Abstract: High speed face milling experiments on AerMet100 steel were conducted using nano-TiAIN coated cemented carbide tools. By analyzing experimental data, it was found that wear patterns of nano-TiAIN coated cemented carbide tools in high speed milling AerMet100 steel included rake face wear, flank wear, breakage of coating, micro-chipping of cutting edge, boundary groove wear, conchoidal avalanche. Wear mechanisms included abrasion, adhesion, diffusion and chemical wear. The results demonstrated that the tool had increased content of element Co in high-speed milling AerMet100 steel.