Introducing Heusler intermetallics for synergic effect of grain refinement and precipitation strengthening in high-strength low-alloy steels

The remarkable combination of strength, toughness, and weldability that characterizes high-strength low-alloy (HSLA) steels make them suitable structural materials for naval and automobile applications. The well-studied effect of a microstructure, comprised of co-precipitated Cu and M2C carbides combined with a low carbon content, stands at the root of this superior synergy of properties. However, to advance in the innovation of stronger, lighter, and compositionally lean steels, new precipitation strengthening routes need to be explored. In this regard, Heusler compounds have proven promising for a selected group of structural alloys but have so far been untested in HSLA steels. Hence, in this work, two compositions close to HSLA-115 steel had been designed with the Fe2SiTi Heusler phase as its major strengthening phase. Modeling and experiments were carried out to describe the evolution of phase transformation and precipitation behavior. Results indicate a record high peak aged hardness of 717 HV arising from the contribution of the Fe2SiTi phase acting as a grain refiner as well as by its high ~8 vol.% of nanosized precipitates formed concomitantly with Cu clusters. Furthermore, the Nb influence on phase stability of this Heusler phase is elucidated through the study of precipitation kinetics. Overall, this work introduces a new design pathway for the development of ultra-high-strength steels by using the Heusler compounds, which benefit from a synergic effect of grain refinement and precipitation strengthening. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The remarkable combination of strength, toughness, and weldability makes HSLA steels suitable for naval and automobile applications. This study explores new precipitation strengthening routes using Heusler compounds in HSLA steels. Two compositions close to HSLA-115 steel were designed with the Fe2SiTi Heusler phase as the major strengthening phase. Modeling and experiments were conducted to understand the phase transformation and precipitation behavior. The results show a record high peak aged hardness of 717 HV, thanks to the contribution of the Fe2SiTi phase as a grain refiner and the formation of nanosized precipitates along with Cu clusters. The influence of Nb on the phase stability of the Heusler phase was also examined. In summary, this work introduces a new design pathway for the development of ultra-high-strength steels using Heusler compounds, benefiting from the synergic effect of grain refinement and precipitation strengthening.