《A Melting and Solidification Study of Alloy 625》.pdf

A Melting and Solidification Study of Alloy 625 M.J. CIESLAK, T.J. HEADLEY, T. KOLLIE, and A. D. ROMIG, Jr. The melting and solidification behavior of Alloy 625 has been investigated with differential thermal analysis (DTA) and electron microscopy. A two-level full-factorial set of chemistries involving the elements Nb, C, and Si was studied. DTA results revealed that all alloying additions decreased the liquidus and solidus temperatures and also increased the melting temperature range. Terminal solidi- fication reactions were observed in the Nb-bearing alloys. Solidification microstructures in gas- tungsten-arc welds were characterized with transmission electron microscopy (TEM) techniques. All alloys solidified to an austenitic (y) matrix. The Nb-bearing alloys terminated solidification by forming various combinations of y/MC(NbC), 3,/Laves, and T/MrC eutectic-like constituents. Carbon addi- tions (0.035 wt pct) promoted the formation of the 7/MC(NbC) constituent at the expense of the y/Laves constituent. Silicon (0.4 wt pct) increased the formation of the y/Laves constituent and promoted formation of the y / M 6 C carbide constituent at low levels (0.01 wt pct) of carbon. When both Si (0.4 wt pct) and C (0.035 wt pct) were present, the y/MC(NbC) and y/Laves constituents were observed. Regression analysis was used to develop equations for the liquidus and solidus temperatures as functions of alloy composition. Partial derivatives of these equations taken with respect to the alloying variables (Nb, C, Si) yielded the liquidus and so