Severe Plastic Deformation of Steels

Abstract

In order to demonstrate the structural changes in steels during severe plastic deformation (SPD), Armco iron, a ferritic steel P800 and a pearlitic rail steel S900A are subjected to a high pressure torsion (HPT) deformation process. The microstructural evolution, the changes in microhardness and the flow stress behaviour are investigated. Depending on the main process parameters like the deformation temperature and the applied strain, the impact of alloying on the evolving microstructure is studied in detail. The results clearly show that pure metals and single phase alloys follow a relatively uniform deformation behaviour. With increasing strain the structural size decreases ending in saturation at an equivalent strain between 10 and 30. In the case of the pearlitic rail steel a continuous growth in shear stress without saturation is investigated in the range of the applied strains. The microstructures of the examined materials Armco iron and P800 contain an ultra fine grain structure whereas for alloy S900A the initially randomly oriented lamellae are heavily bent and broken into small fragments. Possible reasons for the observed differences in the deformation behaviour are discussed.