Characterization of Precipitates in Ti-Stabilized Steels with Low-Energy Electron-Induced X-Ray Spectrometry and Scanning Electron Microscopy

Abstract

Various kinds of precipitates can in¯uence the mechanical properties of Ti-stabilized steels. The qualitative composition of the Ti inclusions can be characterized microscopically, whereas for quantitative information to be obtained time-consuming selective dissolution must be used. The present study aims at chemical speciation of the isolated precipitates as a solid phase with the help of soft-X-ray spectrometry. Whether the method is capable of giving both qualitative and quantitative information on the composition of Ti-mixtures is discussed. The precipitates in Tistabilized steels are investigated after chemical dissolution of the steel matrix with a bromine/methanol mixture (1:10). By combination of soft-X-ray spectrometry with X-ray¯uorescence (XRF) and scanning electron microscopy (SEM) both qualitative and quantitative characterization of the precipitates can be performed. They were found to consist mainly of TiC and TiN.Precipitates in steels consist of small quantities of heterogeneous phases. They are dispersed in the steel and in¯uence its mechanical and fatigue properties, and machinability. For this reason, analysis of these inclusions in steels gives information about the quality and purity of the product. In Ti-stabilized steels various kinds of precipitates, such as TiN, Ti 4 C 2 S 2 , TiS, TiC and Ti 2 O 3 have been found [1]. They can be characterized microscopically (transmission electron microscopy, SEM or electron microprobe) directly in the surface of the steel or after electron-beam remelting, or in carbon extraction replicas of slightly etched surfaces or after isolation [2±5]. In addition, energy-dispersive spectroscopy (EDS) or X-ray diffraction (XRD) can be employed to identify the precipitates. All these analytical methods give information on the qualitative composition of the Ti inclusions. For a quantitative determination the different precipitates can be dissolved selectively after electrolytic or chemical isolation. The isolated phases are then separated by dissolution with different solvents or by means of their mechanical and magnetic properties, and determined by microanalysis [6±8].The aim of the present study is chemical speciation of the isolated precipitates as a solid phase. Therefore a spectroscopical method is needed which is sensitive to the chemical bonding. Soft X-ray spectrometry was chosen for this purpose, whereby the transitions, which involve valence shell orbitals, can be related to the chemical environment of the emitting atom. Soft-X-ray spectra show large chemical effects because both the position, shape and structure of the observed spectral features can change [9±12]. A lot of work has been done on the investigation of the soft X-ray spectra of pure Ti compounds [13±15], but less on their mixtures. Therefore, the present work deals with