What Is Alloy Steel ?

Steels are usually divided into the two main categories of high alloy or low alloy. It is commonly accepted that low alloy steels contain up to 8% alloying elements, and anything over 8% falls into the category of high alloy.

Common alloying elements of steel.

Though not an exhaustive list, these are some of the most popular elements used in alloying steel. It is estimated that approximately 75% of all steel alloys have been created in the last 20 years alone, and development is ongoing. Many alloys require heat treatment to develop their required features further. Although this list gives some idea of the properties that can be affected by different alloying materials, most alloys will contain two or more elements to create a specific desired effect. A typical example is the 4100 series of chromium-molybdenum alloys, widely used in everything from structural projects to military gear.

Aluminium

Aluminium is used in relatively small amounts, resulting in a robust and lightweight metal with great corrosion resistance, though depending on the proportions this can come at the cost of increased brittleness and poor shock-resistance.

Chromium

A small percentage of chromium in an alloy can increase hardness and toughness, although with some loss of ductility. Larger ratios of chromium significantly increase corrosion resistance; stainless steel is the most well-known alloy in this category, with approximately 11% chromium content or higher.

Cobalt