The aluminizing and Al–Si codeposition on AISI HP alloy and the evaluation of their carburizing resistance

Heat resistance casting alloy ACI HP was aluminized or silicon-aluminized for investigating their carburization resistance in a high-carbon potential atmospherized-fluidized-bed which simulated the carburizing environment of the pyrolysis tubing in a ethylene production line. The results showed that the coating layer prepared by the high-activity aluminizing pack was superior to that of the low-activity one. On the contrary, the coating layer provided by the low-activity silicon-aluminizing pack was superior to that of the high-activity one. Experimental results evidenced that silicon could effectively retard the degeneration rate of NiAl and reduce the formation of porous band, which located at the interface between aluminide layer and interdiffusion zone. Moreover, the kinetics of the reaction, D̃=D̃ exp(−Q̃/RT), was empirically determined by the method of Al pack and Al–Si pack. The results showed that, in a low-activity Al–Si pack, Si can effectively reduce both Q̃ and D̃0. As a consequence, it increased the formation rate of aluminide layer, in contrast, it reduced the formation rate of interdiffusion zone.