STRENGTH OF MIXTURES OF BAINITE AND MARTENSITE

Recently published experimental data demonstrate that the strength of mixed microstructures of tempered bainite and martensite can peak at a n intermediate volume fraction of martensite. In the present work, a q uantitative interpretation of these observations is achieved by modell ing the mechanical properties of bainite and martensite in their tempe red states. It is found that the peak in the curve of the strength as a function of the volume fraction of martensite can be attributed to t wo factors. When bainite forms it enriches the residual austenite with carbon, so that the strength of the subsequent martensite increases. In addition, during its deformation, the strength of the bainite is en hanced via plastic constraint by the surrounding stronger martensite. Taking these effects into account, it is possible to predict accuratel y both the trends and the absolute values of published experimental da ta on the strength of mixed microstructures.