Hot Deformation Behaviour and Processing Map of Cast Alloy 825

Abstract Alloy 825 is a nickel-based alloy that is commonly used in applications where both high strength and corrosion resistance are required, such as tanks in the chemical, food and petrochemical industries and oil and gas pipelines. Components made from Alloy 825 are often manufactured using hot deformation. However, there is no systematic study to optimise the processing conditions reported in literature. In this study, a processing map for as-cast Alloy 825 is established to maximise the power dissipation efficiency of hot deformation in the temperature range of 950 to 1250 °C at an interval of 50 °C and strain rate range of$$0.01\, {\text{s}} ^{- 1}$$to$$10.0\, {\text{s}} ^{- 1}$$to a true strain of$$0.7$$using a Gleeble-3500 thermomechanical simulator. The processing conditions are also correlated to the Vickers hardness of the final material, which is also characterised using optical microscopy and scanning electron microscopy, including electron backscattered diffraction. The true stress-true strain curves exhibit peak stresses followed by softening due to occurrence of dynamic recrystallization. The activation energy for plastic flow in the temperature range tested is approximately$$450\,{\text{ kJ mol}} ^{- 1}$$, and the value of the stress exponent in the (hyperbolic sine-based) constitutive equation,$$n = 5.0$$, suggests that the rate-limiting mechanism of deformation is dislocation climb. Increasing deformation temperature led to a lower Vickers hardness in the deformed material, due to increased dynamic recrystallization. Raising the strain rate led to an increase in Vickers hardness in the deformed material due to increased work hardening. The maximum power dissipation efficiency is over$$35\%$$, obtained for deformation in the temperature range 1100-1250 °C and a strain rate of$$0.01\, {\text{s}} ^{- 1}$$-$$0.1\, {\text{s}} ^{- 1}$$. These are the optimum conditions for hot working.