Enhancing tensile properties of ultrafine-grained medium-carbon steel utilizing fine carbides

Highlights: → Tensile properties of UFG carbon steels were enhanced by imbedding fine carbides. → Thinner pearltic lamellae induced finer carbides after caliber-rolling process. → Superior tensile properties were attributed to the enhanced strain hardening rate. → Yield-point phenomenon in UFG steels resulted from stronger effect of particle growth. - Abstract: The aim of the present study is to evaluate the influence of nano-sized carbides upon tensile behavior in UFG medium-carbon steels and to develop a material with improved tensile properties. UFG medium-carbon steels with fine carbides were successfully fabricated by multi-pass caliber rolling at 773 K. Alloying chromium and molybdenum resulted in thinner pearlitic lamellae, which were transformed into finer particles after severe plastic deformation. The UFG steel containing the alloying elements exhibited superior tensile properties, which was attributed to the enhanced strain hardening rate by the imbedded finer particles. Subsequent annealing induced growth of grains and particles, which also recovered elongation at the expense of strength. All UFG steels investigated here showed a yield-point phenomenon due to the decreased hardening rate and lack of mobile dislocations and their sources. The deteriorating effect of particle growth overwhelmed the improving effect of grain growth after annealing of the UFG medium-carbon steel, leading to a reduced strain hardening rate. This resulted in a positive correlation between a grain size and Lueders elongation in the investigated UFG steels.