Mechanical Properties and Fracture of Heat-Resistant Ferritic-Martensitic Steels EK-181, ChS-139 and EP-823 at the Temperatures from–196 to 720°C.

The variations in the short-term mechanical properties of heat resistant ferritic-martensitic 12% chromium steels EK-181, ChS-139 and EP-823 are investigated, followed by an examination of the features of their plastic deformation and fracture under active tension in the temperature range from –196 to 720°C. The temperature curves of the yield strength and relative elongation and the features of fracture of these steels after traditional heat treatment are found to be qualitatively similar. The variations in the ductility and fracture behavior of these steels are attributed to the features of their yield stress temperature dependence. In the region of positive (up to about 450°C) temperatures, these features are determined by a weak temperature dependence of the value of dispersion hardening by nanoscale V(C, N) particles; in the negative temperature range—by a strong temperature dependence of the thermally activated mobility of dislocations in the crystallographic relief (Peierls barrier, solid solution of impurities). The deformation in the neck region of the specimens fractured at Т = 20°C is observed to degrade the martensitic structure, resulting in the curvature and migration of the martensitic lamella boundaries and fragmentation of the martensite laths. After deformation at 650°C, numerous practically equiaxed ferrite grains are observed to form, which indicates the initial stage of recrystallization. [ABSTRACT FROM AUTHOR]