Effects of silicon content and intercritical annealing on manganese partitioning in dual phase steels

Steels of constant manganese and carbon contents with silicon content of 0.34%–2.26% were cast. The as-cast steels were then hot rolled at 1100 °C in five passes to reduce the cast ingot thickness from 80 to 4 mm, air cooled to room temperature and cold rolled to 2 mm in thickness. Dual phase microstructures with different volume fraction of martensite were obtained through the intercritical annealing of the steels at different temperatures for 15 min followed by water quenching. In addition to intercritical annealing temperature, silicon content also altered the volume fraction of martensite in dual phase steels. The partitioning of manganese in dual phase silicon steels was investigated using energy-dispersive spectrometer (EDS). The partitioning coefficient, defined as the ratio of the amounts of alloying element in the austenite to that in the adjacent ferrite, for manganese increased with increasing intercritical annealing temperature and silicon content of steels. It was also found that the solubility of manganese in ferrite and austenite decreased with increasing intercritical temperature. The results were discussed by the diffusivity and the solubility of manganese in ferrite and austenite existed in dual phase silicon steels.