Based on alloy type, the high performance alloys market is segmented into wrought alloy and cast alloy. HTI: The Go-To Heat Treat Specialists By definition, Austempering is a hardening process for medium to high carbon steels and alloy steels wherein, the materials are heated to the hardening temperature and quenched in a molten salt bath.
Provided that the alloy has sufficient harden This dependency. Building No. Engineering Handbook 14 Iron alloys are the most common ferrous alloy. Steel is a solid solution of iron and carbon, the carbon is dissolved in the iron; iron is the solvent and carbon is the solute.
Steel, like water, can go through phase changes. With water, the phases are solid, liquid, and gas. The metals and alloys utilized in foundry are classified into two segments namely ferrous or non-ferrous depending whether they have the presence of iron in them or not. These metals and alloys are melted into a liquid form with the help of foundry equipment that operates at …. Up to a maximum carbon content of 0.
Argus Metals International Argus Media The Argus Metals International service is your trusted source for comprehensive daily non-ferrous market intelligence. This service provides the latest accurate, unbiased pricing and reporting from global non-ferrous markets, including minor metals, …. Nickel Alloy UNS N is a commercially pure wrought nickel, with good mechanical properties and an excellent resistance to many corrosives.
Alloy steels are ferrous alloys based on iron, carbon, and alloying elements such as chromium, molybdenum, vanadium, and nickel. Unless the heat is already very low in these elements, or the amounts added can be tolerated in the final composition, the hot metal should be as low in phosphorus and sulfur as possible.
The carbon recarburizers graphite, coke, and anthracite are quite light and will easily float on the slag, where they can burn wastefully. They should therefore be added very early in the tap, or placed in the ladle before the steel is introduced. The tap should have enough turbulence to provide rapid carbon dissolution.
In foundry practice, recarburizers are added in the ladle, observing the same precautions as described above. The type of recarburizer chosen depends on the cast iron being produced. Crystalline recarburizers, i. If the tap sulfur content is below this value, it may be more efficient to perform primary recarburization with high sulfur petroleum coke and trim with graphite just before casting. When inoculation is to be avoided, as in white irons, coke is the preferred addition agent. However, if nitrogen is known to produce porosity defects, it can either be avoided by using graphite or a low-nitrogen coke or controlled through the addition of titanium, zirconium or similar stabilizing elements.
It should be noted that in adding carbon, a reduction in temperature of 2. In general, such processes become more difficult as carbon content increases. The effect of carbon is first felt in the soaking pit or re-heat furnace. High carbon steels are more sensitive to thermal shock and must be heated slowly to avoid cracking.
Step heating - allowing the ingot to equalize in temperature at several plateaus before the rolling or forging temperature is reached - may be necessary, especially for large cross sections.
Steels with more than 0. This leads to cracking or, at best, unacceptable surface conditions in the final product and almost always requires that the burned ingot be reverted to scrap. High carbon steels should therefore be heated slowly and evenly, avoiding hot spots due to direct flame impingement.
Both hot- and cold-rolling forces increase with carbon content. In hot rolling, the effect becomes more pronounced as the finishing temperature is approached.
An additional 0. The energy required for cold working is strongly dependent on carbon content, a consequence of the proportion of pearlite in the microstructure. The need for intermediate anneals therefore increases with carbon content, all other factors being equal.
It should be noted that the carbon has a relatively strong tendency to segregate in thick sections e. This can lead to nonuniform carbon distribution in the final product, such as the familiar "banding" caused by phosphorus segregation: high P areas rejecting C seen in hot rolled sheet and plate. This is not necessarily detrimental, however.
For steels utilizing microalloying additions, the ratio of atomic percent microalloying element MAE to carbon percent determines the amount of MAE precipitate formed at a given low temperature. Here, both cold rolled and annealed sheet steels rely on carbon content being under 0. Carbon increases the strength of hot rolled steels but decreases the notch toughness, ductility and weldability. Reference Vanadium, Columbium, and Titanium for details on carbon's use in continuously cast and hot rolled steels.
Essentially carbon-free steels such as the maraging grades are heat treated as well, but these are special cases, which will not be considered here.
