Papers by Author: 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).

Abstract: TMP of Al alloys includes hot working with dynamic substructures and deformation bands for texture components combined with static recovery or recrystallization as well as cold working altered by annealing. The above processes are separately tailored for solute (Al, Mg), dispersoid (Al-0.7Fe) and precipitation hardening alloys; aging combined with deformation can raise strength or improve fatigue or corrosion resistance. Hot and cold rolling with suitable holding intervals are managed to combine deformation and annealing textures for planar anisotropy or for producing less fibrous grains to avoid delamination corrosion; grains may be severely refined by discontinuous or continuous recrystallization for superplastic sheet. In hot-billet and impact extrusion as an addition to substructure and texture strengthening, the intense heating near the die may be employed for precipitate solution with exit quenching for press heat treatment to T5 temper. Similarly, friction stir surface treatment and welding provide intense hot straining with additional softening as metal is swept behind the pin. In combination with some of the above, forging provides grain and dispersoid fibering oriented for crack retardation; semi solid forming competes with this.

Abstract: The metallurgical revolution of increased supply and decreased cost followed three stages: 1) coke use in the blast furnace, 2) puddling process for wrought iron (WI) and 3) Bessemer or Siemens processes for steel. The second gave rise to the conversion from wooden (iron-reinforced) machines to iron machines such as railroad engines, ships and long-span bridges, all hot-riveted. The self-made mechanical engineers raised the precision, scale and speed of mechanical shaping technology; this was transferred from WI to ingot steel with little difficulty for the same products with increased strength. Accurately measured mechanical properties of WI and steel were related for the first time to microstructure and processing by David Kirkaldy to improve Clyde-built ships and to propel metallurgy from artisanal to science-based.

Abstract: Inherent failure mechanisms at elevated temperature are primarily wedge crack growth at triple junctions arising from differential grain boundary (GB) sliding at higher stresses and pore formation on sliding boundaries due to vacancy diffusion at lower stresses and higher T. The behaviours of these mechanisms have been ascertained in creep where they can be studied over long periods. They continue to operate in hot working although their effects per unit strain have been reduced by decrease in fractional contribution of GB sliding. Dynamic recovery (DRV) significantly develops a stable substructure that strongly mitigates stress concentration. In alloys of austenitic steel, Ni and Cu, dynamic recrystallization (DRX) aids DRV in reducing stress concentrations and the migrating GB isolate fissures so they cannot propagate. Solutes and precipitates generally reduce ductility by diminishing DRV and DRX. Large particles and inclusions, notably on GB, introduce new sources of fissure nucleation, lowering ductility; solidification segregation and low melting constituents, especially if they spread along the GB, create severe problems.

Abstract: In this study, the effect of various solution and aging treatments on microstructure and mechanical properties of an as cast Al-5.5Zn-1.2Mg alloy has been investigated by optical microscopy, hardness measurements and room temperature tensile test. The solution heat treatments performed at temperatures between 400 and 490°C have little effects on hardness while electrical conductivity values increased at the lower temperature because of dissolved atoms and vacancy rich clusters. Concerning aging, only T6 improves mechanical properties of the undeformed alloy, while aging performed on tensile tested samples results in a decrease of hardness due to accelerated kinetics and heterogeneous nucleation of equilibrium phase stimulated by dislocation network. Tensile tested samples of the as cast alloy exhibits the fastest recrystallization time during annealing because of the absence of fine precipitates and the high strain hardening.

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.

Abstract: The modeling of extrusion of various Al alloys and their particulate metal matrix composites was conducted by DEFORM™ finite element analysis to develop strain rate, stress and temperature distributions through the peak load and into steady state following development of the hot zone. The hot strength and ductility, constitutive constants and microstructural evolution had been determined by hot torsion. The relative load-stroke curves were determined for several billet temperatures, extrusion ratios and ram speeds. The grid distortion and distributions of important internal parameters define the evolution of microstructure. The extrudability was estimated on the basis of load, ductility and the potential for modeling the microstructure developed.

Abstract: Double-twist torsion tests were used to determine static softening in the hot working range of three tool steels – W1, a carbon steel (1.03% C - 0.8% other elements), A2 and D2, a medium and a high alloy steel, containing 8.45% and 14.82% alloying elements. The carbon steel, that was single-phase austenite in the hot-working range, experienced rapid static recrystallization due to increased diffusion rate caused by C in hot austenite, very little alloying solute and no carbides. Carbides in alloy tool steels, which exist throughout the hot-working range, have a retarding effect on the progress of recrystallization but are responsible for enhancing initiation due to formation of nuclei at the strain concentration near the particle/matrix interface. Static recrystallization (SRX) of the alloy tool steels was compared with austenitic stainless steels, with similar strengths but much greater alloying content, and with microalloyed steels, as well as with the dynamic recrystallization kinetics.

Abstract: Thermomechanical processing (TMP) involves both thermal and mechanical treatments that define both product shape and microstructure/properties. Since the industrial revolution, machines of augmented power, size and precision have given rise to TMP that challenged explanation of the crystal mechanisms. In wrought iron, lamellar ferrite exhibited high transverse crack resistance due to fine slag stringers that as flux facilitated welding of puddled bars in forging of shafts or rolling of plates for bell-welding into pressure tight pipes; the substructure developed in the iron as working continued below 900°C strengthened it. Patenting of high C steel wire led to an optimum cold-drawn structure for outstanding strength and toughness. Hot forming technology, combined with the refining potential for austenite decomposition gave rise to controlled rolling for enhanced ferrite nucleation, ausforming to refine martensite and intercritical rolling to deform the ferrite or to spheroidize the carbides. Cold rolling and annealing have been scheduled to impart suitable strength, grain size, substructure and texture.

Abstract: Specimens of commercial purity aluminum were subjected to a strain path change test during high temperature deformation. Specimens were deformed at 4000 C and strain rate of 0.1 s-1 up to various strains of 0.2, 0.5, and 1. Then in a strain path change test, specimens were first deformed to a strain of 0.5, and subsequently deformed to strains of 0.2 and 0. In order to further the understanding of the deformation mechanisms in aluminum, the subgrain sizes and misorientations were characterized in detail by comparative studies using optical microscopy in polarized light (POM), orientation imaging microscopy (OIM/SEM) and transmission electron microscopy (TEM). The analysis revealed that while subgrain size is relatively insensitive to strain, overall misorientations increased with increasing strain. These analyses confirmed a strong bimodal distribution of boundaries during deformation coupled with a low fraction of medium angle boundaries. The results contribute to the understanding that dynamic recovery in aluminum maintains subboundaries with low misorientation but as grains elongate and more subgrain become adjacent to grain boundaries the fraction of high angle boundaries rises.