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Technical Paper


Figure 2: Formation of slag layer on top of steel melt in the crucible of the metal casting simulator (exemplary without sample equipment)


2-2: Results and discussion of laboratory corrosion tests


Figure 3 displays the three different samples after corrosion test. Above the slag line, all three sample bars show a colour change from black to grey, most likely due to oxidation of carbon. On top of the molten metal, the slag had a thickness of 5 mm. But the slag yields at the side walls of the crucible and samples to a thickness of 10 mm. Above the slag line, some slag covers the sample bars irregularly over a height of 3 to 10 mm. At macroscopic scale, no specific differences between the samples are detectable. The edges of the samples are not sharp anymore, but no particular washout is visible. At the slag refractory interface some pores are detectable, which could be related to degassing as consequence of carbon oxidation.


Digital microscope investigations at magnifications in range of 20 – 200x on polished surfaces of the samples revealed much more clear differences in corrosion behaviour (figure 4). It is obvious that compared to sample MgO- C-CMA and MgO-C-MA the interface of sample MgO-C-REF presents


MgO-C-REF


MgO-C-MA


MgO-C-CMA


Slag infiltration (µm)


MgO-C-REF MgO-C-MA MgO-C-CMA 1200 800 200 Microscopic Observation


Fissures, grain-matrix de- bonding, grain break-outs


No Fissures, rough surface, some grain break-outs


No fissures, smooth surface, slag sticking on surface


Figure 4: Slag-refractory interface at polished samples after corrosion test (50x magnification) and observations


MgO-C-REF MgO-C-CMA MgO-C-MA


many more fine cracks as fissures. It is not possible to measure directly the total slag infiltration depth, as the initial sample edge cannot be discerned.


But, taking the highest and lowest part of the slag-refractory interface into account, an infiltration depth of more than 1.2 mm can be calculated at sample MgO-C-REF. Unlike this reference sample, the slag-refractory interface of sample MgO-C-MA does not show fine fissures, but has a wavy character. This indicates that some of the coarse and fine grains of the material have been washed out. The average slag infiltration depth was calculated being in the range of 800 µm. In contrast, sample MgO-C-CMA shows a very sharp slag-refractory interface indicating much less interaction of the refractory material with slag. Furthermore, the slag infiltration depth


Figure 3: Samples after corrosion test in steel casting simulator November 2018 Issue ENGINEER THE REFRACTORIES 17


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