Hall-Petch relationship for austenitic stainless steels processed by large strain warm rolling

The deformation microstructures and their effect on the yield strength of austenitic stainless steels processed by large strain warm rolling were studied. The samples of 304 L and 316 L type steels were subjected to caliber bar rolling to total strains of 2 at temperatures of 773-1173 K. The structural changes were characterized by the development of continuous dynamic recrystallization. A decrease in the rolling temperature resulted in significant grain/subgrain refinement and an increase in the yield strength at room and elevated temperatures. A power law function was obtained between the deformation grain and subgrain sizes with a grain size exponent of 0.3. Therefore, the yield strength could be expressed by a modified Hall-Petch relationship including a term of substructural strengthening, which was evaluated using the obtained size relation. The numerical factors normalized by shear modulus for both structural and substructural strengthening terms depended quite weakly on tensile test temperature in the range of 293-873 K that suggested the deformation mechanisms being invariant up to 873 K. On the other hand, the thermally activated mechanisms led to the yield strength decreasing much faster than shear modulus as the tensile test temperature increased above 873 K.

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