Copper precipitation at engine operating temperatures in powder-forged connecting rods manufactured with Fe–Cu–C alloys

Abstract The effect of copper precipitation on the mechanical properties of Fe–Cu–C alloys prepared for Powder Metallurgy and used to manufacture connecting rods for the automotive industry through powder forging was evaluated at engine operating temperatures, ranging between 100 °C and 150 °C. Tensile tests were conducted at room temperature as well as at 120 °C and 150 °C on specimens machined from connecting rods. The test results clearly indicated an improvement in the strength of Fe–Cu–C alloys at 120 °C and 150 °C. Scanning and transmission electron microscopies were employed to investigate the strengthening mechanism causing the improvement. The microscopy investigations pointed to stress-induced second phase precipitation strengthening in super-saturated Fe–Cu–C alloys even at these relatively low temperature levels as copious Cu nano precipitates were observed in the specimens submitted to tensile testing at 120 °C and components submitted to engine dynamometer testing. Clear evidence of interactions between dislocations and copper precipitates was found in both tensile specimens and components.