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Localized Deformation Behaviour of Thermally Aged Stainless Steel Castings
Studsvik Nuclear.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).ORCID iD: 0000-0003-1498-5691
2014 (English)In: Fontevraud 8 - Contribution of Materials Investigations and Operating Experience to LWRs’ Safety, Performance and Reliability, SFEN , 2014Conference paper (Refereed)
Abstract [en]

Thermal ageing effects on the properties of structural materials in Light Water Reactors, is an increasingly important issue when life extension programs are aiming at 60-80 years in service. Thermal ageing of cast and welded austenitic stainless steels containing some δ−ferrite is well known and various fracture mechanics methods have been used to quantify mechanical property evolution. Thermal aging largely affects the δ−ferritic phase and often causes a change of fracture from δ−ferrite cleavage initiation to δ−ferrite to austenite phase boundary decohesion.

The objective of the present work is to investigate deformation behaviour of the two phases in cast austenitic stainless steel (CASS). This is a part of a larger effort of testing and modelling the small scale deformation and cracking mechanistics of aged solidification structures in Austenitic SS. The combined effects of thermal ageing, deformation rate and temperature on the local deformation are investigated. Focus is on the stress and strain states of the phase boundary regions and effect of phase structure. Tensile tests are conducted followed by microstructural evaluation using hardness measurements, metallography and SEM/EBSD-analysis.

It is seen that the effect of thermal ageing on tensile properties of the tested CF8M material is significant. The YS, UTS increase and fracture strain decreases with increased thermal ageing.

A strain rate sensitivity is seen and increases and changes mode with ageing, mainly attributed to the austenite’s change of deformation mechanistics, indicating the importance of including austenite ageing in the evaluation of mechanical changes. Strain appears to be more localized when increasing the deformation rate for the highly aged state. The ferrites tendency to deform over fracture increases with strain rate.

Place, publisher, year, edition, pages
SFEN , 2014.
Keyword [en]
Thermal Aging, Deformation Behaviour, CASS, EBSD
National Category
Engineering and Technology
Research subject
Materials Science and Engineering
URN: urn:nbn:se:kth:diva-164100OAI: diva2:803810
Fontevraud 8 - Contribution of Materials Investigations and Operating Experience to LWRs’ Safety, Performance and Reliability

QC 20150414

Available from: 2015-04-13 Created: 2015-04-13 Last updated: 2015-04-14Bibliographically approved

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