STRUCTURE AND PROPERTIES OF LOW-CARBON STEELS AND IRON AFTER DEFORMATION UNDER SUPERPLASTICITY CONDITIONS.

The superplasticity effect during upsetting of low-carbon steels develops in the temperature range Ac//1//S-Ac//3//S and is characterized by a simultaneous reduction in deformation resistance, absence of residual hardening for ferrite, and deformation by a grain boundary sliding mechanism. After superplastic deformation the microstructure is characterized by retention of the original grain size or refinement, a developed subgrain structure, low dislocation density and absence of pore type defects. This results in high impact strength compared with that obtained after deformation at higher temperatures. With an increase in carbon content the superplasticity effect develops to a lesser degree, and there is a reduction in the difference in impact strength after deformation in a superplasticity regime and at higher temperatures.