Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/52—Manufacture of steel in electric furnaces
  • C21C5/5264—Manufacture of alloyed steels including ferro-alloys
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/56—Manufacture of steel by other methods
  • C21C5/562—Manufacture of steel by other methods starting from scrap
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
  • C21C7/0025—Adding carbon material
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C35/00—Master alloys for iron or steel
  • C22C35/005—Master alloys for iron or steel based on iron, e.g. ferro-alloys
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
  • C21C7/0056—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
  • C21C2007/0062—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires with introduction of alloying or treating agents under a compacted form different from a wire, e.g. briquette, pellet
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to a process for making a steel melt containing carbide forming elements from iron based raw material and a mineral containing the carbide forming element, preferably molybdite, a mineral consisting essentially of M0O 3, as the carbide forming element.
• It also relates to a mixture comprising a mineral containing a carbide forming element and an oxygen containing material, for example a mineral or mill scale, to be used as a source for alloying elements during steel manufacturing from iron based raw material and the use of molybdite for preparing Fe 2 Mo0 4 in a melting furnace during the production of a molybdenum alloyed steel melt.
• molybdenum in the slag or in dust, the leaching of molybdenum from landfills has turned out to be a challenge, and thus both slag and dust pose an environmental hazard. From economic as well as environmental view points, it is essential that the loss of molybdenum is minimized during an electric arc furnace melting process. In the electric arc furnace practice, alloying with molybdenum to the steel bath is normally carried out by the addition of ferromolybdenum alloy.
• Ferromolybdenum alloy is manufactured by refining molybdenum oxide (M0O3) containing mineral.
• M0O3 molybdenum oxide
• the refining of M0O 3 from mineral form to ferromolybdenum is a bottleneck in today's available assets of ferromolybdenum and a important factor for the cost increase of molybdenum as an alloying element.
• the mining capacity of M0O 3 in mineral form exceeds the refining capacity.
• the evaporation of M0O 3 to the dust is the main cause of loss of molybdenum (about 8.6 % of total molybdenum input).
• the loss of molybdenum to the slag phase is only about 1.3 % of the total molybdenum input.
• Mill scale presents a valuable resource of iron and alloying elements.
• the yield loss from mill scale is quite substantial.
• the loss of iron through mill scale in the steel production could reach up to 1% wt.
• Today, mill scale is used as a source of oxygen and is added to the steel melt for refining of phosphorous.
• Hot work steels are particularly sensitive to high phosphorous contents.
• the cost of scrap metal is proportional to the inverse content of phosphorous, which gives a strong economical incentive for an efficient phosphorous refining during the production of steel from scrap metal.
• mill scale for phosphorous refinement about 25% of the mill scale from these steelworks can be recycled. The rest has thus far been deposited.
• a main object of the present invention is to provide a process for making a steel melt containing a carbide forming element from iron based raw material and a mineral containing the carbide forming element, while reducing high losses of the carbide forming element primarily to the vapor phase due to the high vapor pressure of the carbide forming element above the melt of raw materials.
• this object is achieved with a process comprising the steps of:
• particulate mineral containing a carbide forming element and carbon and, in addition, mill scale and/or CaO or other slag former containing CaO, said alloy mixture preferably being encapsulated in a closed container, said container preferably being placed in the centre of the melting furnace,
• M denotes a metal or alkali metal element such as Fe, Ca, Mg, Ni
• X denotes a carbide forming element such as Mo, Cr, Ti, Nb, Zr, W etc.
• a reduction of the losses is positive for the environment, since the amount of carbide forming element leached out from deposited dust and slag will be reduced.
• the present invention minimizes the loss of carbide forming element to the dust and slag and is beneficial to the environment and the economy of the process for making alloyed steel melt.
• the molybdite, carbon, mill scale and/or CaO containing slag former are mixed before charging them in the container.
• the mass of steel scrap usually is on the order of sixty (60) times that of the molybdite.
• the melting of the charge is suitably carried out in an electric arc furnace or induction furnace, but the invention shall not be limited by this. It shall be understood that the basic principles of this invention can be applied in connection with any melting furnace using iron based raw material such as steel scrap and iron granules. Relating to melting of steel scrap the invention can be applied in connection with any melting furnace using scrap as a raw material.
