Nov 3, 2015 - Fe-Cr-Mn Austenitic Alloys,' Radiation-Induced Changes in ... reduced level of long-term radioactivity and thereby reduce the cost and safety ...
Frank A. Garner^ and Howard R. Brager^
Neutron-Induced Swelling of Fe-Mn and Fe-Cr-Mn Austenitic Alloys REFERENCE: Garner, F. A. and Brager, H. R., "Neutron-Induced Swelling of Fe-Mn and Fe-Cr-Mn Austenitic Alloys,' Radiation-Induced Changes in Microstructure: 13th International Symposium, ASTM STP 955, F. A. Garner, N. H. Packan, and A. S. Kumar, Eds., American Society for Testing and Materials, Philadelphia, 1987, pp. 195-206. ABSTRACT: An effort is underway to explore the potential of Fe-Cr-Mn austenitic alloys as substitutes for Fe-Cr-Ni alloys in fusion reactors. This substitution is desired to achieve a reduced level of long-term radioactivity and thereby reduce the cost and safety hazards associated with disposal of reactor components at their end of life. Neutron-induced swelling data to 50 dpa are now available at 520°C for three reduced activation alloy series and for lower exposures at 420 and 600°C. These three series cover simple binary and ternary alloys, solute-modified ternaries, and a variety of commercially available Fe-Cr-Mn alloys. The swelling of these alloys is initially similar to that of Fe-Cr-Ni alloys but then changes in response to phase instabilities that develop in the Fe-Cr-Mn system. KEY WORDS: Fe-Mn alloys, Fe-Cr-Mn alloys, austenitic alloys, voids, swelUng, neutron irradiation, reduced activation, phase instabilities, ferrite
In the U.S. fusion materials program it is desired to develop structural materials that can be either recycled or disposed in a manner that will not require costly deep burial [1,2]. This necessitates the use of elements whose transmutation products decay quickly enough to exhibit a substantially reduced level of long-term radioactivity. Unfortunately, this objective requires either a strong limitation or the near total elimination of several of the most commonly used metallurgical elements. Examples of these are nickel, molybdenum, and niobium. It has been proposed that low activation iron-based austenitic and ferritic alloys can be developed by finding substitutes for these and other elements that develop long-lived activation products [3,4]. For austenitic alloys the major effort has been directed toward the substitution of manganese for nickel [3-6]. Compared to nickel, however, manganese is a rather reactive element, leading to concerns about its higher vapor pressure, potentially lower corrosion resistance, and possible instability in both thermal and radiation environments. All of these concerns are in addition to the well-known problems of void swelling, irradiation creep, and embrittlement found in Fe-Cr-Ni alloys. This paper examines the swelling behavior of Fe-Cr-Mn alloys as a function of composition and irradiation temperature. Three sets of alloys were irradiated side by side in the Fast Flux Test Facility (FFTF) using the materials open test assembly (MOTA) that controls the temperature to within ±5°C. ' Fellow scientist and fellow scientist, respectively, Westinghouse Hanford Co., P.O. Box 1970, W/A-58, Richland, WA 99352. Copyright by Downloaded/printed Copyright® 1987 bGarner y ASTM Frank
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RADIATION INDUCED CHANGES IN MICROSTRUCTURE TABLE 1—Composition of simple Fe-Cr-Mn alloys, wt%. Alloy
Fe
Cr
Mn
R66 R67 R68 R69 R70 R71 R72 R73 R74 R75
80 70 80 70 65 75 70 65 60 65
5 15 0 10 15 0 0 5 10 0
15 15 20 20 20 25 30 30 30 35
Experimental Details The first set of alloys contained three binary Fe-Mn and six ternary Fe-Cr-Mn alloys with low levels of other solute elements. These alloys are all in the annealed condition (1030°C, 0.5 h, air cool) and were chosen to investigate two composition ranges, that of the existing commercial alloys (12-20Mn and 2-18Cr) and that of higher manganese alloys (25-35Mn and 0-15Cr). The latter subgroup was chosen on the assumption that the correlation found between swelhng resistance and Invar properties in the Fe-Cr-Ni system was also valid in the Fe-Cr-Mn system [7], The second set of alloys involved solute modification of six of the simple alloys. All contained 0.5% nickel and 0.4-1.0% silicon since commercial alloys generally have significant and comparable amounts of these elements. Nitrogen and carbon were varied as austenizing elements and phosphorus and boron levels were also chosen to be representative of commercial practice. Hardening elements, namely, vanadium, tungsten, and aluminum, were chosen to be consistent with reduced-activation considerations [1,2]. A variety of thermal-mechanical starting states were employed. The third set of alloys contained five commercially available alloys, some in a variety of thermal-mechanical starting states. The compositions of all three sets of alloys are shown in Tables 1, 2, and 3, and the preirradiation treatment conditions are given in Table 4. TABLE 2—Composition of Phase IV solute-modified Fe-Cr-Mn alloys, wt%. Alloys
Mn
Cr
C
N
X-75 R76 R77 R78 R79 R80 R81 R82 R83 R84 R85 R86 R87 R88 R89
30 30 30 30 30 30 20 15 15 15 15 15 15 15 15
2.0 2.0 2.0 5.0 10 10 15 5 5 5 15 15 15 15 15
0.10 0.60 0.40 0.05 0.05 0.50 0.05 0.40 0.60 0.70 0.05 0.10 0.10 0.30 0.50
0.15 0.05 0.15 0.15 0.10 0.10 0.10 0.10 0.05 0.10 0.15 0.35 0.10 0.30 0.10
V
P
B
1.0
0.05 0.05
0.005 0.005
0.005
2.0 0.05
W
1.0
1.0
2.0
0.005 1.0
2.0
2.0 2.0
Al
0.05 0.05
0.005 0.005
i.b
2.0 2.0
Ni
Si
0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 1.0 0.4 0.4 0.4 1.0 0.4 0.4
Copyright by ASTM Int'l (all rights reserved); Tue Nov 3 18:42:38 EST 2015 Downloaded/printed by Frank Garner (Radiation effects Consulting) pursuant to License Agreement. No further reproductions authorized.
GARNER AND BRAGER ON NEUTRON-INDUCED SWELLING
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