Chemical reactions during submerged arc welding with FeO-MnO-SiO 2 fluxes
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INTRODUCTION
W E L D I N G fluxes have been designed to satisfy a multiplicity of requirements such as arc stability, weld metal protection, weld metal deoxidation and alloying, slag detachability, etc. These requirements would be better fulfilled with further understanding of the many chemical reactions occurring simultaneously during welding. The purpose of this investigation is to initiate a systematic examination of the pyrometallurgical reactions and processes involved in welding steel. By performing experiments in which only a small number of parameters are varied in a well defined manner we hope to gain an understanding of the kinetic and thermodynamic factors which influence the composition of the weld metal and the quality of the weld. Within this framework, we examine the thermodynamics and kinetics of the chemical and phase reactions which may be operative during welding in order to place limits on the range of possible reactions and processes which might occur in the complex range of materials, densities, temperatures, and states which lie in the relatively small distance between the filler metal feed and the metal to be welded. Despite suggestions to the contrary, it is unlikely that equilibrium could be attained (except in small volumes) even at the high temperatures involved; this is so because of the very large temperature and density gradients, the presence of different phases--slag, metal, and plasma--the large electric currents, and the large radiative transfer of energy from the arc. Despite the expected departures from equilibrium, one may utilize equilibrium considerations, albeit cautiously, to place constraints on the chemical reactions and mechanisms involved in welding. A common approach is to assume that a state of thermodynamic equilibrium is attained locally, on the basis that the high temperatures and high surface-to-volume ratio counteract the short time available for reactions to be completed. Chemical equilibrium between slag and metal during the 1. ERNESTO INDACOCHEA ts Assxstant Professor, Department of Civil Engineering, Mecharncs and Metallurgy, University of lllinols at Chicago, Chicago, IL MILTON BLANDER is Senior Sc~ennst, Chemical Technology Dwlslon, Argonne National Laboratory, Argonne, IL NILS CHRISTENSEN ~s Professor, SINTEF, Norwegian Institute of Technology, Trondheirn, Norway. DAVID L OLSON ~s Professor, Department of Metallurgical Engineering, Colorado School of Mrnes, Golden. CO Manuscript submitted May 3, 1984.
METALLURGICAL TRANSACTIONS B
welding process was initially suggested by Bojko. 2 Measurements were later conducted methodically by Babcock, -~ Bischof, a Christensen, 5 Claussen, 6 and others. These investigators interpreted their results as a h~gh-temperature equilibrium between slag and metal. An inspection of the mass action indexes derived from their data revealed that these indexes varied widely for the various consumables studied. Christensen and Chipman 7 pointed out that no single slag parameter had been devised that will account accurately for
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