Characterization of the sintered steel Astaloy CrA for the simulation of induction surface hardening of small-modulus gear wheels

Sintered steel components allow for near-net-shape manufacturing, minimizing machining costs and material waste. Due to their cost-effectiveness further enhanced by customisable material properties achieved through alloying and porosity, sintered steel components are receiving growing recognition, particularly for the production of complex-shaped parts such as gears used in the automotive industry.

As the fatigue limits and wear resistance of gears significantly depend on their surface layer conditions, post sintering heat treatment processes are essential. Induction surface hardening is particularly advantageous, as it offers localized heating, close to contour hardening and low distortion. Due to complex interactions between process parameters and the resulting material state, numerical methods have shown to be a time and resource efficient tool for the optimization of heat treatment processes. To obtain accurate simulation results, detailed material models that reflect on the electromagnetic, metallurgic as well as thermomechanical behaviour of the alloy used are required.

This study focuses on the experimental characterization of the porous sintered steel Astaloy CrA (Fe-1.8%Cr-0.6%C) and the development of a finite-element model for induction surface hardening. Porosity-dependent electromagnetic and thermophysical material properties were experimentally acquired across a wide temperature range and for all relevant phases. Additionally, phase transformation kinetics during heating and cooling were obtained using dilatometry. To simulate the induction hardening process, the material properties were integrated into a coupled electromagnetic-thermo-metallurgical finite-element simulation.

The simulations accuracy was validated through a case study involving a small-modulus gear wheel subjected to induction hardening. The microstructure and hardness distribution predicted by the simulation was compared to experimental measurements obtained from metallographic and mechanical analysis.

The findings provide valuable insights for optimizing induction hardening processes, further enhancing the application potential of sintered steel components in industrial applications.