Int. J. Materials and Product Technology, Vol. 62, Nos. 1/2/3, 2021 111 Copyright © 2021 Inderscience Enterprises Ltd. Effect of low-temperature isothermal holding on microstructure and mechanical properties of hot rolled high carbon Nb microalloyed steel plate Indrajit Dey Department of Metallurgy and Materials Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah-711103, India Email: indrajit.rs2017@metal.iiests.ac.in Rajib Saha Product Development Group, R&D Division, Tata Steel Limited, Jamshedpur-831007, India Email: rajib.saha@tatasteel.com Swarup Kumar Ghosh* Department of Metallurgy and Materials Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah-711103, India Fax: +91-33-26682916 Email: skghosh@metal.iiests.ac.in *Corresponding author Abstract: Two high carbon steels, one plain carbon (HC0) and the other, Nb microalloyed (HC1) are selected in the present research. Both experimental steels were initially hot rolled after complete homogenisation and then air cooled to room temperature. These hot rolled plates were then subjected to low temperature isothermal holding followed by air-cooling to room temperature. Isothermal holding above the martensite start temperature (Ms) results in the formation of bainite with some amount of high carbon martensite whereas, isothermal holding below Ms leads to the formation of predominantly martensite. The increase in isothermal holding temperature from 200°C to 300°C results in lowering the hardness, estimated yield strength and ultimate tensile strength values marginally for HC0 whereas, it decreases the hardness, estimated yield strength and ultimate tensile strength values significantly for HC1 steel which may be attributed to the expected formation of some amount of coarse niobium carbide (NbC). Keywords: hot rolled steel plate; low-temperature isothermal holding; microstructure; mechanical properties. Reference to this paper should be made as follows: Dey, I., Saha, R. and Ghosh, S.K. (2021) ‘Effect of low-temperature isothermal holding on microstructure and mechanical properties of hot rolled high carbon Nb microalloyed steel plate’, Int. J. Materials and Product Technology, Vol. 62, Nos. 1/2/3, pp.111–125.