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Technical Paper


www.ireng.org MATERIALS FOR STEEL LADLE PURGING PLUGS Bin Long a , Buhr Andreas b , In-Ho Jung c , Shengli Jin d , Harald Harmuth d


a Almatis Qingdao, Qingdao, China b Almatis GmbH, Frankfurt, Germany c McGill University Canada, Canada


d Abstract


This paper provides a summary of extended investigations performed on cement- and hydratable alumina bonded refractory materials for steel ladle purging plugs. The main wear factors of purging plugs, which are erosion due to intense stirring, corrosion by iron-oxide slag during oxygen lancing, and spalling due to thermal cycling, were addressed in the investigation by theoretical thermodynamic evaluations using FactSage, mechanical property testing including hot modulus of rupture, and fracture behaviour testing using the wedge-splitting


test.


Chair of Ceramics, Montanuniversitaet Leoben, A-8700, Leoben, Austria e


Jerry Dutton, Stourbridge, United Kingdom


due to horizontal cracking caused by thermal cycling of purging plugs. New developments in steel metallurgy are concentrated around clean steel, alloy steel, tool steel, and higher manganese steel. This will make the working conditions for purging plugs even more challenging.


This paper provides a summary of investigations for the comparison of cement bonded with CaO-free hydratable alumina bonded refractory castables for the purging plug application, which were discussed in detail in previous publications [6,7]


. It would be very difficult or impossible to In addition, microstructural


investigations were performed in order to explain material differences. The results provide a basis for the assessment of the different binder concepts especially for the purging plug application and indicate the potential, which hydratable alumina bonded materials could have in this area. Industrial and academic partners of the FIRE-network from three different continents have successfully cooperated in this study.


Key words: Al2O3 -MgO-CaO; FactSage analysis; Cement bonded castable;


No-cement castable; Hydratable alumina; Fracture behaviour; Spalling; Microstructure; Steel ladle purging plug.


1. Introduction


Purging plugs in the steel ladle bottom are used for stirring the steel in the ladle during metallurgical treatment (Figure 1). Their use is essential for the process. Clogged purging plugs cannot perform their function and therefore the hot surface of the purging plug is examined after each heat to ensure the gas channels/slits are open. In the case of residual steel or slag being present on the surface, pure oxygen is blown through a lance onto the surface to melt and wash any residue. During that process an iron oxide slag is formed which attacks the refractories at temperature above 2000°C.


A low- or ultra-low-cement castable (LCC or ULCC) in the Al2O3 -MgO-


CaO system, based on corundum and with addition of spinel has become the standard solution for purging plugs over the past 20 years [1-5]


. CaO-


free hydratable alumina bonded castables (no cement, NCC) could be an alternative for the purging plug application, because the absence of CaO would increase the resistance against iron oxide slag. In addition, the mechanical properties would change by replacing cement with hydratable alumina binder, which would influence the fracture behaviour. In industrial applications, the purging plugs are dried at temperatures around 400°C or pre-fired at temperatures up to 1600°C. This changes such properties as strength and fracture behaviour. In this regard, it is important to investigate the influences of pre-treatment temperature on the mechanical behaviour of purging plugs.


The main wear factors for purging plugs are erosion due to intensive stirring during the process, corrosion by aggressive iron-oxide rich slag at elevated temperatures during frequent cleaning operations of the clogged purging plug surface by “oxygen lancing”, and spalling of layers from the hot face


16 Figure 1: Schematic picture of purging plug and steel ladle


2. Experimental Three types of castable Al2


O3 O3 -MgO-CaO, Al2 O3 -CaO, and Al2 O3 -MgO were


produced using tabular alumina (T60/T64, Almatis), magnesium aluminate spinel (AR 78, Almatis), reactive alumina (CL 370, Almatis), and dispersing alumina (ADS 3, ADW 1, Almatis) as stated in table 1. For the Al2 CaO and Al2


O3 was used as binder. For the Al2O3 -MgO-


- CaO systems, calcium aluminate cement (CA-14 M, Almatis) -MgO castable, a hydratable alumina


(Alphabond 300, Almatis) was used as the binder. This paper reports results for two or five percent cement, or four percent hydratable alumina in the formulation. Results with higher cement contents and lower or higher hydratable alumina contents were reported in a previous paper [6]


.


Raw materials were dry mixed in a Hobart mixer for 1 min and then wet mixed after adding the water. The wet out time for the two types of mixes


ENGINEER THE REFRACTORIES July 2018 Issue


simulate the conditions during “oxygen lancing” in practical tests in the laboratory. Therefore thermodynamic evaluations using FactSage were applied to assess differences between the binder concepts. The mechanical properties were tested and especially the hot modulus of rupture (HMoR) provides good indication on the erosion resistance of the material. Apart from the usual thermal shock resistance testing in the refractory industry, more sophisticated fracture behaviour investigation via the wedge splitting test according to Tschegg [8]


of the different materials after firing at 1650°C was investigated in order to explain different mechanical behaviour after sintering.


, Jerry Dutton e


COMPARISON OF CEMENT- & HYDRATABLE ALUMINA-BONDED ALUMINA-SPINEL


was carried out. In addition, the microstructure


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