Lattice Misfit between Inclusion and Acicular Ferrite in Weld Metal of Low Carbon Low Alloy Steel
To clarify the mechanism of acicular ferrite formation in low carbon submerged arc weld metals of a Ti-B system with different aluminum contents, the lattice misfit between inclusion and acicular ferrite was investigated. The inclusions were directly sliced into thin foils by a focused ion beam device and crystallographic analyses were performed using a transmission electron microscope. These inclusions were surrounded by a narrow Ti-enriched layer which was identified as TiO. Our results showed that the Baker-Nutting orientation relationship was satisfied between the narrow TiO on the inclusion surface and acicular ferrite.
Al-O比が異なるTi-B系低炭素鋼溶接金属の組織形成挙動
Microstructure development in weld material containing Ti and B has been in-situ observed by using laser scanning conforcal microscopy, with various cooling rate. The samples with different aluminum contents were prepared for the observation. In the sample with low Al/O ratio (0.48–0.73), acicular ferrite microstructure transforming from intragranular nucleation site was in-situ observed. On the other hand, with high Al/O ratio, the bainite microstructure originating from grain boundary of austenite was in-situ observed. The transformation temperature decreased with increasing aluminum content. It was cleared that the microstructure difference was due to the different inclusion in the matrix. Based on those observations, the chemical composition, cooling rate and the microstructure were systematically related and the microstructure developments were summarized as a CCT diagram.
Effect of Oxides on Nucleation Behaviour in Supercooled Iron
Synopsis: As a part of the study on the effect of oxides on heterogenuous nucleation during iron solidification, the effects of Al2O3, SiO2, and rare earth oxides were examined, by measuring the critical supercooling of 300g electrolytic iron under special slag in a Tammann furnace. The following results have been obtained. 1) The critical supercooling for heterogenuous nucleation is remarkably lowered than that of homo-