On the role of Manganese Partitioning in Metastable Austenite by Quenching and Partitioning Treatment

With the aim to study the role of frozen concentration gradient of manganese (Mn) element in stability of retained austenite (RA) with multiple-stage martensite transformation, a series of intercritical annealing (IA) temperatures is conducted before quenching and partitioning (Q & P) treatment. Morphology and distribution of RA are observed by field emission gun scanning electron microscope and electron back-scatter diffraction. The volume fraction (7%-16%) and stability of metastable RA is found to be affected profoundly by IA temperature. Thermodynamic and kinetic analysis are conducted to elucidate the evolution of RA in process of IAQP treatment. The predicted levels of RA are in good accordance with measurements. It is found that the inhomogeneous partitioning of Mn in period of IA, combining with the incomplete partitioning of carbon during Q & P, radically regulated the Q & P microstructure. The incomplete partitioning of carbon in RA, with excess carbon segregation at dislocations and boundaries, lead to partition-less bainite transformation owing to the average carbon content in RA lower than the T-o threshold.

Automated summary

A series of experiments were conducted to study the role of frozen concentration gradient of manganese (Mn) element in stability of retained austenite (RA) with multiple-stage martensite transformation, by performing intercritical annealing (IA) temperatures before quenching and partitioning (Q & P) treatment. The morphology and distribution of RA were observed, and it was found that the volume fraction and stability of metastable RA were significantly affected by IA temperature. Thermodynamic and kinetic analysis were conducted to explain the evolution of RA during the IAQP treatment, and the predicted levels of RA matched well with the measurements. The inhomogeneous partitioning of Mn during IA and the incomplete partitioning of carbon during Q & P were found to regulate the Q & P microstructure.