Changes in microstructure and mechanical properties of cip-processed tungsten rods during rotary-swaging and stretching operations

The microstructure of the in rotary swagers hammered rods is gradually transformed from sintered to compact metallic. In order to gain a high quality product, it is essential to optimize the conditions of wire draft production and to control the recrystallization (inductive annealing) process particularly. Tensile strength of swaged rods (wire drafts) is determinative for the next step i.e. stretching on turn-tables. In this study, as a part of the complete process for thin wire (φ < 10 μm) production, changes in microstructure (grain size and grain population density) and mechanical properties (density, hardness and porosity) during swaging and stretching of tungsten to 440 μm are investigated. The mentioned wire is obtained using industrial scale equipments by passing the rod (φ 16 mm) through three rotary-swagers each with H₂/N₂ protected furnaces, inductive annealing (2200-2400 °C) and through three stretching machines (turn-tables). To check the production process in each step, morphological characterization tests are carried out on cross-sectional and longitudinal-section of specimens with stereo microscope and scanning electron microscope.