Low-Pressure Carburizing of Powder Metal Components

Abstract

Abstract Transmission-manufacturers constantly need to adapt their products and manufacturing technologies to meet future’s market and legislation requirements such as cost-efficiency, running-smoothness and drivetrain-agility. Components made of powder metal (“PM-components”) are established in today’s transmission industry as a cost efficient alternative even for high strength and high precision powertrain applications. The PM-material and the applied heat treatment processes have made significant improvements in recent years. One major step in the development was to combine the freedom in alloying-concepts of the PM-technology with the advantages of the Low Pressure Carburizing (LPC) heat treatment process. PM-components must be case-hardened to meet design-intent regarding wear resistance and strength. But when case hardening PM-components using a conventional atmospheric carburizing process, this can lead to serious overcarburizing and even massive carbide-formation. Another major challenge when using the conventional process is to clean PM-parts after the traditional oil-quenching process. Therefore, the process of Low Pressure Carburizing (LPC) combined with High Pressure Gas Quenching (HPGQ) was adapted to the special needs of serial production of PM-components. This heat treatment process offers significant benefits, such as: - no overcarburizing and excessive carbide-formation due to precise diffusion of carbon into the components - reproducible microstructures from part to part and from load to load - clean and shiny parts after quenching - superior control of distortion, - no intergranular oxidation, - better fatigue resistance and - the benefits of an environmentally friendly process. Over the past 25 years, Stackpole and ALD worked on powder metal technology and advanced heat treatment processes. Material, process and equipment have seen significant improvements over the last decades to offer true benefits. This presentation will give an insight into benefits and challenges of PM-components heat treated in low pressure with subsequent gas quenching. The paper refers to the industrial series production of components and it refers to R&D - case studies as well.