The measurement of magnetic saturation of the cobalt binder phase in cemented carbide is used for the evaluation of its composition.

Cobalt is magnetic. WC crystals and cubic carbide crystals(TiC, TaC, NbC, VC, etc) are non-magnetic. As a result, if the magnetic saturation value of the cobalt in a grade is determined and then compared with the corresponding value of a sample containing pure cobalt, the alloying level of the cobalt binder phase can be obtained, as the elements that form the alloy together with cobalt affect the value of magnetic saturation. Thus any change in the optimal binder phase composition can be measured. This test is applied to determine any deviation of the optimal carbon content, since carbon plays an important role in the control of the composition. 

A low magnetic saturation value indicates a low carbon content or the existence ofηphase it the carbides.

A high magnetic saturation value indicates the existence of free carbon and graphite phase.

Both will have adverse effects on the mechanical properties.