Phase and structural transformations in a low-carbon steel that occur upon the collapse of a cylindrical shell

Resumo

An experiment has been performed on the collapse of a thick-walled shell (tube) made of steel 20 (Fe–0.2 wt % C) to a continuous cylinder under the action of explosion. The changes of the microstructure of the cylinder have been investigated that arise under the effect of two factors, i.e., a shock wave, which causes the initial pulse to the collapse, and high-strain-rate deformation upon the subsequent inertial convergence of the shell walls. Changes in the time-dependent temperature distribution in the cylinder have been calculated. As a result of the deformation, the new structure has been obtained in steel 20 due to barothermic quenching that consists of fine crystals of the α phase, which arise during the quenching at the place of free ferrite, and of regions of the retained initial pearlite. It has been shown that the uncommon order of the occurrence of the α → γ transformation is explained by the different degree of heating of the structural constituents of the steel (free ferrite; and pearlite). The conclusion has been drawn that the high-strain-rate deformation that occurs in this experiment can be used as the method that makes it possible not only to differently deform but also to differently heat the different structural components of multiphase materials.