Bending-tension deformations were conducted to AZ31B (Mg-3 mass％Al-1 mass％Zn) alloy sheets with weak basal texture intensity and RD (rolling direction)-split texture, which were processed by high-temperature rolling. Effects of process pass number of bending-tension deformation on the texture formation and related room temperature formability were investigated. 1 pass bending-tension deformation contributed to significant increase in the RD-split angle from 13° to 25°, and additional bending-tension deformation only contributed to slight increase in the RD-split angle. 7 pass bending-tension deformation increased basal texture intensity from 2.9 to about 4.5, which was still much lower than those of commercial AZ31B alloy sheets. Specimens subjected to less than 5 pass bending-tension deformations kept significant stretch formability (8.0 mm of Erichsen value). However, specimens subjected to 7 pass bending-tension deformation exhibited deteriorated Erichsen value of 6.7 mm regardless of the high RD-split angle, low basal texture intensity and high average Schmid factor. As a result of microstructural observation, it was revealed that repetition of bending-tension deformation generated area with coarse grains at near surface. In addition, repetition of bending-tension deformation induced duplex microstructure at the surface, where layers of fine grains and coarse grains were distributed along to the RD on the RD-TD (transverse direction) plane. It was suggested that the above microstructural changes induced inhomogeneous deformation at grain boundaries and in double twinning, resulting in the deterioration of the stretch formability of the specimens subjected to 7 pass bending-tension deformation.

Laser forming is one of a few processing methods that can form a plate material into a curved surface without contact and without using a mold. A combination of multiple curved heating lines is required to form a practical shape. The relationship between heating conditions and deformation has been studied in detail in the field of welding, etc. when the heating line is straight. However, there are not many reports investigating the effect of interference between heating lines on deformation.

Therefore, in this study, we investigated the interference effect of multiple heating lines with different heating order on angular distortion in laser forming under different two conditions, straight heating lines and curved heating lines.

Annealed austenitic stainless steel sheet material with 0.75 mm thick was used as the test material for the laser forming with 1500 W YAG laser before deformation measurement by using a non-contact three-dimensional coordinate measuring device.

From the relationship between the heating order and the angular distortions of the three heating lines arranged concentrically, the influence of the area inside and outside of the curved heating line on the angular distortion behavior of the other heating lines was investigated. When the heating was repeated inside the curved heating line, the inner heating hardly interfered with the angular deformation of the outer heating line, but the angular distortion on the heating line placed inside was changed.

When the heating lines were placed on the outside in order, the amount of angular distortion of the heating lines placed earlier changed depending on the heating lines placed later. When considering the curved heating part by classifying it into the inside and outside of the curve, the ability to interfere with the angular distortion of other heating lines was observed inside, but not outside.

When laser forming curved surface using multiple curved heating, it was found that the classification of the inner and outer regions of the curved heating part and the heating order are important for examining the interference between the heating lines.

Gravity die casting of spheroidal graphite iron had been attempted controlling free nitrogen during preparing base molten iron, magnesium treatment, inoculation and pouring. In this study, the actual CO/SiO₂ reaction temperature of base molten irons was surveyed and magnesium treatment was conducted at that temperature. The mold was made of steel and the cavity size was thickness of 5.4 mm and diameter of 35 mm. As the results, ultrafine graphite nodules were obtained without chill in as-cast condition. They were average diameter of 7 µm and density count of over 3000/mm². Knuckle for automobile was also cast taking the same procedure. Knuckle had no meager defect like shrinkage, chill etc. in as-cast conditions. The possibility of no chill has become extremely higher than former study.

Mater. Trans. 60 (2019) 41-48に掲載．文献25）-27）を追加．

The crystal structure of LnMnO₃ (Ln: lanthanide) has been reported to be orthorhombic from La to Dy are used as Ln, and hexagonal from Ho to Lu. Whereas Kumar et al. reported that orthorhombic and hexagonal phases are co-exist in samples of DyMnO₃ solidified from the undercooled melt under containerless state. We investigated whether this two-phases structure was the result that the hexagonal phase formed as a metastable phase is frozen to room temperature or the result that the solid state phase transformation of the hexagonal ⇄ orthorhombic occurred at the cooling stage.

The surface morphology of the samples, the nucleation of which were triggered by contacting with the Mo wire at given temperatures, indicates that hexagonal and orthorhombic phases are stable at high and low temperatures, respectively. Furthermore, in the experiment where the melt was dropped into water, it was found that if the temperature of the melt was below 1666 K, the XRD pattern of the as-solidified sample showed two phases, h-DyMnO₃ and o-DyMnO₃, whereas above 1666 K, it showed a single phase of h-DyMnO₃. This phenomenon can be quantified in terms of nucleation rate-determined phase selection. That is, the activation energy for nucleation calculated based on the model of the crystal-melt interface proposed by Turnbull and Spaepen suggests that the o-DyMnO₃ phase can be heterogeneously nucleated on the interface of the initially formed h-DyMnO₃ phase.

The effects of Ni concentrations and carbon to oxygen (C/O) ratios on the phase formation during the commercial production process and morphology of nonmetallic inclusions were investigated in Ni-rich Ti-Ni alloys. In the process from casting to forging, a phase change from Ti(C, O) to Ti₄Ni₂O_X occurred depending on the Ni concentration and C/O ratios. The phase change from Ti(C, O) to Ti₄Ni₂O_X was easy to proceed in the alloys with low Ni concentrations and C/O ratios, whereas the Ti(C, O) was stable in the alloys with high Ni concentrations and C/O ratios.