Effect of coiling temperature on impact toughness of hot rolled ultra-high-strength multiphase steel strips

The tensile and Charpy impact properties of four strip samples from two different B-added low-C ultra-high-strength steel strips (Al-treated Ti-treated), coiled at temperature ranges (360–380 °C 450–460 °C), have been evaluated correlated to the microstructural parameters, dislocation density, intensity high-angle boundaries. effects coiling temperatures on evolution mechanical discussed. volume fraction individual phase constituents (namely, granular bainite, upper lower bainite tempered martensite) their hardness, local deformation response strain-hardening ability, as determined nanoindentation testing, influenced bulk such (strength ductility), (upper shelf energy, USE, ductile-to-brittle transition temperature, DBTT) abilities under both quasi-static dynamic loading conditions. dominance (75–90 %) reduced strength (670–722 MPa yield strength), improved ductility (16.7–19.5 % elongation failure) USE (35–42 J) in higher temperatures. In contrast, a martensite (78–82 significantly increased (808–814 MPa), (13.0–14.5 (19–29 samples. DBTT showed complex trend with parameters. It depended level, well ‘effective grain size’ matrix.