Unveiling interactions of tiny particles in advanced steels

The embedded particles, say the non-metallic inclusions, belong to a group of components that decide steel’s mechanical properties and applications. A latest study from NANOMO Research Unit and Process Metallurgy Research Unit at University of Oulu unveils the mysteries of inclusion interactions.

A modern and green life cannot circumvent utilizations of advanced steel, one of the most widely used engineering materials with good environmental credentials. Tiny particles, inclusions, embedded inside of the steel, can substantially change the mechanical properties. Like good and bad knots in wood, small and coherent particles may even strengthen the steel, while larger and incoherent inclusions are detrimental. The latter creates serious problems like breakage of steel wires during drawing, hydrogen‐induced cracking, fatigue failure, and surface flaws. These inclusions are typically composed of oxides, sulfides, and nitrides. Therefore, identifying these inclusions is important for controlling the properties of steels in the metallurgical process.

Determining the chemical components of inclusions is conventionally challenging due to tough iron matrix for inclusion extraction, destructive methods ruining inclusions, and complications of chemical separations within the nanoparticles. Theoretical knowhows are even more elusive since the experimental background could hardly provide knowledge to debut computational simulations. Yet, investigation of the non-metallic inclusions is seemingly stagnant.

In the latest work, researches from NANOMO and Process Metallurgy Research Units employed the cutting-edge synchrotron-radiation-based spectromicroscopy and quantum mechanical calculations to study interactions and formation mechanism of various inclusions within ultra high strength steel. The Finnish Research Infrastructure Roadmap facility MAX IV and the related FIMAX consortium, coordinated by University of Oulu were essential in the enabling the research.

With international collaboration, the team quantitively identified the inclusions of Boron Nitride and Titanium Nitride along with other commonly known ones containing calcium. However, the BN and TiN were individually formed without interactions between each other due to prohibition of BN formation once the Ti fraction becomes high. Looking at the broader prospect, it is foreseen that this study can provide major pathways to control non-metallic inclusions for green steel production.

The current research progress strengthens the collaborations within the University’s national Profiling project: Genome of Steel. As members of the Centre for Advanced Steels (CASR), the NANOMO and Process Metallurgy Research Units benefit the cross-disciplinary research in physical explorations of materials and research field of iron- and steelmaking processes.

The work was recently published in the top-level engineering journal of Scripta Materialia.


Unveiling interactions within non-metallic inclusions in advanced ultra-high strength steel: A spectro-microscopic determination and first-principles elucidation (sciencedirect.com 2021)

Last updated: 9.3.2021