Development of High Strength, Fracture Split Steel Connecting Rods

A new high strength microalloyed steel has been developed for fracture split connecting rods for heavy duty diesel engines that provides advantages in cost saving and weight reduction. This new splittable steel has higher fatigue strength than conventional steel with improved machinability. The key issue with this development is how to increase the mechanical strength without sacrificing both splittability and machinability. This goal was achieved by substituting the conventional high carbon microalloyed steel with a new type of alloy design that combined an optimized splitting capability and con rod geometry.

This research focused on optimizing two major technical considerations for this application - new medium carbon chemical composition with a high silicon range to maximize the splittability without any plastic deformation. Secondly, process parameters for both the hot forging and fracture splitting process were developed to ensure a consistent microstructure and fracture surface. Systematic studies have been conducted to verify several characteristics including material properties during controlled cooling and machining. The con rod with the new type of steel is expected to have a 30% increase in fatigue and yield strength with, at least, a 15% weight reduction.