Development and Validation of a Constitutive Model for the Hot Deformation Behaviour of Austenitic Stainless Steel Relevant to Nigerian Industrial Forming Operations

This study develops and validates a physically based constitutive model for the hot deformation behaviour of AISI 316L austenitic stainless steel, with direct relevance to optimising hot rolling and forging operations conducted at fabrication facilities in the South South and South West geopolitical zones of Nigeria. Accurate constitutive modelling is a prerequisite for finite element simulation-based process design in metal forming, and existing models have not been validated for the specific temperature-strain rate windows relevant to Nigerian industrial equipment capabilities. Hot compression tests are conducted on a Gleeble thermomechanical simulator at temperatures of 900, 1000, 1100, and 1200 degrees Celsius and strain rates of 0.01, 0.1, 1.0, and 10 s-1 to a true strain of 0.8. Flow stress curves exhibiting dynamic recovery and dynamic recrystallisation behaviour are processed to extract constitutive parameters. A modified Zerilli-Armstrong model incorporating dynamic recrystallisation kinetics through an Avrami-type evolution equation is developed and fitted to the experimental data. The model is implemented as a UMAT subroutine in ABAQUS and validated against an independent hot forging experiment with temperature and load measurements. A processing map is constructed from the efficiency of power dissipation and the instability criterion, identifying safe and unsafe processing domains. The study contributes an original constitutive model and processing map for 316L applicable to Nigerian forming process design. Keywords: constitutive model, hot deformation, austenitic stainless steel, dynamic recrystallisation, forming.