Patent Application
20180371562
The invention pertains to a method for producing of ferro-silicon-aluminum master alloys
Ferrosilicon is a master alloy which, in particular, is used for steel and cast iron production, if appropriate together with other materials such as aluminum. Density and melting point of ferrosilicon significantly depend on the content of silicon. The higher the silicon content (mass %) the lower is its density. Generally, for doping of steel alloys standard ferrosilicon alloys are used such as FeSi 45, FeSi 65 and FeSi 75. Said master alloys belong way back to the proven initial materials for reducing and doping of steel alloys. Subject to the required quality of the alloyed or reduced steel one more doping element—aluminum—is added to the melt.
DE 22 23 974 B2 describes a method of producing a doping alloy for reducing and doping of steel which uses a carbonaceous rock with 40 to 50 mass % ash content, 15 to 25 mass % volatile matter, 15 to 25 mass % combined carbon and 2 to 6 mass % sulfur, with calorific capacity of 1.500 to 2.000 kcal/kg as original stock for melting it into a carbon alloy, containing of 25-50 mass % Si, 10-40 mass. % aluminum, 2-10 mass. % of calcium, 0.5-2.5 mass. % of titanium, balance iron and subject to technical specifications various admixtures, as well as micro-admixtures of vanadium and boron if required.
It is known in the prior art (DE 28 53 007 A1) the method of producing silicon containing ferroalloys which consists of pelletizing the mixture of a carbonaceous reducing agent and leading element ore of the resulting alloy with addition of quartzite, of received charge material into the melting furnace and in the following continuous single-stage recovery of the resulting alloy elements.
RU 2251586 C2 discloses the method of producing of ferro-silicon-aluminum alloys using carbonaceous rock with 15-35% carbon, as a silicon-aluminum containing material, with additional charging of coke and/or quartzite. By this way smelting of an aluminum-silicon alloy with aluminum content of 5 to 35% is carried out.
EP 2 295 614 B1 describes an alloy for reducing and doping of steel with the following composition (mass-%):
EA 201100824 A1 describes a method of smelting ferro-silicon-aluminum alloys. Carbonaceous rock, quartzite, metal scrap and wood chips are used as raw materials. The charge materials are sieved to <20 mm size, whereby 75% thereof is charged onto the furnace peripherals.
UA 6198 U describes a method of production of complex deoxidizers (reducers), in particular, ferro-silicon-aluminum alloys. These reducers are used preferably for dead-melted and rimming steels (for steel melting). The raw material for this method is metal scrap.
CN 102839257 A discloses a FeSiAl based reducer used for steel production and having the following composition (mass.-%): 48-54% Al, 18-22% Si, 0.06-0.6% C, 0.006-0.05% S, 0.01-0.05% P, 0.17-0.6% Cu, balance—Fe.
A similar alloy is described in CN 102839292 A having the following composition: (mass.-%): 20-30% Al, 45-55% Si, 22-28% Fe. Following elements can be present as admixtures: <0.008% C, <0.02% P, <0.02% S, <0.05% Cu, <0.005% Ti, <1.0% Mn, <0.05% N.
The known prior art reflecting the process of FeSiAl production is distinct in high carbide forming in slag which is negatively affecting FeSiAl production. In the event the melting furnace becomes impracticable or must be picked out for the next operation which is extremely expensive.
The object of the present invention is to provide for an efficient low-cost production of the FeSIAI master alloy out of simple and cheap raw materials without carbide forming in the melt during the melting process.
Besides, there should be offered an opportunity to replace alloys for reducing and doping of steel, such as ferrosilicon and aluminum which earlier were applied separately.
This objective is solved by Method of producing FeSiAl alloys wherein a carbonaceous rock with an ash content >50% to <65%, is being mixed with quartzite, iron-bearing material, and wood chips, if required, high volatile coal, in a preset ratio of the charge components and the homogenized charge material is being loaded into a melting furnace for melting of FeSiAl alloy, the charged carbonaceous rock can contain i.a. the following chemical composition in the mineral part (ash):
Advantageous improvements of the claimed method can be examined in the correspondent dependent method claims.
The charge is to be mixed and homogenized preferably outside the melting furnace, whereby is to be loaded cone up into the melting furnace with Søderberg electrodes and then the FeSiAl alloy is being smelted.
