Separation of Forged Steel Connecting Rods and Caps by Fracture Splitting

Separation of the rods and caps of integrally hot-forged steel connecting rods by fracture splitting has not been possible with current alloys because the fracture is accompanied by too much ductility to permit accurate rejoining. A development effort was undertaken to devise an alloy which could be cracked with minimal distortion, while maintaining good machinability and adequate fatigue strength. The resulting alloy, upon air-cooling from the forging temperature, develops a microstructure which is essentially all pearlite. Impact tests and rod cracking experiments show that fracture of the new alloy occurs with less distortion than fracture of SAE 1151, a steel with a ferrite-pearlite microstructure. Machinability of the new alloy is comparable to SAE 1151 of the same hardness. Fatigue tests indicate that the new alloy is comparable in strength to current production alloys.