First of all tungsten carbide is not used to make any type of steel. It is a very hard compound of tungsten with the formula W2C used as a material for tipping tools and drills and for use as grains set in the edges of ceramic and other cutting discs. It is also fabricated into complex shapes by sintering which creates a product which is much less likely to break than solid W2C. Tungsten metal, however is used as a hardener for some types of steel
Tungsten carbide has a hardness on the Moh's scale 9.8 and so there is very little other than diamond that will scratch it although other metal carbide compounds may do the trick.
In reference to your previous question about diamond testers there no testers on the market which can tell which type (Type I, II,III etc.) of diamond you have nor can they tell the difference between natural and lab made diamonds. This requires sophisticated and costly equipment only found in professional laboratories.