Effects of multi-directional forging & annealing in microforming of stainless steel

• Main Author: Xie, Sky Shumao.
• Other Authors: Seow Hong Pheow
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Materials::Material testing and characterization
• Online Access: http://hdl.handle.net/10356/15300
• Institution: Nanyang Technological University

Microforming have been an upcoming technology in focus from the manufacturing industry due to its abilities to produce micro-size components that are of near net shape, high production rate and low material loss. Despite the many advantages, the size effect which is due to the limited number of grains in the forming area leads to a deterioration of the material mechanical properties and affect the quality of the final formed product. These will restrict any further processing and limit the usefulness in its application. Stainless steel is widely known for its combination of excellent properties of low cost, high strength and high corrosion resistivity. However, the phase transformation of stainless steel during severe plastic deformation and annealing are exceptionally difficult to predict and thus were not well studied in the past. This is due to the high percentage of alloying elements which causes stainless steel to have multiple strengthening mechanisms and goes through complex phase transformation during processing. Therefore the current investigation has looked into the effects of severe plastic deformation by Multi-Directional Forging (MDF), annealing temperature and duration on stainless steel properties. Micrographs of the surface morphology were studied while the grain size and hardness were also measured in the experiment. Results have shown that for stainless steel, some of the unique transformations which would cause a change in properties are the shear-induced martensitic transformation and the precipitation hardening effect by the formation of chromium carbide. In addition, high straining would cause the material to be highly sensitive to annealing temperature which accelerated the rate of grain growth. In conclusion, it is important to have precision control of the processing parameters to produce a combination of excellent material properties.