal aperture sizes of 125 μιη, more preferably 45 μιη. In one example at least 90 % by weight, more preferably at least 99 % by weight, of the particles of the iron containing powder pass through a test sieve having nominal aperture sizes of 20 μιη.

Carbonaceous powder

The carbonaceous powder is preferably chosen from the group of: sub-bituminous coals, bituminous coals, lignite, anthracite, graphite, coke, petroleum coke, and bio-carbons such as charcoal, or carbon containing powders processed from these resources. The carbonaceous powder may e.g. be soot, carbon black, activated carbon. The carbonaceous powder can also be a mixture of different carbonaceous powders. Regarding the choice of carbonaceous powder, the reactivity of the carbon may be taken into consideration, since the productivity as well as the yield of Mo depends on this factor. A high reactivity is desired. In particular, it is desirable to have a carbonaceous powder that is reactive at lower temperatures (preferably < 700 °C ). For instance German brown coal (lignite) is normally reactive at lower temperatures than petroleum coke, and is hence suitable since it has comparably high reactivity at low temperatures. Also charcoal, bituminous and sub-bituminous coals can exhibit comparably high reactivity. Particularly suitable examples are soot, carbon black, and activated carbon. Graphite may also be suitably due to its high density.

The amount of carbonaceous powder is preferably determined by analysing the amount of oxides in the molybdenum oxide powder and optionally the iron containing powder. Preferably the amount of reducible oxides is determined. The oxygen content can e.g. be analysed by a LECO® TC400. Furthermore the maximum allowed carbon content in the compacts is preferably also taken into consideration. Preferably the amount is chosen to stoichiometric match or slightly exceed the amount of reducible metal oxides in the molybdenum oxide powder and the iron containing powder. However, the amount of carbon may also be sub- stoichiometric. The amount of carbonaceous powder can be optimised by measuring the carbon and the oxygen levels in the reduced compacts (e.g. by reducing green compacts in a lab furnace and measuring carbon and oxygen levels). Based on the measurements the amount of carbonaceous powder can be optimised to achieve desired levels of carbon and oxygen in the produced compacts. Some oxides, which may be present in the molybdenum oxide powder are difficult to reduce with carbon. All oxides with higher affinity to oxygen at the reduction max temperature will remain as oxides in the finished product and therefore do not consume carbon in the reduction process. Such oxides can for instance be oxides of Si, Ca, Al, and Mg and may e.g. be present if cruder grades of molybdenum trioxide are used, e.g. technical molybdenum trioxide. However, in many applications of steel metallurgy these oxides can be handled e.g. by removing them in the slag of steel melt and they can therefore be allowed in the compacts. If lower amounts of these oxides and elements are desired, purer grades of molybdenum trioxide can be employed, e.g. grades that contain less or no amounts of these oxides.

By controlling the amount of carbonaceous powder and matching it with the amount of reducible oxides in the green compacts; the iron and molybdenum containing compacts can be made that has carbon content (after reduction) less than 10 % by weight, preferably less than 5 wt%, more preferably less than 1 wt%, most preferably less than 0.5 wt%.

However it is also possible to provide compacts having deliberately high carbon content after reduction. Eg. 1-5 wt% C. Such compacts may be used when alloying high carbon steel.

Preferably, at least 90 % by weight, more preferably at least 99 % by weight, of the particles of the carbonaceous powder pass through a test sieve having nominal aperture sizes of 125 μιη, and at least 50 % by weight of the particles of the carbonaceous powder pass through a test sieve having nominal aperture sizes of 45 μιη.

In one embodiment at least 90 % by weight, more preferably at least 99 % by weight, of the particles of the carbonaceous powder pass through a test sieve having nominal aperture sizes of 45 μιη, and at least 50 % by weight of the particles of the carbonaceous powder pass through a test sieve having nominal aperture sizes of 20 μιη. In one example at least 90 % by weight, more preferably at least 99 % by weight of the particles of the carbonaceous powder pass through a test sieve having nominal aperture sizes of 20 μιη.

Iron and molybdenum containing green compacts

The compacts may be briquettes, filter cakes, flakes or other compacted agglomerates.

The iron and molybdenum containing green compacts may have a dry matter composition in weight-% of:

1-25 iron containing powder;

5-30 carbonaceous powder;

Optionally

0.1-10 lubricant and/or binder and/or slag former; and

balance 50-90 molybdenum oxide powder.

According to one embodiment the iron and molybdenum containing green compacts having a dry matter composition in weight-% of:

1-15, preferably 1-10 iron containing powder,

5-25, preferably 10-20 carbonaceous powder,

Optionally 0.1-10 lubricant and/or binder and/or slag former; and

balance at least 50-90 molybdenum oxide powder.

In one embodiment the dry matter composition of the green compacts consists of in weight-%: 1-15, preferably 1-10 iron containing powder,

5-25, preferably 10-20 carbonaceous powder,

balance 50-90 molybdenum oxide powder.

