Corrosion resistance of weldable Fe-Al alloys in reducing environments

Conference · Mon Nov 01 04:00:00 EST 1999

OSTI ID:696914

Banovic, S W; DuPont, J N; Marder, A R ^[1]

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1. Lehigh Univ., Bethlehem, PA (United States). Energy Research Center

Low aluminum Fe-Al alloys are being investigated for use as protective coatings in reducing environments. Intermetallic compositions have already demonstrated excellent high temperature corrosion resistance in both oxidation and sulfidation environments, however, they are limited in use due to low room temperature ductility and poor weldability arising from hydrogen embrittlement. Using Gas Tungsten Arc and Gas Metal Arc Welding process without the use of pre-heat and post weld heat treatments, a weldability regime below approximately 10 wt% Al in the overlay has been found. The high temperature sulfidation behavior of alloys located near this crack/no crack boundary (5 to 12.5 wt% Al) was examined using a thermogravimetric balance in a reducing gas mixture of O.l% H{sub 2}-1.0% H{sub 2}S-balance Ar gas at 700 C. Light optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy were used to analyze the surface and cross-sectional morphologies. It was seen that the Fe-Al alloys exhibited lower weight gains than bare water wall tubes (carbon steel) and 309 stainless steel. Aluminum additions to the iron were found to extrinsically affect the iron sulfide reaction product morphology. Low carbon steel, with no aluminum, formed a continuous, and somewhat dense, iron sulfide scale that provided some protection. Small additions of aluminum (5--7.5 wt% Al) resulted in the growth of iron sulfide as nodules or a porous surface scale. Larger additions (above 10 wt%) were found to limit the growth of iron sulfide and significantly reduce corrosion rates. These results indicate that Fe-Al claddings containing 5 to 10 wt% Al show potential promise for applications requiring a combination of weldability and sulfidation resistance in moderately reducing environments.

• DOE Contract Number: AC05-96OR22464
• OSTI ID: 696914
• Report Number(s): CONF-990401--
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
BOILERS
CORROSION PROTECTION
CORROSION RESISTANCE
IRON BASE ALLOYS
METALLURGICAL EFFECTS
PROTECTIVE COATINGS
SULFIDATION
WELDABILITY