Cemented carbide insert with eta-phase core

A method of treating a cemented carbide insert for rock drilling and mineral cutting, the insert comprising a core of cemented carbide and a surface zone of cemented carbide surrounding said core, wherein both the surface zone and the core contains WC with a binder phase based upon at least one of cobalt, nickel or iron, and wherein the core further contains eta-phase and the surface zone is free of eta-phase, wherein an inner part of the surface zone situated next to the core has a content of binder phase being greater than a nominal content of the binder phase in the cemented carbide body and the content of the binder phase increases gradually in the surface zone in a direction towards the core up to at least 1.2 times compared to the nominal content of the binder phase of the cemented carbide body, wherein the method comprises:

• subjecting the insert to a surface hardening process;
• heating the insert to a temperature of or above 50° C. prior to the surface hardening process;
• and
• executing the surface hardening process at an elevated temperature of 50° C. to 450° C., wherein the surface hardening is tumbling.