Iron Ores

                               Iron Ores Iron ore is a type of minreral and rock from which metallic iron is extracted economically. This ore is normally rich in iron oxides and vary in color from dark grey, bright yellow and deep purple to rusty red. The iron itself is usually found in the form of magnetite (Fe3O4), hematite (Fe2O3), goethite (FeO(OH)), limonite (FeO(OH).n(H2O)) or siderite (FeCO3). Different types of iron ores are shown in Fig 1 Fig 1 Types of Iron ores The main ores of iron are hematite (70% iron) and magnetite (72% iron). Ores carrying very high quantities of hematite or magnetite (greater than 62% of Fe) are known as “natural ore” or “direct shipping ore”, meaning they can be fed directly into iron making furnaces. Taconite is low grade silica rich iron ore containing up to 30% magnetite and hematite. This deposit can be processed to produce a concentrate of Fe around 65%. This ore is a major source of iron in USA, Canada and China. Magnetite is also known as magnetic iron ore because it is easily attracted by a magnet. It is a heavy black mineral with metallic luster. Hematite is a steel-gray to iron- black colored mineral which is as hard as magnetite (Moh’s scale hardness is 5.5 to 6.5) but slightly less heavy (usually specific gravity varies from 5.0 to 5.3). It has also a metallic luster. The three primary sources of iron ore are banded iron formations, magmatic magnetite ore deposits, and hematite ore. Banded iron formations (BIF) – These are fine grained metamorphosed sedimentary rocks composed predominantly of magnetite and silica (as quartz). Most of the iron ore is extracted from banded iron formations, the geological structures laid down mostly between 3 and 1.2 billion years ago. Blue...

Chilling of Blast Furnace – its causes and recovery Mar31

Chilling of Blast Furnace – its causes and recovery...

Chilling of Blast Furnace – its causes and recovery The chilling of a blast furnace is a very serious happening during the operation of a blast furnace. The revival of a chilled blast furnace is a big herculean task and it takes a very long time and needs a lot of patience to bring back the furnace to normal condition. In case of hearth chilling, it is not possible to tap liquid slag and hot metal, since the temperature in lower part of the blast furnace becomes very low and the connection between the tap hole and tuyere is lost. This is due to the solidification of the liquid slag which obstructs the liquids flow to the hearth. The chilling of blast furnace is varying from minor to very severe. The chilling of a blast furnace is minor when connection between tuyere and tap hole is lost but there is sufficient heat in the hearth. When the hilling becomes more severe, the hot metal also starts solidifying. In case of most severe chill the hot metal in the hearth also gets solidified. A severe chill in a blast furnace is shown in Fig. 1                       Fig 1 Severe chill as seen from a tap hole Causes of blast furnace chilling Normally blast furnace should give warning signals before furnace shows the symptoms of chilling. The warning signals will consists of Reduction in wind volume and slow burden movement due to furnace running cold Very frequent hanging and slipping in the furnace Temperature of tapped hot metal and liquid slag is lower than normal Tapped liquid slag is viscous and not moving in the runner. Water coming out from the tap hole Blocking of tuyeres and blow pipes with slag or slag-metal mixture Excessive build up...

Cast Iron

                         Cast Iron The term “Cast iron” identifies a large family of ferrous alloys. These are primarily iron alloys which contain 2% or more carbon and from 1% to 3% silicon. The properties of cast iron can be varied widely by varying the percentages of carbon and silicon, by alloying with various metallic elements, and by varying the practices of melting, casting, and heat treatment. Cast iron in its basic form is a brittle material which has a very little impact strength. It has a little or practically no toughness when compared to low carbon steels.  It has a fraction of the tensile strength of low carbon steels.  When a cast iron piece fails it will not deform in a noticeable way and appears to snap apart or break in a manner consistent with a snap.  There is no early warning of a failure. The graphite phase is pure carbon and acts as a natural defect in the material.  The iron is so saturated with carbon that graphite forms (free carbon) and causes the cast iron to be weaker.  Much smaller amounts of carbon is combined with iron (Fe) in the form of iron carbide (Cementite) which is hard and brittle. Cast irons can be classified as either unalloyed cast irons or alloy cast irons. Unalloyed cast irons are essentially iron-carbon-silicon alloys containing small amounts of manganese, phosphorus, and sulfur. There are other specialty cast irons like austenite gray cast iron and inoculated cast irons.  Cast iron can be alloyed as in carbon steels with elements like Chromium (Cr) and Nickel (Ni) etc. There are basically five types of cast irons. These are gray, ductile, malleable, compacted graphite, and white iron. Except in the case of white cast iron, all other cast irons have...

Refractory lining of a Basic Oxygen Furnace Mar28

Refractory lining of a Basic Oxygen Furnace...

Refractory lining of a Basic Oxygen Furnace The purpose of a refractory lining in a basic oxygen furnace is to provide maximum furnace availability during operation of the converter in order to meet production requirements and to ensure lowest possible specific refractory consumption. For this it is essential To optimize lining design To optimize lining maintenance practices To have good technological discipline during converter operation Typical refractory lining is shown in the converter cross section in Fig 1.               Fig 1 Refractory lining of a converter with removable bottom (Cross section) Lining design Wear of refractory lining is due to either the individual or the combined effect of the following agents. i)             Corrosion due to chemical attack of slag ii)            Temperature iii)          Oxidizing atmosphere iv)           Impact and Abrasion v)            Mechanical damage during deskulling Due to varying action of these agents there are many wear areas in the converter Theoretically the refractory lining of a converter is to be designed by the refractory type and different thicknesses so that no material is wasted at the end of the converter campaign. These   mean all the zones (Fig 2) of the converter lining is worn out to the stopping thickness at the same time. But in practice this does not happen and the refractories in some zones are worn out faster than the refractories in other zones. A balanced lining design is always aimed to improve lining life at the optimum refractory cost. A balanced lining is the lining where different qualities and thicknesses of refractories are used in different zone of the converter after careful study of the wear pattern of the refractories in the converter. This type of lining is also called zonal lining since in such type of...

Glossary of terms used for defining steels...

Glossary of terms used for defining steels Abrasion resistant steels – These are alloy steels suitable for applications where resistance to wear is a critical demand. Examples of such applications may include resistance to hard particles grinding under a surface sliding over the top of the steel surface, or resistance to impact from rocks and other hard and heavy materials, or resistance to high velocity abrasive dust and other particles. Boron, Manganese, Nickel, and Chromium are the alloying elements used to make it wear resistant. Acid steel – It is the steel made by an acid process. Advanced high strength steels – These are basically steels for auto body with very high strength to weight ratio. Their mechanical properties evolve from their unique processing and structure. Such steels are produced by controlling the cooling rate, from the austenite or austenite plus ferrite phase, either on the run out table of the hot rolling mill (for hot-rolled products) or in the cooling section of the continuous annealing furnace (continuously annealed or hot dip coated products). Air hardening steels – These are alloy steels which may be hardened by cooling in air from a temperature above the transformation range. Such steels attain their martensitic structure without going through the quenching process. Additions of chromium, nickel, molybdenum and manganese are effective toward this end. Aluminum killed steel – It is a type of steel which is produced when aluminum is used as a deoxidizing agent to remove oxygen from steel during its manufacture. Alloy Steels – Alloy or alloyed steels are defined by the ISO specification 4948/1 in the following manner. Alloy steels are those containing any element listed below in a quantity equal to or greater than the quantity for that listed element. Al-0.10%, B-0.008%, Bi-0.10%,...