Thermal shock and thermal fatigue are recognized as common failure modes for WC - Co cemented carbides (hardmetals) in several applications in volving service temperature changes. However, information on microstructure - performance for these materials when subjected to abrupt changes in temper ature is rather limited. In this investigation, the thermal shock resistance of two WC - Co cemented carbides is studied on the basis of their residual strength after being subjected to temperature changes. The materials studied correspond to grades with dif ferent grain size (medium and ultrafine) but similar binder content. Thermal shock variables include two temperature difference ranges (400ºC and 550ºC) as well as number of abrupt changes (1, 3 and 10). Residual strength results were related to parameters extracted from Hasselman’s theory . It is found that medium - sized hardmetal exhibits a higher strength loss in the first quenching cycle but a greater damage tolerance to repeated thermal shocks than the ultrafine - sized. The assessed residual strength tren ds are in agreement with those expected from evaluation of Hasselman’s parameters for quantifying resistance to either crack initiation or crack propagation induced by thermal shock