Calcium treatment and microalloying are essential components of the microstructural engineering of bar products for enhanced machinability at high cuttiitg speeds, > 150m/min.(492.13 ft./min.), with cemented carbide tools. Dissolution crater wear, by a diffusion mechanism, is the dominant mode of tool wear at these speeds. In order to promote chip fracture, a good dispersion of deformable Type-II manganese sulfides is required. In aluminum killed (AK) steels, calcium treatinent is used to modify the hard, abrasive alumina inclusions which cause tool flank wear. Inclusion engineering by calcium treatment and resulfurization requires a low dissolved aluminum content (0.015-0.020 wt. %) in the liquid steel, in order that liquid calcium aluminate inclusions can form without precipitating solid calcium sulfide inclusions which can cause nozzle clogging. Cmter wear can be minimised by the physical or chemical vapour deposition, PVD and CVD respectively, of a suitable coating on the tool surface, e.g., TiN or HfN, which act as diffusion barriers. The purpose of inclusion engineering in silico-manganese deoxidised steels is to produce glassy oxide inclusions which can form a viscous layer at the tool-chip interface and suppress the tribology of seizure,hence limiting crater wear. In order to achieve this, the aluminum content of the steel has to be controlled to very low levels (<5ppm). Under these conditions, the grain refining role of aluminum nitride has to be replaced by the nitrides and carbonitrldes of micro-alloying elements, such as niobium, titanium and vanadium.