The ratio of equiaxed grains on a cross section and the size of equiaxed grains in a Fe-20 mass% Cr alloy deoxidised with Ti/M (M = Zr or Ce) were studied as function of nitrogen content and particle characteristics such as size distribution, morphology and composition. Fe-20 mass% Cr alloys were melted at 1 600°C, deoxidised, and cooled to 1 400°C followed by water quenching. Thereafter, the particles were separated from the matrix using electrolytic extraction using a 10%AA electrolyte and collected on a filmfilter surface. The inclusion characteristics were determined using SEM. It was found that the number of particles increases with an increased N content. Furthermore, that the solidification structure was clearly affected by the number of primary oxide and oxide-nitride particles in the Ti/Zr deoxidation experiments. However, a similar effect could not be detected in the Ti/Ce deoxidation experiments.

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The pinning effects of different particles on grain growth were investigated in Fe-20 mass% Cr alloys deoxidised with Ti and Zr. More specifically, in-situ observations of the specimen surface were made during heat treatment at 1 200 and 1 400°C in a High Temperature -Confocal Scanning Laser Microscope (HT-CSLM). Initially, primary and secondary particles were investigated using thermodynamic equilibrium calculations and the SEM/EDX observations. Thereafter, the pinning effect of secondary nitride particles on grain boundary migration and the kinetics of the grain growth process were investigated. It was found that secondary nitride particles generally have a considerable effect on the pinning of grain boundary migration during heating treatment. This is especially true for heat treatment at 1 400°C. Despite that the pinning effect of TiN particles decreases due to dissolution of these particles, the implicit pinning effects of ZrO2, ZrO2-ZrN and ZrO2-ZrN-TiN particles appear. Thus, despite that TiN individually is ineffective in causing grain-boundary pinning at high-temperature, TiN is effective as a compound with ZrO2 and ZrN in pinning grain-boundaries at high temperatures. The changing of the uniformity of grain size distributions during grain growth at different N contents and temperatures was discussed based on the consideration of the geometric standard deviation of the grain size distribution (σ g).

Liquid steel samples were taken during ladle treatment and continuous casting of 37 heats of two duplex stainless steel grades. These samples were used to study inclusion characteristics and potential process control using the pulse distribution analysis with optical emission spectroscopy method (PDA/OES). In addition, a few samples were chosen for a scanning electron microscope examination. A simplified approach of presenting the inclusion composition in ternary diagrams using the PDA/OES method is discussed. More specifically, by defining an operating window, potential deviations can be identified early in the steelmaking process. The variation of the B factor for Al (B Al ) with process time was presented showing similar tendencies for several heats. For that reason, the B factor is considered to be a reliable parameter to study any process changes with respect to inclusion characteristics. Parameters such as B Al and the number of inclusions per unit volume larger than 4 mm obtained using the PDA/OES method showed a moderate correlation with a slivers index. Statistically, more data have to be collected for further studies. Nevertheless, the PDA/OES method is judged to be a promising tool to determine a slivers risk factor at an early stage of the process.