IIW 2012 - 35
temperature in a wide variety of applications associated with power generation. This trend is expected to continue with increased demand on the performance of DMWs due to the introduction of new fossil and nuclear powered plants that will operate at higher temperatures and pressures for increased efficiency. These DMWs are known to be susceptible to premature failure. This presentation reviews microstructural evolution and failure mechanisms of DMWs and describes methods for reducing the occurrence of failures. The microstructure of DMWs in the as-welded condition consists of a sharp chemical concentration gradient across the fusion line that separates the ferritic and austenitic alloys. Upon cooling from the weld thermal cycle, a band of martensite forms within this concentration gradient due to high hardenability and the relatively rapid cooling rates associated with welding. Upon aging during post weld heat treatment (PWHT) and/or high temperature service, C diffuses down the chemical potential gradi-
ent from the ferritic 2.25Cr-1Mo steel toward the austenitic alloy. This can lead to formation of a soft C denuded zone near the interface on the ferritic steel, and nucleation and growth of carbides on the austenitic side that are associated with very high hardness. These large differences in microstructure and hardness occur over very short distances across the fusion line (~ 50 – 100 μm). A band of carbides also forms along the fusion line in the ferritic side of the joint. Premature failure of DMWs is generally attributed to several primary factors, including: the sharp change in microstructure and mechanical properties across the fusion line; the large difference in coefficient of thermal expansion (CTE) between the ferritic and austenitic alloys; formation of interfacial carbides that lead to creep cavity formation; and preferential oxidation of the ferritic steel near the fusion line. In general, the large gradient in mechanical properties and CTE serve to significantly concentrate the stress along the fusion line where a
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IIW 2012
Table of Contents for the Digital Edition of IIW 2012
IIW 2012
Contents
Welcome Message
Annual Assembly Location
Colorado
Denver
General Information
IIW 65th Annual Assembly
IIW International Conference 2012 - Program
IIW International Conference 2012 - Abstracts
Speaker Bio Information
Smartphone App
Social Program
Technical Visits
Social Tours
Tour Schedule
Advertising Sponsor Profiles
Commission XIII Fracture Mechanics Seminar
IIW 2012 Sponsors
IIW 2012 - IIW 2012
IIW 2012 - Cover2
IIW 2012 - Contents
IIW 2012 - Welcome Message
IIW 2012 - 3
IIW 2012 - Annual Assembly Location
IIW 2012 - 5
IIW 2012 - Colorado
IIW 2012 - 7
IIW 2012 - Denver
IIW 2012 - 9
IIW 2012 - General Information
IIW 2012 - 11
IIW 2012 - 12
IIW 2012 - IIW 65th Annual Assembly
IIW 2012 - 14
IIW 2012 - 15
IIW 2012 - IIW International Conference 2012 - Program
IIW 2012 - 17
IIW 2012 - 18
IIW 2012 - 19
IIW 2012 - IIW International Conference 2012 - Abstracts
IIW 2012 - 21
IIW 2012 - 22
IIW 2012 - 23
IIW 2012 - 24
IIW 2012 - 25
IIW 2012 - 26
IIW 2012 - 27
IIW 2012 - 28
IIW 2012 - 29
IIW 2012 - 30
IIW 2012 - 31
IIW 2012 - 32
IIW 2012 - 33
IIW 2012 - 34
IIW 2012 - 35
IIW 2012 - 36
IIW 2012 - 37
IIW 2012 - 38
IIW 2012 - Speaker Bio Information
IIW 2012 - 40
IIW 2012 - 41
IIW 2012 - 42
IIW 2012 - 43
IIW 2012 - 44
IIW 2012 - 45
IIW 2012 - 46
IIW 2012 - 47
IIW 2012 - Smartphone App
IIW 2012 - Social Program
IIW 2012 - Technical Visits
IIW 2012 - 51
IIW 2012 - Social Tours
IIW 2012 - 53
IIW 2012 - 54
IIW 2012 - Tour Schedule
IIW 2012 - Advertising Sponsor Profiles
IIW 2012 - 57
IIW 2012 - 58
IIW 2012 - 59
IIW 2012 - 60
IIW 2012 - Commission XIII Fracture Mechanics Seminar
IIW 2012 - IIW 2012 Sponsors
IIW 2012 - 63
IIW 2012 - 64
IIW 2012 - Cover3
IIW 2012 - Cover4
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