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

Significance Statement

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.

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

About The Author

Rumana Hossain ([email protected])

The Recipient of an Australian Postgraduate award for PhD study in Material Science and Engineering at UNSW Sydney in 2015, Rumana Hossain has a Bachelor of Science degree in Mechanical Engineering and a Master of Engineering degree in Advanced Engineering Management from Bangladesh University of Engineering and Technology. Prior to starting her PhD, She was a lecturer at the School of Engineering and Computer Science in Independent University Bangladesh. She is the expertise solid state phase transformation mechanism and mechanical characterization of high carbon steel. Rumana has published several journal papers in the renowned journals including Nature Publishing Group Journal.

About The Author

Dr Farshid Pahlevani is an authority on high temperature metallurgical processes who has made a considerable contribution to the understanding of the behavior of metallic materials at high temperatures and their interactions with other elements (including heat treatment and metal casting procedure). Dr Farshid’s research focuses on liquid to solid phase transformations and he has established the comprehensive knowledge necessary to precisely control the kinetics and thermodynamics of high temperature reactions, metal-oxide interface reactions, and heat treatment and metal’s property correlation.

His international research career, spanning high profile research institutes in Japan, Singapore and Australia, includes considerable experience working closely with industry to improve existing processes to achieve better environmental outcomes and greater cost efficiencies.

About The Author

ARC Laureate Professor Veena Sahajwalla is revolutionizing recycling science to enable global industries to safely utilize toxic and complex wastes as low cost alternatives to virgin raw materials and fossil fuels. As Founding Director of UNSW’s Centre for Sustainable Materials Research and Technology, Veena and her team are working closely with industry partners to deliver the new science, processes and technologies that will drive the redirection of many of the world’s most challenging waste streams away from landfills and back into production; simultaneously reducing costs to alleviating pressures on  the environment. She is reimagining the global supply chain by demonstrating the viability of ‘mining’ our overburdened landfills to harness the wealth of useful elements like carbon, hydrogen and materials like silica, titania and metals embedded in our waste. By using precisely controlled high temperature reactions – that selectively break and reform the bonds between different elements within complex waste mixes – Veena is producing previously unimaginable value-added new ‘green’ materials and products. In the process, she is building an unparalleled portfolio of new science and engineering that is overcoming many of the technical limitations and cost barriers of conventional recycling that currently leaves much of our waste behind.

Acknowledgments
This research was supported under Australian Research Council’s Industrial Transformation Research Hub funding scheme (project IH130200025).

Reference

Rumana Hossain, Farshid Pahlevani, Veena Sahajwalla. Effect of small addition of Cr on stability of retained austenite in high carbon steel. Materials Characterization 125 (2017) 114–122.

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