Study of Cracking Problem of 51CrMoV4 Steel Leaf Springs During Manufacture

Leaf springs are one of the oldest suspension components that are widely used, particularly in wheeled vehicles. The present study deals with the problem of cracking of the heat-treated leaf springs in an industrial company, in particular the 51CrMoV4 steel air linker springs. This steel is characterized by high hardenability, with a blade thickness of 40 mm. Many delayed quench cracks were observed and detected on the fillet zone of some manufactured air linker springs. This cracking was explained by the creation of tensile residual stresses during quenching treatment and after due to the evolution of the retained austenite. Different factors can be behind this detrimental phenomenon such as the quenching parameters, the geometry and thickness of blades, the long time between quenching and tempering treatments, etc. The effects of principal parameters of austenitization and quenching treatments on both the hardness and quality of 51CrMoV4 steel blades were examined experimentally. Results showed that directly proceeding to the tempering process highly diminishes this failure. In addition, the temperature and austenitization time as well as the hot forming time were controlled to ensure the hardening operation of the steel and reduces its cracking sensitivity.