Effect of long-term thermal aging on the fracture toughness of austenitic stainless steel base and weld metals

The effect of thermal aging on the degradation of fracture toughness and Charpy-impact properties of austenitic stainless steel (SS) welds has been characterized at reactor temperatures. The solidification behavior and the distribution and morphology of the ferrite phase in SS welds are described. Thermal aging of the welds results in moderate decreases in Charpy-impact strength and fracture toughness. The upper-shelf Charpy-impact energy of aged welds decreases by 50–80 J/cm2. The decrease in fracture-toughness J integral-resistance (J-R) curve or JIc is relatively small. Thermal aging has minimal effect and the welding process has a significant effect on the tensile strength. However, the existing data are inadequate to accurately establish the effect of the welding process on fracture properties of SS welds. Consequently, the approach used for evaluating thermal and neutron embrittlement of austenitic SS welds relies on establishing a lower-bound fracture-toughness J-R curve for unaged and aged and nonirradiated and irradiated SS welds. The existing fracture-toughness J-R curve data for SS welds have been reviewed and evaluated to define lower-bound J-R curves for submerged arc (SA)/shielded metal arc (SMA)/manual metal arc (MMA) welds and gas tungsten arc (GTA)/metal inert gas (MIG)/tungsten inert gas (TIG) welds in the unaged and aged conditions. At reactor temperatures, the fracture toughness of GTA/MIG/TIG welds is a factor of about 2.3 higher than that of SA/SMA/MMA welds. Thermal aging decreases the fracture toughness of all welds by about 20%. The potential combined effects of thermal and neutron embrittlement of austenitic SS welds are also described. Lower-bound curves are presented, which define the change in coefficient C and exponent n of the power-law J-R curve and the JIc value for SS welds as a function of neutron dose. The potential effects of reactor coolant environment on the fracture toughness of austenitic SS welds are also discussed.

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Evaluation of the Degradation Characteristics of CF-8A Cast Stainless Steel Using Indentation Techniques and EDS

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.306-308.869 ◽

2006 ◽

Vol 306-308 ◽

pp. 869-874 ◽

Cited By ~ 1

Author(s):

Seung Baek ◽

Jae Mean Koo ◽

Chang Sung Seok

Keyword(s):

Fracture Toughness ◽

Stainless Steel ◽

Austenitic Stainless Steel ◽

Structural Changes ◽

Accelerated Aging ◽

Ball Indentation ◽

Indentation Tests ◽

Pump Valve ◽

Cast Stainless Steel

Cast austenitic stainless steel piping pump, valve casings and elbows are susceptible to reductions in toughness and ductility because of long term exposure at the operating temperatures in the LWR (light water reactor). In this study, the three classes of thermally aged CF-8A cast austenitic stainless steel specimens were prepared using an artificially accelerated aging method for 0, 2,679 and 3,572 hours at 400oC. An indentation technique was applied to evaluate of the thermal aging of CF-8A cast austenitic stainless steel. We have performed indentation tests (automated ball indentation and nano-indentation) and EDS (energy dispersive spectroscopy) in order to characterize the micro-structural changes of the phase with aging. The fracture toughness of aged CF-8A cast stainless steel was determined by standard fracture toughness tests and automated ball indentation techniques.

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