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6012 |
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Tuesday, May 21, 2019, Saal Brüssel 4:40 PM Properties of brazed joints 1 |
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Investigation of interfacial reaction during stainless steel brazing by Ni-base filler with EBSD |
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Yasuyuki Miyazawa* / Tokai University, Japan Katsuhiro Kudo / Tokai University, Japan Masaya Iwata/ Tokai University, Japan Yoshi Bizen/ Hitachi Metals, Ltd., Japan |
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Stainless steel is employed as a material of EGR cooler for automobiles due to its toughness or corrosion resistance; brazing of ferritic stainless steel is necessary for such the product. In our laboratory, brazing of stainless steel with Ni-based brazing foil has been investigated studiously for several years. In the previous works, formation of Cr-B intermetallic compounds was confirmed due to the Cr and B contained in the stainless steel and the brazing foil, respectively. Moreover, that caused Cr-depleted layer beside brazed layer. For these reasons, effects of these phases on some properties of the brazed joint were concerned. However, formation mechanism of the Cr-B compounds has not been clarified. Therefore, we investigated the formation mechanism using EPMA and EBSD. We assumed relationship between the growth of the compounds and crystal orientation of the base metal; however, no relationship was confirmed from EBSD results. Nevertheless, diffusion behavior of B into the stainless steel at ³ phase, which was formed during brazing due to diffusion of Ni, was quite different from that of ± phase. That indicated diffusion of Ni or the crystal structure affected on the diffusion of B. Therefore, pure Ni and some other metals were brazed with the Ni-based brazing foil; subsequently, elemental distribution at these brazed layers was analyzed. As a result of the analysis, formation of compound phase composed of B and Ni that had similar shape with the Cr-B compound was confirmed. |