Low Pressure Carburizing and High Pressure Gas Quenching of Chromium-Alloyed PM Parts

Pouloux Patrick - ECM Technologies (France)

Today Low Pressure Carburizing (LPC) followed by High Pressure Gas Quenching (HPGQ) is an established process to produce high performance components of conventional steels in order to combine high surface hardness and fatigue strength. On the other hand, thanks to its ability to combine high quality and cost saving, PM process is more and more popular in the automotive industry, especially in the transmission applications. In order to answer the increasing application performance requirements, chromium-alloyed grades are often used because they provide a cost-efficient way to reach high mechanical properties.
However these materials need specific sintering conditions and cannot be surface hardened by conventional gas carburization and oil quenching. Thus, the alternative LPC & HPGQ applied to PM parts is very promising as the sintering at low pressure avoids contamination and improves the sintered microstructure.
In addition higher sintering temperature can be used, leading to improved sintered structures and mechanical properties. For example, increasing the temperature from 1180°C to 1250°C significantly improves tensile strength and ductility combined with a structure containing very few oxygen after sintering.
Finally by taking into account the main PM specifics that can impact LPC treatment, (i.e. mainly density level, steel composition and core carbon content), one can select the most appropriate parameters to maximize the benefit of this combination LPC+HPGQ & PM process.
As a consequence, the optimization of the material combined with the One-Step process cycle (debinding/sintering/LPC/HPGQ) obtained with the newly developed ICBP® furnace, optimized heat treatment of PM parts can be done in a cost-efficient and environmentally-friendly way.

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