Wear Mechanisms of Carbon-Based Refractory Materials in SiMn Tap-Holes—Part II: In Situ Observation of Chemical Reactions

The purpose of the study presented here is to determine to what extent chemical reactions between carbon-based refractory and slag or metal in the tap-hole of a SiMn furnace can contribute to wear of tap-hole refractory. The results of the study are reported in two parts. In Part I, thermodynamic calculations suggested that reaction between silicomanganese slag and carbon-based tap-hole refractory is possible, and experiments with nominally pure materials support this. However, practical refractory materials are by no means pure materials and contain secondary phases and porosity which can be expected to affect reaction with slag. In Part II, such reactions are examined experimentally, in cup and wettability tests, using commercially available carbon block and cold-ramming paste refractory materials and mainly industrial SiMn slag. Clear evidence was found of chemical reaction at approximately 1870 K (approximately 1600 C), forming SiC and, it appears, metal droplets. Both carbon block and ramming paste refractory reacted with slag, with preferential attack on and penetration into the binder phase rather than aggregate particles. The two types of carbon-based refractory materials showed similar extents of chemical reaction observed as wetting and penetration in the laboratory tests. The differences in refractory life observed practically in industrial furnaces should therefore be attributed to wear mechanisms other than pure chemical wear as studied in this work.National Research Foundation of South Africa (Grant TP2011070800005).http://link.springer.com/journal/116632016-04-30hb201

Design of low-melting point compositions suitable for transient liquid phase sintering of PM steels based on a thermodynamic and kinetic study

The possibility of tailoring the characteristics of a liquid metal is an important asset in a wide number of processing techniques. For most of these processes, the nature and degree of the interaction between liquid and solid phases are usually a focus of interest since they determine liquid properties such as wettability and infiltration capacity. Particularly, within the Powder Metallurgy (PM) technology, it is considered one of the key aspects to obtain high performance steels through liquid phase sintering. In this work, it is proved how thermodynamic and kinetics software are a powerful tool to study the liquid/solid interactions. The assessment of different liquid phase promoters for transient liquid phase sintering is addressed through the use of ThermoCalc and DICTRA calculations. Besides melting temperatures, particular attention is given to the solubility phenomena between the phases and the kinetics of these processes. Experimental validation of thermodynamic results is carried out by wetting and infiltration experiments at high temperatures. Compositions presenting different liquid/solid solubility are evaluated and directly correlated to the behavior of the liquid during a real sintering process. Therefore, this work opens the possibility to optimize liquid phase compositions and predict the liquid behavior from the design step, which is considered of high technological value for the PM industry