Abstract
Current advanced austenitic stainless steels were developed for irradiation resistance from research data accumulated for nearly 20 years on light water, fast breeder, or magnetic fusion reactor (LWR, FBR, and MFR, respectively) materials programs. The austenitic prime candidate alloy (PCA) is an example of an advanced alloy developed for irradiation resistance for the MFR program. The PCA composition has nickel and chromium modifications and titanium additions, relative to the more familiar Type 316 stainless steel, which provide better resistance to void swelling and helium embrittlement. Research on microstructural evolution, phase stability, and solute segregation in the last six to seven years has provided the additional insight to allow the design of newer and better austenitic alloys. These newer steels are based on the combined additions of Ti, V, Nb, C, and P aimed at controlling and improving the formation and stability characteristics of matrix and grain boundary precipitation. These additions promote the formation of fine MC and phosphide phase particles in the matrix which refine the helium bubble distribution and improve void swelling resistance. The additions also promote MC formation at grain boundaries to trap helium bubbles and provide embrittlement resistance. These newer advanced austenitics also show much better unirradiated high-temperature strength than Types 304, 316, or PCA stainless steels. Their strength and precipitation characteristics suggest that the newer advanced austenitics may have a direct spinoff to applications that require improved creep resistance at high temperatures.
Published Version
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