As opposed to the prior art this method enables to produce the FeSiAl master alloys using cheap raw materials (carbonaceous rock, quartzite, iron-bearing material), replacing at the same time common ferrosilicon alloys and addition of aluminum if required.
Distinct from the known prior art the claimed method allows to avoid the use of coke. By a calculated addition of iron-bearing material it is possible to prevent efficiently an undesirable formation of silicon carbides in the melt or considerably decrease it to a minimum. By virtue of the ultimate fall-off of the carbide forming a monolithic dense master alloy is being received which can be used for deoxidation and doping of steel as well as for reducing of magnesium.
Preparation of the carbonaceous rock is carried out, e.g. in jaw or rolling crushers, as well as similar mills. Specifically it is preferable to use grain sizes between 20 mm and 80 mm to be charged into the melting furnace.
Under the carbonaceous rock the specialists understand a coal-bearing rock with 50% to 65% ash content. The carbonaceous rock is a low caloric high-ash layer between the coal layers.
Carbonaceous rock in different deposits has different qualitative attributes and contents. For the claimed method it is preferable to use carbonaceous rock with higher electrical resistance of the rock. Preferred is the range of resistance between 10−6Ω and 10−1Ω. The higher the electrical resistance of the rock the better is it to control the furnace temperature.
The charged carbonaceous rock with ash content of >50% to <65% can contain, i.a. the following chemical composition in the mineral part (ash):
If appropriate quartzite can be added or like carbonaceous rock crushed in an adequate mill whereas the preferred grain sizes are from 25 mm to 60 mm. Usually quartzite consists of 97-98% SiO2 and 1-2% Al2O3.
Iron turnings, burning scale and iron-bearing oxides in the form of hematite and various iron ores and concentrates can serve as iron-bearing material. Preferred are iron turnings.
Iron turnings are added in sizes 5 to 50 mm. Iron turnings can be at least partially oxidized whereas the film oxide thickness should not exceed 0.7 mm. Iron turnings can originate from common wastes of metalworking productions, e.g. milling machines, cutters, etc. Hence turnings can be considered as small sized iron fragments preferably with large oxidizable surface.
As appropriate a certain portion of wood chips or high-volatile coal can be added to the charge mixture. Grain size is preferred from 50 mm to 100 mm.
Similarly wood chips with >50% volatiles are added to the primary material, if needed.
If instead of wood chips, e.g. a high-volatile coal is used it has to have more than 40% of volatile matters.
As already mentioned coke is not used as a primary material. Coke has not enough or has no volatile matters at all and it does not facilitate sufficient porosity of the furnace charge. In case of wood chips or high-volatile coal this is different because they have high percentage of volatile matters.
The main raw materials (carbonaceous rock, quartzite and iron-bearing material) with the required grain sizes are being stored separately in hoppers. Should the need arise to add wood chips or high-volatile coal they are also stored in separate hoppers.
Based on the capacity of the melting furnace, the raw stock—carbonaceous rock, quartzite and iron turnings, and, if required, wood chips or high-volatile coal, are mixed in a defined share proportion preferably outside the melting furnace and are charged to the melting furnace preferably equipped with Søderberg electrodes.
The preferred product should be a FeSiAl master alloys with the following composition (mass-%):
An equipment operating as per the claimed method consists of a melting furnace with at least one Søderberg electrode, various hoppers for storage of, at least, carbonaceous rock containing Si and Al oxides, quartzite, and also iron-bearing materials, if needed hoppers for wood chips or high-volatile coal, if needed preparation and crushing units at least for carbonaceous rock and if necessary for quartzite, mixing and dosing devices for charging mixture, and feeder units for feeding specifically homogeneous mixed charging material around the furnace electrodes.
Advantageous improvements of the claimed equipment can be examined in the corresponding dependent claims.
As already presented the furnace is equipped with several Søderberg electrodes, thus, in particular, the mixed homogeneous charge material is loaded cone-up wise around the electrode(s). Here are used special charging tubes located around the electrode(s). If the desirable conical form is not reached by common furnace charge feeding, special mechanical scrapers are used.
The smelted FeSiAl material can be advantageously used for steel deoxidizing and doping.
