Partitioning of nitrogen atoms and its effect on retained austenite content in an ultra-low-carbon Cr-Mn-N stainless steel

The partitioning of nitrogen atoms and its effect on the retained austenite content (RAC) during quenching and partitioning (Q&P) process were investigated by dilatometry, X-ray diffraction, and field emission transmission electron microscopy with energy-dispersive spectrometer mapping in a 00Cr13Mn8N steel. Nitrogen partitioning by diffusion of N atoms from martensite to austenite occurred at 400 degrees C after quenching. N atoms are enriched in austenite after partitioning, and the stability of these N-rich austenite is improved and retained at room temperature during subsequent cooling. The different quenching temperatures (QTs) result in different phase fractions after partitioning. With the increase in QT, RAC first increases and then decreases, and the maximum RAC is 28.5 vol.% after quenching at 80 degrees C. A mathematical model was developed to rapidly and accurately characterize the phase fraction in Q&P process based on the relative length change of the samples partitioned after quenching at different QTs.

Automated summary

The distribution of nitrogen atoms in 00Cr13Mn8N steel during the quenching and partitioning process led to the enrichment of nitrogen in austenite, improving its stability at room temperature. Different quenching temperatures resulted in different phase fractions, with nitrogen being enriched in austenite and retained at room temperature.