Part 5 of our tool-steel presentation is a continuation of the effects individual alloying elements have on tool-steel chemistries and heat-treated metallurgy.

Tungsten
Tungsten is a unique alloying element to the tool steels and contributes to the formation of finely dispersed carbides throughout the background matrix.
  • Tungsten will elevate the hardening temperature (also known as the austenitizing temperature). It will also form very stable carbides with carbon.
  • The carbides are very complex and dissolve extremely slowly in the steel at elevated temperatures. When the carbides are in solution, the carbides can be made to precipitate out by slowly cooling from elevated temperatures.
  • Tungsten will inhibit grain growth at elevated austenitizing temperatures. It is the basis of the T group of high-speed steels. High-speed steels in the T group will usually form excess carbides within the matrix of martensite. The T group of high-speed steels is not as prevalent as the M series (molybdenum) high-speed steels.
The primary function of tungsten is to give high red-heat hardness in both high-speed steels (at high cutting speeds and feeds) and hot-work steels for forging dies, extrusion dies, aluminum die-casting dies, shot sleeves and, in fact, any steel that is likely to be exposed to high operating temperatures.

Molybdenum
Molybdenum will also form the complex carbides with carbon. It will improve the deep-hardening characteristics of the steel. It is found in tool steels such as hot work, high-speed steel and usually at concentrations of around 4% plus.

It also makes the steel resistant to tempering and assists in the "secondary hardening" characteristics of the steel. It will also assist in age-hardening steels to improve the hardness.

Another benefit from the use of molybdenum is that it will improve the hot hardness of tool steels and will assist in elimination temper brittleness (depending, of course, on the amount present in the steel).