A Study on the Possibility of Determination of Nitride and Dissolved Nitrogen in Steels Containing Al and N by Hydrogen Hot Extraction

Abstract

Hydrogen hot extraction for the determination of metallurgically dissolved nitrogen was investigated. Alminium-killed steel with nitride-nitrogen and dissolved nitrogen was heated in hydrogen stream at 500-1000°C, and after the extraction, total nitrogen retained in steel, nitride-nitrogen and nitrogen as NH₃ in hydrogen collected in diluted sulfuric acid were determined.
A kinetic consideration shows that the technique is only successful when the rate of dissociation of nitride, k₁ and that of precipitation, k₂ are negligibly smaller than that of formation of NH₃, k₃. In this case (k₁+k₂<<k₃), nitride-nitrogen remains unchanged in steel after hot extraction, while dissolved nitrogen is removed from steel as NH₃
Experimental results of aluminium-killed steel showed that the relation (k₁+k₂<<k₃) was not valid and this technique was unsuccessful. In steel having dissolved nitrogen only, aluminium-nitride precipitated during hot extraction, while dissolving of the nitride and removal of nitrogen were observed in steel with nitridenitrogen during hot extraction; this technique did not give the original contents of nitrogen of various states.