Quantitative Analysis of Microstructure in Welded Joint by Image Processing Technique

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The purpose of this study is the quantitaitve estimation ans analysis of the microstructure of metals and alloys and its changing process with the thermal history in the welding, the heat treatment, etc., utilizing the image processing technique. The present theme is composed of the following three parts:1) Decelopment of a new method for the quantitative estimation of the microstructure by the image processing technique, and its application. 2) The simultaneous measurement of the thermal history and the estimation of the microstructural changes under the rapid heating and cooling process. 3) Measurement of the thermophysical properties of the works for the above estimation and developement of some new methods for determination of the thermophysical properties.The results obtained are summarized as follows:1) A new method for the digital length measurement of the perimeter of the relatively small images was proposed, which was named the "three pixel method", and usefulness of this method was confirmed in the particle analysis of microstructure and the nondestructive estimation of the weld defect. 2) A simple measuring system, which was composed mainly of an infrared camera and an image processor, was constructed to estimate the temperature distribution in the work with CW CO_2 laser irradiation. On the other hand, a computer simulation system on structural changes of hypoeutectoid steel in laser transformaion hardening was also developed. 3) The laser flash method was applied to both the laser-beam-penetrative materials and the two-layer composites with the thermal contact resistance at the interface of the layers, in order to determine thermal diffusivity. Two new methods were developed and the effectiveness was confirmed experimentally.