Unless added for specific reasons, e. Carbon dissolves in iron, but the solubility limits depend on crystal structure. High temperature d-ferrite can contain up to 0. Less than 0. The iron-carbon equilibrium diagram Fig. At C F , d-ferrite containing more than 0. Iron containing more than 2. At C F , austenite decomposes eutectoidally into the lamellar composite, pearlite.
Carbon lowers the allotropic g - a transformation temperatures from C F for pure iron to the eutectoid temperature at 0. Below the eutectoid C, F , carbon has a strong influence on the kinetics rate of pearlite formation and reacts with iron to form the nonequilibrium phases bainite and martensite.
Pearlite forms at higher temperatures, between about C F and the eutectoid temperature, becoming increasingly finer in structure as the transformation temperature is lowered. Between roughly C F and the lower limit of the pearlite formation range, austenite transforms to bainite, of which there are two main types: Upper bainite is formed at higher temperatures.
It has an acicular structure containing cementite particles oriented along the boundaries of the ferrite regions. Lower bainite is also acicular, though much finer in structure. In it, the carbide particles are oriented across the ferrite regions, a fact that contributes to its higher toughness. The temperature dividing upper and lower bainite is a function of composition, especially carbon content.
Both bainites grow at rates determined largely by the diffusion of carbon in iron. The diffusionless, or shear, transformation of austenite to martensite at temperatures below about C F is the most important reaction in commercial heat treating. The martensite start, or MC as the eutectoid composition is approached.
If the product application requires a hard, wear resistant surface but a tougher, more ductile core, the steel may be carburized. In this process, carbon is intentionally diffused into the surface layer of a low carbon steel, normally to a depth not exceeding a few thousandths of an inch.
Carburizing is carried out at about C F , and it is important that the steel's composition allows it to remain fine grained at this temperature. After carburizing, the steel will be heat treated as usual.
A full listing of their applications is obviously impossible. Carbon steels are used as castings and forgings, pipe and tubes, sheet and plate, wire, rod, rails and structural shapes. Carbon steels are, of course, the least expensive ferrous alloys and designers will endeavor to specify them unless specific properties necessitate the use of more expensive alloy grades. Carbon steels may be classified in several ways.
Many of these standards identify the same steels by their own individual specifications. The individual user may choose to add such requirements to any general specification to suit his needs. Many large users, such as automotive and construction equipment manufacturers, prefer to establish their own standards, which may be more restrictive than those published by national organizations. Sheet steels tend to have the lowest carbon levels under 0.
In general, ultra-low carbon steels include high formability sheet steels with carbon under 0. Low carbon steels include most hot rolled strip, plate and pipe with 0. Medium carbon steels include the forging grades with 0. The high carbon steels include rail steels with over 0. In decreasing order or abundance, other important members of this series include lanthanum, neodymium, praseodymium and yttrium. While several rare earth metals REM have commercial applications in the electronics and glass industries, they are supplied to steelmakers cost effectively only in the form of mixtures of the metals or their compounds.
The following discussions will therefore deal with the REMs as a group. The REMs are, in fact, plentiful enough that several thousand tons of metal and compounds are used annually. The leading supplier country today is China. Mischmetal is an alloy of REMs with a composition corresponding roughly to rare earth concentrations in the ore, from which they are electrolytically extracted.
It is sold as precast canisters suitable for a plunging addition or as small piglets or pellets. Rare earth silicide contains approximately equal portions of REMs, silicon and iron. It is less reactive than mischmetal, and is not intended for plunging additions.
Silicide is sold in lump form, generally not finer than 1 in. Rather, their function is to control the shape of inclusions remaining in a steel which has already been deoxidized and desulfurized, and their efficient use depends strongly on prior treatments the steel has received.
When REMs are added to steel, no matter in which form, they combine with oxygen and sulfur, and with oxides, sulfides and silicates already present, in many cases reducing them completely. Recommended practice for highest recovery of REM additions includes the following: 1 establishing a tap sulfur content in the range 0.
For a well deoxidized steel, REM additions should be calculated on the basis of 0. For oxide inclusion control, total oxygen must be considered. In practice, therefore, REM additions will range 0. REM silicides are added to the second pouring ladle when reladling a heat, or to the ingot mold.
