Complex Structural Effects in Deformed High-Manganese Steel

Abstract

The research presented in this paper is part of a larger project concerning deformation behavior, microstructure and mechanical properties of high-manganese steels with different chemical compositions and processed under various conditions. The current investigation deals with the development of microstructure and crystallographic texture of Fe-21.2Mn-2.73Al-2.99Si steel deformed in tension until fracture at ambient temperature. The deformation process of the examined steel turned out to be complex and included not only dislocation slip and twinning but also strain induced phase transformations (γ → ε) and (γ → α′). The formation of ε-martensite with hexagonal structure was observed within the microstructure of the steel starting from the range of lower strains. With increasing deformation degree, the α′-martensite showing a cubic structure gradually began to form. Attempts have been made to explain the circumstances or conditions for the occurrence of the deformation mechanisms mentioned above and their impact on the mechanical properties. The obtained results indicate that the strength and plastic properties of the steel substantially exceed those of plain carbon steels. Since both, mechanical twinning and the strain-induced phase transformations took place during deformation, it seems that both types of deformation mechanisms contributed to an increase in the mechanical properties of the examined manganese steel.

The Influence of Cold Deformation and Annealing on Texture Changes in Austenitic Stainless Steel

“…However, Padilha et al [25], testing AISI 304 austenitic steel after deformation by cold rolling, showed that ε'-martensite formed in steel but at low degrees of deformation up to 5% and then, with an increase in the degree of deformation, it was transformed into α'martensite. ε-martensite as an intermediate phase is also observed in high-manganese austenitic steels [16,17,47]. For the tested steel, there are no diffraction lines from the ε phase in the entire range of deformations of 5-80%, which confirms that the phase transformation in this steel occurs along the γ → α' path.…”

“…Annealing of these steels after deformation may lead to the formation of carbides and intermetallic phases [12]. An important structural effect occurring in steels with an austenitic structure Cr-Ni [13][14][15] and high-manganese steels [16][17][18] is the occurrence of a phase transformation during cold plastic deformation, called the TRIP (TRansformation Induced Plasticity) effect and mechanical twinning (called the TWIP effect) [19]. The deformation-induced martensitic transformation is influenced by many factors, such as: temperature, the degree and method of deformation, as well as the chemical composition, size and crystallographic orientation of the austenite grain [20,21].…”