Rapid tool wear is a major demerit of high-speed milling (HSM) applied to cutting of hardened steels, especially the AISI D2. This paper presents an attempt to maximize the tool life by experimentally investigating the effects of cutter’s helix angle, workpiece material hardness, milling orientation, and minimum quantity of lubrication upon tool wear in high-speed side milling of AISI D2, using coated carbide cutters. Effects of these four parameters were studied also upon surface roughness. Statistical analysis upon experimental data revealed that milling orientation was the most significant factor for tool life as well as for surface roughness. The paper also describes the mechanisms of wear undergone by the tools, by making use of SEM photographs and EDS microanalysis. The major wear mechanisms were chipping, adhesion, and diffusion.