Various types of gas injection operations are utilized in the steelmaking industry for bath mixing and, hence, for refining of molten metals. Generation of fine bubbles, metal droplets, and slag droplets are accompanied by bubble rise in the reactor covered with molten slag. Such bubble and droplet generation is not always beneficial for enhancement of the refining efficiency. In this review article the mechanisms of the bubble and droplet generation in a bath subjected to bottom gas injection through a single-hole nozzle are explained using many examples.

Cold sheet gauge rolling in a tandem mill is used to produce many types of steel, including automotive and high-strength steel sheet.

A recirculating oil in water emulsion is used as a lubricant between the roll and material in sheet gauge rolling. With an increase in steel sheet production and the ratio of high-strength steel sheets, the amount of fine iron particles produced by the rolling process also increases. Thus, maintaining the cleanliness of the mill and sheet is difficult when using conventional rolling oil with a non-ionic emulsifier, as dispersion of fine iron particles is not enough efficient.

Therefore, a rolling oil is developed by adding a cationic emulsifier to a conventional rolling oil used for sheet gauge rolling. As a positive charge is produced on the surface of the newly developed oil, it can easily disperse fine iron particles that would otherwise adversely affect the cleanliness of both the mill and sheet.

In this study, the newly developed oil was compared with conventional oil with a non-ionic emulsifier in a laboratory to verify its performance. The following findings were then applied to an actual mill.

The oil developed for sheet gauge production was used in an actual mill to maintain stable emulsion to ensure a high level of productivity without friction pick-up.

Fine iron particles that are inevitably produced owing to the rolling process were effectively removed. The newly developed oil is superior to conventional oil in terms of maintaining the cleanliness of the mill and steel sheet.

Two kinds of advanced image processing were applied to multi-phase microstructures. One is evolutional image processing where optimized filter set was suggested by genetic programing. Another is trainable WEKA segmentation where features are extracted by many kinds of filters, followed by machine learning for classification. Once an optimized filter set is determined, efficiency of image processing for new data set is improved remarkably in comparison with a case of manual image processing.

The change in dislocation structure with recovery and recrystallization of 99.8% cold-rolled pure iron, Fe-0.3 mass%Al and Fe-0.3 mass%Si alloys was investigated by means of X-ray line profile analysis (XLPA) and TEM observation. In as-rolled samples of Fe-Al and Fe-Si alloys, the fraction of edge dislocation density increased in comparison with that in pure iron. In the early stage of recovery, dislocation densities with both edge and screw components remarkably decreased in pure iron, whereas in the Fe-Al and Fe-Si alloys, only the edge dislocation density distinctively decreased. This suggests that edge dislocations with relatively high density in as-rolled Fe-Si and Fe-Al alloys are easily annihilated by the climbing up motion of edge dislocations. In the late stage of recovery, the dislocation density of Fe-Si alloy did not decrease. No structural changes were observed by TEM which suggests that the recovery of Fe-Si alloy is strongly retarded, since Si hinders dislocation movement. In the early stage of recrystallization of pure iron, the formation of large subgrains was clearly confirmed in the lamellar structure. The subgrains show a similar orientation to the neighboring unrecrystallized grains, which represents similar behavior regarded as continuous recrystallization. Fe-Al alloy is similar to pure iron. Whereas, Fe-Si alloy exhibits discontinuous recrystallization in the sense that grains with low dislocation density were confirmed in the unrecovered lamellar structure with high driving force for recrystallization. This is because the Si strongly hinders dislocation movement. This effect agrees with the behavior of dislocation in Fe-Si alloy confirmed by XLPA.

The constant stress cyclic loading test was conducted in order to elucidate the influence of crystal orientation on cyclic deformation behavior in bcc Fe-3 mass%Al single crystal, where the stress axes are [001] and [011]. When the stress amplitude is larger than the cyclic yield strength, materials commonly showed a decrease in cyclic plastic strain followed by an increase and saturation at a certain plastic strain. The amount of saturated plastic strain is independent of stress level; however it depends on crystal orientation. In the case that the stress axis is [001], the abrupt increase in plastic strain took place at 2.0*10⁵ cycles accompanied by extrusion along {211} plane resulting in fatigue fracture, whereas no fracture occurred when the stress axis is [011]. TEM observation into the specimen stressed along [001] revealed that straight dislocations introduced by the very early cyclic load pair-annihilate resulting in a characteristic dislocation structure with heterogeneous distribution of point-like sessile dislocations followed by their increase in density together with the new formation of short dislocations presumably due to the dislocation-dislocation interaction. Meanwhile, in the case the stress axis is [011], point-like sessile dislocations homogeneously distribute with lower density. Future work is needed to clarify the relationship between this unique dislocation structure and the fatigue crack initiation.

A continuous process is proposed for adjusting the particle size of fly ash and removing heavy metals from the ash. The reactor of the process is a cylindrical vessel with a semi-spherical bottom. Many spherical balls are placed on the bottom. A fly ash-laden water jet or a fly ash-laden air-water two-phase jet is injected vertically downwards onto the balls to crush the ash until a predetermined ash size is obtained. The fly ash thus size-controlled is lifted up towards the bath surface by rising water. The flow field near the bath surface is strongly agitated by swirl motion of a bubbling jet. The heavy metals contained in the ash are extracted from the ash into the water near the bath surface and then carried out of the reactor together with the processed ash.