As a fundamental study to clarify the agglomeration and coalescence of alumina inclusions in molten steel from the viewpoint of interfacial chemical interactions, it has been experimentally verified for the first time that significant agglomeration force is exerted between alumina particles in aluminum deoxidized molten steel by using a newly established experimental method. In this method, the agglomeration force exerted between alumina particles in molten steel is directly measured separately from the effect of molten steel flow. In addition, it has been quantitatively demonstrated that the contact angles measured between aluminum deoxidized molten steel and an alumina plate are larger than those between the molten iron-oxygen alloy and the alumina plate, which have already been measured by other researchers. Moreover, it has also been indicated by analyzing the actual measurement values of agglomeration force with an interaction model taking contact angles and interfacial properties into consideration that the agglomeration force between the alumina particles in aluminum deoxidized molten steel derives not from the van der Waals force but from the cavity bridge force occurring due to molten steel, which is unlikely to wet the alumina particles. Meanwhile, it has been assumed that the agglomeration force on spherical alumina inclusions in aluminum deoxidized molten steel calculated on the basis of the interaction model according to the cavity bridge force is greater than the buoyant force and drag force, and the alumina inclusions once coming into contact are therefore not prone to be simply dissociated even under molten steel flow. Thus, they maintain the agglomeration state and are subsequently sintered and form comparatively solidly bonded alumina clusters.
In this paper the loosening and coming out of a roller is considered by using FE analysis when a ceramics sleeve is shrinking fitted to two steel shafts. It should be noted that only small shrink fitting ratio can be applied for the connection because of the brittleness of ceramics. However care should be taken for coming out of the shafts during rotation under such small shrink fitting ratio. In this study therefore the finite element analysis is applied to simulate this behavior. Then, the coming out behavior during rotation can be realized by the simulation where the rotation of the roller is replaced by the shift of the load at an interval of the rotation angle. Under smaller shrink fitting ratio the shaft comes out, but under larger shrink fitting ratio the shaft does not. The effects of the magnitude of the load, friction coefficient, and stiffness of the shaft are also discussed.
For the purpose of edge crack control in hot rolling of 36%Ni-Fe alloys, a high temperature tensile test and laboratory-scale hot rolling experiment were carried out. Intergranular oxidation has been considered to be one of the major factors in edge cracking. Edge cracks which initiate from intergranular oxidation grow to the inner side along coarse grain boundaries as the thickness reduction ratio increases. The depth of intergranular oxidation increases at higher reheating temperatures. However, recrystallization occurs at the crack tip, and this has the effect of suppressing crack growth. This suggests that promoting recrystallization during hot rolling by increasing the reheating temperature, rather than inhibition of intergranular oxidation as such, is effective for suppressing edge cracking.
Effect of the combined addition of molybdenum (Mo) and boron (B) on austenite (γ) to ferrite (α) transformation and precipitation behavior were investigated using low-alloy steels. B-added steel and Mo-B combined steel were held at 923 K (γ region) in order to precipitate boride. B content as precipitates increased and γ to α transformation was promoted with holding time at 923 K. In B-added steel, both M23(C,B)6 and M2B were observed. The transition from M23(C,B)6 to M2B caused by the increase in holding time at 923 K. By contrast, in Mo-B combined steel, no M2B was observed regardless of the holding time. Mo addition suppresses not only the M23(C,B)6 formation but also the M2B formation. M2B contains larger amounts of B than M23(C,B)6. B content as precipitates in Mo-B combined steel was much lower than that in B-added steel due to the suppression of M2B precipitates. The effect of Mo for B containing steel suppresses the precipitation of M23(C,B)6 and M2B and increases more segregated B in austenite grain boundary that contributes to γ to α transformation.
Effect of specimen thickness on ductile fracture energy for ferrite-austenite duplex stainless steel was investigated by using tensile strain test. It was revealed that both uniform and local deformation energies decreased with the decrease in the specimen thickness. Voids in a thicker specimen can be easily formed at the lower plastic equivalent strain because of the steep increase in the triaxiality. The decrease in the local deformation energy was due to the void growth near the fracture surface depending on the steep increase in the stress triaxiality.