ISO 3908:2009 specifies a gravimetric method for the determination of the mass fraction of insoluble (free) carbon in carbides and hardmetals.

This method is applicable to

• carbides of hafnium, molybdenum, niobium, tantalum, titanium, vanadium, tungsten and zirconium,
• mixtures of these carbides and binder metals, free of lubricant, and
• all grades of presintered or sintered hardmetals, produced from these carbides,

having a mass fraction of insoluble carbon between 0,02 % and 0,5 %.