Alternatively, it is also possible to use another quality of FeSiAl in the process of manufacturing of magnesium alloys, e.g. as a reducing agent.
Furthermore it is practical to use FeSiAl alloy for production of various refined grades of ferroalloys.
Table 1 a shows examples of the molten FeSiAl master alloys which could be used for steel production.
Table 1 b shows examples of consumption of quartzite and iron per 1 ton of FeSiAl alloy.
Total iron content percentage consists of:
A thin slag layer, as a rule <3.5 g/cm3, lies on the melt during the steel production.
The addition of the iron turnings is of considerable technical importance for reaching the assigned density of each FeSiAl alloy as per Table 1a. The ratio of Fe total/Fe from iron turnings should be between 1.1 and 1.35, more specific between 1.2 and 1.3.
Due to the above indicated density FeSiAl alloys (table 1a) do not float to the surface of the steelmaking slag but rather penetrate through it thus fulfilling their mission namely: deoxidation or doping of steel.
Aluminum has a density of 2.2 g/cm3. It can happen in traditional combinations of FeSi+Al that aluminum does not penetrate into the steel volume and floats on the surface of the steelmaking slag. Such cannot happen to the FeSiAl alloy as the density increases by virtue of addition of iron turnings.
Table 2a shows examples of FeSiAl alloys which can be used in magnesium production.
Table 2b shows examples of consumption of quartzite and iron per 3 tons of carbonaceous rock.
Application of iron-bearing materials more specifically iron turnings in combination with the carbonaceous rock with high electric resistance more specifically 10−6Ω to 10−1Ω, and also quartzite, if necessary with addition of wood chips or high-volatile coal for the first time ever gives the chance to considerably reduce formation of silicon carbides during smelting FeSiAl alloys. In this case it is possible to use cheap raw materials: carbonaceous rock, quartzite and iron turnings that represents a more economical alternative to traditional raw materials FeSi+Al. In particular purposeful addition of iron turnings increases the density of the melted FeSiAl master alloy so that can be reached the already described advantages of application of this master alloy in the production of steel and magnesium.
Contingent on the used carbonaceous rocks it may contain up to 1.5% titanium, which is not affecting the process of deoxidation and doping of steel or reduction of magnesium.
Iron oxide (FeO) on the surface of turnings disrupts silicon carbide (SiC) and prevents the carbide forming process during the FeSiAl production.
As already mentioned sometimes it is possible to add pre-measured amount of wood chips and alternatively high-volatile coal, thus these materials are used only as an aerator for the furnace charge in order to avoid sintering on the furnace mouth and to achieve a uniform emission of the reaction gases.
Nowadays in the world market there exist, i.a., standard alloys of FeSi65 and FeSi75 which are universally used combined with addition of aluminum in the production of steel or magnesium.
The FeSiAl alloy produced under the claimed method substitutes the above mentioned alloys FeSi75 (+Al) and FeSi65 (+Al).
As a result of the desired prevention of carbide forming during the FeSiAl smelting a dense alloy as master alloy is being made which contributes to better quality of the respective steel and magnesium grades.
Depending on the subsequent compositions of steel and magnesium the content of iron turnings amounts to 5 to 20% of the total mass of the primary materials. The best way is to add iron turnings with a big surface, thus the length of the coils chips may be up to 50-60 mm.
The excess of the iron-bearing material decreases the concentration of basic elements—aluminum and silicon, and its lack leads to undesirable carbide forming in the melt and the master alloy melting process is impaired.
The grain size of the furnace charge for carbonaceous rock and quartzite has to be >20-80 mm.
The known process employs a melting furnace equipped with so called Søderberg electrodes (made of carbon and steel casing). Carbon is slowly reacting with the loaded furnace charge and is partially acting as deoxidizer. Iron in a very small quantity is converted from the electrode casing into the master alloy melt.
If needed, it is possible to use oxide scale, hematite, iron ore and concentrates instead of iron turnings but these materials do not prevent carbide forming as efficient as iron turnings. Another advantage is the fact that application of the object of invention allows to meet the different customers' requirements. So for instance, if required, it is possible to add to the furnace charge and to melt other primary oxide elements either single or combined such as barium, vanadium, calcium, etc. in form of ores or similar.