In regards to elements the iron and molybdenum containing green compacts preferably have a dry matter composition in weight % of: 1-25 Fe, 15-40 O, 5-25 C, less than 15 of other elements besides O, C, Mo and Fe, and balance being at least 30 Mo. Preferably the dry matter composition in weight % is: 1-15 Fe, 15-40 O, 5-25 C, less than 15 of other elements besides O, C, Mo and Fe, and balance being at least 30 Mo.

The elements may further be limited to:

- Iron is preferably within the range of 1.5-10 % by weight.

- Carbon is preferably 7-20 % by weight.

- Oxygen is preferably 15-30 % by weight.

- Molybdenum is preferably 40-65 % by weight.

- Other elements are preferably at least 1 % by weight and less than 10 % by weight, more preferably at least 2 % by weight and less than 7 % by weight. Other elements are preferably only present as impurities.

In subsequent reduction steps, the relative amount of iron and molybdenum will increase in the compacts as the reduction progresses. The same may of course true for the other elements that remain.

The green compacts can be cost efficient substitutes to Mo0 ₃ powder or standard FeMo when alloying in melting practices, considering price and/or yield of the Mo addition into melt.

Typically, such addition could be made e.g. into electrical arc furnace (EAF) and e.g. be a Mo addition into stainless steel, tool steel or high speed steel.

The green compacts may have a geometric density up to 5 g/cm ³ or even up to 6 g/cm ³ .

Preferably the geometric density is in the range of 1.0-4.0 g/cm ³ . In other embodiments the geometric density may be in the range of 1.2-3.5 g/cm ³ , or 1.2- 3.0 g/cm ³ . The geometric density may be less than 4 g/cm ³ . Density can be increased by increasing compacting pressure. A lower geometric density results in higher porosity, which is believed to yield a shorter dissolution time of the compacts. The geometric (envelope) density can be measured in accordance to ASTM 962-08.

Reduced iron and molybdenum containing compacts

The compacts may be briquettes, filter cakes, flakes or other compacted agglomerates.

The iron and molybdenum containing compacts may have a composition in weight % of: 2-30 Fe, less than 30 O, less than 20 C, less than 15 of other elements besides O, C, Mo and Fe, and balance being at least 40 Mo, preferably a least 50 Mo.

Suitably, the reduced iron and molybdenum containing compacts have a composition in weight % of: 1-20 Fe, less than 10 O, less than IO C, less than 15 of other elements besides O, C, Mo and Fe, and balance being at least 40 Mo, preferably a least 50 Mo.

Preferably the content of O is less than 10 % by weight, more preferably less than 8 % by weight, even more preferred less than 6 % by weight, most preferably less than 4 % by weight, and preferably that only a minority of the oxygen content comes from molybdenum oxide that has not been reduced, i.e. a compact that contains MoO _x , where x < 0.5. Preferably essentially all of the molybdenum oxide is reduced to Mo, i.e. where x is around 0. Here, remaining oxygen content mainly comes from oxides in molybdenum oxide powder and the iron containing powder that are difficult to reduce, e.g. oxides of Si, Ca, Al, and Mg. Using purer grades of the molybdenum oxide powder, the iron containing powder, and the carbonaceous powder, the oxygen content of the compacts can, if desired, be made lower than 2% by weight. However, since many of these oxides that are difficult to reduce can be handled in the steel melt metallurgy (e.g. removing them in the slag phase), they may be allowed in the iron and molybdenum containing compact. The lower limit for oxygen may be about 0% by weight, but typically the oxygen is at least 1 % by weight, more typically at least 2 % by weight.

The molybdenum content in the compacts can be controlled by varying the relative proportions of the molybdenum oxide powder in relation to the iron containing powder. For essentially fully reduced compacts (i.e. compacts containing MoOx where x < 0.5) the content of molybdenum is preferably controlled to be in the range of 60-95 % by weight. More preferably the content of Mo is in the range of 65-95 wt%, most preferably the content of Mo is in the range of 70-95 wt%. Surprisingly a very high dissolution rate has been found for reduced compacts having a molybdenum content of 80-95 % by weight. This result is due to the much higher specific surface and is in spite of the very high melting point of these alloys, 2100-2500 °C. By balancing the carbon addition it is possible to control the carbon content of the reduced compacts to be less than 5 wt %, less than 2 wt. %, less than 1 wt. %, less than 0.5 wt. %, or less than 0.1 wt. %. Compacts low in carbon can e.g. be used when alloying low carbon steels. However, in some applications, for example in the production of high carbon steels or cast iron, it may desirable to have a carbon content in the range of 1-5 % by weight.

The iron content of the compacts is preferably within the range of 1-20 % by weight, more preferably 2-10 % by weight, most preferably 2-5 % by weight. The iron content in the compacts can be controlled by varying the relative proportions of the iron containing powder in relation to the molybdenum oxide powder.

