Quantitative analysis of Nb in solution in a microalloyed carburizing steel by electrochemical etching

The amount of Nb in solution in a microalloyed carburizing steel (Nb-modified SAE 8620) was evaluated in different heat treated conditions. The test procedure involved electrochemical extraction, filtration and Inductively Coupled Plasma Atomic Emission Spectroscopic (ICP-AES) analysis. Characterization by X-ray diffraction of the residues collected in the filters was also performed. Results showed that Nb in solution tends to hydrolyze during electrolysis in a 10 vol.% HCl electrolyte, giving misleading measurements of the amount of Nb that dissolved during high temperature heat treatment. Hydrolysis of Nb is prevented by the addition of tartaric acid to the electrolyte. In the full dissolution condition, coarse (Ti,Nb)CN was the only precipitate present. Finer (Nb,Ti)C precipitates were observed after heat treating at 1050 °C.