Patent ID: 8859475

Claim:
A grease composition for bearings used in wind power generators, comprising a base oil which has a kinematic viscosity of 10 to 70 mm 2 /s at 40° C. and a pour point of −40° C. or less, a diurea compound as a thickener, and as an additive an organic sulfonate rust inhibitor that is neutral or has a total base number of less than 50 mgKOH/g, wherein the sulfonate rust inhibitor comprises a zinc salt of benzenesulfonic acid or naphthalenesulfonic acid, wherein the diurea compound is represented by formula (1): wherein R 1 and R 2 , which may be the same or different, represent a straight-chain or branched alkyl group having 6 to 30 carbon atoms, and wherein the sulfonate rust inhibitor is present in a concentration ranging from 0.5 to 10 mass % of the grease composition.