The austenite conditioning during heat treatment determines the mechanical properties of case hardening steels. New developments in carburising process parameters with temperatures up to 1150degreesC require a precise austenite grain size controls The objective of this investigation is the determination of the influence of microalloying with Niobium and Titanium with regard to transformation and precipitation behaviour as well as microstructure stability and the mechanical properties. A standard case hardening steel grade (16MnCr5) was selected together with three microalloyed steels of the same type. Calculations of precipitates in thermodynamic equilibrium have been performed using Thermo-Calc. Heat treatments in the temperature range of 900degreesC to 1150degreesC were carried out to determine grain stability. The evaluation and documentation of the grain size as a function of heat treatment temperature were made using statistical methods and quantitative metallography.