Properties of steel after regulated thermoplastic hardening in macro-, meso-, and microstructure formation

Effect of Thermomechanical Treatment on the Properties of Steel with a Mixed Martensitic-Bainitic Structure

“…The formation of bands in the structure of the steel hardened by the HTMMB technology is obviously due to the processes occurring in the alloyed austenite during its hot deformation. The formation of a band structure in steel may be due to the fact that recrystallization processes have varying flow rates in different areas of the deformed austenite.The process of nucleation and growth of new grains starts mostly at the boundaries of deformed grains and shear bands within them [4]. At a certain stage of the post-deformation soaking elongated areas of fine equiaxed recrystallized grains separated by non-recrystallized volumes are formed near the austenite grain boundaries (Fig.…”

“…If steel with such a structure is subjected to fast cooling below the temperature of the martensite transformation start, martensite crystals first appear in the recrystallized austenite grains (Fig. 3 c) because this transformation in the defective structure of deformed austenite is complicated [4]. In the case of incomplete martensitic transformation a structure consisting of crystals with segregation areas of martensite and a residual austenite zone between them can be obtained.…”

“…Plastic deformation of austenite reduced the size of structural components and led to the formation of a bainite structure with fuzzy boundaries between individual packages and crystals. The reduction in the martensite crystal size to about 5 µm occurred due to the presence of such obstacles as boundaries and sub boundaries of austenite grains in their growth ways and due to the increasing of nucleation points as well [4]. Carbide particles were precipitated in the structure of the lower bainite in the α-phase, which are located at an angle of about 60 degrees towards the longitudinal axis of the crystal.…”

“…High rates of structural strength of steel can be achieved by technological processes combining operations of hot plastic deformation and thermal hardening. Various types of high-disperse structures having high resistance to degradation under dynamic and cyclic loads may be formed by thermomechanical treatment of steel [3,4,5,6,7]. Another promising trend to increase characteristics of structural strength is to make a mixed structure consisting of two or more components, some of which provide high strength, while the other improves crack propagation resistance of steel [8,9].…”