High-temperature stress and strain partitioning in duplex stainless steel

The high-temperature strain partitioning in duplex stainless steel was studied by means of single-pass hot-rolling tests at 1040 and 1245 degreesC. By varying the temperature and the amount of reduction during the hot-rolling pass the influence of the austenite volume fraction and the strain could be investigated. By means of optical microscopy and application of the law of mixtures the partitioning of strain between the ferrite matrix and the austenite islands was obtained. A distinct strain partitioning was observed. At 1245 degreesC, the ferrite-austenite strain ratio increased from 2.8 at 30 % rolling reduction to 4.2 at 80 % reduction. In addition, single-hit hot-torsion tests were performed on single-phase ferritic and austenitic materials, as well as on the duplex stainless steel in order to study the stress partitioning between the phases. The austenite-ferrite stress ratio was found to increase up to 3.5 at 1200 degreesC. The torsion tests confirmed that the deformation behaviour of the duplex stainless steel is mainly determined by the deformation behaviour of the ferritic matrix, in particular during the early stages of deformation. The strain concentration in the ferrite was found to result in a delay of the dynamic recrystallisation of the austenite.