![]() ![]() ![]() The mechanical properties of sintered steel depend on the density, where higher density gives better mechanical properties. Gears with a weight reduction of 15%, half stemming from the lower density material and a half from lightening holes, have been produced. An example of this is lightening holes that can be produced without secondary operation. During the compaction, the material can, to some extent, be placed where it is most needed. The porosity will decrease the overall weight of the component and provide the steel with beneficial sound-absorbing properties, which could be of benefit for the automotive industry with the arrival of electric vehicles where the combustion engine is no longer the main sound source. The complex shape of many parts manufactured for the automotive industry suits the production route of sintered powder metal steel (PM), where the production of near-net-shape components in large quantities, with a small amount of inherent energy from production compared to wrought components, is feasible by pressing and sintering alone. If a prior grain/prior austenite boundary is present within an angle from the crack initiation site, the cracks will follow the boundary and thus propagate intergranular, suggesting that the preferred route of crack propagation in case hardened sintered steel is along these boundaries. Both tested materials show the same crack propagation behaviour. ![]() The cracks were then analysed using EBSD and SEM, revealing detailed and novel information about the crack propagation route in the materials. A novel approach was used to achieve short cracks (10–20 µm) with high repeatability. EBSD was used to study the microstructure before and after case hardening, revealing the relationship between powder particle grains after sintering and prior austenite grains after case hardening. In the present study, crack propagation through the case hardened region of two different PM steels manufactured with different powder size distributions and sintered at different temperatures has been investigated. ![]()
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January 2023
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