College of Engineering
Materials Engineering Department
BS in Materials Engineering
Dr. Blair London
Oliver Racing Parts (ORP; Charlevoix, Michigan) is looking to optimize their manufacturing process for high-strength connecting rod bolts. A high yield strength is desired for the bolts because deformation would result in catastrophic engine failure. The bolts were made of H11, a chromium hot-work tool steel; and MLX17, a precipitation hardenable stainless steel. Tensile testing was performed to determine the tensile and yield strengths of the bolts. Fracture surfaces were imaged via scanning electron microscopy to characterize the failure modes. To observe the effects of bolt heading on microstructure and bolt strength, two batches of MLX17 were prepared; one batch being headed then aged (Group A); the other batch being headed, solution annealed, and then aged (Group B). These bolts were compared to H11 bolts to determine their viability for use, with the results being in the order of highest to lowest yield strength: H11 (272 ksi), MLX17 Treatment B (250 ksi), and MLX17 Treatment A (235 ksi). In the order of highest to lowest tensile strength: H11 (300 ksi), MLX17 Group B (255 ksi), MLX17 Group A (238 ksi). It is suggested that the bolt heading process is causing some overaging in the MLX17 samples, shown by the increase in strength when strain and aging from the heading process are undone through heat treatment. H11 bolts were the strongest tested. Recommendations are to not replace H11 bolts with MLX17 due to a decrease in strength.