Carbide-forming elements are an essential requirement for the steel to have the ability to harden and produce satisfactory hardness results as well as the required mechanical properties on either through- or case-hardening steel.

The carbide-forming elements will have an affinity for the carbon content of the steel to form the appropriate carbides, or special carbides. The carbide-forming elements are as follows:

• Carbon (C)
• Tungsten (W)
• Vanadium (V)
• Molybdenum (Mo)
• Titanium (Ti)
• Niobium (Nb)
• Tantalum (Ta)
• Zirconium (Zr)

Some carbides, known as special carbides, are usually found in the steels such as high-speed steels (HSS series), dimensionally stable steels (D series), hot-work steels (H series) and air-hard steels (A series).

The carbides that are formed and known as special carbides are non-iron-containing carbides that are generally seen as:

• Cr₇C₃
• W₂C
• VC
• Mo₂C

There are also elements that can be present to stabilize the formed carbides. The stability of the formed carbides will depend on how the element is located between the cementite (greater than 0.77% C) and the matrix. The stabilizers are aluminum, copper, phosphorus, silicon, cobalt, nickel, tungsten, molybdenum, manganese, chromium, vanadium and titanium.

It should be noted that manganese is not a strong carbide former. In fact, it is generally considered to be a weak carbide former. Chromium is the most commonly seen element as both a carbide stabilizer and a carbide former.

With the additions of these elements in tool steels and alloy steels, the austenitizing temperature will be elevated. Some of the elements that are added to the tool steels are added to reduce grain growth, which will occur due to the high austenitizing temperatures necessary to achieve hardening.

Vanadium is usually added to approximately 0.10%. Aluminum is another grain-growth inhibitor. However, aluminum is also a nitride former in the presence of nitrogen. Because of the high austenitizing temperatures necessary to achieve hardness, the soaking times at the austenitizing temperature need to be carefully controlled and monitored.