Durability and failure of powder forged rolling bearing rings

The rolling contact fatigue endurance of case-hardened powder forged Fe-2Ni -0.5Mo and Fe-0.7Mn-1Cr-0.2Mo steels is presented. The contact fatigue endu rance of the Fe-Mn-Cr-Mo powder steel is higher than that of the Fe-Ni-Mo a nd of wrought bearing steel. The basic data of 17 powder forged outer and i nner bearing rings are given. The durability of case-hardened powder forged rings reached the basic dynamic load rating up to similar to 150% for Fe-N i-Mo steel and up to similar to 200% for Fe-Mn-Cr-Mo steel. Beside the roll ing stress conditions, there are some special powder metallurgy reasons for failure of the rings by spalling which are initiated to a certain depth be low the raceway in the zone of maximum shear stresses. These are pores, "fr ee" unforged surfaces, hard white etching areas with microcracks in the for m of white bands and/or butterflies generated by pores. The highest durabil ity was recorded for the rings with transcrystalline ductile morphology ver ified on failure tested rings. Failure of the rings can be minimized by man ufacturing under optimal technological conditions. (C) 1999 Elsevier Scienc e S.A. All rights reserved.