Effect of small addition of Cr on stability of retained austenite in high carbon steel

High carbon steels with dual phase structure of martensite and metastable austenite are strong, hard and cost effective. This makes them suitable for a number of industrial applications in high abrasive environments. Nevertheless, the ductility of dual-phase high carbon steel can be questioned owing to the carbon percentage and brittleness of their martensitic structures. Fortunately, it is possible to achieve a good balance of high-energy absorption properties and strength in high carbon steel through alloying as well as well-controlled microstructures.

Several studies have it that retained austenite improves wear resistance and prevents snapping by absorbing energy from attenuation and impacts. In the process, the strains initiate the transformation of the retained austenite to martensite, therefore, contributing to high carbon steel deformation mechanism, its wear resistance and hardness. Therefore, controlling the percentage and stability of retained austenite is focal in optimizing mechanical properties for abrasion resistance in industrial undertakings.

Chromium is normally added to steel to improve its corrosion and oxidation resistance, and high temperature integrity. It has been assumed that the resulting enhanced mechanical attributes is a consequence of the chromium addition, but this demands further investigation. Understanding the critical chromium percentage and its effect on the structure of high carbon steel is important in designing cost effective high carbon steel for a several industrial applications.

Researchers led by Professor Veena Sahajwalla at UNSW Sydney addressed this knowledge gap by investigating the effect of small additions of chromium on the integrity as well as solid state transition of retained austenite in high carbon steel. They investigated three high carbon steel specimens with varying chromium concentrations under compression stress. Their work is published in Materials Characterization.

The research team investigated steels with varying chromium contents in chemical composition. The samples selected had similar retained austenite in order to establish the effects of chromium on the solid-state transformation of retained austenite. Chromium addition caused an increase in the eutectoid temperature and a drop in the eutectoid carbon content. Therefore, Manganese content was adjusted to offset these effects.

They observed that the stability of retained austenite in high carbon steel was improved by increasing chromium content to equal or more than the critical percentage. The mechanical stability of the retained austenite under compressive loads improved when the percentage of chromium increased. Load displacement curve analysis indicated evidence of austenite to martensite transformation under the indenter.

The researchers found that the induced critical load corresponding to martensitic transformation was higher in specimen with higher chromium content. This was consistent with the macro-scale outcomes indicating that chromium enhanced the stability of the retained austenite.

The results of their study are important in designing high carbon steel with excellent properties, however reasonable production costs since the lowest percentage of expensive chromium needed to realize these attributes can be efficiently utilized.