1. INTRODUCTION
Ferrous materials contain iron and steel as their major constituents. The basic source of iron and steel is iron ore, an oxide of iron mixed with alumina, silica, phosphorous, and other materials. Wrought iron is the purest form of iron obtained from the blast furnace, although pure iron is tough to obtain. Iron can be alloyed with many elements, and alloys of iron and carbon are mostly used in many industrial applications. In this article, we will discuss them.
2. PLAIN CARBON STEELS
Carbon is the most important alloying element because it is found in all the alloys of iron. The maximum amount of carbon that can be alloyed with iron is 6.67%. Alloys containing upto 2% of carbon are termed steels or plain carbon steels. Their properties are influenced greatly by the increase in carbon content. The classes of steel are as follows:
- Low carbon steels(upto 0.30% of carbon)
- Medium carbon steels(0.30-0.60% of carbon)
- High carbon steels(0.60-1.70% of carbon)
2.1 LOW CARBON STEEL
This is also called soft or mild steel. They are ductile in nature with low tensile strength, and products such as screws, nuts, bolts, washers, and different machine parts can be made from low carbon steel. Carbon percentage varies upto 0.30%.
2.2 MEDIUM CARBON STEEL
They are less ductile as compared to low-carbon steels. These are widely used in the industry for making shafts, rail axles, gears, steering arms of vehicles, etc. Carbon percentage varies upto 0.30-0.60%.
2.3 HIGH CARBON STEEL
They are much harder than the other plain carbon steels. These materials are used to make tools such as wrenches, punches, files, bars, railroad wheels, etc. Carbon percentage varies upto 0.60 to approximately 2%.
3. CAST IRON
The ferrous alloys which have a carbon content of more than 2% are called cast iron. The practical value of the percentage of carbon normally lies between 2 to 4%. It is very brittle in nature and has a large number of industrial applications. Different forms of cast iron are:
- Grey cast iron
- White cast iron
- Malleable cast iron
- Ductile cast iron
3.1 GREY CAST IRON
When cast iron is slowly cooled, it decomposes into iron and carbon in graphite, called graphitization. This form of carbon is called grey cast iron. It is the cheapest form of cast iron and is widely used in beds of machine tools like Lathe.
3.2 WHITE CAST IRON
The graphitization does not occur when the cast iron is rapidly cooled; it is called white cast iron. It is highly brittle and not used for structural parts. They are used where high abrasive wear is present.
3.3 MALLEABLE CAST IRON
This form of cast iron has free carbon in the form of nodules. They are first achieved by chilling the casting so that white cast iron is formed, and the heat treatment process further transforms into nodules of free carbon. This material is more ductile as compared to grey cast iron.
3.4 DUCTILE CAST IRON
When the graphite present is small, the cast iron would have higher ductility, and thus it is called ductile cast iron. They have a better strength-to-weight ratio and better machinability. Many automobile components are being replaced by ductile cast iron.
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