In the current research, a complex microstructure and crystallographic data were developed
through quenching and partitioning (Q&P) process to improve tensile properties of
commercial pearlitic carbon-silicon steel. Two-stage Q&P process, including full austenitization,
quenching at 220 C, followed by two different partitioning temperatures, was
applied to the as-received specimen to generate a complex microstructure composed of
tempered martensite, bainite, ultrafine carbides/martensite-austenite/retained austenite
particles. Microstructure and crystallographic data were investigated by scanning electron
microscopy, electron backscattered diffraction (EBSD), and X-ray diffraction techniques.
Then, hardness and tensile properties were evaluated to confirm the improvement of
mechanical properties. Dilatation-temperature curves exhibited the kinetics of martensitic
and bainitic transformation during quenching and isothermal partitioning stages. The
presence of nano-carbide particles inside athermal martensite was confirmed by electron
microscopy due to the pre-formed martensite carbon depletion during the partitioning
stage coupled with bainitic transformation. The formation of preferential atomic-compact
<111> direction in BCC (martensite/bainite) plates characterized by EBSD, could enhance
ductility by providing adequate slip systems. Point-to-point misorientation analyses
demonstrated a slight dominance of low angle boundaries proportion in bainitic dominance
structure in Q&P-220-375 specimen, which could be used in phase characterization.
Results revealed that the development of nanoscale carbide dispersed in refined bainite/
martensite matrix boosted the yield and ultimate tensile strength by over 100% and 110%
compared to the initial pearlitic microstructure. However, ductility reduced to half value in
Q&P-220-325 and Q&P-220-375 specimens.