High strain rate deformation of nanostructured super bainite

Outstanding mechanical properties of nanostructured carbide-free hard bainitic steels, also known as super bainite, with microstructural constituents of less than 100 nm thicknesses make them prone to be used in different engineering applications. However, besides their exceptional strength and ductility combinations during ordinary static or quasi-static deformation modes, it would be also interesting to evaluate their mechanical behavior under high strain rate deformation conditions. This article aims to investigate the mechanical performance of nanostructured super bainite isothermally obtained at 300 °C by applying both tensile and compressive high strain rate deformation modes. Hopkinson compressive and tensile tests were performed up to the maximum strain rate levels of 1.82 × 10³ s⁻¹ and 1.040 × 10⁴ s⁻¹, respectively. Results indicated that strength and ductility properties both significantly were dependent on the strain rate values during tension and compression even if the effect of tensile deformation mode was more considerable. The strength level enhanced to almost 3000 MPa at the highest tensile deformation rate. According to the results, the transformation-induced plasticity (TRIP) effect could not be effective in ductility promotion at higher tensile strain rate deformations since the austenite-to-martensite transformation did not take place gradually to produce a proficient transformation-induced plasticity effect. As a result, a premature TRIP effect occurred and resulted in lower energy absorption during deformation processes.