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.
Review of Literature on Probability of Detection for Magnetic Particle Nondestructive Testing
Abstract : A critical review of the available literature concerning the minimum reliably detectable defect size aNDI for magnetic particle testing (MPT) in aerospace applications is presented. Four probability of detection (POD) studies relevant to detection of fatigue cracks in aircraft components were found over the period 1968 to 2011. As the statistical methods used in these four previous studies were either outdated or otherwise deficient, the original data were reanalysed using currently accepted techniques. A meta-analysis of the results is presented, with emphasis on statistical inferences for the defect size expected to be detected with 90% POD. It is shown that the minimum reliably detectable defect size aNDI = 2.0 mm currently specified by the Royal Australian Air Force for wet fluorescent magnetic particle inspection using the continuous method is consistent with estimates of the average performance of MPT derived from the reanalysis of the literature.