SYMPOSIA PAPER Published: 09 February 2018
STP87019850011

Low-Dose Irradiation Effects on Creep Properties of Type 304 Stainless Steel Weld Metal, Heat-Affected Zones, and Welded Joints

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The integrity of large non-replaceable primary reactor components of liquid metal fast breeders largely depends on the properties of weld metal and heat-affected zones. Safety authorities, involved in the licensing of the SNR-300, have required the measurement and interpretation of post-irradiation creep and creep rupture properties of DIN 1.4948 (Type 304) stainless steel weld metal and heat-affected zones.

For the present investigation, weld metal in as-deposited and stress-relieved condition has been subjected to tension and creep tests. The heat-affected zone structure was studied with specimens subjected to temperature cycles representative for different locations in the parent metal near the fusion zone. The specimens were irradiated in the HFR Petten at 823 K submerged in sodium to a total neutron fluence of 5 × 1024 n/m2.

Irradiation has no significant effect on creep and tensile properties of weld metal. The heat-affected zone is strongly affected by low-dose neutron irradiation: its 10 000-h creep strength is about 25 MPa lower than that of parent metal under similar conditions. The creep strength of welded joints is controlled by a strain limit criterion. In unirradiated condition, the weld metal has the lowest ductility and rupture occurs in the weld metal. In irradiated condition the heat-affected zone has the lowest ductility for the higher creep stresses (>175 MPa) and lower rupture times (<3000 h). For lower creep stresses, the weld metal, though not affected by irradiation, determines the creep strength.

Application of a stress relief treatment reduces the dislocation density and changes the carbide population in weld metal to such a degree that the ductility increases considerably with little loss of strength. The grain coarsening in the heat-affected zones, amplifying the irradiation embrittlement, can be suppressed by using low heat input welding techniques. By the improvements of the weld metal and heat-affected zone, the post-irradiation creep properties of welded joints could be improved.

Author Information

van der Schaaf, Bob
Netherlands Energy Research Foundation, Petten, NL
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Developed by Committee: E10
Pages: 703–719
DOI: 10.1520/STP87019850011
ISBN-EB: 978-0-8031-7679-9
ISBN-13: 978-0-8031-0592-8