cycle X XXI Doctoral School in Materials, Mechatronics and Systems Engineering Novel PM Tool Steel with improved hardness and toughness Faraz Deirmina September 2017 NOVEL PM TOOL STEEL WITH IMPROVED HARDNESS AND TOUGHNESS Faraz Deirmina E-mail:
[email protected] Approved by: Ph.D. Commission: Prof. Massimo Pellizzari -, Advisor Prof. Alberto Molinari, Department of Industrial Engineering Department of Industrial Engineering University of Trento, Italy. University of Trento, Italy. Prof. Maurizio Vedani, Department of Mechanical Engineering Politecnico di Milano, Italy. Prof. Elena Gordo ODÉRIZ, Department of Materials Science and Engineering and Chemical Engineering University of Carlos III de Madrid, Spain. University of Trento, Department of Industrial Engineering September 2017 University of Trento - Department of - - - - - - - - - Doctoral Thesis Name - 2017 Published in Trento (Italy) – by University of Trento ISBN: - - - - - - - - - III To my wife, my comrade Camellia, and her adorable children Oblomov, Truffaut and Hugo IV Abstract Ultrafine grained (~ 1μm) steels have been the subject of extensive research work during the past years. These steels generally offer interesting perspectives looking for improved mechanical properties. UFG Powder Metallurgy hot work tool steels (HWTS) can be fabricated by high energy mechanical milling (MM) followed by spark plasma sintering (SPS). However, similarly to most UFG and Nano-Crystalline (NC) metals, reduced ductility and toughness result from the early plastic instabilities in these steels. Industrialization of UFG PM Tool Steels requires the application of specific metallurgical tailoring to produce tools with sound mechanical properties or in a more optimistic way, to break the Strength-Toughness “trade-off” in these materials. Among the possible ways proposed to restore ductility and toughness without losing the high strength, “Harmonic microstructure” design seems to be a very promising endeavor in this regard.