Kinetics of sensitization and de-sensitization of duplex 308 stainless steel

Journal Article · Wed Jun 01 00:00:00 EDT 1988 · Acta Metall.; (United States)

DOI:https://doi.org/10.1016/0001-6160(88)90216-7· OSTI ID:6760073

Devine, T M ^[1]

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1. Materials and Chemical Sciences Div., Lawrence Berkeley Lab. and Dept. of Materials Science and Mineral Engineering, Univ. of California, Berkeley, CA (US)

The kinetics of, and the factors responsible for, sensitization and de-sensitization were determined for duplex 308 stainless steel. Samples consisting of 10 vol.% of ferrite, balance austenite were heat treated at 600 and 550/sup 0/C for times of 15 min-300h. The chromium contents of the ..cap alpha..-..gamma.. boundaries and ..gamma..-..gamma.. grain boundaries of heat treated samples were measured by a potentiostatic electrochemical technique. Transmission electron microscopy of foils and surface replicas of heat treated samples was used to observe carbide precipitation on the boundaries and decomposition of the ferrite. Carbide precipitation occurred exclusively along the ..cap alpha..-..gamma.. boundaries. Most of the chromium in the carbide came from the ferrite phase. However, intergranular corrosion susceptibility resulted from a chromium depleted zone that was formed on the austenite side of the interface and a chromium depleted zone that formed along the ..gamma..-..gamma.. grain boundaries. The latter developed in spite of the absence of carbides along the ..gamma..-..gamma.. grain boundaries. It resulted from grain boundary diffusion of chromium to the carbides growing along the ..cap alpha..-..gamma.. boundaries. There was a maximum in the degree of sensitization with time of heat treatment. At aging times t/sub max/, de-sensitization occurred. This was controlled by the chromium content in the matrix at the carbide-matrix interface. Initially, the rate of de-sensitization was rapid and was produced by chromium diffusing from the ferrite phase into the chromium depleted zone in the austenite. When the ferrite phase started to decompose the rate of de-sensitization decreased and was produced by volume diffusion of chromium in the austenite phase.

• OSTI ID: 6760073
• Journal Information: Acta Metall.; (United States), Vol. 36:6
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CHROMIUM
DIFFUSION
FERRITIC STEELS
CHEMICAL REACTION KINETICS
PERMEABILITY
AUSTENITE
CARBIDES
ELECTROCHEMISTRY
FOILS
GRAIN BOUNDARIES
INTERGRANULAR CORROSION
PHASE TRANSFORMATIONS
PRECIPITATION
SAMPLING
TRANSMISSION ELECTRON MICROSCOPY
ALLOYS
CARBON ADDITIONS
CARBON COMPOUNDS
CHEMICAL REACTIONS
CHEMISTRY
CORROSION
CRYSTAL STRUCTURE
ELECTRON MICROSCOPY
ELEMENTS
IRON ALLOYS
IRON BASE ALLOYS
KINETICS
METALS
MICROSCOPY
MICROSTRUCTURE
REACTION KINETICS
SEPARATION PROCESSES
STEELS
TRANSITION ELEMENTS
360102* - Metals & Alloys- Structure & Phase Studies
360104 - Metals & Alloys- Physical Properties