| The samples of the used direct-bonded magnesia-chrome refractories of a VOD were made into thin sections for the optical and electron microscopic investigations to characterize the failure mechanisms of the lining in the stainless steelmaking conditions. In addition to the extremely hostile conditions imposed on the VOD refractory bricks, the lack of a retardation mechanism of the slag penetration makes them exceptionally more vulnerable compared with those of the carbon-containing MgO-based bricks of LD converters and EAFs. The study on the brick samples using optical microscope, EPMA, X-ray diffraction and EDAX has shown: 1. In the early stage of the process, the matrix of Mag-Chrome brick consisting mainly of MgO fines with M₂ S and CMS bonds is attacked by the low basicity slag and the lime added as a flux, forming low-melting silicates such as CMS and C₃ MS₂ . 2. The alumina foamed as a result of the addition of aluminum to reduce Cr₂ O₃ to Cr is responsible for the formation of no less detrimental low-melting aluminates such as C₄AF, CAS₂, etc. in the later stage. |
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