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PortevinLe Chatelier Effects in a High-Mn Austenitic Steel
GIORGIO SCAVINO, CAROLINA DI SALVO, PAOLO MATTEIS, RAFFAELLA SESANA, and DONATO FIRRAO
High-manganese austenitic steels were recently proposed to fabricate structural car body parts because of their very favorable combination of strength and ductility. They exhibit PortevinLe Chatelier macroscopic plastic localization phenomena at the room temperature, as evidenced by the tensile curves rst by the isolated stress peaks corresponding to the nucleation of deformation bands, which travel along the tensile axis, and then by serrations due to static deformation bands. The bands extend to the whole width of the specimen and cause a local temperature increase along with a slight surface relief. These plastic instabilities were studied during tensile tests at strain rates between 0.0004 and 0.04 s 1, with optical video recording, infrared thermography and optical extensometry, the latter based on digital image correlation. Two types of bands, type A and type C, were observed and are described.
DOI: 10.1007/s11661-012-1445-5 The Minerals, Metals & Materials Society and ASM International 2012
I. INTRODUCTION
HIGH-MN austenitic sheet steels oer a remarkable combination of strength and ductility, with ultimate tensile strengths larger than 1100 MPa and elongationsto-fracture larger than 50 pct,[1] which features make them strong candidates for car body applications for weight reduction. In fact, car body steels, in addition to showing high tensile strength, must also display high biaxial ductility, to allow for the deep drawing of complex shapes, as well as the capability to absorb great quantities of energy during a crash to insure the vehicle safety.
Much study has already been published on alloy development, microstructure analysis, and mechanical properties of these steels.[19] In particular, it was ascertained that they exhibit plastic deformation not only by dislocation slip but also by mechanical twinning,[7] with the newly formed twin boundaries acting as obstacles to dislocation movement in the same way as grain boundaries do.[1] For this reason, these steels are referred to as TWIP (Twinning-Induced Plasticity) steels.
These steels also exhibit the PortevinLe Chatelier (PLC) macroscopic plastic localization phenomena when subjected to tensile tests at the room temperature;[1014] these latter phenomena have been attributed either to plain dynamic strain aging due to interactions between mobile dislocations and point-defect complexes including interstitial C atoms,[13] or to more...