| dc.description.abstract | Dynamic strain aging is a metallurgical phenomenon associated with solutedislocation interaction induced plastic instabilities during plastic deformation. This phenomenon leads to mechanical properties variation in metallic alloys, thus, being relevant for forming procedures and applications which operate at temperatures above room temperature. The objective of this study was to investigate the susceptibility of a ferritic stainless steel 430 to dynamic strain aging by means of tensile tests performed at a temperature range of 25 to 600oC and a fixed strain rate of 103s1. Mechanical properties analysis was performed in terms of the yield strength, ultimate tensile strength, total strain hardening, uniform elongation,t otal elongation, non-uniformelongation,strain hardening exponent and resistanceco efficient.Strain hardening behavior was assessed via modified Crussard-Jaoulanalyses, strain hardening rate and the instantaneous strain hardening exponent curves. Dislocation substructure development with deformation temperature was evaluated by means of transmission electron microscopy. Mechanical properties alteration and the occurrence of the PortevinLe Chatelier effect indicated dynamic strain aging occurrence from 250 to 500oC. In the dynamic strain aging regime, negative strain rate sensitivity was observed, as well as a maximum in mechanical strength and in total strain hardening, while uniform deformation presented a decreasing behavior throughout all the investigated temperatures. Dislocation substructure analyses of samples deformed in approximately 7% at 25, 400 and 600oC revealed a cellular substructure in the samples deformed at 25 and 400oC; at 400oC, an array of straight and parallel dislocations was observed in conjunction with the cellular substructure; a substructure of subgrains and the formation of a fine precipitate dispersion was observed at 600oC. A ductile surface fracture, characterized by a network of dimples and voids, was observed at all investigated temperatures, with a refinement in dimple size being observed on the dynamic strain aging regime and an increase of dimple size in high temperatures. Transmission electron microscopy and full width at half maximum analyses indicated an increase in dislocation multiplication as a result of dynamic strain aging. Strain hardening analysis revealed three stages in the investigated temperatures; an extra stage was identified in the dynamic strain aging regime and associated with dynamic strain agings influence on dislocation interaction and multiplication during plastic deformation. Dynamic strain aging in a ferritic stainless steel 430 resulted in an increase in mechanical strength and strain hardening parameters, accompanied by a reduction in uniform elongation. These variations were attributed to an increase in dislocation density, a decrease in dynamic recovery and the formation of a parallel dislocation array. Dimple size variation in fracture surface was related to the fluctuation of the nonuniform elongation. Future research is recommended to accurately establish the mechanism responsible for dynamic strain aging in the studied steel | |
