METALS Effect of molybdenum on phase transformation and microstructural evolution of strip cast steels containing niobium Lu Jiang 1, * , Ross K. W. Marceau 1 , Thomas Dorin 1 , Peter D. Hodgson 1 , and Nicole Stanford 1,2 1 Institute for Frontier Materials, Deakin University, Geelong, VIC 3216, Australia 2 Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia Received: 14 May 2018 Accepted: 7 September 2018 Published online: 14 September 2018 Ó Springer Science+Business Media, LLC, part of Springer Nature 2018 ABSTRACT Molybdenum (Mo) is known to have a complex effect on phase transformations and precipitation in steels manufactured by conventional casting. The present work aims to examine the effect of Mo on phase transformations in Nb-con- taining steels produced by strip casting. Advanced experimental techniques have been utilised to simulate the strip casting process, and the microstructural features of the rapid solidification are retained for further study. Two cooling conditions from the austenite phase field were examined, isothermal holding and continuous cooling. It was found that at high cooling rates, the addition of Mo delayed the nucleation of bainite and lowered the bainite start temperature, but did not alter the bainite growth rate. The addition of Mo was also found to result in a slower transformation rate of polygonal ferrite under both isothermal and continuous cooling conditions. Thermodynamic simulations indicated that Mo did not affect the growth velocity of the polygonal ferrite, and quantitative metallography showed the nucleation density was significantly reduced by Mo addition. For the slowest continuous cooling rate, the addition of Mo completely inhibited pearlite formation, with bainitic ferrite forming instead. This has been suggested to be the result of the suppression of pearlite nucleation, rather than inhibition of growth. Introduction Direct strip casting (DSC) is a near-net-shape casting technology, which produces thin strips directly from the liquid metal. Unlike conventional casting pro- cesses that undergo a series of complex secondary processing operations such as hot rolling, in-line coiling or annealing, direct strip casting integrates casting and subsequent hot rolling in a single and continuous route with rapid solidification and high cooling rates [1–3]. Consequently, direct strip casting offers significant cost reduction and energy savings, but is limited in scope for thermomechanical pro- cessing of the as-solidified sheet. Address correspondence to E-mail: l.jiang@deakin.edu.au https://doi.org/10.1007/s10853-018-2908-x J Mater Sci (2019) 54:1769–1784 Metals