Flow stress modeling of ultra-thin austenitic stainless steel for proton exchange membrane fuel cell incorporating strain rate, temperature, and grain size

Hot forming process is a potential route for manufacturing metallic bipolar plates with fine flow channel geometries and higher dimensional accuracy. To facilitate the design of the hot forming process for bipolar plates, effects of temperature, strain rate, and grain size on the flow behavior of ultra-thin 316 L austenitic stainless steel were investigated. Uniaxial tensile tests over 973-1173 K and 0.001-0.1 s-1 were conducted with digital image correlation techniques. Experiment results present the flow stress of ultra-thin 316 L stainless steel decreases with decreasing strain rate, increasing temperature, and increasing grain size. The flow behavior of ultra-thin 316 L stainless steel is significantly affected by strain rate, temperature, grain size, and their coupling effects. A new flow stress model incorporating strain rate, temperature, and grain size is developed to capture the complex deformation behavior of ultra-thin 316 L stainless steel. By comparing calculated flow stresses with experimental data, the reliability of the developed flow stress model is verified with an average absolute relative error of 4.5%, indicating that the developed flow stress model is capable of accurately describing the flow stress dependency of ultra-thin 316 L stainless steel on strain rate, temperature, and grain size.