Addition is made to the pouring stream to insure adequate dispersion. Fines should be avoided as these have a tendency to clump. Tap silicon levels should not be near specified maximum values, due to the full recovery of silicon from this addition agent.
REM oxide fumes are generally believed to be non-toxic. Mischmetal additions are made by plunging precast canisters of the REM alloy into the ladle. Canisters of appropriate weight, depending on residual sulfur level, are attached to the end of a billet to provide deep immersion in the ladle.
The above recommendations regarding desulfurization, deoxidation, slag treatment and ladle temperatures apply. Further precautions against reoxidation are strongly advised. The fact that some reoxidation will invariably occur reduces recovery from plunging below that obtainable with ingot mold practice. If reoxidation is severe enough, sulfur will revert to the melt from REM oxysulfides. Mischmetal additions may also be made to the molds, lbs.
The REMs are known to cause severe nozzle blockage even worse than aluminum and their use with continuous casters is not recommended.
Oxygen content can get too low, allowing calcium sulfides to form. Sulfur is effectively controlled, even in low-Mn steels, and there is a greatly reduced danger of high temperature transverse cracking. Although REM treatment in the U. The hot workability of high chromium steels is also said to be improved by this treatment since the REMs refine the coarse grained structures these grades are known to exhibit.
The existence of REM carbides has been reported but their stability should be low compared to such normal alloy carbides as chromium, vanadium, columbium, etc. Sulfide, oxide and silicate inclusions can be soft enough at hot working temperatures to deform into long stringers oriented parallel to the hot rolling direction. Their presence is especially harmful to transverse ductility and impact strength since they act as infinitely sharp internal notches, or crack initiators.
They can reduce formability and lead to edge splitting during press-brake bending of wide sheets. A more serious problem is the lamellar tearing internal longitudinal splitting that occurs when heavy plates containing inclusion stringers are welded. The REM inclusions that form after rare earth treatment of a deoxidized, low sulfur steel are harder, and have a higher melting range, than the inclusions they replace.
They do not deform during hot working but remain globular even through the unidirectional deformation seen in a hot strip mill. Without inclusion stringers, the steel will have transverse and through-thickness ductility and toughness essentially equal to the normally higher longitudinal properties. This lack of directionality is especially important in carbon and HSLA steels for automotive applications, and in the skelp and plate used to produce oil and gas transmission lines.
It has been known for some time that REMs can be used to modify graphite structures in cast iron. Original applications involved the use of REMs as nodularizing agents in hypereutectic irons, followed by claims they can improve the properties of grey iron by causing the formation of vermicular graphite.
It imparts corrosion and oxidation resistance, is a mild hardenability agent, improves wear resistance and promotes the retention of useful strength levels at elevated temperatures. Tool steels, superalloys and other specialty metals, though often high in chromium content, are produced in smaller quantities and therefore rank lower in over-all chromium application. Having almost no chromium ore deposits of its own, the U.
Kazhakstan has moderate reserves but a high chromium production rate. Turkey, Finland and Brazil supply significant tonnages as well. Chromium is relatively abundant in the Earth's crust but, on occasion, political and economic factors have created an artificial shortage. As a result, chromium conservation has been the subject of intensive study.
While such programs may have limited effectiveness, the unique properties of chromium as an alloying element, such as in the stainless steels, will doubtless keep demand high. The remaining chromium is most commonly supplied as ferrochrome, of which several grades are commercially available. The principal impurities in ferrochrome are carbon and silicon. As is often the case, carbon level is most important in determining the price differential between the various ferrochrome grades.
Low carbon ferrochrome, once quite common, is now added mostly for final chemistry adjustments in the production of stainless steel.
Another low carbon ferrochrome alloy once widely used is ferrochrome silicon. It is used in the EAF to maintain silicon levels in the bath to prevent chromium oxidation and for final chromium adjustments. High carbon ferrochrome, or at least the grades commonly designated charge chrome, remains the most widely used chromium addition for the production of stainless and alloy steels.
The reduced availability of the high Cr:Fe ores made the lower cost, low Cr:Fe ratio ores from South Africa more attractive and forced the steel industry to make the change to the widespread use of charge chrome. Carbon and silicon have an inverse relationship in smelting ferrochrome, i.
