Cemented carbide containing sub carbide phases, M6C and M12C, known as eta-phase, increases the lifetime milling cutters due to increased resistance to comb cracks. When milling, the inserts much sustain high temperatures, meaning edgeline toughness and thermal fatigue resistance are needed. To obtain this, finer grains and higher binder content are needed. In this study, WC-Co cemented carbides with eta-phase and Cr as well as a higher binder content are investigated. The microstructure is the focus, with parameters such as eta-phase particle size and volume fraction, WC grain size being evaluated. Another part of the study is the investigate the effect of Cr on heat treatment. The addition of Cr in a WC-Co cemented carbide with eta-phase has shown to give rise to smaller eta-phase particle sizes and WC grain size as compared to without Cr. Also, increasing the volume fraction of eta-phase has less influence on WC and eta-phase particle size. Heat treated samples without Cr is shown to increase the coercivity of the samples at 700 degrees Celsius, without change in WC grain size. The effect is also leading to an increase in hardness. But with addition of Cr, the effect seems to diminish.