ACCURATE AND PRECISE REFERENCE METHOD FOR THE DETERMINATION OF CHROMIUM IN HIGH-ALLOY STEEL

Methods for determining chromium in high-alloy steels based on potentiometric titration after oxidation of chromium(III) to chromium(VI) with peroxodisulphate were studied using different dissolution procedures, viz., dissolution in HClHNO3 and fuming with H2SO4H3PO4, dissolution in HClHNO3 and fuming with HClO4, dissolution in HClHNO3HF in a microwave oven, fusion in sodium peroxide in a zirconium crucible and dissolution in dilute H2SO4 and oxidation with H2O2. A back-titration was used with dichromate after addition of solid ammonium iron (II) sulphate. The dissolution procedures were tested on 24 certified reference materials (0.01-3.3% C, 10-325% Cr). All procedures except the second gave good results for samples with ≤ 0.8% C. For samples with ≳ 0.8% C, the third and fourth procedures gave significantly higher values and better precisions, and gave the best results for all samples. The relative standard deviations were, with few exceptions, below 0.2%. © 1990.