SYMPOSIA PAPER Published: 01 January 1989
STP24576S

The Effects of Phosphorus and Boron on the Behavior of a Titanium Stabilized Austenitic Stainless Steel Developed for Fast Reactor Service

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Austenitic stainless steels are used for core component materials in liquid metal cooled reactors (LMRs). To extend the lifetime of LMR fuel assemblies, considerable effort was expended by the U.S. breeder materials program to find ways to minimize radiation induced dimensional changes (swelling and creep) and to maximize the creep rupture strength. After various elements were shown to affect strongly swelling and creep behavior, compositional modifications to a commercial grade austenitic stainless steel (American Iron and Steel Institute 316 UNS S31600) produced an alloy with significant improvement in swelling resistance over the standard 300 series alloys. Changes were primarily in the concentrations of chromium, nickel, silicon, and titanium. ASTM Specification for Austenitic Stainless Steel Tubing for Breeder Reactor Core Components (A 771-83) was approved in 1983 for the new alloy, designated UNS S38660.

Substantial improvement can be produced in the creep rupture behavior of this alloy. Elements such as phosphorus and boron, typically present in trace quantities, have a significant influence on the creep strength of austenitic stainless steels. Several heats of alloy S38660 were made that systematically varied the phosphorus and boron contents. Uniaxial creep tests were conducted at 704°C (1300°F) to evaluate the effects of these elements on the creep rate and the rupture life. The results of these tests were used to guide the production of reactor grade fuel pin cladding for further evaluations. Pressurized tube specimens were tested in the laboratory and also in a fast reactor. Results of these investigations have shown that the elements phosphorus and boron, present in minute but controlled amounts, increase both the in-reactor and ex-reactor rupture life and reduce both in-reactor swelling and creep rate. Microstructural evaluations were also conducted to help ascertain the mechanisms by which the improved properties were obtained.

Author Information

Hamilton, ML
Pacific Northwest Laboratory, Richland, WA
Johnson, GD
Westinghouse Hanford Company, Richland, Washington
Puigh, RJ
Westinghouse Hanford Company, Richland, Washington
Garner, FA
Pacific Northwest Laboratory, Richland, WA
Maziasz, PJ
Oak Ridge National Laboratory, Oak Ridge, TN
Yang, WJS
Knolls Atomic Power Laboratory, Schenectady, NY
Abraham, N
Department of Energy, Washington, DC
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Details
Developed by Committee: A01
Pages: 124–149
DOI: 10.1520/STP24576S
ISBN-EB: 978-0-8031-5097-3
ISBN-13: 978-0-8031-1259-9