A study of micro-particles in the dust and melt at different stages of iron and steelmaking

Akademisk avhandling som med tillstånd av KTH i Stockholm, framlägges till offentlig granskning för avläggande av Teknisk Doktorsexamen, tisdagen den 20 december kl. iii To my beloved parents iv v Abstract This study focuses on two different types of micro-particles selected from different stages off iron and steelmaking processes. These particles are dust particles generated due to mechanical wear of iron or particles and clusters formed in molten stainless steel alloyed with rare earth metals (REM). Firstly, the influence of three factors on the size distribution of the dust generated from iron ore pellets was investigated. The investigated factors include the characteristics of iron ore pellets, applied load on a pellet bed and partial reduction of iron ore pellets. Secondly, three dimensional investigation of REM clusters extracted by using electrolytic extraction are carried out to evaluate the size distribution of the clusters. Moreover, an extreme value distribution (EVD) analysis has been applied for the observed REM clusters. A planetary mill was used to investigate the influence of the characteristics of pellets on the dust generation. It was observed that the size of pellets can influence the wear rate under the given experimental conditions. The pellets with larger size (13.5< Deq <15.0 mm) showed a 10 to 20% higher wear rate as compared to small sized pellets (9.5< Deq <12.5 mm). Based upon the analysis of the dust generated during the wear experiments, the mechanism of wear of pellets was identified as abrasion and collision wear. In addition, a pellet bed setup was designed to study the influence of applied load on the dust generation and friction forces in a pellet bed. A varied load of 1 to 3 kg was applied on the pellet bed. An increase of ~67% was observed in the friction and the dust generation in the bed as the applied load increased from 1 to 3 kg. Moreover, it was observed that a higher friction in the pellet bed can lead to an increased amount of airborne particles. The mechanical wear of pellets reduced at 500 °C (P500) and 850 °C (P850) was carried out in a planetary mill. It was found that P500 pellets exhibit a ~ 16 to 35% higher wear rate than reference unreduced pellets. For the P850 pellets, the mechanical wear is inhibited by a formation of a metallic layer at the outer surface of the pellets. Further, the dust generated due …