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Nitrogen transfer into plasma heated steel melts as a function of arc polarity
Author(s) -
Neuschütz Dieter,
Zhai Yuyou,
Hauck Alejandro
Publication year - 1994
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.199401061
Subject(s) - plasma torch , anode , plasma arc welding , crucible (geodemography) , chemistry , nitrogen , plasma , argon , arc (geometry) , cathode , mass transfer , analytical chemistry (journal) , tungsten , inert , quenching (fluorescence) , heat transfer , plasma activation , electrode , materials science , metallurgy , thermodynamics , chromatography , mathematics , physics , computational chemistry , geometry , organic chemistry , quantum mechanics , fluorescence
Heating liquid steel in the tundish with argon stabilized plasma arcs is one example of the increasing importance of mobile and inert heating systems in metallurgy. Unwanted nitrogen pick‐up caused by infiltrated air, and possibly aggravated by the activating effect of plasma, should be minimized by selecting the optimum current mode and torch polarity. With this aim in mind, the nitrogen transfer kinetics have been investigated on 150‐kg low carbon steel melts at different nitrogen partial pressures as a function of arc polarity. The experimental plasma plant was equipped with a 2000‐A torch, housing a thoria stabilized tungsten electrode, and a counter electrode located at the bottom of the crucible. The torch could be operated with DC of either polarity or with AC. Kinetic models of nitrogen transfer have been developed, which show good agreement with experimental results. Arc polarity has a significant effect both on the rate of nitrogen pick‐up in the arc area (pumping effect) and on the mass transport in the melt (stirring effect). Of all configurations tested, the torch as cathode is the most suitable arc configuration for inert heating, since the particularly active N + ions in the plasma are repelled by the melt surface. Furthermore, the relatively strong stirring effect of the plasma jet leads to the highest heat transfer efficiency. On the other hand, where controlled nitrogen pick‐up is required, the highest nitrogen transfer rates are obtained with the torch poled as anode.