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Last edited 20 Feb 2019
Types of steel
Steel is one of the basic materials used in today’s civil engineering industry due to its proven high strength and durability. Steel is an alloy of iron and a number of other elements, mainly carbon, that has a high tensile strength and relatively low cost.
The different mechanical and physical properties that are required for the specific application determine the different type of steel that is produced. Grading systems identify steels based on properties such as:
- Melting point.
- Thermal conductivity.
There are many different types of steel, broadly categorised according to their chemical composition into the following groups:
Carbon steel is a combination of iron and carbon. The percentage of carbon is varied to produce different qualities of steel. The higher the level of carbon, the stronger, but more brittle the steel tends to be:
- Low carbon steel is easily workable. Wrought iron is a form of low carbon steel, often used for decorative ironwork such as railings and gates.
- Medium carbon steel can be used for structural steelwork.
- High carbon steel is often used for the manufacture of tools and high-strength wire.
- Ultra-high carbon steel is non-malleable, hard and brittle. Cast iron is a form of ultra-high carbon steel.
Alloy steels are produced from carbon steel and one or more alloying elements. These additions can improve the mechanical properties of the alloy. For example, steel combined with manganese is very hard and strong, while steel combined with aluminium is more uniform in appearance.
Weathering steel (also known by the trademark COR-TEN steel) is a form of high-strength, low alloy steel, chemically composed to form a stable, rust-like appearance that can resist corrosion and abrasion, by forming a protective surface layer, or patina.
Steel combined with chromium (and sometimes nickel) is called 'stainless steel'. Stainless steels generally do not form rust on their surfaces and do not discolour. The level of chromium is typically between 10-20%, with a level of 11% making the steel around 200 times more corrosion resistant than steels that contain no chromium. Stainless steel can be classified into three main categories based on their metallurgical structure: austenitic, ferritic and martensitic.
For more information, see Stainless steel.
Tool steels are steels containing varying amounts of tungsten, molybdenum, cobalt and vanadium that have properties that are particularly suitable for use as tools and can be used to create moulds for injection moulding. They are abrasion, impact and/or corrosion resistant.
Galvanisation can be used to help prevent steel from corroding. This involves coating steel in zinc. The coating of zinc prevents corrosive substances from reaching the base metal. The zinc also acts as a sacrificial anode, meaning that if the coating is scratched, the remaining zinc will still protect the exposed steel.
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