Abstract
Two austenitic-ferritic duplex steels with different nitrogen content were subjected to cyclic loading in a wide interval of fatigue lives with controlled plastic strain amplitude and controlled stress amplitude. Cyclic hardening/softening curves, cyclic stress-strain curves and fatigue life curves were measured and parameters of individual curves were evaluated. Both types of loading result in nearly identical cyclic stress-strain curves and fatigue life curves. Cyclic stress-strain curve and Wohler curve of a superduplex steel are higher than those of duplex steel but Manson-Coffin curves of both steels are identical. The experimental data and evaluated parameters characterize the fatigue resistance of both advanced materials in a wide interval of fatigue lives.

Key words
duplex steel, fatigue life, cyclic plasticity, plastic strain amplitude

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