Martensitic transformations and martensite structure in thermomechanically strengthened high-nitrogen steels

Structure and properties formed as a result of martensitic transformations during cooling and cold working, and subsequent tempering in metastable carbon- and nitrogen-containing austenitic iron alloys were studied using magnetometric, X-ray diffraction and electron microscopy analyses as well as mechanical tests. Hot deformation in a cycle of high-temperature thermomechanical treatment influences the martensitic transformations, martensite structure and tempering processes in dependence on steel composition, structure and treatment regime. The austenitic high-nitrogen chromium and chromium-manganese steels are noticeably strengthened under rather small strain. At high strains, they are inclined to the martensitic transformation. The cold working accelerates the tempering processes in all the steels studied. The strengthening by high-temperature thermomechanical treatment or cold working of the nitrogen-containing steels remains up to higher heating temperatures. Alloying of nitrogen-containing steels by vanadium retards the decomposition processes during tempering and aging and makes dispersion hardening of the austenite and martensite more effective.