The below table indicates oxide components to be added if required:
Examples of embodiments of the invention are presented and described as follows:
The supplied carbonaceous rock 1 is being fed to the bin (hopper) 2 connected to a vibration feeder 3 or a similar device. Through the only indicated conveyor 4 the carbonaceous rock 1 gets into the crusher 5, for example a jaw crusher. In this way the crushed carbonaceous rock 1 is being screened with a screen 6 to grain sizes 0 to 20 mm and >20 to 80 mm. Grain size >20 to 80 mm is further being used in the furnace charge.
In further process stages the respective mixture (carbonaceous rock >20 to 80 mm, quartzite >25 to 60 mm) is being fed via conveyors to hoppers 13, 14 (
Another hopper 15 contains also required primary material—iron-turnings 15a with size between 5 and 100 mm, preferably 5 to 50 mm. Through a dosing strain-gauge weigher 16, 17, 18 the preset portions of carbonaceous rock 1 (hopper 13), quartzite 7 (hopper 14), as well as iron turnings 15a (hopper 15) are being transported to a belt conveyor 19, whereby the primary materials 1, 7, 15a are being homogenized.
If required another hopper B can be fed with wood chips H, size 50-100 mm, which is admixed to the charge consisting of carbonaceous rock 1, quartzite 7 and iron turnings 15a. As described earlier it is possible to use high-volatile coal instead of wood chips H.
Via next transport equipment/device 20, shown here as a belt conveyor, the prepared homogenized furnace charge material consisting of carbonaceous rock 1, quartzite 7 and iron turnings 15a (if required wood chips H) is being discharged into the furnace (not shown here). If necessary further homogenization steps like screw mixing or similar can be conducted on the way to the furnace (which is not shown here).
Further the object of the invention is described more detailed in examples:
For example: the following homogenized furnace charge materials are used to produce FeSiAl 65/15:
Raw Material
Carbonaceous raw material (high-ash coal with ash content 45-50%, carbonaceous rock with ash content 55-65%) is characterized through different content of ash, volatiles and humidity. For example one batch of carbonaceous raw material may contain lumps with different ash content. Therefore it is very important to blend the composition of the supplied batch of the carbonaceous raw material. This can be achieved through its thorough mixing during crushing and screening and also during its storage.
Quartzite is being delivered already screened. The effective screen size is 25-60 mm.
Iron turnings are being delivered crushed with 5-50 mm screen size. 50-100 mm oversize should not exceed 10%. The iron turnings can be oxidized. Oxide film thickness should not exceed 0.7 mm.
1.1. Crushing and Screening of Raw Materials
The unit for furnace charge handling consists of a standard set of a jaw crusher and a screen—the crushing and screening unit (CSU). The set contains a bin (hopper) with a vibration feeder in which a pay-loader loads the carbonaceous stock. And the raw materials are transported to the bin (hopper) from different parts of the heap. From the bin (hopper) the raw materials are moved proportionally and uniformly to the crusher with 100 mm distance between the crusher jaws. After crushing the carbonaceous stock is transported to the screen having a mesh of 20 mm where the raw materials are screened into two sizes of 0 to 20 mm and >20 to 80 mm. Size >20 to 80 mm is the effective size needed for the production and is being stored.
1.2. Storage of the Carbonaceous Stock
After crushing the effective size of the carbonaceous raw material is stored in even layers on the whole defined surface. This is achieved by using a traversing conveyor with a splitter or directly by a pay-loader. Thus is obtained a pile of 3-4 layers of the carbonaceous stock. The feeding of the carbonaceous stock to the weighing bin (hopper) is done from the end of the pile while the layers are being mixed.
In this way mixing and blending of the raw material batch is made during crushing, piling and charging of the carbonaceous stock into the weighing bin (hopper).
1.3. Weighing of Raw Materials
Weighing is carried out with the use of common batching units consisting of a 20-60 m3 dispensing bin (hopper), a vibration feeder, tensometric balance of strip or bin type, reversible-shuttle belt. There should be at least three batching units for the carbonaceous stock, 1-2 units for the quartzite and 1 unit for the iron turnings. The three batching units for the carbonaceous stock are designated for batching different batches with various ash contents. Hence it is possible to mix in different proportions the carbonaceous material of 45% and 65% ash content or coal with 30% ash content and carbonaceous rock with 65% ash content thus obtaining the required ash content needed to smelt one or another alloy grade.
