Microstructual Prediction of Ferrite-Pearlitic Microalloyed Steel in Controlled Forging

Abstract

Controlled forging is greatly effective in the weight reduction of automobile components as mentioned in the first report1), because of very fine microstructure. Its fine microstructure can be obtained by the control of forging temperature, strain and cooling rate. Thus, the optimization of the forging process is very important. Process modeling using finite element method (FEM) is very effective for the optimization of forging process, which has been widely used in controlled rolling. In the process modeling of controlled forging, austenite microstructure prediction and ferrite-pearlite microstructure prediction transformed from recrystallized and work-hardened austenite must be discussed respectively. Moreover, it is also necessary to predict yield strength, tensile strength, fatigue strength and ductility for the purpose of weight reduction. However, there are few process modeling systems which satisfy these requirements. In this attempted study, the construction of a process model of controlled forging which can predict the above-mentioned microstructure have been attempted. In the prediction of the austenite microstructure, Sellers' model showed good a result. In the prediction of the ferrite-pearlite microstructure transformed from recrystallized austenite, good results were obtained by using an effective austenite interfacial area. On the other hand, concerning the ferrite-pearlite microstructure transformed from work-hardened austenite, it was confirmed to be predicted precisely by the use of 'effective retained strain' which is newly suggested.