Abstract
Subgrain size of austenitic stainless steel type SUS304L and high purity aluminium deformed in torsion at various strain rates and temperatures was measured. And room temperature compression tests were carried out on these samples with subgrain size ranging from about 0.5 to 6 μm for austenitic stainless steel and from about 2 to 30 μm for aluminium. The preservation of subgrains formed during high temperature deformation leads to the enhancement of the subsequent mechanical properties of the material. The room temperature strength of substructure strengthened materials correlates well with the size of retained subgrains and is shown to obey the modified Hall-Petch relation: σ=σ0+KD−1⁄2+kd−m. Here, σ0 and KD−1⁄2 are the normal Hall-Petch terms and kd−m is the strength increment ascribable to the presence of a hot worked substructure. The exponent m was observed to be about unity for these two materials. The strength increment due to the presense of subgrains was observed to be proportional to the power of the temperature compensated strain rate in high temperature deformation. The mechanism of substructural strengthening was attributable to the complex arrangement of dislocations in the small angle subgrain boundaries.
