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Title: Elucidating environment-assisted cracking of engineered duplex stainless steel weld microstructures
Author: Reccagni, Pierfranco
ISNI:       0000 0004 7971 1488
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2019
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Environment assisted cracking (EAC) is the name used to describe a group of degradation mechanisms that cause failure of materials in service as a combined result of corrosive environment, mechanical stress and susceptible microstructure. Duplex stainless steels (DSSs) have outstanding EAC resistance, provided by the different mechanical, electrochemical and hydrogen diffusivity properties of the two phases. The optimal microstructure morphology, can be altered in the heat affected zones (HAZs) of welded components, with this region of the weldment offering lower EAC resistance. This work presents a detailed observation on the effects of arc-welding on the austenite morphology in the HAZ of a multi-pass DSS2205 TIG weld and in thermo-mechanically simulated HAZs. Austenite morphological changes, formation of precipitates and internal galvanic activity in the simulated alloys have been evaluated using a combination of microstructure characterization techniques, scanning kelvin probe microscopy (SKPFM) potential surveys and electrochemical measurements. The relevance of these observations has been validated performing EAC testing on a real-scale multi-pass tungsten inert gas (TIG) weld. The results showed a marked reduction in internal galvanic activity in the simulated HAZs, offering an electrochemical explanation for the enhanced SCC susceptibility of this region. Different degrees of hydrogen embrittlement resistance for different austenite morphologies were observed, with grain boundary austenite (GBA) showing the lowest resistance to crack progression. Austenite morphology showed an effect also on the anodic dissolution of ferrite - a precursor of SCC attacks - and a qualitative relationship between phase boundaries orientation, applied stress and preferred cracking paths was devised.
Supervisor: Engelberg, Dirk ; Akid, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: SKPFM ; GLEEBLE ; EBSD ; Duplex stainless steel ; TIG Weld