Structure and properties of low-carbon steels and iron after deformation under superplasticity conditions

Abstract

1. The superplasticity effect during upsetting of low-carbon steels develops in the temperature range Ac1S-Ac3S, to a greater extent close to Ac3S with deformation rates\(\dot \varepsilon\)≅ sec−1, and it is characterized by a simultaneous reduction in deformation resistance, absence of residual hardening for ferrite, and deformation predominantly by a grain boundary sliding mechanism. 2. After superplastic deformation in the temperature range Ac1S-Ac3S the microstructure of low-carbon steels is characterized by retention of the original grain size or refinement, presence of a developed subgrain structure, low dislocation density within the body of grains, and absence of pore type defects, which gives a high impact strength compared with that obtained after deformation at higher temperatures. 3. With an increase in carbon content in low-carbon steels (up to 0.3% C) 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.