High temperature oxidation and NaCl-induced accelerated corrosion of hot-dip aluminized 9Cr-1Mo and 310 stainless steel

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Title: High temperature oxidation and NaCl-induced accelerated corrosion of hot-dip aluminized 9Cr-1Mo and 310 stainless steel
Author: Tsaur, Charng-Cheng
Abstract: The behaviors of high temperature corrosion on hot -dip aluminized on 9Cr -1Mo and 310 stainless steels when catalyzed by NaCl and cyclic heating environment were studied experimentally . The corrosion behavior and morphological development were investigated by weight gain kinetics , metallographs , depths of attack , metal losses , and X -ray analyses . The results of 310SS deposited with salt mixtures show that weight gain kinetics in simple oxidation reveals a steady -state parabolic rate law after 3 hr , while the kinetics with salt deposits display multi -stage growth rates . NaCl is the main corrosive specie in high -temperature corrosion involving mixtures of NaCl /Na2SO4 and is responsible for the formation of internal attack . Uniform internal attack is the typical morphology of NaCl -induced hot corrosion , while the extent of intergranular attack is more pronounced as the content of Na2SO4 in the mixture is increased . The thermal -cycling test results of 310SS deposited NaCl and coated 7wt %Si /93wt %Al show that the aluminized layers have good corrosion resistance during the first four cycles of testing , while degradation occurs after testing for five cycles . The reason for degradation of aluminized layers is attributed to the formation of interconnecting voids caused by aluminum inward diffusion , chloridation /oxidation cyclic reactions and the penetration of molten NaCl through the voids into the alloy substrate . The 9Cr -1Mo steels coated with 7wt %Si /93wt %Al oxidized at 750 , 850 , and 950 ?C in static air show that oxidation kinetics followed a parabolic rate law at 750 and 850 ?C . The cracks propagated through the FexAly layer due to the growth of brittle FeAl2 and Fe2Al5 at 750 and 850 ?C . The voids condensed in the interface of intermetallics and substrate are attributed to the Kirkendall effect . At 950 ?C , the fast growing aluminide layer has a different expansion coefficient than oxide scale , leading to scale cracking , oxygen penetration , and internal oxidized , evidenced by a rapid mass gain .
URI: http : / /hdl .handle .net /1969 .1 /1375
Date: 2005-02-17

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High temperature oxidation and NaCl-induced accelerated corrosion of hot-dip aluminized 9Cr-1Mo and 310 stainless steel. Available electronically from http : / /hdl .handle .net /1969 .1 /1375 .

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