The following text was automatically extracted from the image on this page using optical character recognition software:
The Effects of Aging for 50,000 Hours at 343*C on the
Mechanical Properties of Type 308 Stainless Steel Weldments
David J. Alexander
Metals and Ceramics Division
Oak Ridge National Laboratory
P. O. Box 2008, Oak Ridge, TN, 37831-6151
Randy K. Nanstad
Metals and Ceramics Division
Oak Ridge National Laboratory
P. O. Box 2008, Oak Ridge, TN, 37831-6151
Abstract
The effects of long-term aging at intermediate temperature on the mechanical properties of type 308
stainless steel weld metals have been studied. Three multipass shielded metal-arc welds with ferrite
levels of 4, 8, or 12% were aged up to 50,000 h at 343 *C. Tensile and Charpy V-notch specimens
were used to determine the effects of aging on the mechanical properties of the weld metal. Aging
had little effect on the yield strength of the weld metal, but did result in a slight increase
(approximately 5 %) in the ultimate tensile strength. The ferrite content had little effect on the yield
strength of the materials, but the ultimate tensile strength increased slightly with higher ferrite
content. In contrast to the small effect on the tensile properties, the impact properties were
significantly degraded by aging. The extent of the degradation increased with increasing ferrite
content and continued to increase with increasing aging time. Spinodal decomposition and the
precipitation of G-phase particles in the ferrite phase are believed to be responsible for the
degradation of the mechanical properties.
Key words: stainless steel, welds, ferrite, austenite, aging, embrittlement, spinodal decomposition,
impact properties, tensile properties
Introduction
Stainless steel is used extensively in the piping of light water reactors (LWRs). Frequently the piping
systems contain welds made with type 308 stainless steel filler metals which typically contain 5 to
15% ferrite. This ferrite strengthens the welds, improves the weldability, and increases the resistance
to stress corrosion cracking. However, the ferrite phase may become embrittled after exposure to
elevated temperatures. Therefore, the possible degradation of the mechanical properties of these
welds as a result of long-term aging at operating temperatures must be considered. The phenomenon
of 475*C embrittlement has been studied extensively for duplex cast and wrought stainless steels (see,
for example, Ref. 1). However, there has been relatively little research directed toward weldments
operating at the somewhat lower temperatures typical of the LWR environment. Therefore, several
welds were fabricated to study the effect of long-term aging at 343*C, the upper operating
temperature limit for LWR piping, on the mechanical properties of such welds. The results of aging
