Fundamental study on isolation and determination of various carbides in steels was carried out by means of hydrochloric acid, sulphuric acid, phosphoric acid, and potentiostatic electrolytic methods.
The results are as follows:
1. TiC, VC and NbC are very stable chemically, and are isolated by the electrolytic method quantitatively, and even by any mineral acid method easily.
2. ZrC in steel in relatively unstable and is decomposed gradually with the mineral acids. It is, however, able to be isolated by the electrolytic methods using any electrolyte.
3. Cr7C3/(Cr, Fe)7C3and Cr23C6/(Cr, Fe)23C3are isolated by the phosphoric acid method at room temperature. In case of isolating the chromium carbides, the electrolytic method is often adopted, but those using dilute hydrochloric acid and hydrochloric acid-ethyl alcohol or-ethylene glycol show more or less lower yield of the chromium carbides than former.
4. Mo2C is so unstable chemically that it decomposes not only in some mineral acids but also in water and alcohol. It is, however, isolated by means of the acid method using phosphoric acid (2+1), and by means of the electrolytic method using sodium citrate almost quantitatively.
5. Fe3C/(Fe, M)3C is isolated nearly quantitatively by the electrolytic method using sodium citrate-citric acid. In the electrolytic method using sodium citrate, i.e. neutral medium, the isolation of iron carbide depends on the condition of electrolysis remarkably.