Experimental Research On Quantilaline Prediction Of The Phase-Transforming Products Of A 45 Steel During Quenching And Tempering Processes

In order to optimize the quenching and tempering processes, increase efficiency and decrease energy consumption, it is necessary to develop a reliable quantitative analysis tool and establish the related database.There are complicated interactions among temperature, phase, and stress during quenching and tempering processes of steels. Such as phase transformation will result in changes of material parameters and mechanical properties. At the meantime hidden heat of phase transformation will affect the temperature field of the workpiece. Calculation of fraction of phase transformation is very important during numerical simulation of the temperature field and the stress field. In the paper, the influence of stress on the transformation kinetics and transformation plasticity during pearlite transformation, and the rule of phase transformation during tempering of a 45 steel have been studied.Based on the thermal simulation experiments, material parameters of pearlite, martensite, austenite have been measured, including coefficient of linear thermal expansion, Young's modulus, plastic modulus, yield strength and et al. It provides a basis for subsequent experiment and numerical simulation.It has been found that applied stress has significant influence on pearlite transformation. As the applied stress increases, the incubation time of pearlite phase transformation decreases, while the velocity of phase transformation increases. In addition, the parameter of transformation plasticity increases with applied stress when it is small than yield stress. The quantitative mathematical models of stress-induced transformation for pearlite are established and the models for transformation plasticity are modified. The calculated fraction of phase-transforming product with new models agrees very well with the measured values.Experiments also show that phase transformation may occur ever during rapid heating of martensite. Based on the concept of tempering parameter , a new kinetic equation of phase transformation during tempering process has been developed. With this new kinetic equation, process of phase transformation during tempering can be predicted more accurately and conveniently. The calculated fraction of phase- transforming product agrees well with the measured values during martensite tempering.The transformation kinetics during tempering of martensite under applied stress has been studied. When applied stress is smaller than yield stress, stress does not have significant influence on the process and the maximum fraction of phase-transforming product. So the results of numerical simulation of tempering process will not be influenced significantly without considering the effect of stress.