Fundamental Science and Technology of Flash Processing Robustness for Advanced High Strength Steels (AHSS)

“Flash processed” low carbon steel sheets were characterized using in-situ IR imaging, ex-situ dome deformation testing and microscopy. Due to flash processing set-up, cooling water flow and steam interfered with robust infrared temperature measurements. Though preliminary, rapidly heating the steel sheet to greater than 1170°C and then water quenching a few seconds later can result in through thickness microstructural gradients, where the center is harder than the exterior surfaces. This microstructural configuration sometimes results in a dome displacement ~75% relative to that observed in the more ductile as-received material. The presence of aluminum nitride (AlN) inclusions was confirmed, a likely byproduct from a de-oxidization reaction, and may reduce dome displacement (similar to strain to failure) significantly. Based on thermodynamic calculations, a high flash processing temperature (>1170°C) is recommended to dissolve these AlN inclusions in the austenite phase.