Deformation behaviour and notch sensitivity of a super duplex stainless steel at different strain rates and temperatures

Abstract

For the successful development of a structure, understanding of mechanical behaviour of the selected material is an important issue to prevent damage or accidents. Mechanics of the material failure depends on its chemical composition, heat treatment, grain size, strain rate, type of loadings etc. Apart from material properties, the performance of the structure is also affected by its geometry, crack/notch/hole/groove and manufacturing processes. In construction of offshore, marine, power plant and oil-gas industry structures, super duplex stainless steel is one of the suitable materials. Therefore, the objective of the paper is to study the deformation behaviour and notch sensitivity of a super duplex stainless steel, SDSS 2507 at different strain rates (0.0001–0.1s−1) and temperatures (25–200 °C) under tensile, compressive and flexural (three-point bending) loads. Heating rate and soaking time are 8 °C/min and 15 min respectively. Experiments are conducted on electromechanical universal testing machine using suitable fixtures. The steel is found positive sensitive to the strain rate and temperature, where the phenomenon of dynamic strain ageing (DSA) is observed during thermal effects. Fractography analysis is correlated with the typical stress-strain curves. Heat treatment (heating rate 12 °C/min and soaking time 1–3 h) enhances the tensile strength of the steel upto 18% at 400–600 °C for strain rate 0.001s−1, whereas at 700 °C, the strength decreases by 31% and the energy dissipation decreases by 88% due to its brittle behaviour. Notch profiles (C, U and V) on the flat tensile specimens of the steel decreases the energy dissipation by nearly 67–74% at 0.001s−1. Ductile-brittle transition temperature exists between 600℃-700℃ in tensile tests. Compression tests are conducted for varying geometries of cylindrical specimens. Flexural behaviour of the steel is investigated for 120–160 mm span lengths and flat-transverse orientations. Existing material models (Cowper-Symonds and Johnson-Cook) are evaluated.