Lighter, Stronger, Durable: Advances in Zn-Coated Sheet Steel
The International Conference on Zinc and Zinc Alloy Coated Steel Sheet (Galvatech) is a premier international conference on cutting-edge technologies for the processing and performance of coated steel sheets for automotive, electrical appliance and construction applications.
Corrosion protected galvanized advanced high strength steels with high ductility (AHSS HD) like the investigated dual phase steel (DP1200HD) tend to show an elevated risk of liquid metal cracking (LMC) during resistance spot welding (RSW). LMC is an intergranular cracking mechanism driven by temperature, tensile stresses, plastic deformation and the presence of liquid zinc. Crack initiation and growth is caused by liquid metal embrittlement (LME) where the material experiences a drastic loss of ductility of up to 95 percent depending on the loading conditions. The aim of this work is to experimentally investigate LME and to develop a model to predict the local LMC during RSW.
The prediction of LMC is addressed with laboratory scale hot tensile tests with uncovered and galvanized steel sheets at a Gleeble 3800 thermomechanical simulator and extensive laboratory scale resistance spot-welding tests. All gained material and process data are subsequently used for creating a physically based and validated LMC indicator, which is dependent on temperature, plastic strain and strain rate. Newly developed and validated finite element models of the welding process accounting for all relevant multi-physical phenomena provide deep insight in the RSW process and help to understand the influence of different conditions leading to LMC. The LMC indicator enhances the capabilities of these models and provides predictions for the onset of LMC. Taking advantage of the LMC indicator allows modifying the welding process such that a significant reduction of LMC during RSW can be achieved.
City Hall Vienna
The lifetime of pot bearings is one of the major sources of maintenance shutdowns on a continuous galvanizing line. However the lifetime between different lines can be very different whereas the general process windows may look the same
A simple model is proposed to quantify the expected wear rate, considering the bearing geometry and process parameters. A viable model would help operators understand if a decrease of the bearing life is linked to variations in the process window.
The model has been used to explain the differences in bearing wear on several CGL using the same bearing materials. Validation showed that the observed trend is in relation with the model prediction. Next step will consist in comparing various lines and maybe set some coefficients to include the differences in bearing materials used (e.g. superalloys and ceramic).
This model approach attempts to put a little more science into bearing lifetime prediction.