Dispersion Control of Fine Titanium Nitride Precipitates in Steels in the Liquid Phase Using the Hansen Solubility Parameter

Fine precipitates formed in steels significantly influence their mechanical properties. However, an accurate evaluation of their size distribution remains challenging. To determine the size distribution of these precipitates, a combination of extraction from steels by the electrolytic dissolution method and asymmetric flow field-flow fractionation (AF4) hyphenated with inductively coupled plasma-mass spectrometry (ICP-MS) was employed. Dispersing these precipitates in the liquid phase is necessary to achieve an accurate measurement of their size distributions by this method. In this study, a novel approach was established to improve the dispersion state of titanium nitride (TiN) precipitates in the liquid phase by utilizing the Hansen solubility parameter (HSP), enabling accurate size distribution analysis. Following an investigation of the dispersion state of TiN reagent in 29 types of solvents, the Hansen solubility sphere method was applied, and the HSP value was determined to be (δd, δp, δh) = (19.4 ± 0.1, 16.9 ± 0.0, 20.5 ± 0.1). The appropriate relative energy difference (RED) for TiN was examined by changing the RED. It was found that a good dispersion state required a RED of less than 0.76. Furthermore, a solvent mixture of ethylene glycol and dimethyl sulfoxide (RED = 0.50) was applied for transmission electron microscopy observation and AF4-ICP-MS analysis of the TiN precipitates extracted from the steels. Both analyses were successful because of the good dispersion of the TiN precipitates in the solvent mixture. Consequently, this approach can be useful for quantitatively analyzing the size distribution of various fine precipitates in steels by improving the dispersion state in the liquid phase.