Phase transformations in Cr–Mn white cast irons

Abstract

Increasing the manganese content of white cast irons containing (wt-%) ∼11%Cr, 2·5%C, and <1%Si changes the as-cast matrix from pearlitic to austenitic. The percentage increase of manganese required strongly depends on the carbon content of the alloy. No carbide precipitates could be traced in the as-cast austenitic matrix at low magnifications, but oil quenching treatment of the same alloy from 1100°C results in distinct carbide precipitates embedded in austenite. Tempering of both as-cast and oil quenched austenitic alloy in the temperature range 450–550°C results in fine carbide precipitates followed by pearlitic transformation during prolonged tempering and martensitic transformation during subsequent cooling to room temperature. The activation energy calculated from the tempering data indicates that most of the carbide precipitates are of type M₇C₃. Arrested cooling of the as-cast austenitic alloy at 930°C after austenitising at 1100°C results in fine carbide precipitates embedded in austenite which transforms into martensite on tempering. Ausaging (conditioning) of the as-cast austenitic alloy at 780°C results in fine carbide precipitates embedded in (probably) martensite.

MST/645