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Abstract:The microstructure of the as-quenched plate martensite in a high-C steel 100Cr6 was characterized by means of electron microscopy and atom probe tomography. The carbon redistribution behavior was investigated at the atomic scale, which revealed the nature of the transformation dynamics influenced by carbon and other substitutional alloying elements. A model was proposed to predict the carbon redistribution at twins and dislocations in martensite, which was based on their spatial arrangements.

A Fe–Al–Mn–Ni–C steel is designed explicitly to precipitate intermetallic phases in specific phases of a duplex steel. CALPHAD‐assisted alloy design is carried out with respect to an innovative “solublility‐assisted precipitation” (SAP) mechanism. A four phase equilibrium comprising of ferrite, austenite, κ‐phase (Fe3AlC), and B2‐phase (NiAl) is stabilized in a suitable annealing window. The processing conditions are adjusted according to elemental partitioning and consequential stabilization of κ‐phase in austenite and B2‐phase in ferrite. The feasibility of the SAP mechanism is validated by investigation of microstructure and precipitation evolution using electron microscopy and site‐specific atom probe tomography.

In-situ annealing experiments using synchrotron diffraction depict the separation of {100}-superlattice peaks ascribed to C-enrichment of pre-existing, Clean L´12-ordered structures into C-rich κ-carbides of alike crystal structure during heating of a high-Al lightweight steel. The peak separation is the first experimental in-situ investigation of the transformation sequence during Fe3AlC-phase formation. A detailed analysis of the lattice parameter evolution and thermal expansion behavior was carried out to validate the assignment of phases by comparison with theoretical calculations and available experimental data.