Thermomechanical processing of iron, titanium, and zirconium alloys in the BCC structure

Abstract

The body centered cubic (bcc) metals undergo a high level of dynamic recovery during elevated temperature straining so that the stress increases monotonically to a steady-state value σs. The strain rate and σs are related by means of the power, the exponential, or the sinh law with an Arrhenius temperature relationship. The activation energy for a iron has values of 250–280 kJ/mol, whereas for β titanium and β zirconium it is in the range 134–184 kJ/mol. The structure developed during hot working consists of elongated grains containing subgrains of dimension inversely proportional to σs. In warm working of α iron (limited to below 0.66T m), the textures are similar to those for cold working. In working β titanium and β zirconium which is limited to above 0.6T m except in β stabilized alloys or as matrix in α+ β processing, the bcc textures transform into α textures. The α iron relies principally on substructure strengthening in association with carbides. The β phases can be thermomechanically processed to provide equiaxed or lamellar a in a variety of dimensions and combinations, with or without substructure. Hot working of the bcc refractory metal alloys, principally molybdenum, is similar to hot working of α iron.