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Abstract
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This article investigates the strength and ductility properties of a low-alloy
steel with a carbon content of 0.32 wt.% after performing one-, two- and three-
step austempering processes. Dilatometry tests were used to extract the
mandatory data for heat treatment process design, and FE-SEM and XRD
were used to evaluate the microstructural characteristics of the heat-treated
materials. Quasi-static tensile tests and high strain rate Hopkinson tests were
performed to evaluate the strength-ductility combinations. The results
showed that step-austempering procedures ended in microstructural features
such as nanoscale bainitic ferrites and austenite films in bainitic sheaves
separated by austenite microblocks. The size and morphology of the
microstructural constituents were comparable to those of ordinary nanos-
tructured high-carbon bainitic steels after one-step isothermal bainitic heat
treatment. In addition, it was confirmed that a significant improvement in
mechanical properties could be achieved by changing the chemical composi-
tion. Finally, the strength values obtained at very high strain rates were
comparable to those of ordinary nanostructured bainitic steels with high
carbon content obtained by a one-step isothermal heat treatment process.
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