Speaker
Description
Non-metallic inclusions (NMI) are detrimental for the mechanical properties of steel since they usually act as defect initiation sites. NMIs could assume exogeneous (e.g. refractory, mould flux) or endogenous (e.g. re-oxidation) origins. The number and sizes of NMI that can be tolerated in tool steels which are used for demanding applications are even more stringent than regular steel grades. At Uddeholm AB in Sweden, some of the cast steel ingots are used as consumable electrodes in electroslag remelting (ESR) treatment to decrease macrosegregation and also the number and size of NMIs to obtain high-quality clean steel products. As the final cleanliness of the remelted ingot is partly inherited from the incoming electrode, it is crucial to develop a comprehensive understanding of its cleanliness. This study investigates the occurrence of mold-flux-originating NMIs by a combination of 2D and 3D methods in a cast tool steel electrode, motivated by such NMIs often have been found to be of large size. 2D inclusion analysis was performed using SEM-EDS on a polished metal surface to study the elemental distribution within the NMIs; 3D inclusion analysis was carried out using electrolytic extraction (EE) technique followed by an analysis of the filtered inclusions using SEM-EDS to gain large statistics of the location, size, morphology, and the compositions of the NMIs. Then, thermodynamic calculation was performed to evaluate the interaction between mould-flux inclusions and ESR slags. The results of this study could be used to improve the existing ingot casting process and also to optimize the ESR process for the production of high cleanliness steels.
| Speaker Company/University | KTH Royal Institute of Technology |
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