Experimental studies of necking and fracture limits of boron steel sheet under hot stamping conditions

Boron steel is the most widely used material in hot stamping applications for forming automotive body panels with complex shapes and ultra-high strength. Due to high austenitic transformation temperatures thermal cycle required stamping, however, it difficult evaluate formability of using standard punch test methods developed room-temperature testing. In this study, a high-temperature modification recently biaxial method has been determine, single procedure first time, limit curves (FLCs) fracture (FFLCs) 22MnB5 boron sheet thickness 1.5 mm under conditions that are representative industrial processes. A direct resistance heating strategy developed, proposed cruciform specimen design modified use. For tests target range 750 925 °C, resulting specimens had highest temperature at centre difference less than 45 °C gauge area occurred close all investigated. Limit strains onset necking have determined by applying digital image correlation (DIC) obtain full-field strain measurements, providing an experimental foundation constructing both FLCs FFLCs applications.