Lubricant composition

A grease composition, comprising:

• a base oil in which a urea compound is blended as a thickener;
• a fatty acid metal salt;
• a metal dithiocarbamate;
• and
• an acid value improver having an effect of increasing an acid value of the lubricant composition,
• wherein when a ratio of a content of the fatty acid metal salt (mass %)/content of the metal dithiocarbamate (mass %)]is defined as X, and
• a ratio of a content of the fatty acid metal salt (mass %)/total acid value of the lubricant composition (mgKOH/g) is defined as Y,
• X is 0.38 to 1.35, Y is 0.027 or more, and the following relationship (A) is satisfied,
• Y≤0.1547X2−0.1388X+0.07 (A),
• wherein the fatty acid metal salt is a salt form of a linear or branched fatty acid and metal,
• wherein a content of the metal dithiocarbamate is 0.001 to 0.400 mass %, and
• wherein the metal dithiocarbamate is a compound represented by the following formula (I):
• wherein, in Formula (I), M represents Zn;
• n is an integer corresponding to the valence of the metal;
• and R1 and R2 independently represent a primary alkyl group, a secondary alkyl group, an aryl group or an alkylaryl group, which have 2 to 18 carbon atoms,
• wherein the fatty acid metal salt is at least two selected from the group consisting of copper stearate, iron stearate, zinc stearate, and magnesium stearate, and
• wherein the acid value improver is a phosphate ester,
• wherein a content of the acid value improver is 1 to 3 mass %, and
• wherein the phosphate ester is one or more selected from alkyl (C12, C14, C16, or C18) acid phosphate, isotridecyl acid phosphate, oleic acid phosphate, tetracosyl acid phosphate, ethylene glycol acid phosphate, 2-hydroxymethyl methacrylate acid phosphate, dibutyl phosphate, bis(2-ethylhexyl) phosphate, diethyl benzyl phosphate, triphenylphosphine, monoethyl phosphate, mono n-butyl phosphate, mono n-octyl phosphate, mono n-lauryl phosphate, or mono (2-hydroxyethyl methacrylate) phosphate.