The basic batching unit is one of the weighing bins (hoppers) for carbonaceous raw material depending on the speed with which other raw materials are transported for weighing. After weighing all raw materials are fed to one reversible-shuttle belt. The raw material is placed layer-wise on it. Thereby is reached a uniform distribution of the carbonaceous raw material, the quartzite and the iron turnings. Further the charge mix is discharged from the reversible-shuttle belt to the inclined belt conveyer which feeds the charge mix to the melting shop on a mark with the furnace bins (hoppers).
1.4. Furnace Bins (Hoppers) and Furnace Bath Charging
The charge gets from the inclined belt conveyer through a hopper mechanism to a running inclined belt conveyor on the furnace bins (hoppers) mark over the furnace bath. The furnace bins (hoppers) are sequentially fed by furnace charge. The charge from the furnace bins (hoppers) is discharged into the furnace bath through charging tubes, if necessary, and depends on the speed of its smelting in the furnace bath. There are ten charging tubes, i.e. three near each electrode and one charging tube in the center between the electrodes. The charge is steadily fed to the electrodes. If required it is scraped to the electrodes with special steel scrapers (for small electric furnaces of up to 5 MVA) or with special devices for charge distribution (for electric furnaces of 10-33 MVA) to the electrodes creating 300-600 mm high charge cones around the electrodes. It improves settling of fumes of gaseous silicon (SiO) and aluminum (Al2O) suboxides.
The ferrosilicon aluminum smelting process can be divided into three intervals depending on the temperature and preferential behavior of the different reactions.
The temperature interval/range of T=1,400-1,500° C. is characterized by active decrease in mullite concentration in the reaction mixture. Following reactions are taking place in this temperature interval/range depending on the way of heating the charge in this temperature interval/range:
SiO2,solid+Csolid={SiO}+CO (1)
SiO2,solid+2Csolid+Fe=SiFe+2CO (2)
[Si]+Csolid=SiC (3)
SiO+Csolid=Siliquid+CO (4)
{SiO}+2Csolid=SiCsolid+CO (5)
SiO2 solid→SiO+½O2 (7)
SiO2 solid+CO={SiO}+CO2 (7)
Al2O+Csolid=2Alliquid+CO (8)
Among them the greatest product yield is only produced by the reaction leading to formation of silicon carbide. The change of its quantity in the reaction mixture is characterized by prompt burst starting from temperature >1.550° C.
In a temperature interval/range 1,650-2,050° C. in the wake of temperature rising the following reactions start to run:
SiO2,solid+Siliquid=2SiO (9)
SiOgas+SiCsolid=2Siliquid+CO (10)
SiO2+SiC=SiO+Si+CO (11)
With further rise of temperature (above 1,800° C.) following reactions are developing:
2Al2O3 solid+9Csolid=Al4C3 solid+6CO (12)
2Al4C3 solid+3SiO2=8Alliquid+3Siliquid+6CO (13)
⅔Al2O3+2SiC+Fe=2SiFe+ 4/3AlFe+2CO (14)
Al2O3 solid+2C=Al2O+2CO (15)
Al2O3 solid+3C=2All+3CO (16)
Al2O3+SiC=Al2O+SiO+CO (17)
A specific feature of this temperature interval/range is the formation of aluminum carbide which is easily neutralized in surplus of silica with formation of ferrosilicon aluminum.
At temperatures over 2,050° C. the content of silicon carbides in the charge drops substantially and concentration of silicon and aluminum in the metal rises. Whereby the silicon carbide is mainly consumed for interaction with alumina, Si- and Al-suboxides with formation of a silicon-aluminum alloy:
2Al2O3+SiCsolid=4Alliquid+SiOgas+CO (18)
Al2Ogas+SiCsolid=2Alliquid+Siliquid+CO (19)
Alliquid→Algas (20)
But simultaneously form >2,100° C. temperature level the evaporation of aluminum increases.
This example presents a ferrosilicon aluminum alloy in the charge of which was added manganese as oxide material, besides carbonaceous rock, quartzite and iron turnings (wooden chips if required).
