Study On The Interaction Between A508-3 Steel And Refractories For Ladle Lining

A508-3 steel is one of the nuclear reactor pressure vessel materials. Ladle refining technology is an effective method to ensure accurate chemical composition and high cleanness of A508-3 steel. Therefore, ladle refractories should not only have the excellent service performance such as slag corrosion resistance, thermal shock resistance, oxidation resistance, but also meet the demand of clean steel such as the removal of harmful elements and inclusions in the molten steel. More and more researchers have been attracted to pay much attention on this subject.Domestic A508-3 steel and ladle refractories were studied in this paper. The induction furnace dipping experiment was carried out to simulate the steelmaking process. The relationship among A508-3 steel, refining slags and carbon containing refractories was investigated by means of OM, SEM, XRD, DTA, etc. The original microstructure of MgO-C refractories is mainly composed of periclase and graphite. The original microstructure of Al₂O₃-MgO-C refractories is mainly composed of corundum, spinel, periclase and graphite.TGA results showed that thoughout the whole heating process 20℃-1300℃, the total weight loss of MgO-C sample was 1.1427mg, 16.93% of the total mass, while the total weight loss of Al₂O₃-MgO-C sample was 0.4414mg, 6.45% of the total mass, which was less than MgO-C sample. When the temperature is below 1070℃, reaction rule is basically the same between Al₂O₃-MgO-C sample and MgO-C sample. When the heating temperature is in the range of 1070℃-1170℃, the weight gain of Al₂O₃-MgO-C sample was 0.2234mg, 3.26% of the total mass.Molten steel corrosion mechanism of MgO-C and Al₂O₃-MgO-C refractories is nearly the same. Molten steel penetrated into grain boundaries of the main phase, left with many small holes and intergranular and intragranular Fe precipitation. At 1500℃, the carbon pick-up of MgO-C refractories in molten steel increased with time passing. 50 minutes later, carbon content of the molten steel reached the maximum, 4 times as high as carbon content of the original steel. MgO-C refractories brought MgO into the molten steel to form single MgO and complex oxide inclusions.In the slag corrosion resistance test of carbon-containing refractories, slag corrsion layer of MgO-C refractories is divided into slag layer and permeable layer. Slag layer is composed of C2AS phase, a small amount of periclase and holes; permeable layer consists of a large number of periclase grains, C2AS phase is in the grain boundaries. Al₂O₃-MgO-C refractories slag layer can be divided into slag layer, permeable layer and the original layer. Slag layer is composed of C2AS, CMAS and MA; C2AS, MA, CA2 and CA6 formed respectively from permeable layer to the original layer. The slag layer thickness of MgO-C refractories increases with slag alkalinity and time. The thickest slag layer is about 1.7mm with the slag basicity (CaO/SiO₂) 6.25 for 40 minutes.CaO-MgO-Al₂O₃-SiO₂ quaternary oxides in A508-3 molten steel can form simple oxides such as SiO₂, CaO, MgO, Al₂O₃ and complex oxide such as C2S, CAS2, C2F, A3S2.