Effect of thermomechanical treatment parameters on mechanical properties of duplex ferrite–martensite structure in dual phase steel

Abstract

The quantitative effects of the variables used in the thermomechanical treatment (TMT) of a dual phase steel, in the temperature region of intercritical annealing, have been studied by statistical design of experiments. The initial microstructure has tremendous influence on the final microstructure and properties of the steel. The kinetics of transformation is enhanced by the deformation process as has been evidenced by optical and TEM microstructures. The mechanical properties such as tensile strength, yield stress, and relative elongation have been correlated with the TMT parameters and are brought out in the form of regression equations. Percentage phase of ferrite or martensite formed owing to thermomechanical treatment by two different routes has also been quantified in the form of regression equations. The adequacies of the equations were assessed by a Fisher F test and the accuracies of the equations have been further verified by performing random experiments in the range of variation of the variables. Isoproperty lines have been constructed using the regression equations developed. The equations can predict the properties within the range of variation of the variables.