Physical simulation of hot deformation and microstructural evolution of AISI 1016 steel using processing maps

Abstract

The hot deformation behavior of AISI 1016 steel is studied by performing hot compression tests in the Gleeble® 3800 physical simulator in the temperature range 750–1050°C after austenitization at 1050°C for 5min. The strain rates used vary from 0.01 to 80s−1 and the total true strain achieved is 0.7. The microstructural evolution is described based on light optical and scanning electron microscopy of the deformed and water quenched samples. An EBSD measurement on selected sample in the two-phase field is used to determine the microstructural changes in the ferritic phase. Then, processing windows are created using dynamic materials model, modified dynamic materials model, and strain rate sensitivity maps, which are correlated with the microstructural development. In order to determine the flow instability ranges produced by flow localization, different instability parameters are employed and compared. The processing map obtained using the power dissipation efficiency, η, correlates well with microstructural changes observed due to the dependency of this parameter on strain rate sensitivity m. Although instability zones predicted by the instability parameter κj are similar to these predicted by flow localization parameter α, the latter approach is physically explained by the thermal softening due to adiabatic flow at high strain rates. Using sinh type constitutive equation, the average apparent activation energy for hot deformation of AISI 1016 steel is 290kJ/mol and the stress exponent n is 3.8, indicating plastic deformation by dislocation gliding and climbing.