| Abstract Scope |
Bending is the most common forming method for structural steels; however, ultrahigh-strength steels (UHSS) suffer from limited formability, resulting in strain localization, surface defects, and irregular bend geometries. Surface integrity, particularly roughness and residual stresses, strongly influences bendability. This study examines the effects of surface modification on a 4 mm thick bainitic-martensitic UHSS sheet under four conditions: as-rolled, dry electropolished, ultrasonic burnished, and a combination of dry electropolishing and ultrasonic burnishing. Three-point bending tests with Digital Image Correlation (DIC) were used to evaluate strain distribution, while X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) characterized residual stresses and microstructure. Dry electropolishing showed reduced bendability. In contrast, ultrasonic burnishing reduced surface roughness and increased hardness and residual stresses. The findings demonstrate that ultrasonic burnishing effectively decreases the bendability by increasing both subsurface hardness and stress states in UHSS. |