DETERMINATION OF THE OPTIMAL PARAMETERS FOR THE THERMO-MECHANICAL TREATMENT OF CHROMIUM-MOLYBDENUM MARTENSITIC STEEL WITH ALLOYING NITROGEN

摘要

True Strain Diagrams (SSD) have been obtained and maps of maximum true strains, σ_(max) during hot deformations, as well as maps of hardness after thermo-mechanical treatment of the Crl 1N and Crl1Mo1N steels have been developed, which can be used for selecting hot deformation patterns and thermo-mechanical treatment. Alloying of the Crl 1N steel with molybdenum (1,41% Mo) increases the true strain of hot deformation, inhibits the processes of nitride and carbide-nitride precipitation and growth, and widens the permissible range of hot deformation temperatures in the cycle of thermo-mechanical treatment assuring the high-strength state of material after quench hardening to be obtained. The course of phase transformations (i.e. ageing processes and the γ→α austenitic-ferritic transformation) during hot deformation of nitrogen steel with 11% Cr leads to a decrease in yield stresses, the appearance of a maximum in strain stress diagrams, and a decrease in the strength level and corrosion resistance after quench hardening. Deformation of nitrogen steels at high temperatures (> 1100 ℃) is undesirable because of the formation of large-seized precipitated particles and the growth of grains.