Effect of Carbon on the Determination of Nitrides in Steel by Cold Nitric Acid Method

The effect of carbon on the quantitative determination of nitride-nitrogen in steel by dissolution in cold nitric acid has been investigated. (1) Nitrides are quantitatively extracted from steel with nitric acid aquaoud solutions at a temperature of -5°C and in the concentration range of 1:6 to 1:8. (2) The nitride-nitrogen in low carbon steel is accurately and rapidly determined by this method. (3) For the steel sample with a higher carbon content, the residue extracted by the method yields an erroneously higher result. (4) The reason for the erroneous result is that organic-nitrogen compounds are synthesized from the carbon in steel with nitric acid during the dissolution. (5) By heating the residue in a He stream to expel the organic-nitrogen compounds, the nitrogen in nitrides of Ti, Zr, V in steels is quantitatively determined.