How many kinds are there?
The term "tungsten carbide" refers to a family of products, and not to a single product as is commonly believed. This common belief (or lack of knowledge of the products) leads to some incredibly vague specifications which leaves the applicator or part manufacturer free to choose any product containing any kind of tungsten carbide. This leads to a selection strictly based on price, and this is detrimental to the end user of the products.
Note: The hardness scale indicated below is the Vicker's scale, ranging from 0 Hv to 8000 Hv, where 8000Hv is the hardness of diamond. Tungsten carbides are too hard to be measured using the Brinell or Rockwell C scales.
Sintered Tungsten Carbide
| Hardness: 1200-1500 Hv
This is a composite material made of extremely fine particles of tungsten carbide bound together with cobalt (7% to 15% according to the grade). This material can be formed into a specific shape (inserts for cutting machines, nozzles for spraying or blasting). It can also be crushed to be incorporated in other hardsurfacing products (tube rods, powders for spraying etc.).
Solid Tungsten Carbides
| Hardness: ~2200 Hv
(also called "monocrystaline carbides")
This is a single phase material produced by combining tungsten and carbon metallugically and then applying a thermal process. This material is then crushed, selected by mesh size and incorporated in other hardsurfacing products according to the mesh size (tube rods, powders for spraying, cord products).
Spherical Tungsten Carbides
| Hardness: 3500-4000 Hv (SPHEROTENE®)
These tungsten carbides are manufactured by a different process. The combination of the extremely high hardness (half way up to diamond) and of the spherical shape enable to reach exceptional abrasion/erosion resistance when included in hardfacing products such as TECHNOSPHERE®
It should also be mentioned that the relatively soft sintered carbides can also be shaped into spheres and incorporated into hardsurfacing products. Solid tungsten carbides can be manufactured through different processes resulting in different hardness. Spherical tungsten carbides can also be manufactured through different processes resulting in variations in hardness, shape (spherical or non spherical) and also solid versus hollow spheres.
The mesh size of the particles of tungsten carbide included in the various hardsurfacing products is also very important. The mesh size varies from a few microns to possibly 3/8". The nature of the abrasive/erosive environment dictates the selection of a particular mesh size for maximum efficiency. Consequently the abrasion/erosion resistance of the various commercial hardsurfacing products varies greatly, and should be investigated by the person who specifies "tungsten carbide hardfacing".