In-situ X-ray diffraction studies for enhanced understanding of the martensite transformation during AM of steels

Purpose and goal:

The overall aim of the project, a collaboration between SSAB, Uddeholm and KTH, was to increase the understanding of the microstructure evolution in steels when exposed to extremely high cooling rates as is typical during additive manufacturing (AMI) using the the method laser beam powder bed fusion (PBF-LB). The goal was to study phase transformations during the process using in-situ high-energy x-ray diffraction with a focus on the transformation from austenite to martensite for different iron-carbon alloys during cooling after laser melting.

Expected results and effects:

The results of the project highlight how the high cooling rates after laser melting affect the martensite transformation in iron and iron-carbon alloys. Particularly interesting is that the new data generated in the project shows a lower transformation temperature than obtained at conventional process conditions.

These results contribute to acceleration of development of new high-strength steels tailored for AM, which in the long run has an effect on the industrialization of AM as well as on enabling improved performance and new application areas for steels. Approach and implementation:

The project group consisted of KTH, SSAB and Uddeholm. Beamtime was obtained on the microXAS beamline, Swiss Light Source, and measurements were performed together with PSI in Nov. 2022. Subsequently, data analysis and complementary microstructure characterization with SEM and EBSD were performed.

Knowledge exchange between academia and industry has taken place continuously through regular meetings and active participation of all parties in the project´s activities. Wider dissemination of results takes place through scientific publication and conference presentation.