Types of Steel and their Uses

At present, if engineers were to rebuild the Eiffel Tower, the steel required would only be one-third the amount originally used.

Iron is the most abundant element on the planet, occurring extensively throughout the Earth's mantle and the core. However, in its pure form, iron is very soft and readily oxidized to form iron oxide (rust). This quality hinders the use of this metal for a variety of purposes.

In order to overcome this drawback, up to 2% (by weight) of carbon is added to pure iron, to impart strength and durability to it. The material thus produced is called steel.
Steel is used widely in industries due to its hardness and high tensile strength. Trace amounts of other metals are added to impart different qualities to the steel.

It is classified based on the metals and elements added to it. There are more than 3,500 different varieties and grades of steels available today, each differing in their chemical, physical, and structural attributes. Over 75% of this variety has been produced in the past two decades, in response to the specific requirements of various industrial sectors.

This variant of steel contains a specific percentage (by weight) limit of other elements. It comprises 1% carbon, 0.6% copper, 1.65% manganese, 0.4% phosphorus, 0.6% silicon, and 0.05% sulfur. The varying range of carbon content in this alloy, gives rise to further four types.

Low Carbon Steel
It contains less than 0.30% of carbon. It is highly malleable and ductile, and has a low tensile strength. Its tensile strength can be improved by cold-rolling it between two polished rollers under high pressure conditions. It is used to make metal sheets, wires, boxes, cases, pipes, rivets,chains, vehicle frames, etc.

Medium Carbon Steel
It contains 0.30% to 0.60% carbon by weight. It is mildly ductile, and has more tensile strength than low carbon steel. It also shows resistance towards wear and tear. It is often hardened by subjecting it to heat treatment, called tempering. It is used to produce crank pins, axles, crankshafts, rails, boilers, etc.

High Carbon Steel
It comprises 0.60% to 1.0% of carbon. It is hard, strong, and brittle. Heat treatment yields a higher wear resistance in this type of steel. It is used to manufacture springs and high strength wires. It is also used in shock absorbing machinery.

They are characterized by addition of 10 - 20% weights of alloy metals like chromium, manganese, etc, to increase the strength, durability, and mechanical properties of the alloy as a whole. The different alloy steels produced depends on the element/metal alloyed with the steel.

It is strong, elastic, and has a high tensile strength. It is used to manufacture automobile and machine parts, safes, and rock crushers.

Vanadium imparts strength and hardness to the steel. It also causes the alloy to be resistant to corrosion, and have the ability to absorb shocks. It is used to produce objects which vibrate when in use, such as springs, axles, and gears.

It has a property called hot-hardness, which allows the alloy to remain hard and function in high-heat conditions. The hardness is even observed to be improved when the alloy is heated. It is wear-resistant, and is used to make cutting tools.

It is highly resistant to wear, strain, and shocks. It is used to produce the railway switches and crossings, jaws of rock and ore crushers, gears, and safes.

Tungsten increases the heat tolerance and the melting point of the alloy. It is used in machines and tools that have to withstand high temperatures.

It is used in the production of kitchen utensils, razor blades, containers, pressure vessels, surgical instruments, hot water tanks, wires, cables, machines involved in food processing, etc. It is classified into various types based on the crystalline structure and mechanical properties.

Ferritic Stainless Steel
This type contains chromium and trace amounts of carbon. The molecular structure resembles that of low carbon steel. It is not tough or hard, hence its applications are limited. It is characterized by its magnetic nature and by the ability to resist cracking in the presence of stress and corrosion.

Austenitic Stainless Steel
This is the most common type of stainless steel. It shows presence of nickel, manganese, and nitrogen. These elements impart the alloy with the ability to be welded and formed into any desired shape. It is however, susceptible to stress corrosion cracking.

Martensitic Stainless Steel
This type is similar to ferritic steel but has a higher carbon content (almost 1%). It exhibits high strength and moderate corrosion resistance. It is also magnetic and has a low weldability.

Duplex Stainless Steel
It is a combination of ferritic and austenitic steels in equal amounts. This enables the duplex steel to be stronger than both the components. It is resistant to corrosion, moderately weldable, and is weakly magnetic.

Precipitation Hardening Stainless Steel
This is a hardened variety of steel, that results from addition of 17% chromium and 4% nickel. Copper, niobium, and aluminum are also added in variable quantities. It is moderately resistant to corrosion, and can be molded to intricate shapes. it is also used in engine components and for nuclear waste casks.

It refers to the variety of steel alloys that are highly suitable to be used to make various tools and implements. The compositions vary according to the tool-specific quality required in the alloy.

High-Speed Tool Steel
It includes tungsten, vanadium, and molybdenum steel alloys that are hard and can retain this hardness when subjected to high temperatures. This ability makes it ideal for use in high-speed machinery and in tools such as drills, punches, reamers, taps, saws, etc.

Hot-work Tool Steel
It includes chromium, tungsten, and molybdenum alloys that can withstand heat for prolonged periods of time. It is used to make tools involved in forging, casting, extrusion, hot-shearing, and punching blades.

Cold-work Tool Steel
It includes alloys that show least distortion while hardening, which can be via oil or air. Lowered distortion is attributed to it due to its high chromium content. It is quite sturdy and does not crack easily. It is used to make knife blades,coining tools, stamping dies, etc.

Shock-Resistant Tool Steel
It contains low silicon, molybdenum, and carbon content. It is moderately tough and abrasive, and can resist shock at a wide range of temperatures. It is used to manufacture screwdrivers, chisels, punches, and tools used in riveting.

Mold Steel
It includes low carbon steels, which are used to make compression and injection molds for plastics. It is also used in zinc die casting.

Special-Purpose Tool Steel
It is a low alloy class of steels, that is characterized by a moderate toughness and malleable nature. It is used to produce taps, wrenches, and arbors.

Water-Hardening Tool Steel
It is the most widely used tool steel, due to its low cost. It is characterized by its need to be water quenched, in order to impart hardness to the object. It also exhibits a high resistance towards surface wear, and is used to produces files, hammers, cutters, blades, sledges, etc.

The American Iron and Steel Institute (AISI) in collaboration with SAE international has laid down a nomenclature system and a few guidelines that help classify, grade, and name each type and subtype of steel according to its various properties and composition. Steel varieties are ordered and produced according to these SAE steel grades.