The effect of alloying Ce on the SCC behavior of alloy 600

High purity model alloys with major composition Ni-15Cr-9Fe-0.03C (600CE0) and Ni-15Cr- 9Fe-0.03C-0.04Ce (600CE4) were produced. Using these model alloys the effect of alloying Ce on the SCC behavior of Alloy 600 was evaluated. To obtain carbides precipitated on grain boundaries, the thermal treatment was performed on both the solution annealed alloys. Microstructural examinations using SEM and TEM EDX showed that the same structural carbides, Cr7C3, were precipitated on both the alloys and no significant difference in the amount of Cr depletion along grain boundaries was observed between the two model alloys. However, it was shown that the coverage of grain boundary carbides was higher in the Ce-bearing alloy (600CE4). The SCC susceptibility of the alloys was investigated in 40%NaOH solution at 315 .deg. C. Being evaluated in terms of maximum crack depth, the SCC susceptibility of the alloy turned out to be reduced by the addition of Ce. The increased resistance to the SCC in the alloy 600CE4 was considered to be attributable to the increased coverage of grain boundary carbides