Papers by Author: H.J. McQueen

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Authors: Paola Leo, Emanuela Cerri, H.J. McQueen, P.P. De Marco
Abstract: Microhardness and hardness maps have been measured in different sections of samples processed by Equal Channel Angular Pressing (ECAP). In order to investigate the homogeneity of the hardening induced by ECAP as a function of deformation, the hardness maps have been based on samples deformed at different strains (after one and four passes). After one pass the specimen’s outer side, both on its cross and longitudinal planes, is less hard than all other zones. Moreover, after 4 passes via route Bc, the hardening induced on the sample cross section is lower at the surface than in the central area of the billet. The reduced hardness regions are compared to the distributions of plastic equivalent strain generated by finite element analysis.
Authors: H.J. McQueen
Abstract: After 1780, wrought iron (WI) provided a structural material and steel was cherished for its hardness and cutting qualities. When available in quantity after ~1860, steel’s structural strength and wear resistance were recognized in normalized condition in armor plates, rails and drawn wire. The responsible microstructure component was pearlite in which the lamellar spacing of ferrite and carbides could be refined by simple bulk heat treatments that are practiced with small modification until today. The strength and toughness rose as the layer thickness decreased the ferrite slip length and the carbide cracking. In hot working, the strength rises as much as 200% (while ductility falls) with fraction of pearlite; below the transus compared to austenite just above it, strengths are equal at about 0.7C (ductilities equal at 0.35C).
Authors: H.J. McQueen, Paola Leo, Emanuela Cerri
Abstract: Constitutive equations for hot working are of great importance in optimizing forming processes to balance reductions in preheating and force, to avoid defects and to improve properties. Flow curve shapes and. constitutive parameters are affected by variations in composition, in homogenization, in grain morphology and significantly in texture. Confidence in published analyses is enhanced by existence of many data for the same or similar alloys. In this paper, constitutive equations have been collected for commercial Mg alloys from torsion, compression and tension tests in the range from 10-3 to 10 s-1 and 180 – 500°C. Some data were determined by the authors’ but more came from published reports; in some cases they have been re-calculated in a common manner. The deformation and restoration mechanisms that control the flow curve shape and the material parameters are summarized. Microstructure investigations of strained samples are illustrated. Applications to extrusion or rolling are discussed; comparisons to Al are made as appropriate.
Authors: H.J. McQueen, N.D. Ryan, E. Evangelista
Authors: Wolfgang Blum, H.J. McQueen
Authors: Wolfgang Blum, Q.S. Zhu, R. Merkel, H.J. McQueen
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