The industry has developed a large number of specialty compositions to serve the needs of a variety of applications. As an example, low carbon ferrochrome can be supplied in a range of carbon grades from 0. Induction furnace production of ELC stainless would be a typical application, whereas the intermediate grades of 0.
Other applications for special composition low carbon ferrochromes are the low carbon, low nitrogen ferrochrome and the low carbon, low nitrogen, low silicon ferrochrome. These latter two low carbon ferrochromes have frequently been used as a substitute for chromium metal in the production of certain high temperature or nickel-base specialty alloys. Reactor grade ferrochrome is a low carbon ferrochrome with a very low cobalt content. It can be used as a substitute for chromium metal in the production of nuclear equipment components.
Refined high carbon ferrochrome provides a ferrochrome with both low silicon and titanium contents. A low phosphorus grade of charge chrome is available to control phosphorus levels in stainless and high alloy steels, when needed.
Ferrochrome silicon was originally developed as a process ferrochrome to be used in the production of low carbon ferrochrome. It was subsequently introduced to wrought stainless steel producers in the s as a lower cost form of low carbon ferrochrome. The use of these alloys has also declined in direct relationship to the growth of AOD refining. Nitrogen-bearing low carbon ferrochrome provides a simple means of making a nitrogen addition to chromium bearing steels, particularly conventionally melted stainless grades.
These grades of stainless can also be produced economically with elemental N2 in the AOD. Pure metallic chromium metal is produced both aluminothermically and electrolytically. The vacuum grade of electrolytic chromium requires a second stage of carbon reduction refining which is not required for the vacuum grade of aluminothermic chromium.
Chromium metal is used primarily in superalloy, high temperature and other alloys in which tight restrictions on residual elements found in ferrochrome prevent its use, i. Other binary aluminothermic chromium alloys available for special alloying requirements are high carbon chromium and chromium molybdenum. Iron foundries occasionally use chromium briquettes in cupola melting; however, lower cost crushed charge chrome as a ladle addition has largely replaced this practice. Standard sizes of ferrochrome range from 8 in.
Bulk delivery is most common although smaller packaging in super sacks or drums is available, especially for higher unit cost grades. Chromium-containing HSLA steels, ferritic stainless grades and even some tool steels may be produced in the BOF using a charge of hot metal, scrap and alloy addition agents, including charge chrome. In all practices, however, proper selection of charge materials, careful process control - particularly with regard to slag chemistry - and precise analytical techniques will result in maximum chromium recovery.
Thorough surface conditioning is important. Heating for hot working must be performed slowly since stainless steels have considerably lower thermal conductivity than plain carbon steels.
Rapid heating can lead to surface burning. Soaking should generally be performed above C F but specific ranges vary with the grade in question. Overheating should be avoided at all costs since excessive grain coarsening to which the stainless steels are particularly sensitive can lead to difficulties in rolling or forging. Ferritic and martensitic stainless grades series hot roll and forge quite easily.
Austenitic grades series , on the other hand, are stiffer at high temperatures than carbon or alloy steels and will exert greater roll stresses for equivalent reductions.
Austenitic stainless steels may be rolled at normal rates after hot working: the air hardening martensitic grades should be cooled slowly to avoid the likelihood of thermal cracking during subsequent conditioning, where applicable.
All stainless steels are annealed prior to cold working. Further, chromium has a strong tendency to form hard and stable carbides. This property gives chromium steels the ability to resist softening during tempering and makes the resulting products hard and wear resistant. However, it also means that for a given hardness level, chromium steels will require somewhat higher tempering temperatures, or longer tempering times, than their plain carbon counterparts.
This effect increases with increasing chromium content. Tool steels, and alloy steels containing significant quantities of carbide-forming elements such as chromium, require higher austenitizing temperatures in order to dissolve the carbides completely. As in the case of stainless steels, chromium has a tendency to promote grain growth, therefore careful control of austenitizing temperatures is important in chromium alloy and tool steels. Some chromium steels contain vanadium to counteract this phenomenon.
Chromium and nickel-chromium alloy steels are particularly susceptible to several heat treatment-related embrittlement mechanisms. These should be understood and care taken to avoid them. Temper embrittlement is the loss of ductility or increase in ductile-to-brittle transition temperatures after tempering in the range of C F or slow cooling through this range.
