Effects of Dynamic Strain Aging on Strain Hardening Behavior, Dislocation Substructure, and Fracture Morphology in a Ferritic Stainless Steel

Dynamic strain aging at different temperatures and its effects on the strain hardening behavior, dislocation substructure and fracture morphology in a stainless steel grade 430 was investigated. Sheet type specimens were subjected to tensile tests performed at a temperature range of 298 K to 873 K. Subsequently, the strain hardening behavior of the material was depicted via modified Crussard–Jaoul analysis, strain hardening rate, and instantaneous strain hardening exponent curves. Changes in the dislocation substructure during the tests were characterized by means of X-ray diffraction and transmission electron microscopy. Scanning electron microscopy was used to investigate the fracture morphology of the specimens. The results indicated the occurrence of dynamic strain aging from 523 K to 773 K by the presence of the Portevin–Le Chatelier effect. These results were reinforced by the strain hardening analysis that revealed a three staged behavior at most of the studied temperatures, except during the dynamic strain aging regime, which presented an extra stage. Different substructures were observed as a function of the test temperatures: cellular dislocation substructure in the samples deformed at 298 K and 673 K, an array of straight and parallel dislocations in conjunction with a cellular substructure at 673 K, and finally a subgrained substructure with fine precipitates was formed at 873 K. A ductile surface fracture presenting a network of dimples and voids was present at all investigated temperatures, with a dimple size refinement being observed during the dynamic strain aging regime.