Assessment of Embrittlement of VHTR Structural Alloys in Impure Helium Environments Page: 4 of 63
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Table 1 Chemical compositions of the tested alloys
Element Ni Cr Fe Co Mo Ti Al C Si Mn Cu P B S
Alloy 617 54.1 22.2 1.6 11.6 8.6 0.4 1.1 0.05 0.1 0.1 0.04 <0.001 <0.002
Alloy 800H 30.65 19.7 46.24 0.1 --- 0.54 0.56 0.061 0.42 1.27 0.2 0.024 0.001
Table 1 presents the chemical compositions of the as-received alloys. All 617 and 800H samples
used in these studies were provided by Dr. Richard Wright at Idaho National Laboratory (INL),
Idaho Falls, ID, USA. The materials from INL were cut from much larger samples and were
solution annealed. Before the creep crack growth testing, both Alloy 617 and Alloy 800H were
solution treated (ST) at 1200 0C for one hour and then quenched in water, as suggested by
Special Metals. Because the Alloy 617 and Alloy 800H materials will ultimately be used for
extended periods of time and at high temperatures during heat exchanger service, the materials
were further heated to 850 0C for 2000 hrs in air to age the materials. During the aging process,
small coupons of the candidate alloys were removed at specific time intervals. Hardness and
tensile testing of the aged coupons were performed to evaluate the mechanical properties of the
alloys as a function of aging time (testing details to follow). Rolling direction was tracked
throughout all stages of the sample preparation.
Compact tension (CT) specimens for the creep crack growth (CCG) experiments were fabricated
from the aged alloy materials. Figure 1 presents the CT specimen geometry defined by ASTM
standard E1457-07 . After an investigation into the necessary stress levels needed to induce
creep crack growth within the candidate alloys, along with a comprehensive evaluation of the
anticipated stress levels in the load-bearing components of the CCG testing apparatus, design
values of W = 50 mm, B = 6.25 mm, and a = 27.5 mm for the CT specimens were chosen.
Electric discharge machining (EDM) was used to fabricate the CT specimens, with the
orientation of the crack being aligned with the rolling direction of the samples. Fine-wire EDM
was used to machine the final 3.75 mm length of the crack at a width of -100 pm.
B 4 Wotoi.vu 0 0-+
- - - 2H =1.2W
+ 0.010W 0.05W a
Figure 1 Geometry of compact tension (CT) specimens as defined by ASTM standard E1457-07. Values of
W = 50 mm, B = 6.25 mm, and a = 27.5 mm were chosen for the studies presented herein.
Coupons of -40x10x5 mm3 were prepared by electrical discharge machining. Dogbone
specimens for tensile testing were fabricated from the aged coupons by electrical discharge
machining after heat treatment was completed. Figure 2 presents the tensile specimen geometry
defined by ASTM standard E8 . EDM machining was again used to fabricate the specimens.
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Crone, Wendy; Cao, Guoping & Sridhara, Kumar. Assessment of Embrittlement of VHTR Structural Alloys in Impure Helium Environments, report, May 31, 2013; United States. (digital.library.unt.edu/ark:/67531/metadc836772/m1/4/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.