MIXED STRUCTURES IN CONTINUOUSLY COOLED LOW-CARBON AUTOMOTIVE STEELS

Mixed microstructures have been studied in low- carbon microalloyed st eels suitable for automotive applications, after continuous cooling fr om the hot-rolled condition. Microstructural features such as polygona l ferrite, bainitic and acicular ferrite and microphase constituent ar e identified using transmission electron microscopy. The influence of these mixed structures on the tensile strength, impact toughness and f racture behaviour is examined. It is found that improvements in impact toughness as compared with microalloyed medium- carbon ferrite/pearli te steels can be achieved from these predominantly acicular structures developed by controlling alloy composition and continuous cooling of these lower carbon steels.