Papers by Author: Hidenori Terasaki

Abstract: The present study aims to clarify the development of blocks and packets in lath martensite in Fe–18Ni maraging steel using three-dimensional observations. The specimens were step-quenched in order to clarify the sequential development of the three-dimensional morphology in a prior austenite grain. In a prior austenite grain, we found that five independent packets formed during the early stage of martensitic transformation. Four of the packets exist along the prior austenite grain boundaries and one packet grows from the boundary edge into the prior austenite grain. Each packet consists of a single block, although the fraction of martensitic transformation is 50.6%. The observed rules of the block-selection are as follows: (1) the blocks have near Kurdjumov–Sachs orientation relationship with adjacent austenite grains and elongated directions of the laths are parallel to adjacent grain boundaries and (2) transformation shear directions of the laths are parallel to adjacent grain boundaries.

Abstract: Time-resolved X-Ray Diffraction (TRXRD) experments were carried out to identify the phase transformation during welding in-situ. For the martensitic steel weld with different chemical compositions, the solidification behavior was directly analyzed in the time-resolution of 0.01 seconds. The halo pattern from the weld pool gives basis to observe the phase transformation during solidification process of weld. Furthermore, the latest development of TRXRD system was outlined. The importance of detector area was discussed and brand-new TRXRD system in real and reciprocal lattice space was presented.

Abstract: Heterogeneous nucleation and growth of acicular ferrite in HSLA steel weld-metal were in-situ observed by using laser scanning confocal microscopy. The applied thermal cycle simulated cooling rate of large heat-input welding. The high time-resolved images made for heterogeneous nucleation at inclusion and hard impingement between ferrite plates to be clear. Furthermore, the crystal orientation relationships between observed substrate for the heterogeneous nucleation and nucleated solid were analyzed.

Abstract: Unidirectional solidification for low-carbon steel weld metal was characterized by using Time-Resolved X-Ray Diffraction (TRXRD) system. Solid-state phase transformation was also insitu observed in reciprocal lattice space. It was shown that TRXRD analysis had a potential as a comprehensive characterization technique for solidification and phase transformation process in welding. It made for the growth behavior of dendrites in unidirectional solidification and α γ δ − − phase transformation in steel weld metal to be characterized.

Abstract: Microstructure formation of CP-Ti and TiB reinforced titanium were in-situ observed during the thermal cycle simulated for Tungsten Inert Gas (TIG) welding, by using laser scanning confocal microscopy. Under the in-situ observation of TiB reinforced titanium, heterogeneous nucleation of α-phase at inclusion was clearly detected and plate growth was shown in high timeresolution. Furthermore, it was observed that grain boundary of β -phase was pinned by the inclusions. Microstructure difference between pure and TiB reinforced titanium was explained based on those in-situ observations.

Abstract: In order to understand the microstructure changes during welding processes , kinetic information about the phase transformation is essential. In our research group, in-situ observation systems consisting of undulator beam and imaging plate and two dimensional pixel detector have recently been used. These make it possible that phase transformation can be identified in real-time under the condition of directional-oriented solidification . In the present work, a combination of analyzing method: the in-situ observation system by X-ray diffraction technique using intense synchrotron radiation, and morphological observation by high-temperature laser scanning confocal microscopy is suggested to analyze the phase transformation during the welding process. Using the results acquired by these analysis methods, phase evolution of hypereutectoid carbon steel, during fusion welding was analyzed. The primary phase was directly identified as an austenite phase. Precipitation of pearlite phase was observed followed by the martensitic transformation.