Improvement of tensile properties by controlling the microstructure and crystallographic data in commercial pearlitic carbon-silicon steel via quenching and partitioning (Q&P) process

In the current research, a complex microstructure and crystallographic data were devel-oped through quenching and partitioning (Q&P) process to improve tensile properties of commercial pearlitic carbon-silicon steel. Two-stage Q&P process, including full austeni-tization, quenching at 220 degrees 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 domi-nance 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.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

A complex microstructure and crystallographic data were developed through quenching and partitioning (Q&P) process to improve the tensile properties of commercial pearlitic carbon-silicon steel. The two-stage Q&P process produced a microstructure composed of tempered martensite, bainite, ultrafine carbides/martensite-austenite/retained austenite particles. Electron microscopy and X-ray diffraction techniques were used to investigate the microstructure and crystallographic data. Hardness and tensile properties were evaluated to confirm the improvement in mechanical properties. The presence of nano-carbide particles inside athermal martensite and the formation of preferential atomic-compact < 111 > direction in BCC plates were observed. The development of nanoscale carbide dispersed in refined bainite/martensite matrix significantly increased the yield and ultimate tensile strength, but reduced ductility compared to the initial microstructure.