The method for isolation and determination of TiN and (Ti, Nb)(C, N) precipitated in Nb-Ti bearing steels has been investigated in the cooperative research of the Precipitate Analysis Subcommittee of Iron and Steel Analysis Committee of Iron and Steel Institute of Japan. Also, the precipitation behavior of TiN and (Ti, Nb)(C, N) in the steels has been studied. The results are summarized as follows ; (1) TiN, (Ti, Nb)(C, N) and other precipitates were extracted by potentiostatic or galvanostatic electrolysis in 10% acetylacetone-1% tetramethylammonium chloride-methanol electrolyte. (2) Only the TiN in the above mentioned precipitates was insoluble and remained by 60°C-10% brominemethanol solution treatment. Consequently, the amount and composition of TiN and (Ti, Nb)(C, N) could be determined quantitatively by analysis of the residues extracted by using the method of (1) and the residues after this treatment.(3) The size of TiN was several micrometers, the amount of TiN did not change with heating temperatures between 1000 and 1250°C, and the atomic ratio of Ti to N was stoichiometrically one to one. (4) Total amount of Ti and Nb in the precipitates decreased with an increase in heating temperature, because the small size of (Ti, Nb)(C, N) dissolved. (5) Both lattice constant and composition changes in (Ti, Nb)(C, N) showed that Nb and C dissolved preferably into the matrix and the composition of the precipitates approached to that of TiN with an increase in heating temperature. (6) Such behavior of precipitates agreed well with rough calculation from the solubility products.
