Complete Calculation of Steel Microstructure for Strong Alloys

Strong steels also have to be tough and hence rely on fine microstructures such as bainite or martensite, produced commercially by continuous cooling transformation. Depending on the detailed requirements, the steel-design process may explicitly require other higher temperature phases to be absent in the final microstructure. Such a procedure can be made easier by the availability of a good method for calculating the transformation characteristics of a steel as a function of its chemical composition, austenite grain structure and cooling conditions. We present here a method for doing so using simultaneous transformation theory and mechanistic models for allotriomorphic and idiomorphic ferrite, Widmanstätten ferrite, pearlite, bainite, martensite and retained austenite. All of these details including thermodynamic and kinetic definitions of each of the phases have been incorporated into a computer algorithm which seems to correctly reproduce the trends expected from physical metallurgy principles, but on a firm quantitative basis.