PURPOSE: To obtain the title lubricant which has excellent adhesion, sufficient heat resistance, high solubility in water and excellent lubricity by dispersing a lubricant composition containing a graphite powder, potassium borate and others in water.

CONSTITUTION: The subject lubricant is obtained by dispersing a lubricant composition containing (A) 20 to 85wt.%, preferably 40 to 75wt.% of graphite, preferably of less than 30μm particle sizes, and (B) 15 to 80wt.%, preferably 80 to 70wt.% of a binder consisting of potassium borate and/or lithium borate in water so that the components (A) and (B) exceed 80wt.%, particularly 90wt.% in total. Less than 10wt.% of a dispersant is very effective and CMC, polysaccharides, PVA or the like are cited as a dispersant. The lubricant is effective, particularly when it is coated onto a mandrel bar in the operation of milling by means of a mandrel mill.