Sheets of coarse-grained S304H austenitic steel were processed by high-pressure sliding (HPS) at room temperature and a ultrafine-grained microstructure with a mean grain size of about 0.14 µm was prepared. The microstructure changes and creep behavior of coarse-grained and HPS-processed steel were investigated at 500-700 °C under the application of different loads. It was found that the processing of S304H steel led to a significant improvement in creep strength at 500 °C. However, a further increase in creep temperature to 600 °C and 700 °C led to the deterioration of creep behavior of HPS-processed steel. The microstructure results suggest that the creep behavior of HPS-processed steel is associated with the thermal stability of the SPD-processed microstructure. The recrystallization, grain growth, the coarsening of precipitates led to a reduction in creep strength of the HPS-processed state. It was also observed that in the HPS-processed microstructure the fast formation of σ-phase occurs. The σ-phase was already formed during slight grain coarsening at 600 °C and its formation was enhanced after recrystallization at 700 °C.

Institute of Physics of Materials Czech Academy of Sciences Zizkova 22 616 00 Brno Czech Republic

Kyushu Institute of Technology Kitakyushu 804 8550 Japan

Magnesium Research Center Kumamoto University Kumamoto 860 8555 Japan

Synchrotron Light Application Center Saga University Saga 840 8502 Japan

Technology Department Nagano Forging Co Ltd Nagano 381 0003 Japan

UJP PRAHA a s 156 10 Praha Zbraslav Czech Republic

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