A study of chromium carbide precipitation at interphase boundaries in stainless steel welds
Sensitization is a deleterious process which can occur in stainless steels. It is caused by grain boundary or phase boundary precipitation of chromium carbides and the resulting formation of a chromium depleted zone adjacent to these boundaries. The carbides in question actually have the composition (Cr,Fe){sub 23}C{sub 6} (usually written M{sub 23}C{sub 6}), and precipitate in the temperature range 450--900{degree}C. Since a minimum chromium content is required to maintain the passive film necessary for resistance to electrochemical attack, the result of chromium depletion is that the steel becomes sensitized'' to possible intergranular corrosion. Sensitization often occurs as a result of welding operations. The material close to the fusion line reaches temperatures within the sensitization range. This region is called the heat affected zone (HAZ). Since many welds are multi-pass welds, the actual weld bead of one pass may lie in the heat affected zone of the next pass. The weld bead of the first pass might therefore be sensitized. Furthermore there are applications where welds will be exposed to sensitizing temperatures for very long periods of time, such as welded labels on retrievable nuclear waste containers. For these reasons the sensitization behavior of the actual weld-bead microstructures must be understood. It has been known for many years that duplex stainless steels (steels with both ferrite and austenite phases present at room temperature) have superior resistance to intergranular corrosion. A model has been proposed to explain the sensitization behavior of these alloys. This work will be concerned with testing the validity of aspects of this model using transmission electron microscopy and further understanding of the sensitization process in duplex stainless steel welds. 52 refs., 23 figs.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- DOE/DP; DOE/ER
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6552861
- Report Number(s):
- LBL-29311; ON: DE91000360
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CHROMIUM CARBIDES
NUCLEATION
STAINLESS STEEL-308
SEGREGATION
FERRITES
HEAT AFFECTED ZONE
MICROSTRUCTURE
PRECIPITATION
WELDED JOINTS
ALLOYS
AUSTENITIC STEELS
CARBIDES
CARBON COMPOUNDS
CHROMIUM ALLOYS
CHROMIUM COMPOUNDS
CHROMIUM-NICKEL STEELS
CORROSION RESISTANT ALLOYS
CRYSTAL STRUCTURE
FERRIMAGNETIC MATERIALS
HEAT RESISTANT MATERIALS
HEAT RESISTING ALLOYS
HIGH ALLOY STEELS
IRON ALLOYS
IRON BASE ALLOYS
IRON COMPOUNDS
JOINTS
MAGNETIC MATERIALS
MATERIALS
NICKEL ALLOYS
OXYGEN COMPOUNDS
SEPARATION PROCESSES
STAINLESS STEELS
STEEL-CR20NI11
STEELS
TRANSITION ELEMENT COMPOUNDS
ZONES
360102* - Metals & Alloys- Structure & Phase Studies