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B-Area: Numerical investigation of the manufacturing process for case-hardened PM-gears

Person in Charge: Dipl.-Ing. Philipp Nusskern
Motivation and objectives:
A new approach for case hardening of powder metallurgical (PM) steels is surface densification prior to heat treatment, hence avoiding carbonization.
Objective of the project is to develop a simulation tool for the manufacturing process of case-hardened PM-gear components in order to predict the microstructure evolution, the hardness as well as the porosity and residual stress distribution. Results of filling, compaction, sintering and rolling are provided by the IWM Fraunhofer Freiburg.
Research findings of the simulations should help to optimize processes and procedures within the process chain.
Methods Results

The numerical description of case-hardening of PM-components requires material parameters in dependency of carbon concentration and porosity. Therefore a method to determine effective diffusion coefficients had to be developed. For quenching simulation the transformation behaviour was measured by quench-dilatometry, the mechanical beahviour was determined by deformation dilatometry and the thermo physical parameters were detected by DSC- and Laser-Flash testing.

A mechanical surface treatment prior to case hardening enables to adjust a definite carbon profile during carburizing and so surface hardening of PM-components. The built-up numerical tools are able to predict the carbon depth profile and microstructure evolution in good agreement to the experimental results. The residual stress distribution, especially  the compressive residual stresses in the surface layer, are overestimated.
Nevertheless the simulations show the potential to describe case-hardening of graded porous PM-components.