Lode Duprez

High-temperature stress and strain partitioning in duplex stainless steel

Abstract The high-temperature strain partitioning in duplex stainless steel was studied by means of single-pass hot-rolling tests at 1040 and 1245°C. 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°C, 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°C. The torsion tests confirmed that the deformation behaviour of the duplex stainless steel ...

Influence of composition on crack sensitivity of ferritic stainless steel.

Abstract The high temperature cracking of 17 wt-%Cr ferritic stainless steel during continuous casting was investigated in detail. No relationship between the high temperature internal cracking and the ductile to brittle transition temperature (DBTT) was found. The experimental results imply that the cracking is owing to a combination of factors: a high ferrite potential, a hot ductility gap, and the weaker grain boundary cohesion. The 17 wt-%Cr Ti stabilised grades were found to be the most sensitive ferritic grades for crack formation at high temperatures. The ductility was evaluated by means of hot tension tests. At 1200°C, the fracture surfaces of the Ti free ferritic steel had an intergranular character. At temperatures between 700 and 1100°C, the fracture surfaces were dimpled. Below 600°C cleavage fracture occurs. The 17 wt-%Cr Ti stabilised steel contained solidification related cracks. These cracks widen during the further cooling and could clearly be seen on the surface of a cracked specimen. The Ti stabilised grades had a ductility gap at 1100°C. The DBTT was measured by means of Charpy tests. Most grades had a DBTT higher than 200°C. Type AISI 430Ti and AISI 409 ferritic steel both had a lower DBTT of ~ 90°C.