Stretch-flange-formability is an important property for ultra high strength steel (UHSS) sheets for pressforming. In this study, microscopic deformation behaviors during punching and following stretch-flangeforming were investigated using three types of 980 MPa grade UHSS sheets with either two ferrite/martensite dual-phase structures or a martensite single-phase structure in order to clarify how the microstructure affects the stretch-flange-formability of UHSS sheets. The results of this investigation revealed following conclusions. Microscopic plastic-flow or micro-void density generated by punching is not the dominant factor of the stretch-flange-formability of UHSS sheets. During hole-expanding, cracks were mainly initiated at the fractured surface part and the cracks became longer and deeper from the punched surface with the increase of hole-expanding ratio. Deep cracking resistance in this process is important to improve the stretchflange-formability. The existence of strain gradient induced by hole punching is considered to be one of the reason for the highest hole-expanding ratio of the martensite single phase steel. During hole-expanding, the micro-cracks propagate mostly along the phase interfaces in the dual-phase steel sheets in the case of poor stretch-flange-formability, while the micro-cracks are tend to propagate through ferrite and martensite phases in the case of high stretch-flange-formability. The analysis of the hardness of ferrite and martensite suggests that the difference in hardness is the dominant factor of the stretch-flange-formability of the dualphase steel. In addition, the volume fractions of phases also influence the formability.

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A simple trap model of solar hard X-ray bursts is discussed in which nonthermal electrons trapped in a magnetic bottle precipitate into the lower chromosphere through the resonant scattering by whistlers. In -such a model, the X-ray spectra produced from trapped and precipitating electrons have 9 different spectral shape, and both of the spectra will initially soften with time, provided the precipitation dominates over collisional degradation.

This paper describes the dislocation configuration around an indentation on the ( 111) surface of a Si single crystal. X-ray Lang topography was used. The Burgers vector was identified for each section of the dislocation clustering region based on the change of the contrast of the diffraction pattern with various diffraction vectors. Additionally, the mechanism of dislocation interaction was discussed resulting in the observed configuration. The following results were obtained. The dislocation clustering region was divided into the inner and the outer territories, each of which was further divided into several sections with different Burgers vectors. It was assured that dislocations in the outer territory were perfect, while they split into partial dislocations in the inner territory. Therefore dislocation interactions were possible in the inner territory resulting in stair-rod dislocations. The observed configuration could be explained by the mechanism of the dislocation interaction.

This paper describes how X-ray topographic images taken around indentations are affected by temperature. Vickers indentations were made on the (111) surface of Si single crystals. In the low-temperature range (0-400° C), the images resemble the number “8” and show a twofold symmetry. On the other hand, they show a threefold symmetry, similarly to a nest of triangles, in the elevated temperature range (higher than 500° C). The difference in the topographic images reflects the difference in the mechanisms of deformation by indentations. It was concluded that the change of the images with temperature rise was attributed to the relative increase in plastic deformation in a microscopic sense rather than elastic deformation.