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Title: The effectiveness of aluminizing in protecting iron-base alloys in sulphidizing gases at high temperature

Abstract

Following earlier research which has shown that Al{sub 2}O{sub 3} scales are more effective than Cr{sub 2}O{sub 3} scales in protecting iron-nickel-base alloys against sulfur-containing gases, several commercial steels, 310 stainless, 314 stainless, and 321 stainless, and an experimental ferritic steel, FeCrAlHf, have been pack aluminized to develop aluminide coatings for applications in mixed-gas environments of high sulfur and low oxygen potential. Results are presented for long-term exposures to H{sub 2}/1.6% H{sub 2}O/1.1% H{sub 2}S at 750C and 1,000C under thermal-cycling conditions. Short-term tests in this environment at 750C led to considerable sulfidation of the uncoated, Cr{sub 2}O{sub 3}-forming alloys. The aluminized alloys were much more resistant to sulfidation than the uncoated materials, with relatively little degradation being observed after 200 hr at 750C. Even at 1,000C, with the exception of the ferritic steel, the coated systems showed reasonable degradation resistance for 500 hr. Eventual sulfidation resulted from the back diffusion of aluminum into the substrate and dilution of the coating surface in this element until an Al{sub 2}O{sub 3} scale was unable to reform and base metal sulfides could develop. The composition of the substrate was important in determining the rate of aluminum depletion from the coating, with interdiffusionmore » being faster in ferrite-rich matrices than the austenite matrices. The structures of the various aluminized systems are presented and their mechanisms of protection and breakdown are discussed and correlated with their performances under these high-temperature conditions.« less

Authors:
;  [1]
  1. Univ. of Manchester (United Kingdom)
Publication Date:
OSTI Identifier:
5477221
Resource Type:
Journal Article
Journal Name:
Oxidation of Metals; (United States)
Additional Journal Information:
Journal Volume: 36:3-4; Journal ID: ISSN 0030-770X
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; FERRITIC STEELS; PROTECTIVE COATINGS; SULFIDATION; STAINLESS STEEL-310; STAINLESS STEEL-321; STAINLESS STEELS; ALUMINIUM; ALUMINIUM OXIDES; BOILERS; CHEMICAL COMPOSITION; CHROMIUM OXIDES; CORROSION RESISTANCE; CORROSION RESISTANT ALLOYS; DECOMPOSITION; DIFFUSION; HEAT EXCHANGERS; HEAT RESISTING ALLOYS; HYDROGEN; HYDROGEN SULFIDES; MICROSTRUCTURE; OPTICAL MICROSCOPY; PERFORMANCE; TEMPERATURE RANGE 1000-4000 K; THERMAL CYCLING; WATER VAPOR; ALLOYS; ALUMINIUM COMPOUNDS; AUSTENITIC STEELS; CHALCOGENIDES; CHEMICAL REACTIONS; CHROMIUM ALLOYS; CHROMIUM COMPOUNDS; CHROMIUM-NICKEL STEELS; COATINGS; CRYSTAL STRUCTURE; ELEMENTS; FLUIDS; GASES; HEAT RESISTANT MATERIALS; HIGH ALLOY STEELS; HYDROGEN COMPOUNDS; IRON ALLOYS; IRON BASE ALLOYS; MATERIALS; METALS; MICROSCOPY; NICKEL ALLOYS; NONMETALS; OXIDES; OXYGEN COMPOUNDS; STEEL-CR18NI10TI; STEEL-CR25NI20; STEELS; SULFIDES; SULFUR COMPOUNDS; TEMPERATURE RANGE; TITANI; TRANSITION ELEMENT COMPOUNDS; VAPORS; 360105* - Metals & Alloys- Corrosion & Erosion

Citation Formats

Green, S W, and Stott, F H. The effectiveness of aluminizing in protecting iron-base alloys in sulphidizing gases at high temperature. United States: N. p., 1991. Web. doi:10.1007/BF00662964.
Green, S W, & Stott, F H. The effectiveness of aluminizing in protecting iron-base alloys in sulphidizing gases at high temperature. United States. doi:10.1007/BF00662964.
Green, S W, and Stott, F H. Tue . "The effectiveness of aluminizing in protecting iron-base alloys in sulphidizing gases at high temperature". United States. doi:10.1007/BF00662964.
@article{osti_5477221,
title = {The effectiveness of aluminizing in protecting iron-base alloys in sulphidizing gases at high temperature},
author = {Green, S W and Stott, F H},
abstractNote = {Following earlier research which has shown that Al{sub 2}O{sub 3} scales are more effective than Cr{sub 2}O{sub 3} scales in protecting iron-nickel-base alloys against sulfur-containing gases, several commercial steels, 310 stainless, 314 stainless, and 321 stainless, and an experimental ferritic steel, FeCrAlHf, have been pack aluminized to develop aluminide coatings for applications in mixed-gas environments of high sulfur and low oxygen potential. Results are presented for long-term exposures to H{sub 2}/1.6% H{sub 2}O/1.1% H{sub 2}S at 750C and 1,000C under thermal-cycling conditions. Short-term tests in this environment at 750C led to considerable sulfidation of the uncoated, Cr{sub 2}O{sub 3}-forming alloys. The aluminized alloys were much more resistant to sulfidation than the uncoated materials, with relatively little degradation being observed after 200 hr at 750C. Even at 1,000C, with the exception of the ferritic steel, the coated systems showed reasonable degradation resistance for 500 hr. Eventual sulfidation resulted from the back diffusion of aluminum into the substrate and dilution of the coating surface in this element until an Al{sub 2}O{sub 3} scale was unable to reform and base metal sulfides could develop. The composition of the substrate was important in determining the rate of aluminum depletion from the coating, with interdiffusion being faster in ferrite-rich matrices than the austenite matrices. The structures of the various aluminized systems are presented and their mechanisms of protection and breakdown are discussed and correlated with their performances under these high-temperature conditions.},
doi = {10.1007/BF00662964},
journal = {Oxidation of Metals; (United States)},
issn = {0030-770X},
number = ,
volume = 36:3-4,
place = {United States},
year = {1991},
month = {10}
}