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Review Article

# Methodology for Estimating Thermal and Neutron Embrittlement of Austenitic Stainless Steel Welds During Service in Light Water Reactors

[+] Author and Article Information
O. K. Chopra

Environmental Science Division,
Argonne National Laboratory,
Argonne, IL 60439

A. S. Rao

Division of Engineering,
U.S. Nuclear Regulatory Commission,
Washington, DC 20555

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received July 22, 2015; final manuscript received October 21, 2015; published online April 28, 2016. Assoc. Editor: Haofeng Chen.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Pressure Vessel Technol 138(4), 040802 (Apr 28, 2016) (16 pages) Paper No: PVT-15-1166; doi: 10.1115/1.4031910 History: Received July 22, 2015; Revised October 21, 2015

## Abstract

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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## Figures

Fig. 3

Typical ferrite morphology in two different welds [27]

Fig. 2

Solute distributions predicted by different models in a frozen bar from the liquid of composition Co: (a) equilibrium cooling, (b) solute mixing in the liquid by diffusion only, (c) complete mixing in the liquid, and (d) partial solute mixing in the liquid (Reproduced with permission from Davies [88] and Brooks et al. [81]. Copyright 1973 by The Minerals, Metals & Materials Society; Copyright 1983 by The Minerals, Metals & Materials Society.)

Fig. 1

The 70% constant Fe vertical section of the Fe–Ni–Cr system (Reprinted with permission from Brooks et al. [81]. Copyright 1983 by The Minerals, Metals & Materials Society.)

Fig. 8

Fracture-toughness J-R curves for unaged austenitic SS welds at 100–427 °C. Chain dash and solid line represent lower-bound curves [12,13,27,39, 5964,70,ib7,ib7,ib7, 101,ib1,ib1,ib1].

Fig. 9

Fracture-toughness J-R curves for aged austenitic SS welds at 288–427 °C. Chain dash and solid lines represent lower-bound curves [12,13,27,39,59,104].

Fig. 4

The Charpy transition temperature curves for a few austenitic SS welds and a SA 508 class 3 low-alloy steel weld [27,61]

Fig. 5

Plots of Charpy-impact energy of unaged [1,12,13,5769] and aged [5759] austenitic SS welds as a function of test temperature

Fig. 6

Tensile yield and ultimate stress of austenitic SS welds [1,12,13,27,5769]. Solid lines are the best fit to the data.

Fig. 7

Fracture-toughness J-R curves for SS welds at (a) room temperature and (b) 288–427 °C. Solid line represents lower-bound curve [27].

Fig. 10

Fracture-toughness J-R curves for Linde 80 welds at 200 °C and 288 °C and the lower-bound J-R curve for unaged austenitic SS welds

Fig. 11

Fracture-toughness JIc for unaged and aged austenitic SS welds, with or without Mo

Fig. 12

Fracture-toughness lower-bound J-R curves and the data on unaged and aged 304, 316 L, and CF-3 welds used to develop the ASME Code IWB-3640 analysis

Fig. 13

Fracture-toughness J-R curves for unirradiated and irradiated types 308 and 316 SS welds at 427 °C and 370 °C, respectively [39,106]

Fig. 14

Coefficient C of the J-R curve as a function of neutron dose for austenitic SS welds. The data points plotted at 0.007 dpa are for nonirradiated materials.

Fig. 15

Exponent n of the J-R curve as a function of neutron dose for austenitic SS welds. The data points plotted at 0.007 dpa are for nonirradiated materials.

Fig. 16

J2.5 as a function of neutron dose for austenitic SS welds

Fig. 18

Fracture-toughness J-R curve data for as-welded Type 316L GTA weld at 288 °C in air and BWR environment with 300 ppb DO [102]

Fig. 17

Fracture-toughness JIc values as a function of neutron dose for austenitic SS welds. The data points plotted at 0.007 dpa are for nonirradiated materials.

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