It is now known to be related to impurities such as phosphorus, tin, arsenic and particularly antimony. Unless special care is taken, these impurities are invariably present in sufficient concentrations to cause damage. The presence of more than 0. Unless otherwise impossible, as in the slow cooling of large forgings or castings, care should be taken to avoid the dangerous temperature range.
Aluminum tends to reduce this problem, but 0. In martensitic stainless steels, the critical temperature for embrittlement is raised to about C F. It can be cured by heating to temperatures above the embrittlement range for several hours.
Sigma phase embrittlement results from the precipitation of the iron-chromium compound FeCr after holding austenitic or ferritic stainless steels for long periods of time in the range C F. Slow cooling from the range C F produces the same effect, as does quenching from this range followed by subsequent heating in the range C F.
It is found in chemical, food processing, architectural, automotive and other decorative and functional applications. Like the remainder of the series, it is austenitic in structure and does not transform to martensite on cooling from elevated temperatures.
Thus, Type L has carbon restricted to 0. Many stainless grades, series and others, may be modified with additions of sulfur or selenium for improved machinability. Type is the most popular of the ferritic stainless steels, and has been widely used in automotive exhaust systems and fuel tanks. Lacking nickel, it is less expensive than the austenitic grades. Type , a martensitic grade, and its lower silicon modification, Type , are extensively used for steam turbine blading and for such mechanical uses as valve parts, pump components, shafts and screens.
Cutlery is manufactured from Type C, a martensitic stainless high in both chromium and carbon. Chromium imparts hardenability, wear resistance and a measure of corrosion resistance.
Bearing steels, such as AISI , contain up to 1. Carburizing and nitriding steels contain chromium as in the Nitralloy series since chromium has a strong affinity for both carbon and nitrogen. Here, chromium is usually used in combination with other strong carbide or nitride formers such as vanadium, aluminum and molybdenum to form thin but extremely hard nitrided cases.
Chromium improves the resistance of steels to hydrogen attack. Chromium and chromium-molybdenum steels have long been standard materials in applications where hydrogen-bearing atmospheres are present: petrochemical plants, petroleum refineries, power boiler tubing, etc. It is believed that chromium carbide, being stable at elevated temperatures, resists the strong reducing power of hydrogen present in these environments.
The presence of chromium carbide also gives structural steels the ability to resist softening at elevated temperatures. This leads to greater creep and stress-rupture resistance. Steels selected for elevated temperature service will contain increasing amounts of chromium and molybdenum depending on the expected service temperature.
Chromium contents may range from a minimum of 1. Chromium is the most important element in tool steels, after carbon. Besides imparting hardenability, chromium forms a variety of carbides depending on composition and heat treatment. These carbides, along with those of vanadium, molybdenum and other constituents, provide the necessary wear and abrasion resistance.
As mentioned above, chromium does have a tendency to promote grain growth, and since most tool steels require high austenitizing temperatures, vanadium is frequently added as well. Its behavior is similar to nickel, in that it forms a complete series of solid solutions with iron at elevated temperatures and is also extremely soluble in ferrite.
It is a potent ferrite strengthener; this solid solution strengthening persists to quite high temperatures, and cobalt is therefore found in several grades of high speed tool steels, among others.
Like nickel, cobalt is ferromagnetic. This led to its use in a series of magnetic steels as well as the widely-used Alnico alloys. About one-quarter of the cobalt in the U. To a certain extent, it is interchangeable with nickel in this regard. Because of the high cleanliness standards imposed on these latter alloys, many of them are produced by specialty-alloy and stainless steel mills.
Although large reserves are known to exist around the world, cobalt has often been in short supply - occasionally to the point of allocation. Political unrest in Africa and labor disruption in affiliated nickel production see Nickel have been major contributors to the cyclic supply situation.
The U. Purity generally depends on the means of production, but grades in the range While not strictly an addition agent, scrap must be considered as an increasingly important source of cobalt. Unfortunately, superalloy scrap often contains high concentrations of nickel and is therefore not acceptable for tool steel production: however, maraging and ultrahigh strength steel producers can benefit from this additional source, as can suppliers of the superalloys themselves.
