Transformation Induced Plasticity during Precipitation Strengthening of Maraging Steels - Tom Bell Young Author Award Candidate

The proper heat treatment of steels is imperative to achieve desired characteristics for specific applications. Consequently, the accurate simulation and prediction of the microstructural evolution, as well as the distortion and the residual stress state after heat treatment, are of great importance in ensuring the usability of the component.

In laser-based additive manufacturing, high-temperature gradients lead to the formation of residual stress. Therefore, the heat-affected zones are tempered/aged under the influence of stress. The existing research on the influence of stress on precipitation during tempering/aging heat treatment shows a considerable gap in the state of knowledge about transformation-induced plasticity (TRIP). TRIP is the anisotropic and permanent deformation caused by a phase transformation under stress lower than the material’s yield strength. Therefore, this work’s goal is to gain a better understanding of TRIP effect and its dependencies during the formation of precipitates due to tempering/aging.

This investigation focuses on various maraging steels, which are suitable materials for laser-based powder bed fusion. These steels underwent continuous aging under different external compression stresses, using a dilatometer. Subsequently, the amount of TRIP strain has been separated from the total strain for each experiment. Afterward, the relationship between the maximum TRIP strain and the applied stress was examined to determine the TRIP constant specific to each maraging steel, which can be used in order to model and simulate the development of TRIP during aging.

The results prove the existence of the TRIP effect during precipitation of intermetallic phases in maraging steels and offer a basis for further investigations regarding the post-heat treatment material state and its prediction.