Evaluation of Control Cooled, NB-Treated SAE 1141 steel Connecting Rod

Material properties of niobium (Nb)-treated SAE I 141 steel connecting rod produced by control cooling were evaluated in comparison with quenched and tempered connecting rod of the same steel. The microstructure of the control cooled connecting rod is predominantly bainitic compared with tempered martensite for the quenched and tempered rod. Tensile strengths are comparable, while yield strength and ductility are lower for the control cooled connecting rod. There are small variations in hardness of the control cooled connecting rod depending on the section thickness in contrast with the uniform hardness for the quenched and tempered rod. Component high-cycle fatigue resistance is lower for the control cooled connecting rod due to the lower yield strength. Both connecting rods meet the fatigue strength performance requirements for the rod design evaluated.