The reduced compacts can be cost efficient substitutes to Mo0 ₃ powder or standard FeMo, when alloying in melting practices, considering price and/or yield of the Mo addition into melt. Typically such addition could be made e.g. into an electrical arc furnace (EAF) and e.g. be a Mo addition into stainless steel, tool steel or high speed steel.

Depending on the purity of the powder mixture, the compacts may contain further elements including oxides that are difficult to reduce. Other elements apart from Mo, Fe, C and O may be allowed up to less than 15 % by weight. Preferably the total amount of other elements besides O, C, Mo and Fe is less than 10 % by weight, more preferably less than 7 % by weight. The amount of other elements is mainly controlled by the purity of the molybdenum trioxide, but may also come from impurities in the iron containing powder, the carbonaceous powder, and from reactions with elements in the surrounding atmosphere during heating, reduction, or cooling. Using high purity grades of molybdenum trioxide, iron containing powder and the carbonaceous powder; the total amount of other elements besides O, C, Mo and Fe can, if desired, be kept lower than 1 % by weight. If present in the compacts, elements from the group of Si, Ca, Al, and Mg are mainly bound as oxides. For instance, in a steel melt, silicon bound as silicon oxides may be easier to handle than silicon that is dissolved in the lattice of the alloy. The other elements may in some embodiments be limited to at least 1 % by weight or to at least 2 % by weight. Other elements include impurities. Preferably, in some embodiments, the other elements in weight % are limited to:

max 2 N, more preferably max 1 N;

max 1 S, more preferably max 0.5 S;

max 2 Al, more preferably max 1.5 Al;

max 2 Mg, more preferably max 1 Mg;

max 2 Na, more preferably max 1 Na;

max 4 Ca, more preferably max 2 Ca;

max 6 Si, more preferably max 3 Si;

max 1 K, more preferably max 0.5 K;

max 1 Cu, more preferably max 0.5 Cu;

max 1 Pb, more preferably max 0.1 Pb;

max 1 W, more preferably max 0.1 W;

max 1 V, more preferably max 0.1 V;

and remaining elements is preferably max 0.5 each, more preferably max 0.1 each, most preferably max 0.05 each.

In some embodiment, the content in weight % of Si is in the range of 0.5-3, the content of Ca is in the range of 0.3-2, the content of Al is in the range 0.1 -1, and/or the content of Mg is in the range of 0.1- 1.

Preferably, if present, the elements of the group of Si, Ca, Al and Mg are to at least to 50% by weight bound as oxides in the compacts, preferably at least to 90 % by weight.

The nitrogen content mainly depends on the nitrogen level in the atmosphere during reduction and cooling of the compacts. By controlling the atmosphere in these steps the nitrogen content can be made lower than 0.5 wt%, preferably lower than 0.1 wt% and most preferably lower than 0.05 wt%.

Reduced compacts may be produced with a geometric density up to 6 g/cm ³ , preferably less than 4.5 g/cm ³ . It may be less than 4.0 g/cm ³ . For quick dissolving in steel melt it is preferred that the reduced compacts have a geometric density in the range of 1.0-4.0 g/cm ³ . Other possible ranges includes 1.2-3.5 g/cm ³ , 1.2-3.0 g/cm ³ , 1.5-3.9 g/cm ³ and 2.0-4.0 g/cm ³ . The given upper and lower limits of the ranges may be combined with one another to form new ranges. Density can be controlled by varying the briquetting pressure for the green compacts. A higher reduction temperature may also increase density. By controlling process parameters it is possible to produce reduced compacts having geometric density below 2.0 g/cm ³ as well as reduced compacts having geometric density between 2.0-4.0 g/cm ³ , or even higher up to 6 g/cm ³ .

A lower density results in higher porosity, which is believed to yield a shorter dissolution time of the compacts. On the other hand a higher density increases the amount of Mo for a given volume. The geometric density measured in accordance with ASTM 962-08.

EXAMPLE A mixture was prepared by mixing 180 g of a fine grained iron powder (< 40 μιη, >99 wt% Fe, X-RSF40 from Hoganas AB) with 1000 g molybdenum oxide (Mo03 92.5 wt%, Si02 7.5 wt%, < 40 μιη) and 176 g graphite powder (< 40 μιη). 7 dl of Water was added to the mixture. The mixture was compacted in a briquetting machine using a compaction pressure of 75 kg/cm2. The green briquettes were thereafter dried at room temperature to a moisture of 0.5 wt%. The green briquettes was visually examined and handled. No identification of cracking was observed. The green briquettes were reduced in a batch furnace at a temperature of 1300 °C for a time period of 20 minutes, in a 95 vol-% N ₂ and 5 vol-% H ₂ atmosphere.

The reduced briquettes were thereafter allowed to cool to a temperature around 100 °C before evacuating the atmosphere and removal from the furnace. The reduced was visually examined. No identification of cracking was observed.