Andrea Chittaro's scientific contributions

ABS is commissioning a new hot rolling line dedicated to the production of grinding balls. The process requires an adequate combination of induction heating, rolling, and quenching to achieve the desired characteristics for the final grinding balls made of high carbon steels. This study focuses specifically on the on-line quenching process. Firstly, a finite element model is built up. Different ball diameters are considered in the simulations, and the cooling conditions are directly applied as boundary conditions. This numerical model enables the determination of the characteristic cooling rate depending on the process parameters and as a function of the ball diameter. Moreover, integrating metallurgical models in the simulation is instrumental to determine the final structure and to assess the final hardness of the ball. However, to be predictive, accurate material data related to the studied steel grades is needed. Several campaigns of dilatometric tests are conducted to characterize high carbon steel grades. Then, specific tests are carried out to study the kinetics of isothermal transformations of the studied grades. The TTT diagram is directly used in the material model. For each grade, the Continuous Cooling Transformation diagram is also constructed thanks to dilatometric tests. Finally, specific dilatometric tests are conducted to study self-tempering and partitioning effect of a reduction of the cooling rate for temperatures around the martensite start temperature.