Estudos de prevenção da corrosão de refratários utilizados em carro-torpedo
Resumen
The high competitiveness generated by the world metallurgical scenery
has been taking the Integrated Steelworks to look for an incessant way the
increase of the efficiency of the refine pre-treatment processes, especially Pig
Iron Hot Metal Desulfurization at Torped Car. As collateral effect, the refractory
lining used in these equipment has been submitted to operational conditions
more and more severe leading to an increasing the wear rate. In this sense, the
Post Mortem Study of a based Al2O3/SiC/C/MgAl2O4 refractory lining (ASCM)
used at CSN Torped Cars was carried out. It was concluded that a slag
containing a big amount of calcium aluminum-silicate, interacts with the
refractory microstructure promoting the corrosion. It was also identified a
concurrent mechanism by alkaline incorporation, besides corundum to betaalumina
transformation and SiC oxidation by Na2O resulting in better conditions
to the graphite of protection, and consequently, improving the refractory lining
campaign. In order to prevent the corrosion of the Torped Car Refractory Lining,
a new technology was developed by using a Impregnation Technique of the
Cerium Solution SIT/Ce, which the Cerium Solution is able to fill up partially the
opened porous of the ASCM microstructure, improving the corrosion resistance
and thermal-mechanical properties. The protection mechanism was identified
carrying out dynamic slag test and fracture energy test, followed by
microstructure characterization by using of the Scanning Electronic Microscopy
(SEM), X-Ray Diffraction and Mercury Porosimeter. Another New Protection
Technology of Torped Car Refractory Lining was also developed based on
Protecting Layer Formation - FPL. This technique consists of changing the Slag
Composition, resulting in an improved wear resistance. Preliminary simulations
were carried out in order to optimize the dopant concentration at the slag,
followed by tests in rotative oven simulating the wettability refractory material by
doped slag. As consequence the Technology of FPL was implemented at
Industrial Scale resulting in an additional Protection Mechanism of CSN Torped
Car Refractory Lining. By taking account the ASCM refractory lining
microstructure, it was observed that main corrosion spots are located in the
material fine fraction (matrix). Besides, the matrix which includes the primary
bonding system, additional pores are generated to the existing ones as
consequence of the resin oxidation during Torped Car heating up. Therefore, it
was evaluated the effect of the Doping Bonding System in relation to the
thermal and mechanical properties and corrosion resistance. It was achieved an
improvement of both indicating the feasibility of The Doping Technique of the
Bonding System – DBS/CeO2.