Virtual Design and Validation

Abstract

Application of products with properties locally adapted for specific loads and requirements has become widespread in recent decades. In the present study, an innovative approach to manufacture tubes with tailored properties in the longitudinal direction from a boron-alloyed steel 22MnB5 was developed. Due to advanced heating and cooling strategies, a wide spectrum of possible steel phase compositions can be obtained in tubes manufactured in a conventional tube forming line. A heat-treatment station placed after the forming line is composed of an inductive heating and an adapted water-air cooling spray system. These short-action processes allow fast austenitizing and subsequent austenite decomposition within several seconds. To describe the effect of high inductive heating rates on austenite formation, dilatometric investigations were performed in a heating rate range from 500 K s-1 to 2500 K s-1. A completed austenitizing was observed for the whole range of the investigated heating rates. The austenitizing was described using Johnson-Mehl-Avrami model. Furthermore, series of experiments on heating and cooling with different cooling rates in the developed technology line was carried out. Complex microstructures were obtained for the cooling in still as well as with compressed air, while the water-air cooling at different pressures resulted in quenched martensitic microstructures. Nondestructive testing of the mechanical properties and the phase composition was realized by means of magnetization measurements. Logarithmic models to predict the phase composition and hardness values from the magnetic properties were obtained. Subsequently, a simulation model allowing virtual design of tubes in the FE-software ANSYS was developed on basis of experimental data. The model is suited to predict microstructural and mechanical properties under consideration of the actual process parameters.