Experimental investigation on low-carbon quenched and partitioned steel

This work is part of a wider study concerning Q&P steels subjected to different thermal cycles. The Q&P processes were carried out on the Gleeble 3800 thermomechanical simulator The steels investigated are identified as Si, Al and Mo steels. The first results, presented in this article, are relative to a silicon steel after quenching from different temperatures (always in the alpha+gamma intercritical field), followed by partitioning at different temperatures and for different times. The aim of these treatments was to evaluate the influence of process parameters on the microstructure and consequently on the mechanical properties. The microstructure was investigated by optical and scanning electron microscopy (SEM); the phases were identified by electron back scattered diffraction (EBSD); the volume fraction of retained austenite, at room temperature, was measured by X-ray diffraction; and HV hardness measurements were performed. Transmission electron microscopy (TEM) examinations are in progress. Some mechanical properties were measured by tensile tests. The mainly phases present in the microstructure of the steel were: ferrite, lath martensite and "retained" austenite. Their morphology and relative amounts depend on the thermal cycle. In particular; the treatments seemed to influence especially the austenitic areas undergoing transformation and their rate of transformation, the sizes and the more or less acicular morphology of structural elements. In some samples, the presence of tempered martensite and / or bainite was found too.