Revealing the influence of Mo addition on interphase precipitation in Ti-bearing low carbon steels

Mo is widely used as an effective microalloying element to improve mechanical performance of inter phase precipitation steels, but the precise role of Mo in interphase precipitation behavior is not fully understood. In this contribution, interphase precipitation behavior in a series of Ti-Mo-bearing low carbon steels is systematically studied, and the role of Mo in interphase precipitates and its coarsening behavior is revisited. It is found that (Ti, Mo)C precipitates instead of TiC are formed in the Mo-containing alloys, and the average site fraction of Mo in (Ti, Mo)C is almost independent of the bulk Mo content. Moreover, the number density of interphase precipitates can be substantially enhanced by a minor addition of Mo, albeit it does not further rise with increasing the bulk Mo content. This is because the Mo fraction in (Ti, Mo)C rather than the bulk Mo content governs the driving force for precipitation nucleation and the interfacial energy of the (Ti, Mo)C/alpha and (Ti, Mo)C/gamma interfaces. In addition to the reduced interfacial energy, decrease of Ti trans-interface diffusivity has been identified as another key reason for the enhanced carbide coarsening resistance in Mo-containing alloys. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Molybdenum (Mo) is commonly used as an effective microalloying element in interphase precipitation steels to improve mechanical performance. However, the specific role of Mo in interphase precipitation behavior is not fully understood. Research has shown that in Mo-containing alloys, (Ti, Mo)C precipitates form instead of TiC, and the average site fraction of Mo in (Ti, Mo)C is independent of the bulk Mo content. Additionally, the number density of interphase precipitates can be significantly enhanced by a minor addition of Mo, with the Mo fraction in (Ti, Mo)C governing the driving force for precipitation nucleation and the interfacial energy of the interfaces.