Hot dip aluminization of 304L SS and P91 ferritic-martensitic steel - Comparison of interface morphology and growth kinetics of reaction zones

P91 ferritic/martensitic and AISI 304L austenitic stainless steels were hot dip aluminized (HDA) in 99.9% pure aluminum in a pit type vertical furnace at three different temperatures i.e. 750, 800 and 850 degrees C for 1 to 10 min. Evolution of interface morphology, type and distribution of phases and growth kinetics of the reaction zones were studied using a variety of experimental techniques. Though similar intermetallic compounds formed in both steels, their distribution, morphology and growth kinetics were distinctly different. In P91 F/M steel, aluminized surface adjacent to the substrate had wide Fe2Al5 layer with serrated morphology containing high volume fraction of 2-3 mu m sized Cr rich intermetallic phases. Width of FeAl3 phase present adjacent to this layer did not show much variation with HDA conditions. Above FeAl3, on the surface, the pure Al top coat contained nonequilibrium phases. Compared to P91 steel, width of the aluminized layer in 304L SS was less (35 +/- 5 mu m vs 120 +/- 15 mu m at 800 degrees C-10 min) and the Fe2Al5 layer had a planar interface with the substrate. Optimum temperature-time combination to get thin, uniform, defect free surface aluminide layer in P91 F/M and 304L steels were found to be 750 degrees C-2 min and 800 degrees C-1 min respectively. Growth kinetics of surface aluminide layers in both steels were studied, kinetic parameters were determined and compared with information available in literature.

Automated summary

Hot dip aluminizing of P91 ferritic/martensitic and AISI 304L austenitic stainless steels in pure aluminum was studied. The evolution of interface morphology, type and distribution of phases, and growth kinetics of the reaction zones were investigated. While similar intermetallic compounds formed in both steels, their distribution, morphology, and growth kinetics differed noticeably. The optimal temperature and time combination to obtain thin, uniform, defect-free surface aluminide layers were found to be 750℃-2 min for P91 F/M steel and 800℃-1 min for 304L steel.