Solidification of an alloy 625 weld overlay |
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Authors: | J N DuPont |
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Affiliation: | (1) Energy Research Center, Lehigh University, 18015 Bethlehem, PA |
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Abstract: | The solidification behavior (microsegregation, secondary phase formation, and solidification temperature range) of an Alloy
625 weld overlay deposited on 2.25Cr - 1Mo steel by gas metal arc welding was investigated by light and electron optical microscopy,
electron microprobe, and differential thermal analysis techniques. The overlay deposit was found to terminate solidification
at ≈ 1216 °C by aγ/Laves eutectic-type reaction. The Laves phase was highly enriched in Nb, Mo, and Si. The solidification reaction and microsegregation
potential of major alloying elements in the overlay deposit are compared to other Nb-bearing Ni base alloys and found to be
very similar to those for Alloy 718. Solidification cracks observed in the overlay were attributed to the wide solidification
temperature range (≈170 °C) and formation of interdendritic (γ+Laves) constituent. Reasonable agreement is obtained between the calculated and measured volume percent (γ+Laves) constituent with the Scheil equation by treating the overlay system as a simpleγ-Nb “binary” and using an experimentally determinedk
Nb value from electron microprobe data. |
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