| Abstract Scope |
Ultra-High Strength Steels (UHSS) are critical for heavy-duty applications like construction/agriculture. However, their high-strength/low-ductility character inhibits formability, resulting in failure during bending, particularly along the rolling direction. Three grades of hot-rolled, direct quenched UHSS are compared, ranging from heavily pancaked/textured to almost equiaxed through slight processing variations. Each has a complicated multi-phase microstructure, particularly in the first 150μm of subsurface, due to decarburization. Novel 5-phase identification and Prior Austenite Grain (PAG) reconstructions are applied to reveal microstructural differences between the grades, and are spatially correlated to high-resolution SEM-DIC bending tests. Results reveal that pancaked microstructures, although stronger and of similar ductility in uniaxial tension, suffer from early surface cracking during bending, in contrast to the equiaxed microstructure which does not fail. Advanced microstructure-correlated strain analysis and slip system identification (Vermeij et al., Acta Materialia, 2023) explain this contrast, highlighting the importance of precise processing/composition control for UHSS. |