Accelerated Spheroidization of Cementite in Sintered Ultrahigh Carbon Steel by Warm Deformation

What is it about?

Evolution of microstructure and hardness in quenched ultrahigh carbon steel Fe-0.85Mo-0.6Si-1.4C by warm compression on a Bähr plastometer-dilatometer at 775 °C and at 0.001 to 1 s−1 strain rate range is reported. The material was prepared via powder metallurgy: cold pressing and liquid phase sintering. Independent of strain rate, the initial martenstic microstructure was transformed to ferrite and spheroidized cementite. Strain rate had an effect on size and shape of spheroidized Fe3C precipitates: the higher the strain rate, the smaller the precipitates. Morphology of the spheroidized carbides influenced hardness, with the highest hardness, 362 HV10, for strain rate 1 s−1 and the lowest, 295 HV10, for the lowest strain rate 0.001 s−1. Resultant microstructure and ambient temperature mechanical properties were comparable to those of the material that had undergone a fully spheroidizing treatment with increased time and energy consumption, indicating that it can be dispensed with in industrial processing. All our results are consistent with the Hall–Petch relation developed for spheroidized steels.

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Why is it important?

Efficient control of microstructure in advanced steels is essential for optimizing mechanical properties and reducing industrial processing costs. Traditional spheroidizing heat treatments for ultrahigh carbon steels are time-consuming and energy-intensive, which limits their industrial application. It has been shown that warm deformation can significantly accelerate cementite spheroidization, enabling the production of fine, ductile, and strong microstructures in a much shorter time. This is important because it allows complex, multi-stage heat treatments to be replaced with more efficient thermomechanical processing routes, reducing production time, energy consumption, and overall manufacturing costs. Additionally, accelerated spheroidization through warm working creates new opportunities for tailoring the properties of powder metallurgy steels for high-performance applications, such as in the automotive and tooling industries. This strategy enables mechanical properties that are comparable to or better than those obtained using traditional methods, supporting the development of more sustainable and cost-effective manufacturing technologies for advanced steel components.