Steel is an alloy, consisting mainly of iron, with a carbon content of 0.2% to 2.1% by weight. Though the use of carbon is most common for the production of this metal alloy, other alloying materials like tungsten, chromium and manganese are also used.
The proportions and forms in which these elements are used, affect the properties of the steel that is produced – increasing the carbon content, for instance, increases its strength. This fact is particularly useful for making different types of steel for different purposes – the strength of steel needed to make a beverage can is obviously different from the one needed to make railway tracks.
There are various types of steel, and the use of this alloy is widespread across industries and infrastructure owing to its many useful properties
es and characteristics.
Properties of Steel
1- Tensile Strength
Tensile strength is the amount of stress that a substance can take before becoming structurally deformed. The tensile strength of steel is comparatively high, making it highly resistant to fracture or breakage, which is a key point in its use in infrastructure building.
2- Ductility
One of the useful mechanical properties of steel is its ability to change shape on the application of force to it, without resulting in a fracture. This property is known as ductility, which enables it to be used in the making of different shapes and structures ranging from thin wires or large automotive parts and panels.
3- Malleability
Malleability is closely linked with ductility and allows steel to be deformed under compression. It allows this alloy to be compressed into sheets of variable thicknesses, often created by hammering or rolling.
4- Durability
The hardness of this alloy is high, reflecting its ability to resist strain. It is long-lasting and greatly resistant to external wear and tear. Hence it is considered a very durable material.
5- Conductivity
Steel is a good conductor of heat and electricity. These properties make it a good choice for making domestic cookware, as well as electrical wiring.
6- Lustre
One of the physical properties of steel is its attractive outer appearance. It is silvery in colour with a shiny, lustrous outer surface.
7- Rust Resistance
The addition of certain elements makes some types of steel resistant to rust. Stainless steel, for instance, contains nickel, molybdenum and chromium which improve its ability to resist rust.
In addition to the above, the following is an indicative properties chart, which illustrates the differences in the properties of different types of steel. Steel is identified by grades, which are defined by specific organizations that set standards for grading. Mild steel and two grades of stainless steel, 304 and 430 are discussed below.
Other mechanical properties of structural steel that are important to the designer include:
1- Modulus of elasticity, E = 210,000 N/mm²
2- Shear modulus, G = E/[2(1 + ν)] N/mm², often taken as 81,000 N/mm²
3- Poisson’s ratio, ν = 0.3
4- Coefficient of thermal expansion, α = 12 x 10-6/°C (in the ambient temperature range).
