报告时间：2017年5月22 (星期一) 9:00-11:00am
报 告 人：Prof. Marcel A.J. Somers
工作单位：Technical University of Denmark, DEN
Marcel A.J. Somers was born in 1960 in Vlissingen, The Netherlands. He studied physical metallurgy at Delft University of Technology (TUD) and acquired his Ir. degree (comparable to M.Sc) in 1985 and his Dr. Ir. degree (equivalent to 4 years of research) in 1989. After employments with Philips and at TUD, he became full Professor of Physical Metallurgy in 1997 at the Technical University of Denmark (DTU), where he has led the Section for Materials and Surface Engineering at the Department of Mechanical Engineering since 2000. He has (co-)authored over 200 international publications, including several patents. He is the co-founder of two companies in the field of thermochemical surface engineering and has received several honours and awards for his scientific, teaching and innovation activities.
The case developing during low temperature surface hardening of austenitic stainless steel by nitriding, carburizing or nitrocarburizing consists of a supersaturated interstitial solution of nitrogen and/or carbon in austenite. The favorable properties of this so-called expanded austenite depend on the profiles of interstitial concentration and associated composition-induced residual stress over the case. The prediction of composition and stress profiles for a certain steel grade from process parameters as gas composition, temperature and time would enable targeted surface engineering of stainless steels. Furthermore, such a numerical model would enable the design of stainless steel compositions that are tailored for optimal performance during low temperature surface hardening.
In the present contribution a numerical model is presented to predict the interdependent composition and stress profiles over the expanded austenite case as developing during low temperature nitriding of austenitic stainless steel. The model departs from fundamental parameters as determined experimentally on homogeneous powders and foils and a diffusion model that incorporates the interaction of composition and stress as well as the elastic-plastic accommodation of composition-induced lattice expansion in the case.
The presentation includes the following topics:
- Interstitial solubility, interstitial diffusion and phase stability of homogeneous expanded austenite;
- Crystallography, thermal expansion and magnetism of homogeneous expanded austenite;
- Residual-stress measurement in expanded austenite cases;
- Numerical modelling aspects of composition- and stress profiles;
- The effect of deformation in stainless steel on the developing case.