Failure analysis on the collapse of leaf spring steels during cold-punching

In this paper, the collapsing fracture of 60Si2Mn spring flat steels during cold-punching is analyzed by use of an optical microscope, a scanning electronic microscope, an optical stereomicroscopy, an energy dispersive spectrometer, an inductively coupled plasma-mass spectrometry, the hardness testers and a Charpy impact tester. The results show that the collapsing fracture of 60Si2Mn spring flat steels during cold-punching is due to the non- homogenization of microstructures and the nonmetallic inclusions. When the spring flats are cold-punched, the different deformation properties of the inclusions, the ferrites and the cementites initiated micro-cracks. The micro-cracks propagate along the interfaces of ferrites and cementites. The collapsing fracture is characteristic with transgranularity, cleavage and pearlites. The large space lamella pearlites with low strength are the main reason of the cleavage transcrystalline fracture. The prevention measurements are suggested.