Cobalt oxide is readily reduced in all but the most oxidizing steel baths and may be added to the electric furnace or the AOD see Nickel. More common practice in tool and alloy steel production, however, is to melt down a high scrap charge, adjusting final cobalt values with virgin metal. The thermal strength of the quartzite for example is of special importance, because it is connected to the gas permeability of the charge where too much fine sized material may prevent gas flow.
The carbon quality is important for the environmental performance of the process, because the coal and coke contains normally sulphur and some other unwanted elements. If for instance carbon contains mercury or other vaporous elements, they will evaporate in the process and will be transferred as part of the off-gas into the environment. Production of Ferro-silicon, Silicon Metal and Silico-calcium.
Raw material is normally supplied to or closed to the plant by truck and train. Several ferro-silicon and silicon plants are located near the sea or a river where boats are mainly used for transportation of raw materials and products.
The loading and unloading of raw material is done with the use of crane grips, front-end loaders or dumper trucks. The different raw materials that are used for the Si, FeSi and SiCa-production are preferably stored on hard surfaces in order to prevent contamination.
The reductants are normally stored indoors, to avoid the material from humidity caused by rain. Some of the reductants can have self-igniting characteristics. In these cases, appropriate ways of surveying have to be implemented to avoid self-combustion, e. Ferro-silicon, silicon metal and silicon-calcium are commonly produced in low-shaft three phase submerged electric arc furnaces.
The electric arc furnaces can be of the open or semi-closed type. The furnace normally rotates e. The rotation gives rise to some difficulties in obtaining good capture efficiency of the fugitive emissions at the tap-hole as the location of the tap-hole will rotate with the furnace.
A typical electric arc furnace for the production of ferro-silicon is shown in the following figure. The limitations of the process are that the impurities, such as, aluminium and calcium in 74 to 76 percent ferroalloy should not be more than 0. Because of the patented nature of the process the information is not available in detail.
However the patent claimed that there is no substantial silicon loss. Wise reported in the refining of ferro-silicon by injecting chlorine deep inside the ladle of molten bath.
Chlorine injection was carried out by hydraulically operated dispenser tubes. The author reported that chlorine requirement was of the order of 30 parts per parts by weight of the melt. During the process the silicon level got reduced because of volatilisation to silicon tetrachloride and calcium chloride level thus formed cannot be removed completely.
Silicon level had to be replenished for adhering to the required composition. Further removal of aluminium level to less than 0. The slag of composition CaO. The slag was removed and refined metal was separated. Mere the aluminium level in FeSi was brought down from 1. The term SLAG for the molten oxide is analogy from the production of other metals, where the ore normally contains more of impurity elements that are less nobler than the metal that is to be produce.
The main metal is extracted as metal phase and the less noble impurities are left as slag which is normally the mix of impurity oxides and being in molten form can easily be separated from the metal phase. When sufficient heat is available, all the oxygen in the bottom deposit will evaporate, while pure Si-SiC will be left to form deposits at the furnace bottom at normal operating conditions.
An optimum carbon content in the burden gives a maximum silicon recovery at operational conditions. If the carbon content is lower than the optimum, all the SiC intermediate is consumed, but the loss as SiO is higher than at the optimum. Some SiO is lost even all the optimum carbon content.
If the carbon content is increased beyond the optimum, the loss as SiO will decrease, but the silicon loss as SiC more than balances the gain. This SiC is deposited at the furnace bottom and when deposit becomes too large it will obstruct the operation severely.
The optimum carbon content depends on the state of the furnace. Operation needs to be observed continuously to determine the carbon input close to optimum. Work on process optimisation has illucidated the problem of fines generation during this crushing process.
Fines, defined as having a particle size under 10mm, are likely to be trapped in the slag, while coarser materials would need a longer dissolution time.
Thus fines resulting from any crushing process can be sold only to a limited extent or at a low price. A Bridgman furnace has been used in order to allow for a certain uncoupling of the growth rate and the temperature gradient. Such a furnace has a hot and a cool zone as seen in figure 1.
The distance between these zones and their temperatures determines the temperature gradient. A crucible is translated through this temperature field at a uniform rate growth rate.
