Over the last two decades, powder forging (PF) has been proven as a very reliable way to successfully manufacture connecting rods for both gasoline and diesel applications. The inherent value in the near net formed product (NVH performance, material utilization efficiency, total cost economics) coupled with the attractive strength levels achieved with the introduction of HS150, HS160, and HS170 materials [1, 2, 3], have made it possible for PF connecting rods to meet and exceed the increasing performance specifications required by the next generation of diesel and gasoline engines.
The goal of this work was to continue the research performed so far in developing new higher strength materials for PF connecting rods [1, 2, 3, 4, 5, 6] in order to further optimize the chemical composition of Fe-Cu-C systems for maximum performance. A new machinability enhancer (consisting in calcium oxide, commercially known as KSX), with a rounder and finer particle shape, was used as a replacement for manganese sulfide (MnS) [7, 8, 9, 10].
Static and dynamic tests were carried out on specimens and on series production components. The enhanced features of KSX particles resulted in higher and more consistent dynamic properties. The optimization of copper levels further contributed in improving the strength and its consistency over the range specified in the standards. Tensile testing on specimens and fatigue testing on components clearly proved that materials with higher and more consistent strength (lower scatter during fatigue testing) were developed.
Machinability (boring and drilling) and crackability were evaluated as well on materials with no machinability enhancer additions, with 0.32% MnS, and with 0.10% KSX. Results showed that only 0.10% KSX could successfully replace 0.32% MnS.
A side by side comparison of the strength of these optimized materials with C70 forged steel and the newly introduced 36MnVS4 microalloyed steel used to manufacture connecting rods through drop forging was completed.