NOMATEN HYBRID-SEMINAR March 24: Design and development of lightweight austenitic steels for high temperature applications

NOMATEN HYBRID-SEMINAR

online: https://meet.goto.com/NCBJmeetings/nomaten-seminar
In-person: NOMATEN seminar room (102)

Tuesday, March 24^th  2026 13:00 PM (CET)

Design and development of lightweight austenitic steels for high temperature applications

Sairam Kotla, PhD
Nomaten CoE, National Centre for Nuclear Research, Otwock, Poland.

Abstract:

Fe-Mn-Al-C-based lightweight austenitic steels (LWAS) are widely investigated as potential substitutes for conventional Ni-Cr steels to minimise the carbon footprint. However, grain boundary embrittlement by κ-carbide deteriorates the ductility, limiting their extension to elevated temperature properties.  An alloy design strategy that not only retards the κ-carbide precipitation but also imparts balanced strength-ductility at elevated temperatures is essential. The present investigation explores the dual role of molybdenum as a κ-carbide retarder and elevated temperature strengthener, through alloy design (CALPHAD) in combination with a conventional processing route. Four lightweight austenitic steels with the compositions: Fe-30Mn-5Al-1C-(0-3) wt. % Mo with varying molybdenum are designed and processed using vacuum induction melting and hot deformation. The role of molybdenum is investigated in terms of (a) static recrystallisation behaviour, (b) room-temperature tensile deformation, and (c) high-temperature deformation (monotonic tensile and tensile creep). Molybdenum addition retarded recrystallization kinetics by solute drag in 0.5-Mo alloy, additionally by Zener drag due to molybdenum enriched carbides in 2 and 3 - Mo alloys causing a shift in recrystallization temperature by ~ 100 °C. The room temperature tensile properties (YS & UTS) of as-recrystallized alloys increased with increase in Mo from 0 to 3 wt.%, through its solid solution hardening and precipitation hardening by Mo-enriched carbides, while the interphase decohesion leading drop in fracture strain. The high-temperature uniaxial tensile properties revealed dominance of interstitial strengthening by carbon up to 673 K, beyond which substitutional hardening by Mo in 0.5-Mo alloy and additionally precipitation hardening by Mo-enriched carbides in 2- and 3-Mo alloys. Serrated flow behavior observed is characterized to be due to dynamic strain ageing phenomena(DSA) by carbon at low temperatures and molybdenum at elevated temperatures. Tensile creep behavior revealed a decrease in creep rates with increase in Mo from 0 to 3 wt.% Mo by two orders of magnitude. The creep mechanistic parameters along with crept microstructures revealed dislocation-based creep mechanism is active in the investigated conditions. A detailed overview of the influence of Mo correlating the microstructure and mechanical properties will be discussed.
 

References: 
[1] K. Sairam, et al Scripta Materialia,230 (2023) 115399
[2] Kotla Sairam et al Trans IIM, 77, (2024), 2431-2437
[3] K. Sairam, et al Metall Mater Trans A 56, 1799–1816 (2025)
 

Bio:

Dr. Kotla Sairam Goud is currently working as a Postdoctoral Researcher in the Functional Properties Group at NOMATEN, NCBJ with Prof. Łukasz Kurpaska. He did his Bachelor’s in Mechanical Engineering, followed by a Master’s in Materials Technology from NIT Warangal, during which carryout thesis project at IGCAR, Kalpakkam, India. Later, he pursued doctoral studies in the materials science and metallurgical engineering department at IIT Hyderabad with Dr. Korla Rajesh. His primary research interests include alloy design, deformation behaviour of materials at room and high temperatures, creep and micromechanical testing, with microstructural characterization. His current research at the NOMATEN focuses on developing high entropy alloys with high radiation resistance and good mechanical properties at elevated temperatures.