Water-soluble lubricant oil

A water-soluble lubricating oil, comprising:

• a water-soluble base (A) comprising at least one polyether (A1),
• a corrosion inhibitor (B), and
• an antioxidant (C);
• wherein the polyether (A1) comprises a polyether (A1-1) represented by formula (1),
• wherein R1 is hydrogen or a hydrocarbon group having a valence of k and 1 to 12 carbon atoms;
• A1 is an ethylene group;
• R2 is hydrogen or a hydrocarbon group having 1 to 8 carbon atoms;
• k is an integer of 1 to 6;
• and j is an integer to allow the polyether (A1-1) to have a number average molecular weight of 62 to 8,000, and
• wherein the corrosion inhibitor (B) comprises at least one corrosion inhibitor selected from the group consisting of a triethanolamine and a cyclohexylamine EO adduct,
• wherein the water-soluble lubricating oil contains the polyether (A1) in an amount of 88.0 to 98.9% by weight, the corrosion inhibitor (B) in an amount of 1.0 to 10.0% by weight, and the antioxidant (C) in an amount of 0.1 to 2.0% by weight, based on the total weight of the polyether (A1), the corrosion inhibitor (B), and the antioxidant (C), and
• wherein when the water-soluble lubricating oil is measured by a pendant-drop method using a 0.1% by weight aqueous solution of the water-soluble lubricating oil, the water-soluble lubricating oil has a surface tension of 31 mN/m or higher.