Fe-Cr Melt Nitrogenation When Exposed to Nitrogen Plasma

Abstract

The nitrogen absorption/desorption for pure iron and Fe-C alloys have been investigated in detail in levitated melts. However, limited study seems to be made while molten Fe-Cr alloy is exposed to nitrogen plasma. Nitrogen plasma offers an attractive means to nitrogenise Fe-Cr alloys in view of rapid absorption to higher nitrogen content. Several workers have reported that sulphur in the melt renders higher nitrogen. Industrially melt with higher nitrogen with sulphur may not be attractive. The experimental condition of present study solves this problem. Melts were made to observe the effect of arc current, plasma gas composition, surface active elements (SAE) in melt on melt nitrogen content. It was noted that the nitrogen was first absorbed upto certain maximum limit [Nmax] followed by its desorption on continued plasma exposure may be due to nitrogen bubble formation. The maximum nitrogen level in melts could be enhanced when rate of absorption in plasma arc zone was much higher with low desorption occurring in non-plasma arc zone of the melt. The use of higher melt temperature and low SAE in melt rendered higher absorption rate. The slower desorption rate could be obtained by maintaining lower SAE and temperature in melts. The nitrogen absorption in plasma arc zone followed first order reaction rate, however, desorption was probably depended on bubble formation frequency.