Effect of mechanically imposed stresses on the contact fatigue resistance of two cast irons with high hardness matrix

This work presents a study on the influence of residual stresses on the contact fatigue resistance of a gray cast iron and a ductile iron. Contact fatigue tests were conducted in a ball on washer machine. The specimens were taken from bars of gray and ductile iron produced by continuous casting. After machining, specimens of both materials were quenched and tempered to the same matrix hardness, of about 800 HV. Two different test configurations were used: (1) regular washers and (2) reduced washers. Specimens in the first group were tested without the imposition of an external force and those from the second group were assembled in a die, which was tightened to a preset level of deformation, so that the induced external stresses could be representative of the presence of residual stresses during the tests. All tests were conducted until the occurrence of spalling, under lubrication and with a maximum Hertz contact pressure of 3.6 GPa. Finite element modeling was used to analyze the level and distribution of the imposed stresses. Results showed that the imposition of compressive residual stresses did not alter the fatigue life of gray iron, but increased life scatter for ductile iron.