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.
Microscopic observation of inclusions contributing to formation of acicular ferrite in steel weld metal
The strength and toughness in low carbon low alloy steel welds is improved by the refinement of microstructures resulting from the formation of acicular ferrite. The behaviour of the nucleation and growth of acicular ferrite has been extensively studied and the weld metal of refined acicular ferrite is practically used in industry. It is known that inclusions in weld metal strongly contribute to the nucleation of acicular ferrite. The present authors made dynamic observations of the nucleation and growth of acicular ferrite at inclusion sites using a high temperature laser scanning microscope. In the steel weld metal of a Ti–B system, the formation of acicular ferrite is reported to be controlled by the weight ratio of aluminium and oxygen (Al/O ratio) which is an index of oxygen potential after the completion of deoxidisation by aluminium. The proper control of the Al/O ratio results in the formation of MnAl2O4 oxide of a spinel structure whose capability of the acicular ferrite nucleation is governed by a specific lattice misfit between nucleated ferrite and this oxide. It is considered that the addition of titanium is essential because titanium assists the formation of MnAl2O4. 8 However, there are reports depicting that there is no specific lattice orientation between ferrite and oxides of a spinel structure. As to the role of titanium, the researchers reported that it brings about catalysis or acts as the first nuclei for acicular ferrite nucleation. In spite of the fact that the acicular ferrite production technology is practically used in industry, the mechanisms of the acicular ferrite nucleation have been not completely clarified yet and thus, the development of nucleation control technologies for a further improvement of weld metal toughness is hindered. In the present study, the inclusions were formed by varying Al/O ratios. Thus formed inclusions were directly sliced into thin foils and crystallographic analyses were performed using a transmission electron microscopy (TEM). The formation of a multiphase type of inclusions and the existence of titanium enriched layers on the interface between the inclusions and nucleated ferrite were clarified by an electron diffraction analysis and an energy disperse X-ray spectroscopy (EDS). Experimental
Formation of unexpected ions from a first-generation polyamidoamine dendrimer by use of methanol: an artefact due to electrospray emitter corrosion?
We report the formation of unexpected ions during the analyses of a first-generation polyamidoamine dendrimer in negative ion mode using an ion trap equipped with an electrospray ionisation source. These surprising ions corresponded to an increase of 12 m/z units over those expected. The formation of the unexpected ions was dependent on the tuning of the solution flow rate and the capillary high voltage. In addition, measurements of unusual value of the current suggested that a reaction was occurring in the corona plasma. The influence of methanol in this phenomenon was demonstrated by using CD(3)OH in the sample preparation. We propose two structures to explain the observed adduct based on the results of MS(2) experiments and by referring to previous work dealing with 12 m/z units addition. We showed that a corona discharge caused by alterations taking place to the electrospray capillary emitter was the origin of these unexpected ions. Finally, we discuss the mechanism involved in the formation of the ions and we propose means to control such artefacts.