FeSiAl Alloys with Manganese
A. Carbonaceous rock 2.99 tons, size >20-80 mm
B. Quartzite—0.126 tons, size 25-60 mm
C. Iron turnings—0.09 tons, size 5-30 mm
D. Manganese ore 0.457 ton, size 10-60 mm
At the end of the melting process is obtained a FeSiAl alloy with Manganese with the following average composition (mass-%):
This example presents a ferrosilicon aluminum alloy in the charge of which was added barium as oxide material besides carbonaceous rock, quartzite and iron turnings (wooden chips if required).
FeSiAl with Barium
A. Carbonaceous rock 3.03 tons, size >20-80 mm
B. Quartzite—0.397 tons, size 25-60 mm
C. Iron turnings—0.091 tons, size 5-30 mm
D. Barium ore—0.306 tons, size 10-50 mm
At the end of the melting process is obtained a FeSiAl alloy with Barium with the following average composition (mass-%):
This example presents a ferrosilicon aluminum alloy in the charge of which was added calcium as oxide material besides carbonaceous rock, quartzite and iron turnings (wooden chips if required).
FeSiAl Alloy with Calcium
A. Carbonaceous rock 3.17 tons, size >20-80 mm
B. Quartzite—0.42 tons, size 25-60 mm
C. Iron turnings—0.11 tons, size 5-30 mm
D. Lime−0.143 tons, size 10-30 mm
At the end of the melting process is obtained a FeSiAl alloy with Calcium with the following average composition (mass-%):
This example presents a ferrosilicon aluminum alloy in the charge of which was added chrome as oxide material besides carbonaceous rock, quartzite and iron turnings (wooden chips if required).
FeSiAl Alloy with Chrome
A. Carbonaceous rock 3.0 tons, size >20-80 mm
B. Quartzite—0.455 tons, size 25-60 mm
C. Iron turnings—0.1 t, size 5-30 mm
D. Chrome ore 0.325 t, size 8-50 mm
At the end of the melting process is obtained a FeSiAl alloy with Chrome with the following average composition (mass-%):
The following example presents a ferrosilicon aluminum alloy in the charge of which was added vanadium as oxide material besides carbonaceous rock, quartzite and iron turnings (wooden chips if required).
FeSiAl Alloy with Vanadium
A. Carbonaceous rock 2.93 tons, size >20-80 mm
B. Quartzite—0.54 tons, size 25-60 mm
C. Iron turnings—0.118 t, size 5-30 mm
D. Vanadium pentoxide briquettes (V2O5) 0.15 tons, size 10-30 mm
At the end of the melting process is obtained a FeSiAl alloy with vanadium with the following average composition (mass-%):
This example presents a ferrosilicon aluminum alloy in the charge of which was added titanium as oxide material besides carbonaceous rock, quartzite and iron turnings (wooden chips if required).
FeSiAl Alloy with Titanium
A. Carbonaceous rock 2.88 tons, size >20-80 mm
B. Quartzite—0.36 tons, size 25-60 mm
C. Iron turnings—0.129 tons, size 5-30 mm
D. Rich titanium slag 0.26 tons, size 10-40 mm
At the end of the melting process is obtained a FeSiAl alloy with titanium with the following average composition (mass.-%):
This example presents a refined ferrochrome (FeCr) alloy in the charge of which besides chrome ore and lime was added FeSiAl alloy as reducing material.
A. Chrome ore 2.29 t, size 5-15 mm
B. Lime—1.3 ton, size 10-25 mm
C. FeSiAl—0.5 ton, size 5-10 mm
At the end of the melting process is obtained a FeCr alloy with the following average composition (mass-%):
The following example presents the process of production of one ton magnesium metal with the use of FeSiAl alloy as a reducing agent. The beginning of the process includes briquetting of crushed doloma (calcined lime dolomite) and FeSiAl with size 0.1-5 mm. The reducing process is running for 8 hours in a retort at 1,200° C. and vacuum 10−2 atm.
A. Doloma—1.7 ton, size 0.1 to 2.0 mm
B. FeSiAl—0.25 ton, size 0.1-5 mm
At the end of the smelting process is obtained a pure magnesium metal (99.9%) and slag.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15000931.4 | Mar 2015 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/000506 | 3/23/2016 | WO | 00 |