The heater is made of an induction coil connected to a 12 kW high frequency generator. The frequency varies from kHz to 1,3 MHz depending on the dimensions and the physical properties of the workpiece and has not been measured in this study. Indirect induction heating has been achieved by surrounding the sample by a susceptor. The susceptor consist of a MoSi2 tube with the same length as the coil inside which it is placed.
It is believed that the susceptor absorbs all the power of the induction field thereby efficiently shielding the sample as it is heating it. The penetration depth of the induction field has been calculated to be 0,5mm and the thickness of the susceptor is about 12 mm.
The sample is molten in the hot zone of the furnace and solidifies before it enters the cold zone. Samples are typically 20 cm long and have a diameter of 8 mm. They are prepared from a mixture of solar-grade silicon and pure iron that are molten by induction heating in a graphite crucible, and then cast by sucking into quartz glass tubes by vacuum.
Pure calcium and pure aluminium are added for the impurity containing ferrosilicon. The carbon contamination of the sample is estimated to be below 0. Elemental mapping in an electron micro-probe has been carried out to determine the distribution of the additional elements Al and Ca. The calcium distribution could not be analysed probably because of a too low concentration.
The aluminium distribution has been found to be dependent on the growth rate and is probably related to the growth of the intermetallic cells.
In the samples containing very clear intermetallic cells, aluminium is segregated on the boundaries of these cells. At low growth rate, aluminium seems to be more soluble in the intermetallic. In any case, the solubility in silicon is very low and not detected by this method. Ferro-nickel FeNi as well as ferro-chrome is the major alloying agent in the production of stainless steel.
Laterite ore is the main raw material. Laterite ore is characterised by a relatively low nickel content 1. Besides laterite ore, coke or coal is the second raw material that is needed in the ferro-nickel production.
Coke or coal is used as a reducing agent because the ferro-nickel production takes place by a carbo-thermic process. FeNi can also be produced from secondary raw materials, such as spent catalysts and sludge from the galvanising industry. The production of ferro-nickel from primary raw material is carried our exclusively by the rotary kiln-electric furnace process.
As mentioned before the raw material carries a significant amount of water, therefore the first step of the process is a drying operation. The next process step is homogenisation where the different ores are mixed with coal and pelletised dust, which is recycled from the main process. The dry feed mix is then fed to a rotary kiln. The rotary kiln is used to de-hydrate the ore by calcination and to pre-reduce the nickel and iron oxide.
The hot pre-reduced calcine can be introduced directly to the smelting furnace or by insulated containers. The containers may be used for two reasons, first to conserve the heat and second to add coke or coal required for complete reduction before they are discharged into the electric furnace, where or melting and final reduction occurs.
Ferro-nickel smelting today only takes place in electric arc furnaces. In the electric furnace the reductive smelting operation occurs by the combined action of carbon electrodes and added solid carbonaceous reductant. The slag melting temperature in the ferro-nickel smelting process is strongly dependent on the FeO-content.
The operation mode of the furnace therefore changes if the slag melting temperature is above or below the melting temperature of the metal. If the melting temperature of the slag is higher than the melting point of the metal the furnace can easily be operated with a covered bath. In this case the electrode tips are not immersed in the slag and the final reduction of the nickel and iron oxides takes mostly place in the hot charge which covers the slag layer.
If the melting temperature of the slag is below the melting temperature of the metal the furnace is more difficult to operate. In order to reach the melting temperature of the metal the electrodes should penetrate deep in to the slag layer. The highest bath temperature will then be around the electrode tips where smelting takes place in the slag-metals interface.
These operating conditions result in a high generation rate of CO-gases, which requires an open bath surface around the electrodes. To reduce a high content of nickel oxides commonly the burden contains an excess proportion of carbon. These also increase the amount of iron that will be reduced and the final carbon content of the crude ferro-nickel.
To reduce the iron and carbon content a further refining step is necessary. To avoid further refining several process improvements had been made. The electric furnace produces a molten ore, which is reduced to ferro-nickel by using ferro-silicon in a further ladle furnace. In the shaft furnace a briquetted ore is reduced with a reducing gas low sulphur naphta.
