Studies on Phase Analysis of Molybdenum Carbides in Steel

Abstract

The chemical behaviour of molybdenum carbides were studied, in an attempt to establish a phase analytical method for them, of the steels of Fe-Mo-C system which were subjected to heat treatment to precipitate molybdenum carbides M₃C, Mo₂C, M₂₃C₆, and M₆C.
Molybdenum carbides were chemically less stable than carbides of vanadium, niobium, and titanium as to be dissolved to some extent even by H₂O, CH₃OH or C₂H₅OH. Their chemicalstabilities were found to increase in the following order M₃C M₂₃C₆ M₆C Mo₂C.
The quantitative extraction of all the molybdenum carbides was achieved by 9 N-H₂SO₄ dissolution at room temperature, but low results were obtained by other methods.
As regards the separation and the determination of Mo₂C, the satisfactory results were obtained in case of co-existence with M₃C either by 9 N-H₂SO₄ dissolution HCl·CH₃OH treatment or by 30 N-H₃PO₄ dissolution, but only the approximate values were obtained when Mo₂C was co-present with M₂₃C₆ and M₆C.
The following points were clarified by the experiments;
(1) M₃C was not stable towards H₂SO₄, H₃PO₄, and HCl.
(2) Mo₂C was stable towards H₂SO₄ and H₃PO₄.
(3) M₂₃C₆ was stable towards H₂SO₄, but not towards H₃PO₄ and HCl.
(4) M₆C was stable towards H₂SO₄ and H₃PO₄, but not towards HCl.