• the time required for the chemical reactions that takes place during the process is in some ratio in inverse proportion to the particle size of the mixed ingredients, viz. mill scale, carbon and molybdite. Therefore, in order to establish optimal process conditions the particle sizes shall be as small as possible in order to provide good mixing properties and a large reactive surface area whereby the time which is required for the chemical reactions to be completed will be reduced.
• the retention time has to be adapted to the actual particle sizes so that the retention time at the specified temperature ranges is sufficient in order for the chemical reaction to be able to take place in sufficient degree.
• the molybdite suitably has a particle size of essentially less than 1 mm, preferably it is in the form of fine powder grains.
• the ideal particle size of molybdite should be in the range of 0.1 to 1.0 mm.
• the mill scale advantageously has a small particle size, preferably of essentially less than 10 cm. Performed tests have shown that mill scale with a particle size of max 3 cm is superior to mill scale with a particle size of 1-7 cm. Mill scale in the form of powder is presumed to provide even better process conditions, but is yet to be evaluated. However, it shall be understood that mill scale may be used in the form and sizes which they fall at the forging mill. Additionally, since mill scale is porous it provides a large reactive area and mix relatively well with carbon and molybdite, particularly if these ingredients are in powder form. Mill scale amount required should be the same as the stoichoimetric amount needed for the formation of Fe2Mo04.
• the available carbon has a particle size of less than 10 mm.
• the carbon particle size could be even smaller than 5 mm.
• carbon with a particle size of essentially 0.3-1 cm has been used with successful results.
• molybdite and mill scale is used with even smaller particle sizes, e.g. in powder form, it is presumed that the particle size of carbon shall be in the same range.
• Carbon amount required should be in the range of 15-25% of the mass of mixture (mill scale+C+MoOs). This carbon amount should cover both the reduction of Mo03+FeO x and the expected reoxidation of carbon during scarp melting.
• CaO acts as a slag former it reacts with M0O3 to form CaMo0 4 .
• CaO with particle sizes of essentially 1-2 cm have been successfully used.
• CaO in powder form shall be used.
• Another object of the present invention is to provide a new additive for use in the making of a steel melt containing carbide forming element.
• the additive is a mixture comprising particulate mineral containing a carbide forming element and carbon and additionally either mill scale or at least one CaO containing slag former or both.
• the mass of the mill scale preferably is about that of the particulate mineral containing the carbide forming element, but the amount has to be determined based on the content of various oxides in the mill scale.
• the mineral has a particle size of essentially less than 1 mm and the mill scale a particle size of less than 10 cm, preferably max about 3 cm.
• the particulate mineral and the mill scale is in the form of a fine powder.
• the particulate mineral is essentially consisting of molybdite, M0O3, and is used for preparing Fe 2 Mo0 4 in a melting furnace during the production of a molybdenum alloyed steel melt.
• the molybdenum source is molybdite, a mineral consisting essentially of following process steps are applied:
• the present invention minimizes the molybdenum loss to the dust and slag and is beneficial to the
• the molybdite and carbon and the possible mill scale and/or CaO or other slag former are mixed before charging them in the steel container. Smaller particle sizes are believed to be
• ingredients preferably shall be as small as possible
• ferromolybdenum are formed in the container by reactions (1), (2), (3) and (4) when molybdite is mixed with carbon and calcium oxide, and by reactions (1), (2), (5), (6), (7) and (8) when molybdite is mixed with carbon and mill scale.
• the container may be rigid or flexible, i.e. a steel barrel or a big bag (bulk bag, super sack) of paper or plastics, for example.
• the container remains intact during heating at least to a temperature which is high enough for the Fe 2 Mo0 4 or CaMo0 4 to have formed, i.e. at around 800-900 K, to prevent or at least minimize the loss of molybdenum to the slag or dust.
• the melting of the charge is suitably carried out in an electric arc furnace, and as will be described below, the formation of CaMoC ⁇ and Fe 2 Mo04 has been observed by high-temperature XRD in the temperature interval 773- 873 K. During subsequent heating to higher temperatures the container shall collapse and release the Fe 2 Mo04 or CaMoC ⁇ formed therein into the steel melt.
• a first amount of steel scrap is charged in the electric arc furnace.
• the container containing the alloy mixture is charged on top of the first amount of steel scrap, preferably in the center of the melting furnace.
