Mechanical properties of cold-rolled annealed strips made of hypereutectoid tool alloy steel

The article presents a study of the mechanical properties of annealed 0.9-Cr tool high-carbon chromium steel after cold rolling with various reductions, which is not presented as a material in the standard GOST 21996-76. An assessment of the initial microstructure of the steel under study and its mechanical properties showed that the hot-rolled rolled steel has insufficient ductility, characterized by a pearlite-cementite structure and parameters of the tested elongation of δ5 in the range of 2.9 – 3.4 %. To increase the plasticity required for cold rolling deformation, a cyclic annealing mode with exposures above the critical point Ac3 has been developed, providing a favorable structure of spheroidized perlite and the carbide phase. The peculiarity of the formation of granular perlite, carbide phases and their spheroidization, mainly of a diffusive nature, during this annealing is confirmed by the absence of a sharp yield point and the short length of the yield point in the tensile diagram below. Evaluation of the mechanical properties of annealed samples after cold rolling with a relative reduction of 67% to a thickness of 0.99 mm allows rolling with the possibility of obtaining the required temporary tear resistance of ≥ 1580 MPa and hardness ≥ 486HV according to standart GOST 21996-76 for high-strength heat-treated cold-rolled strips without the risk of damage to the rolling rolls.