Study of the Mechanical Properties of Cold-Rolled, Annealed Strips Made of Hypereutectoid Alloy Tool Steel

The mechanical properties of annealed, high‑carbon chromium tool steel 9Kh after cold rolling with various reductions were investigated; this steel is not listed as a material in State standard State standard GOST 21996–76. Evaluation of the initial microstructure and mechanical properties showed that the hot‑rolled condition of the material exhibits insufficient ductility, characterized by a pearlite–cementite structure and an tested uniform elongation δ5 in the range of 2.9–3.4%. To increase the ductility required for cold deformation by rolling, a cyclic annealing regime with holds above the critical temperature Ac3 was developed, yielding a favorable spheroidized pearlite and carbide phase structure. The features of pearlite formation and spheroidization, the carbide phases, and their influence on mechanical properties under this annealing are confirmed by the absence of an upper yield point and by a short yield plateau on the presented tensile curves. Assessment of the mechanical properties of annealed samples after cold rolling with a 67% reduction to a thickness of 0.99 mm indicates that rolling can produce the required ultimate tensile strength σu ≥ 1580 MPa and hardness ≥486 HV according to State standard State standard GOST 21996–76 for high‑strength, heat‑treated cold‑rolled strips, without risk of damaging the work rolls.