The fatigue crack growth rates of Type 316 stainless steel and 16-3-2 gas tungsten are welds were measured in air and high-carbon liquid sodium at 510°C (950°F) for secondary sodium loop Liquid Metal Fast Breeder Reactor applications. Loading variables such as low frequency, load ratio, and hold time at peak load were studied, Supporting studies show that carburization of crack faces occurs prior to any crack tip carburization for the crack sizes and load frequencies of this study. Thus, a carburization effect on da/dN is not shown for relatively short-term tests. Low stress intensity, ultra-tow frequency tests to simulate service would be required to show this effect. The crack growth rate curve for 16-8-2 welds was below Type 316 base metal curves for both air and high-carbon sodium at 510°C (950°F). Crack growth rate curves for Type 316 and 16-8-2 welds in high-carbon sodium were below the corresponding curves for air.

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