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Effect of molybdenum on phase transformation and microstructural evolution of strip cast steels containing niobium

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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-containing 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.

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The work in this study was funded by ARC Discovery Grant (DP160101540). The authors would like to acknowledge the support of the Deakin Advanced Characterisation Facility. The authors are grateful to David Gray for the help of casting alloys. Laboratory support provided by Maggie (Huaying) Yin and assistance with dilatometry testing from Jerome Cornu are also acknowledged. The continued support of Prof. Tanya Monro and Prof. Emily Hilder is gratefully acknowledged.

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Correspondence to Lu Jiang.

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Jiang, L., Marceau, R.K.W., Dorin, T. et al. Effect of molybdenum on phase transformation and microstructural evolution of strip cast steels containing niobium. J Mater Sci 54, 1769–1784 (2019).

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