Iron ore is the hematite Fe2O3 or Fe2O3. FeO which is magnetite Fe3O4 as a rule. Other iron ores are FeCO3 and FeS2, limonite, and Siderite. Hematite is in fact the principal ore used for the production of iron and steel.Â
Ferrous Metals:- These are the most important metals known for their strength wide ability and ease of forming and machining. A wide range of properties can be obtained by suitable alloying. According to the percentage of carbon present these are classified as wrought iron, cast iron and steel.
Types of Irons
1.0 Wrought Iron
This is almost pure iron with a low carbon and manganese contact. Wrought iron is not normally considered a corrosion-resistant material. It has, however excellent resistance to atmospheric corrosion. Similarly, alkalis and alkaline solutions concentrated and cold sulphuric acid and organic compounds cause a minimal attack on the metal.
Uses of Wrought Iron
It is found to be extensively used at elevated temperatures.
1. Steam supply lines.
2. Condensate return lines,
3. Heating coils.
4. Exhaust lines.Â
5. Smoke stacks are the same as the typical high-temperature applications.
2.0 Cast Iron
This is usually 2.5 to 4.5% carbon. In general, it is cheap and easy to cast even in complicated shapes because of its fluidity in the molten state. Cast iron can be classified into two types. (i) Grey cast iron, (ii) white cast iron, depending on the form in which the carbon is distributed in iron. In grey cast iron, the carbon is in the form of graphite, distributed as free crystals throughout the iron. White cast iron has a chemical combination of iron and carbon. The formation of the two types of cast iron depends on the rate at which it is cooled from the molten state.
(i) Grey Cast IronÂ
The compressive strength is about 3 to 4 times its tensile strength and the hardness number is between 180 and 240 on the Brinnel Scale. Generally cast iron has no outstanding resistance to acids or acid solutions. It is not corroded by alkali solutions of less than 30% concentration at any temperature.
Applications of Grey Cast Iron
Its applications are in pumps and valves, special piping, acid coolers, acid reactions and concentration vessels. Many reaction kettles and vats were made of enamelled cast iron in the older days.
(ii) White Cast Iron
Due to its highly brittle nature, it is seldom used as such. Usually, grey cast iron is chilled to produce a hard superficial depth of white cast iron. It is used in such parts as furnace bars, teeth and jaws of crushing and grinding machines. Such components have good wear resistance. White cast iron can be made malleable by heat treatment. The resultant castings can withstand shocks better and are used for pipe fittings, gear wheels, housing, pulleys, etc.Â
A high-duty cast iron can be produced by the use of small quantities of calcium silicide. The resultant structure after heat treatment has a better tensile and shear strength. It is used for the fabrication of pressure vessels and high-pressure and temperature pipes and fittings.
3.0 Alloy Cast Iron
The basic properties of cast irons have been improved by alloying and by changes in foundry methods, which have extended their range of applications. Since alloy casting possesses good mechanical properties coupled with good corrosion resistance, they are exceedingly useful to process industries.
High silicon iron is very hard and brittle, which makes it exceedingly difficult to match as well as vulnerable to mechanical shock and excessive strain. The superior degree of chemical resistance makes these cast irons extremely useful in severe applications. They are practically unaffected by sulphuric acid at all temperatures. Hot strong nitric acid does not affect this material. In addition, 3% molybdenum imparts a high degree of resistance to attack by hydrochloric acid and chlorine-containing chemicals. High silicon irons are not attacked by atmospheric conditions.
Although high silicon cast irons have excellent chemical resistance they have poor mechanical properties. The addition of silicon and a small percentage of copper and nickel give an alloy of superior mechanical properties and good chemical resistance. It has resistance to most organic compounds and solvent, alkalis and phosphoric acid. It also resistant to atmospheric oxidation flue gases, hydrocarbon as wellas wet and dry ammonia.
A series is of alloy cast irons containing varying percentage of high nickel with copper and chromiumare known as Ni-resist which possess a unique combination of engineering properties such as corrosion resistance, wear resistance, strength, heat resistance, toughness, good castbility and machinbilty.