Carburization behaviour of Haynes 556 exposed to CH₄/H₂ gas mixtures

Author: Yin, Ruchuan

Source: Materials at High Temperatures, Volume 21, Number 2, May 2004 , pp. 111-117(7)

Publisher: Science Reviews 2000 Ltd

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Abstract:

The carburization behaviour of Haynes 556 has been studied after cyclic and isothermal exposures to CH₄/H₂ carburizing gas mixtures at high temperatures for 500h exposures. A thermodynamic analysis indicated that 1000°C was an approximate critical temperature, below which the environment should result in mixed oxidizing/carburizing behaviour, while above this temperature reducing carburizing behaviour should occur. The experimental results agree with the thermodynamic analysis. Below 1000°C Haynes 556 suffered external carburization and oxidation, typically at 800°C in 2% CH₄/H₂ where the external reaction products comprised Cr₇C₃ and Co₃W₃C (major phases), and (Co,Mn)(Mn,Co)₂O₄ and TaO_x (minor phases). At temperatures in excess of 1000°C exclusive external carburization occurred, typically at 1100°C in 10% CH₄/H₂ resulting in the formation of Cr₇C₃ (major phase) and (Cr,Fe)₇C₃ (minor phase). Metal dusting was not experienced under highly carburizing conditions (a_c>1) in this study. The morphology of an outer carbide layer is both temperature- and timedependent, while its continuity is more temperature-dependent rather than time-dependent.

Keywords: Haynes 556; carburization; reducing environment; continuity

Document Type: Research article

DOI: http://dx.doi.org/10.3184/096034004782749980

Affiliations: 1: Materials and Corrosion Section, Sabic Technology Center, P.O. Box # 11425 Jubail Industrial City 31961, Saudi Arabia. or yinruchuan@yahoo.com, Email: ruchuany@sabic.com

Publication date: 2004-05-15

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Materials at High Temperatures serves the needs of those who develop and use materials for high temperature applications. It publishes peer reviewed contributions relating to high temperature applications in the power, chemical, engine, processing and furnace industries.
The effects of high temperatures on corrosion, fatigue, creep, strength and wear in alloys, intermetallics, ceramics, refractories and composites are covered. Papers dealing with aspects of materials usage including modelling of behaviour and life prediction will be particularly welcome. The journal has a policy of emphasizing practical aspects and authors presenting results from research programmes are encouraged to relate these, if possible, to actual or potential applications.
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