• a second amount of steel scrap is charged on top of the container and first amount of steel scrap.
• the sizes of scrap shall be adapted to frequency of the actual melting furnace according to the conventional practice known by skilled persons in the field.
• large sized scrap is normally charged in the top of the furnace and starts to melt first, while small sized scrap are charged in the bottom of the induction furnace.
• the first amount of steel scrap can be a low alloyed small size steel scrap, mostly sheet-steel clippings.
• the second amount of scrap contains a first portion of small size scrap and a second portion of briquettes of pressed car scrap.
• the mass of the pressed car scrap is about twice that of the small size scrap, and to achieve a desired content of molybdenum in the steel melt, the mass of steel scrap usually is on the order of 50-70 times, preferably sixty (60) times that of the molybdite.
• the molybdite has a particle size of essentially less than 1 mm
• the mill scale to be mixed therewith has a particle size of essentially 1-7 cm and is used in an amount such that the mass of the mill scale is about that of the molybdite.
• the mill scale preferably is size separated or reduced to a size, where most of the pieces are smaller than 3 cm.
• the carbon has a particle size of essentially 0.3-1 cm and present in an amount such that the mass of carbon is between one fourth and half of the mass of the molybdite, and the CaO possibly used for slag forming preferably has a particle size of essentially 1-2 cm.
• the Ml mixture was aimed at using mill scale and molybdite mineral to provide the transformation of M0O 3 into Fe 2 Mo0 4 with further reduction by carbon to form Fe 2 Mo.
• the pure substance of Fe 2 Mo0 4 showed the highest molybdenum yield (up to 99 %) during laboratory trials, but the direct usage of initial components (named Fe 2 Mo0 4 precursors) is much more attractive in a view of lower material cost.
• the M2 mixture is the stoichiometric mixture of carbon and molybdite mineral, which should give pure Mo after reduction.
• the mixture serves as a reference to compare the Mo yield from different mixtures and to see the influence of other oxides in the mixtures on M0O3 reduction.
• the M3 mixture was aimed at using lime and molybdite mineral to provide the transformation of M0O3 into CaMo0 4 above 600 C before the reduction by carbon, which should be more beneficial in the case of fast heating or oxygen presence in a system.
• the M3 mixture showed lower Mo yield than that of Ml and M2 in the laboratory results.
• Indomix, Dolomet, and Alumet are trade names of marketed slag formers having the compositions specified above. All of them contain various amounts of CaO.
• the weighing of the components of the mixtures was performed on a balance with 1 kg detection limit. The mixing was made in a rotary mixer with a capacity of 75 kg. If it was not possible to put all the initial materials in the mixer for a single batch, the components of a mixture were divided in two portions. No grinding or other size reduction of initial materials was performed during this investigation. However, in the trials specified in Table III, in contrast to the mixtures used in heat numbers Ml -HI and M1-H6, for heat number M1-H2 only small pieces of mill scale (mostly smaller than 3 cm size) were collected to make the mixture.
• the yield of molybdenum was calculated for each heat. As it was not possible to measure the mass of the liquid steel after each trial, the yield of the liquid metal from the scrap was assumed to be equal to be 96 % based on previous observations. During previous heats, a scrap yield range of 95-98 % was observed for the same type of scrap, and because of the similar type of scrap used for each heat, the scrap yield was expected to be approximately the same. The scrap yield value affects the molybdenum yield calculation in the current test.
• liquid metal mass was estimated based on average metal yield for such types of scrap and furnace. Additionally, the mass of liquid slag was calculated based on known amount of CaO input and CaO concentration in final slag.
• the slag compositions are presented in Table V. Table V. - Results of slag analysis for the experimental trials
• the molybdenum yield is very close to the laboratory results (Table IV).
• the carbon content is in the range 0.05-0.08 %, while the charging carbon content was some 0.072 %. That means that a minor decarburization occurred due to oxidation. Also, all the mixtures had 10 % more carbon, which is believed to be consumed by additional oxidation.
• the analysis of the slag composition showed that a good refining of phosphorous could be obtained in all heats, the content of FeO in the slag being an indicator of this. Heat M1-H6 however deviated from the others in several respects and the results are not considered to be representative for the invention.
• the performed tests have shown that the inventive process is capable of giving a very high yield of molybdenum in the steel.
