The Effects of Austempering and Cryogenic Processing on the Mechanical Properties of Forged E4340 Steel for Automotive Engine Connecting Rods

The components in top-fuel dragster and stock car engines undergo significantly more force than their production passenger vehicle counterparts do. Therefore, they must be manufactured and processed to withstand those forces so that they do not catastrophically fail while in service. In this project, the effects of austempering and adding a cryogenic processing step to the control quench and double temper heat treatment on the tensile and hardness properties of E4340 high-strength steel were examined. Tensile test samples were machined from raw connecting rod forgings and underwent either a quench-double temper heat treatment, an austempering heat treatment, or the quench-double temper heat treatment with an added cryogenic processing step after the quench. The mechanical properties caused by each heat treatment were then measured through hardness and tensile testing. The average yield strength produced through austempering was less than that produced through the current heat treatment or through cryogenically processing. The cryogenically processed and control samples had statistically similar yield strength values, which is likely due to the difference in retained austenite between the two sample groups being relatively small.