This book presents modern concepts of the formation of structural-phase states, defect structure, and properties of high-speed steel 1.3355 after high-temperature tempering and electron-beam treatment (EBT). It employs methods of modern physical materials science, particularly transmission electron microscopy, to establish quantitative parameters of structure, phase composition, and fine substructure and to reveal the physical nature of hardening of high-speed steel after tempering and EBT. The book also formulates model concepts for the formation of gradients of structural-phase states during surfacing and subsequent treatments. It is intended for a wide range of specialists, including scientific researchers and engineers working in the field of materials science and the physics of condensed systems, as well as teachers, postgraduates, and students specializing in materials science.