Portevin - Le Chatelier effect in a Mn-alloyed thermomechanically processed austenitic steel
Russo, Spena P
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A 0.5 wt.% C, 22 wt.% Mn austenitic steel, recently proposed for fabricating automotive body structures by cold sheet forming, exhibits a localized plastic flow instability when subjected to uniaxial tensile deformation in a certain range of strain and strain rate. This peculiar plastic behavior, often attributed to the Portevin-Le Chatelier (PLC) effect, was investigated experimentally by constant strain rate tensile tests and by standard Erichsen test, performed with polished specimens. During the tensile tests, the strain localization appears first as macroscopic deformation bands (forming about 60° angle with the tensile axis and involving the full specimen width) spreading over the entire specimen length, and then of series of successive stationary bands, each adjacent to the preceding ones, producing serrations on the stress-strain curves, and transient or permanent specimen surface markings. No surface relief was observed during the Erichsen tests. X-rays analyses excluded the occurrence of second phases and deformation-induced martensitic transformations. SEM analyses showed both ductile fracture surfaces and relief attributed to mechanical twins on the specimen surfaces.