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Thermodynamic modelling of microstructural processes during HFI-welding

Simulated manganese distribution at 1,500 °C (left) and evaluation of an electron microprobe (EMP) measurement of an HFI-weld for the quantification of Mn depletion in the ferrite line (right)
Simulated manganese distribution and evaluation of an electron microprobe

Mannesmann Line Pipe GmbH has recently introduced an innovative model for the prediction of depletion of alloying elements in HFI-welds. Such a depletion can affect the mechanical and technological properties of HFI-welded pipes. Up until now, there has been neither a scientific explanation in literature for this phenomenon nor an established method for its quantification.

The company has commissioned Salzgitter Mannesmann Forschung GmbH with the task of developing thermodynamic models of the microstructural processes that occur during HFI-welding. To start with, the scientists at the research center worked out a method by means of which the depletion of alloying elements can be derived from electron microprobe (EMP) measurements. For this purpose, density distribution shifts of the various alloying elements in the ferrite line and the base material are determined. In a second step, an innovative phenomenological model was developed via integrated simulation for a qualitative and quantitative prediction regarding the redistribution of elements. This model is based on purely physical assumptions and is related to thermodynamical computations of the redistribution of alloying elements during the microstructural processes considered. The model's predictions are in agreement with the results of experiments conducted on a broad spectrum of materials used in production.

The resultant new findings enable Mannesmann Line Pipe to adapt its process control with a view to optimizing product properties.


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