03:00 pm
Interaction of molten secondary metallurgical ladle slag with MgO-C refractories
Anton Yehorov | TU Bergakademie Freiberg | Germany
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Authors:
Anton Yehorov | TU Bergakademie Freiberg | Germany
Marcel Mix | Intocast AG | Germany
Natalie Fröse | Intocast AG | Germany
Prof. Dr.-Ing. Olena Volkova | TU Bergakademie Freiberg | Germany
Three various types of industrial MgO-C refractory were investigated by finger testing: standard, with addition of 2.5 wt% metallic aluminium, and with 2.5 wt% MagARMOUR CMA (mixture of alumina, magnesia, calcia). Prior to the finger testing experiment, all refractory samples were carbonized for 60 minutes at a constant temperature of 1000 °C in a graphite box. After the carbonation, the samples were immediately immersed in the molten desulphurizing slag (1650 °C) for 60 minutes. Afterwards, the MgO-C samples with adhered slag were perpendicularly sectioned and further SEM/EDX analysed with a focus on the interaction area. In addition, FactSage was applied to model the interaction between refractory and slag based on thermodynamic calculations. As a result, the wear properties of investigated refractories against the desulphurization slag were discussed, specifying the beneficial effect of protective additions.
03:20 pm
High Durability Ladle Treatment Lance for Steel Secondary Refining
Keisuke Yamada | Krosaki Harima Corporation | Japan
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Authors:
Keisuke Yamada | Krosaki Harima Corporation | Japan
Yoshihiro Sasatani | Krosaki Harima Corporation | Japan
Akira Nomura | Krosaki Harima Corporation | Japan
Takafumi Sato | Nippon Steel Corporation | Japan
Dr. Shunsuke Matsui | Nippon Steel Corporation | Japan
Secondary refining of steel in the ladle has been implemented widely with the LT lance which is inserted and blows argon or nitrogen gas into the molten steel to maintain its uniformity in composition and temperature. Major factors affecting on the life of the lance are considered to be corrosion at the slag line as well as crack extension and peeling-off the tip part of the refractories. A longitudinal cracking occurred in the tip part also terminates the life of the lance quite shortly, so the lance must be required to endure in the condition of high temperature corrosive environment with high spalling resistance. A new material was developed for the lance to satisfy the above requirements by processing through suppression of spinel expansion with reduced magnesia content and densification with reduced water content using a proper dispersant. The material exhibited both low apparent porosity and residual expansion with keeping an appropriate strength at temperatures higher than 1200 degree centigrade, together with high thermal spalling resistance. Thus, a parameter, crack index determined by the thermal spalling test was able to correlate intensively with a parameter of thermal shock damage resistance and the fracture energy. Finally, the LT lance with newly developed material was successfully applied to an actual operation in the secondary refining process of the stainless steel with a prominent performance of increasing durability both in the average life and cumulative immersion time in the molten steel from 11.1ch and 88min to 18.0ch and 121min.
03:40 pm
Graphene added Carbon MgO-C for Slag zone in steel ladle
Goutam Ghosh | Tata Steel | India
Prasanta Panigrahi | Tata Steel Limited, India | India
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Authors:
Goutam Ghosh | Tata Steel | India
Brijender Singh | Tata Steel | India
Prasanta Panigrahi | Tata Steel Limited, India | India
Magnesia carbon (MgO-C) refractories are widely used in iron and steel industries due to its excellent corrosion resistance to
basic slag. There are limitations in quantity of Carbon, (mainly by using natural flaky graphite), beyond a threshold limit, as
it adversely impacts coked properties, thermal conductivity and Carbon pick-up by steel. To mitigate this adversity, in recent
past, there have been several approaches to use of Nano-particle carbon, as it has been reported to have improved the thermosmechanical properties of MgO-C, by suitably modifying the binding structure. In Tata Steel, Graphene (TSG), as a form of
nano-carbon particle was used to develop improved quality MgO-C for the slag zone in the steel ladle. The objective was to
get improved oxidation resistance, corrosion resistance, and hot bending strength of MgO-C. The developed bricks were tried
in the steel-making shop ladles slag zone. Aluminum killed steel ladle slag showed the lowest corrosion when Graphene added
MgO-C brick was used in slag zone. The new class of graphene added magnesia carbon brick has a lower wear rate compared
to regular quality of magnesia carbon bricks.
Keywords: Magnesia carbon, corrosion, oxidation, performance
04:00 pm
Effects of Calcium Magnesium Aluminate Binder on Properties of Alumina-Magnesia Castables for Steel Ladle
Dr. Kun Ming Chen | China Steel Corporation | Taiwan
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Authors:
Dr. Kun Ming Chen | China Steel Corporation | Taiwan
Dr. Chia Hung Kuo | China Steel Corporation | Taiwan
Dr. Tung Hsin Su | China Steel Corporation | Taiwan
The starting material of the alumina-magnesia castables contains Al2O3 and MgO, which formed the alumina-magnesia spinel phase during high temperature service. This phase formation consequently resulted excessive expansion and cracking that lead to poor performing castables. The main purpose of this study is to observe the improvements in the properties of alumina-magnesia castables by adding Calcium-Magnesium-Aluminate (CMA) binder and reducing MgO powder addition. The corrosion resistance was defined by the deepest penetration depth of molten steel. The results revealed that the steel corrosion resistance was enhanced as CMA binder increased when comparing to original alumina-magnesia castables. However, the addition of CMA binder had no significant improvement on thermal shock resistance. Furthermore, corrosion behavior was observed in 0% and 2% CMA binder samples through microstructural analysis. The corrosion was firstly occurred in the matrix region and then the aggregate area could have been exposed during high temperature service which resulted in spalling and reduced performance. It was also found that 2% CMA binder added sample had a distinct interface layer. Further analysis by SEM/EDS showed that the refractory interface layer was mainly alumina-magnesia spinel phase. This spinel phase could block the continuous penetration of molten steel. In this study, the refractory matrix area was enhanced by the addition of CMA binder into the castables, thereby improved the ladle lifespan.