Abstract: A 65Mn steel spring leaf used in a certain type of product was found to break at the peak position when testing elastic force. Failure cause of the spring leaf was analyzed through the chemical composition, microstructure and microhardness test and the processing process analysis, and the then the process was improved. The results show that due to the high quenching temperature, high quenched hardness, and lower temperature tempering after quenching, the elimination of quenching stress is not sufficient, causing the spring leaf to produce microcracks under the combined effect of axial compressive stress and quenching residual stress during the installation of the fixture when the spring leaf is tempered at high temperature. The microcracks expand and transform during subsequent strong pressure treatment, resulting in brittle fracture. After adopting the improved process of 815 ℃ quenching+280 ℃ low temperature tempering+390 ℃ high temperature tempering, the hardness of the spring leaf can meet the technical requirement, the fracture is 100% ductile fracture, and no brittle fracture occurs again.

Key words: 65Mn steel spring leaf, microcrack, brittle fracture, process improvement