Changes in inclusion characteristics during sampling of liquid steel

Abstract

In order to improve the process control during the steelmaking process, it is essential to obtain knowledge, as well as interpret information, on the characteristics of non-metallic inclusions in liquid steel samples. The purpose of the present study is to evaluate the effect of different sampling conditions on the inclusion characteristics. The changes in number, size and composition of primary inclusions due to the precipitation of secondary inclusions are studied. This is investigated in laboratory scale samples from an Fe-10 mass-%Ni alloy as well as industrial steel samples with varying contents of oxygen and sulphur. The results show that in most cases, the inclusion population can be separated, using a size condition, into primary (>0?6 mm) and secondary (,0?6 mm) inclusions. Overall, the Lollipop sample with a 6 mm thickness can be recommended, because most of the secondary inclusions in low sulphur steels can be removed from the total particle size distribution. However, during sampling of liquid steel containing high levels of sulphur, a significant amount of sulphides precipitate heterogeneously onto primary inclusions, making it impossible to use size or morphology to separate the population. Finally, the numbers of secondary inclusions in the steel samples were found to increase significantly with an increased sample cooling rate. However, the number of primary inclusions was found to be almost constant and independent of the sample cooling rate.

Effect of Slag Protection System and Sample Geometry on Homogeneity of Total Oxygen Content in Samples from Liquid Steel

“…However, a too tight mold can constrain the expansion of the gas, resulting in a higher gas pressure inside the mold. As shown in a previous study, the pressure inside the mold varies during sampling, with a maximum at about 1.3 atm 6. The theoretical amount of reoxidation, calculated from equation 3, at temperatures between 100 and 500 °C is 14‐30 ppm (at 1 atm) and 19‐39 ppm (at 1.3 atm).…”

Assessment of inclusion analysis via manual and automated SEM and total oxygen content of steel

“…Moreover, these parameters directly affect the cooling rate of the sample, which influences the analysis. According to Ericsson [23], the number of secondary inclusions in liquid steel samples increases significantly with the rise in the cooling rate of the samples. The protection adopted may also interfere in the results of inclusion characterization.…”

“…Immersion samplers are common in industry since they can be used both for SEM and total oxygen determination. Table 2 [20][21][22][23] shows some of the types of samplers and possible protection methods adopted. Important parameters to be considered when choosing a sampler are penetration, depth and immersion time, since these determine whether the sampler is completely filled with steel.…”

Evolution of Different Inclusions during Ladle Treatment and Continuous Casting of Stainless Steel

“…Based on the study of O. T. Ericsson,31) the cooling rate of the 12 mm thickness lollipop sampler is 20-25°C/s for a 316L stainless steel. The secondary inclusions, which formed during fast cooling and solidification, would precipitate homogenously and have separate peaks in the particle size distribution.…”