FEM and multi-objective optimization of steel case hardening

Author(s): 
P. Cavaliere, A. Perrone, A. Silvello

CHALLENGE - Steel case hardening is a thermo-chemical process employed to solve wear and fatigue damage in materials. The process is strongly influenced by many different variables such as material properties and processing parameters. In the present study, the influence of such parameters affecting the carburizing quality and efficiency was evaluated with the aim to streamline the process by numerical–experimental analysis allowing for optimal conditions. 

SOLUTION The optimization software used is modeFRONTIER; a set of input parameters was defined (steel composition, carbon potential, carburizing time, etc.) and evaluated on the basis of an optimization algorithm carefully chosen for the multi-objective analysis. By coupling ANSYS calculations and modeFRONTIER correlations with the experimental data the solutions for each condition were obtained. Actually, the final analysis was the inspection of different conditions performed on spur gears. The results confirm that to obtain high bulk hardness it is necessary to employ longer carburizing times, such necessity is lower if just superficial hardness is required. The Pareto curve identifies those designs with a good compromise between superficial and bulk hardness.​ 

BENEFITS modeFRONTIER was used to find optimal solutions. It was calculated that carbon concentration on the surface is mainly dependent on carbon potential with a factor four with respect to carburizing time and temperature. The dependence on carburizing time tends to increase in the material bulk. At the end of the study different optimized designs were identified to achieve the maximization of surface and bulk hardness of the carburized steel identifying that to obtain high bulk hardness it is necessary to employ longer carburizing times, such necessity is lower if just superficial hardness is required. Furthermore, there's an excellent agreement between numerical and experimental data for carbon and microhardness profile also in the case of very complex geometries.

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