Solubility of carbon in tetragonal ferrite in equilibrium with austenite

There are precise observations which indicate the reluctance of excess carbon within bainite or martensite to partition into adjacent austenite in spite of prolonged heat treatment at temperatures where carbon is mobile. To explain this, we report the first calculations of the solubility of carbon in tetragonal ferrite that is in equilibrium with austenite. It is found that the solubility is dramatically increased relative to the cubic form of ferrite, and the implications of this are discussed briefly.