Metallurgical aspects of deformation processing

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The research proposed covers the following five distinct topics. Non-Equilibrium Phase Diagrams. The Fe-C phase diagram is generally employed in the planning of steel rolling schedules. It is based on the presence of undeformed austenite (the high temperature phase). However, when austenite is being deformed in rolling mills, this "equilibrium" diagram no longer applies. We are carrying out tests as much as 100 deg. C above the predicted transformation temperature and forming ferrite (the low temperature phase), indicating the inapplicability of the conventional diagram. In experiments on various steels, we are determining how the actual phase daigram depends on strain, composition, etc. The High Temperature Flow Curve under Conditions of Dynamic Recrystallization. The accurate modeling and control of rolling mills requires the ability to predict the flow stress (deformation resistance) of steel with accuracy. When steel begins to recrystallize during deformation, a process known as dynamic recrystallization, this goal becomes more difficult to achieve. We have developed methods for the accurate modeling of such curves using what are known as Avrami kinetics and are continuing to improve this approach. Physical Metallurgy of Mg Alloys. Mechanical twinning is very common in Mg alloys. Although there are six symmetrical varieties of such twins, only a few of them form. We are determining the 'laws' of "variant selection" that govern their formation. Another important focus is on the effect of rare earth additions on the behaviors of such alloys. These are being investigated using mechanical tests. Linear Friction Welding of Titanium Alloys. Titanium compressor blades can be joined to compressor discs by solid state processes (without melting). The conditions that are required to make strong welds are being determined by means of appropriate tests. Torsion Simulation of Rolling. We are continuing to do torsion simulations to determine the three critical temperatures of hot rolling in a variety of steels with a view to improving rolling schedules.