• an alloy mixture containing a stoicio metric mixture of molybdite, carbon and either or both of mill scale and calcium oxide the molybdenum content in the steel can be regulated by adapting the amount of alloy mixture in proportion to the desired content of the alloying element and the yield.
• a yield in the range of 99% like in the laboratory trials using pure substance of Fe 2 Mo0 4 is likely to be obtainable, particularly when alloy ingredients in powder form are used and thoroughly mixed and particularly when mill scale is used for transformation of molybdite in the mineral.
• the mixture according to the invention for alloying of steel shall preferably have the following chemical composition:
• the molybdenum yield of heat M3-H5 is 92.4 %, and only one heat was tested for this mixture. This yield is close to the laboratory results for 16 g heat size. The molybdenum yield in the laboratory results for 0.5 kg heat size was only 78 %, which must be considered as unreliable. The molybdenum yield with a mixture of Mo0 3 , C, and CaO can reach a maximum of 92.4 %. Mo0 3 + C + mill scale mixture
• Heat M1-H2 Since it was presumed that mill scale of larger size results in poor mixing of mill scale with Mo0 3 and carbon, in heat M1-H2, the size of the mill scale size selected was smaller than that used in heats Ml -HI and M1-H6. For heat M1-H2, mainly small pieces (max 3 cm) were taken during mixture preparation. For the heats Ml -HI and M1-H6 the size distribution of the mill scale was such that some of the pieces were more that 10 cm. Heat M1-H2 shows the best molybdenum yield of 95.9 %. When the content of M0O3 in the slag is considered, it can be seen that the loss of molybdenum to the slag is the least for heat M1-H2, which supports the conclusion that mill scale of smaller sizes provides better process conditions.
• the weighing error from the balance has some influence on the calculated molybdenum yield.
• the detection limit of the balance used was 1 kg. This error will produce ⁇ 2 % uncertainty for the molybdenum yield.
• scrap yield can affect the molybdenum yield. For example, a variation of 1 % in scrap yield will result in a variation in calculated molybdenum yield of approximately 0.9 %.
• the invention also relates to a process for preparing ferroalloy, for example Fe 2 Mo0 4 , in a furnace comprising the steps of: a) charging the furnace with an amount of an alloy mixture containing a particulate mineral containing a carbide forming element and carbon and, in addition, mill scale and/or CaO or other slag former containing CaO, said alloy mixture preferably being encapsulated in a closed container,
• the process of the invention makes it possible to avoid the high cost of using ferromolybdenum as alloy addition agent by using the less expensive mineral molybdite in making a molybdenum containing steel melt from steel scrap.
• the inventive process reduces the economic and environmental impacts by minimizing molybdenum losses to exhaust dust and slag.
• the invention makes it possible to increase the amount of recycled mill scale since mill scale can be used not only for phosphorous refining, but at the same time as an ingredient in an alloy mixture which stabilizes molybdite through a series of reactions during the manufacturing of the steel melt.
• the invention is not limited to the above described examples using molybdenum but may advantageously be used in connection with a number of carbide forming elements.
• a mineral containing vanadium oxide, V 2 O 5 , or chromium oxide, FeCr 2 0 4 , Cr 2 0 3 may be used.
• inventive process may be applied to melting processes for production of ferroalloy (e.g. ferromolybdenum) in a separate process which can be added to a steel melt for alloying purposes.
• ferroalloy e.g. ferromolybdenum
• the invention can be applied to oxidizing as well as reducing melting processes, in the reducing process in order to adjust the alloy content of the steel scrap.
• Various melting furnaces may be applied where the alloy is processed by a heating from low temperature which provide a temperature increase of the alloy mixture in the container in the interval of 600-900 K during a sufficient retention time.
• the alloy mixture may be charged in small containers and their form need not be compact, rather a more spread-out form may be advantageous since the alloy mixture will more quickly through heated, providing better conditions for completion of the chemical reactions.

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• Metallurgy (AREA)
• Organic Chemistry (AREA)
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Citations (5)

• 2010
  • 2010-06-30 SE SE1050721A patent/SE1050721A1/sv not_active Application Discontinuation
• 2011
  • 2011-06-29 WO PCT/SE2011/050875 patent/WO2012002897A1/en active Application Filing
  • 2011-06-30 TW TW100123037A patent/TW201217548A/zh unknown

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