A national workshop organized Indian Institute of Metals
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New Horizons in Metallurgy, Materials, and Manufacturing

A national workshop organized by Indian Institute of Metals
December 14th - 16th 2020

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Advanced characterization and Calphad in design and development of advanced high strength steels


avatar Dr. R. Veerababu Scientist of special steels group at Defence Metallurgical Research Laboratory (DMRL)
Hyderabad
  • Bio

    Dr. R. Veerababu obtained his B.Tech in Metallurgical Engineering from NIT Warangal in 2002 and M.E. in Metallurgy and PhD in Materials Engg from IISc, Bangalore respectively in 2004 and 2016. Currently, he is a scientist of special steels group at Defence Metallurgical Research Laboratory (DMRL), Hyderabad. Earlier he worked in electron microscopy group of DMRL. His areas of work involve design, and development and indigenization of advanced high strength steels for naval applications. His areas of research include physical metallurgy and advanced microstructural characterization of high-performance steels such as ultra high strength and high toughness steels for aerospace applications and high strength low alloy (HSLA) steels for naval applications using electron microscopy and 3D atom probe. He has published more than 12 journal papers, and 3 DMRL technical reports and delivered more than 10 invited talks in national and international seminars/conferences/workshops. He is a life member of IIM, MRSI and EMSI.


  • Abstract

    Microstructure plays an important role in achieving the desired set of mechanical properties. Any design and development of new grades of steels or improvement in properties of the existing steels necessitates the understanding of the structure-property correlations through extensive microstructural characterization. Once the microstructure at different length scales has been understood, microstructural engineering through modification of the phases and phase fractions, size and distribution of the second phase via modification of the composition and processing windows may be applied to achieve the desired properties. This article describes our efforts in advanced characterization of ultra-high strength (UHS) steels using electron microscopy and 3D atom probe supported by thermodynamic calculations in the Calphad framework. TEM and APT characterization of UHS steel developed earlier at DMRL revealed the presence of atomic scale clusters of both carbon rich and carbon lean clusters. It is believed that these clusters can significantly influence both strength and toughness along with other strengthening mechanisms. These carbon lean clusters have been used as the base to tailor the microstructure for enhanced mechanical properties. ThermoCalc has been employed extensively to design a new set of compositions for experimental validation and optimization of the processing windows. Experimental results on the designed alloys reveal the decomposition of M2C carbide, which is not normally observed in this class of steels, as well as stabilization of austenite with increase in Cr and Mo over and above the existing DMRL UHS steel. Atom probe results further suggest the formation of clusters and their composition approaches towards M2C with increase in tempering temperature. The volume fraction and Cr/Mo ratio of the M2C type clusters broadly correlates well with the ThermoCalc predictions.