![]() ![]() On the other hand, spinel inclusions could facilitate the formation of equiaxed crystal in ferritic stainless steel containing titanium through promoting the formation of titanium nitride, TiN, which has good lattice consistency with delta ferrite. However, there are few thermodynamic data of high chromium steel under the condition of low temperature because many studies have mainly targeted low alloyed steel with high liquidus temperature. Presence of MgO∙Al 2O 3 in molten steel facilitates nozzle clogging due to the strong adherability as mentioned above. Increase of alumina content in inclusion promotes precipitation of MgO∙Al 2O 3 phase. Alumina content in entrapped slag particle increases during the production process because of temperature drop from ladle to casting. Some inclusions found in steel products have been reported to originate from refining slag entrapped during AOD (Argon Oxygen Decarburization) or ladle process. Therefore, acquisition of thermodynamic data in lower temperature below 1873 K are also important, especially at as low as 1773 K. 1, 2, 3, 4) The temperature of molten high chromium steel during casting is lower than that of liquid iron or low alloyed steel. As a result, nozzle clogging decreases productivity and small debris flaked from the deposition results in surface defects. MgO♺l 2O 3 spinel inclusions are apt to adhere to the inner wall of the SEN (submerged entry nozzle) during casting. There exist the other problems of plant operation from refining to casting. The shortcomings intrinsically result from its high melting point and high hardness. MgO♺l 2O 3 spinel inclusions in high chromium steel are known to be detrimental to surface quality and mechanical properties such as formability and resistance to fatigue and fracture. Therefore, equilibrium experiments under various conditions and reliable technique of thermodynamic calculation with high accuracy are desired. However, the calculated phase stability diagrams vary among studies even in liquid iron or low alloyed steel. In TiO X–Al 2O 3–MgO system inclusion, commercial thermochemical software predicts that boundaries of Ti 2O 3, Ti 3O 5, Al 2O 3 and TiOx–Al 2O 3 shift toward lower titanium content in high chromium steel. However, the region replaced by liquid oxide is understood differently in low alloyed steel and high chromium steel. Calcium, which is used to avoid the negative effect of MgO∙Al 2O 3 inclusion, enlarges liquid region in phase stability diagram. ![]() Temperature dependencies of deoxidation equilibrium constants below 1873 K are also scattered. The direction of boundaries shift is affected by chromium content differently. However, the effect of chromium content on boundaries of MgO, MgO∙Al 2O 3 and Al 2O 3 in phase stability diagram are much different among the researchers. Therefore, effects of temperature and content of elements on phase stability diagram should be clarified in chromium bearing steel. Controlling inclusion content in high chromium steel is very important to prevent submerged entry nozzle from clogging in continuous casting and avoid the negative impacts of inclusions on steel properties. ![]()
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