Computer Modelling for the Yield Strength of the Mixed Micro-Structures of Bainite and Martensite

Abstract
The strength of mixed microstructures of bainite and martensite can peak at an intermediate volume fraction of martensite has been published by recently experimental studies. A quantitative interpretation of these observations is achieved by modelling the mechanical properties of mixed microstructures of bainite and martensite. The peak in the curve of the strength as a function of the volume fraction of martensite can be attributed to two factors. It enriches the residual austenite with carbon when bainite forms, so that the strength, of the subsequent martensite increases. In addition, the strength of the bainite is enhanced via plastic constraint by the surrounding stronger martensite. This means the bainite is under a tri-axial stress state. Taking these effects into consideration for the computer modelling, it is possible to predict accurately both the trends and the absolute values of published experimental data on the strength of mixed microstructures.