Assessment of microstructure and mechanical properties of dual phase C Mn AHSS during thermomechanical processing via electron microscopy and high speed nanoindentation

Abstract

1 newlineAbstract newlineThis study employs a correlative methodology, utilizing nanoindentation and electron newlinemicroscopy, to understand the microstructure and local mechanical properties of Advanced newlineHigh Strength Steels (AHSS). These steels consist of a ferrite matrix combined with a newlinereinforcing secondary constituent such as pearlite, bainite, or martensite. The initial newlinemicrostructure is obtained by hot rolling above the austenite non-recrystallization temperature newline(TnR) and subsequent coiling at various transformation temperatures. This process resulted in newlinemicrostructures comprising of ferrite combined with pearlite, bainite, and martensite, while newlinemaintaining a similar nominal carbon content. Subsequent processing, including cold rolling newlineand annealing in the recrystallization and intercritical regimes, was employed to study the newlinemicrostructural and mechanical property evolution. Local mechanical properties were newlineassessed using high-speed nanoindentation mapping. Hardness data was deconvoluted using a newlineclustering algorithm to determine the hardness of individual constituents. , Excellent newlineagreement between microstructure and hardness at the micrometer length scale was observed newlinein all cases. Despite identical nominal compositions, the three distinct dual-phase initial newlinemicrostructures exhibited differences in the area fraction and hardness of ferrite and newlinesecondary constituents. Similar trend was observed after subsequent thermomechanical newlineprocessing, such as cold rolling, recrystallization, and intercritical annealing, the newlineexperimental observations were reconciled based on processing conditions and the length newlinescale of the microstructure and potential underlying mechanisms are presented. This study newlineshowcases the capability of nanoindentation mapping to capture local variations in hardness newlineat the length scale encountered in DP steels, opening avenues for correlative characterization newlineand the development of next-generation AHSS and multiphase steels. newline