The Effect of Copper Precipitation on Mechanical Properties at Operating Temperature of the Materials Used to Manufacture Powder Forged Connecting Rods

The operating environment in an engine can have negative effects on the performance of connecting rods, as it is well-known that the strength of most steels quickly deteriorates at higher temperatures. Although the mechanical properties of the materials used to manufacture connecting rods have been widely characterized at room temperature, their strength has not been investigated at higher temperatures. This work was undertaken to fill this gap as well as analyze the behavior and evaluate the properties of these materials at engine operating temperatures. Tensile tests and compressive yield strength tests were conducted at 120 C (248 F) and 150 C (302 F), on specimens machined from connecting rods. The strength of the materials used to manufacture connecting rods through steel forging quickly declines at operating temperatures, while, on the contrary, the strength of the materials used to manufacture powder forged connecting rods improves. Scanning electron microscopy and transmission electron microscopy were employed to investigate the powder forged materials in order to explain the strengthening mechanism causing this improvement. Copious Cu-rich nano precipitates were observed in the specimens tested at higher temperatures.