Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 714, Issue -, Pages 1-13Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2017.12.088
Keywords
Grade 91 Steel; Heat-affected zone; Post Weld Heat Treatment; Type I Cracking; Type IV Cracking
Categories
Funding
- Discovery Program of the Natural Sciences and Engineering Research Council (NSERC) of Canada
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Increasing the post-weld heat-treating temperature from 600 degrees C to 840 degrees C causes a transition of creep rupture locations from the Type IV cracking in the intercritical heat-affected zone to the Type I cracking in the fusion zone in the Grade 91 steel weldments. The specimens following a heat-treatment at temperatures below the A(1) temperature of the base metal failed in the Type IV cracking mode after high-temperature creep tests at 650 degrees C. The creep-damaged region associated with the Type IV cracking mode is consistently located in a softened zone, which is identified as the intercritical heat-affected zone. In the specimens heat-treated at temperatures close to or above the Al temperature of the base metal, the fusion zone enters the intercritical temperature between its A(1) and A(3) temperatures. The fusion zone experienced a partial austenitization to become a mixture of retained ferrite and new martensite, which is believed the most creep-susceptible. The same microstructure, a mixture of retained soft ferrite and new hard martensite, caused nucleation and growth of cavities in the both Type IV and Type I damaged regions. Therefore, it is suggested that the same creep mechanism may have contributed to both cracking modes in Grade 91 steel.
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