The influence of plasma surface modification technology (without melting or with micro-melting) on the mechanisms of phase transformations, hardness and wear resistance of high-carbon steels (U12 and 150KhNM) and cast irons (SCh18, SCh40, VCh80, 300Kh25N3S3) is studied. In the modified zone, an ultrafine structure of high-speed quenching (processing without melting) or high-speed crystallization (processing with micro-melting) is formed during modifying hypereutectoid steels. This leads to an increase in hardness and wear resistance by 2.5–3.5 times. For grey and high-strength cast irons, the structure of the modified zone and the level of operational properties depend on the type and phase composition of the matrix and do not depend on the shape of the graphite inclusions. For high-strength cast iron, the highest wear resistance is achieved by plasma modification without surface melting, and for grey cast iron—with micro-melting of the surface. The increase in wear resistance of white high-chromium cast iron after plasma modification is due to the dispersion hardening of the matrix phase as a result of the separation of ultrafine particles of secondary carbides.