The subsequent electric furnace is then only used to melt the metal and to separate it from the slag. Ferro-nickel produced by the conventional process needs further refining. Besides the reduction of iron and carbon, the impurities like sulphur, silicon and phosphorus should be removed. For ferro-nickel refining a variety of equipment is available e. The purified ferro-nickel is cast into ingots or granulated under water.
The dust containing off-gas from the rotary kiln, the electric arc smelling furnace and the refining step is treated by an appropriate abatement system. The dust content can be pelletised and recycled to the raw material blending station. A flow sheet of a ferro-nickel production is presented in the above figure.
FeNi can also be produced from nickel containing residues used as secondary raw material. These residues, mostly spent catalysts from the grease production, are burned in a rotary kiln in order to concentrate the Ni-content as Ni-oxide in the flue dust. The flue dust containing off gas is cleaned in a membrane bag filter, where the collected dust is used as the raw material for the smelting process. The production of FeNi then takes place in a submerged electric arc furnace.
The molten alloy is tapped, granulated in water and packed in drums or big-bags for supply. During the last 4 decades, we supplied around 40 furnaces. It should be mentioned that the furnace in New Caledonia represents the best available technique for producing FeNi.
The customer has already announced his intention to purchase a second furnace with an identical power rating of 99 MVA. The availability of two container transfer cars and two hoists for each bin line ensures interchange ability of these components and therefore allows uninterrupted furnace operation even if one of the transfer cars or hoists fails. The solution provides the highest flexibility and allows a clear definition of the paths for incoming raw materials and outgoing products.
This system has proved its effectiveness on a large scale in several of our reference plants and yields the best flexibility. The tapping machines are of great importance. We provide a liter and a liter machine. The machines will also be installed in the new rectangular furnaces for Onca Puma in Brazil.
The process gas produced in the electric furnaces is completely combusted inside the furnace and at the same time by the addition of diluting air cooled down 10 approx. This concept avoids any formation of an explosive mixture of carbon monoxide and air inside the furnace and the build-up of accretions in the off-gas duct due to post combustion.
To minimize the capacity of the de-dusting plant, the off gas is routed through a water-cooled duct. After leaving this part of the duct, further cooling of the off gas is effected by hair-pin coolers. Before entering the filter bag house, the off gas temperature is decreased to the allowable entrance temperature by quenching with the secondary fumes collected via hoods above the metal and slag tap holes.
The submerged arc furnaces use Soderberg electrodes where the electrode may be formed by hot paste, briquettes, blocks or paste cylinders. The electrode paste is charged on top of the electrode in accordance with its consumption.
The material is subject to increased heat as it moves downwards in the electrode column. To control the smelting process the furnace operation can be based on resistance or current control, so that the electrodes are lifted and lowered when necessary to keep resistance or current constant. This means certain requirements to the electrode sealing to prevent air leakage into the furnace. As an alternative another practice is commonly used where the electrode moves only during slipping and otherwise stand in place.
During the smelting process the metal oxides are reduced by the coke, with metal carbides as the final product. The reduction produces large volumes of CO gas from the reaction zone under the electrode tips. In an open furnace the CO gas is burned at the surface of the furnace. By using a closed, sealed furnace the volume of the off-gas can be reduced by a factor of and by the factor of in case of a semi-closed furnace. The investment cost for the off-gas cleaning systems for closed furnaces are much lower than for open furnaces.
The cleaned CO-gas can be used as fuel for raw material preheating, coke drying and similar processes, substituting oil or other fossil fuels. Energy can be recovered from semi-closed furnaces in the form of steam or hot water.
LC FeCr can also be produced by the so-called Simplex process. Silico-chromium is also used as an alloying element in the steel industry. It can be produced in the same kind of three phase submerged electric arc furnaces as used for HC FeCr production. The high generation rate of CO makes it important to use a porous burden e.
Ferro-silicon, silicon metal and silico-calcium SiCa are used as additives in different industrial activities. Vanadium alloyed steel is therefore used for high speed cutting tools. Ferro-vanadium FeV can be produced by a carbo-thermic or a metallo-thermic reduction of vanadium oxides, assisted by the presence of iron. Because carbon is used in a carbo-thermic reduction, the final carbon content of the produced alloy is high.
The production of ferro-vanadium by using carbon as a reducing agent is therefore only possible if there are no requirements for a low carbon content. All rights reserved.
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