What Is Alloy Steel?

Steel is a common and versatile material with uses in construction, manufacturing, engineering and more, and in this article, we will be exploring alloy steels. Steels fall broadly into four categories: carbon, stainless, tool and alloys. Technically speaking every steel is an alloy, as it is created by combining iron with carbon, however, to be officially designated as an “alloy steel” it must contain one or more other elements in addition to these two. The reason for creating alloy steels is to improve the metal’s mechanical or physical properties, such as strength, workability or corrosion resistance.

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

 Cobalt alloys have increased hardness and dramatically improved resistance to scaling at high-temperatures, making them a popular tool steel.  

 Silicon

 Silicon is used in small amounts, generally around 3%, to slightly improve strength while increasing magnetism and acting as a highly effective deoxidiser. This makes them useful within electrical applications such as  transformer,  motors, and generators.

 Manganese

 Manganese improves both ductility and hardness, reduces brittleness and greatly increases wear and shock resistance. These alloys are the ideal choice for hammering or where the metal will be under stress.

 Nickel

 Another deoxidiser, nickel greatly increases corrosion resistance when used in higher proportions. It also improves strength and hardness without compromising on ductility like some alloys.

 Tungsten

 As well as increased strength and hardness, tungsten alloys are primarily used for their impressive heat-resistance with a higher melting point than most steels. This ability to retain toughness under high temperatures makes them ideal for high-speed tools and machinery parts such as drill bits and cutting blades.

 Vanadium

 Vanadium alloys are a great all-round choice, with increased tensile strength, toughness, wear-resistance and corrosion-resistance. These are often alloyed with chromium to retain a workable level of formability.

Applications and uses of alloy steels

Alloy steels have limitless uses across a wide variety of industries.

Within the construction industry, alloy steels are used to create a wide array of products, including girders, bars, pipes, plates, sheets, rods, beams and much more. Large-scale infrastructure projects such as bridges, motorway barriers, electrical pylons and railways are all primarily built from types of steel. Stainless steel and other alloy steels are used in many fixtures and fittings such as fasteners, brackets and sockets; the list is almost endless.

Steel alloys are found almost everywhere you look and sometimes in unexpected places; for example, titanium-steel has recently become a fashionable choice in the jewellery industry. Other products involving steel alloys include many household appliances, cooking equipment, homeware, food containers, medical equipment, automobiles, aerospace products, lighting - everything from the paper clip to the latest iPhone!