ABSTRACT
Bulk metalworking of steels are carried out at elevated temperatures where deformation of austenite takes place. In general, very large strains are imposed in these operations, where simultaneous softening processes occur during deformation to prevent the occurrence of fracture. Conventional processing maps provide useful information under uniaxial compression at various temperatures and strain rates. However, shear stresses are almost always present in common forging and rolling operations due to biaxial flow, heterogeneities, and other geometrical factors. Lubrication at high temperatures is also unpredictable. This shear stress is a chief cause for grain fragmentation in high pressure torsion (HPT).
The aim of the present chapter is to characterize the constitutive response of the work piece to optimize the hot working parameters. As an example, maraging steel, which is used for the manufacturing of the rocket casings using ring rolling process, is discussed as a potential candidate for (HPT). This chapter is organized in two parts, which presents the potential of combining conventional uniaxial test data with HPT, in order to achieve both nanofragmentation as well as microstructural optimization. Part I deals with a brief introduction to the current status of processing maps pioneered by Prasad and coworkers. Part II highlights the complexity of extending such maps to address the combined effects of compression, pressure, and torsion.
