Alloy steel

The properties of steel are transformed with the addition of alloys – such as chromium (Cr), manganese (Mn) and silicon (Si) – and tempering (controlled heating and cooling cycles in manufacture). While adding no more than 0.05% alloy to a plain carbon steel can almost double its strength, the cost is raised only very slightly. Other alloys, such as copper (Cu) and Cr, are added to improve corrosion resistance and yield materials that can tolerate extremely corrosive environments, or be left outdoors unpainted for more than a century.

Steel is relatively low cost and grades have been developed to suit almost every imaginable application. Its properties are highly tailorable and as a result, it is used in packaging (coated mild steel or naked stainless), automotive (steels with tensile strength of more than 550 MPa are known as advanced high-strength steel, AHSS), furniture, construction, buildings, bridges, heavy duty equipment, manufacturing equipment, laboratory environments and shipbuilding. Its tolerance to low and high temperatures in service depends on the grade, with some tool steels able to withstand extreme loads and shocks, and maintain incredible hardness (equivalent to granite and concrete) at over 500 degC.

Heat treatment (tempering) is a critical step in the production of many high performance steels. It is as important as the ingredients for the mechanical properties of the final part. Typically carried out once forming and welding have been completed, a steel item may be worth many more times the initial cost of the base metal by this point. Therefore, processes have been developed to reduce the risk of distortion, cracking and other defects. It has evolved into a sophisticate and critical step in the production of many types of steel.