A solid lubricating coating film capable of imparting favorable lubricity and corrosion resistance to a connection for oil country tubular goods. Two or more solid lubricants are dispersed in a binder resin. Graphite is contained in an amount of 50% or more and 90% or less of a total weight of the solid lubricants, and the graphite has a scaly shape and an average particle diameter of 10.0 m or less. A solid lubricant made of one or more materials selected from BN, mica, talc, MCA, MoS.sub.2, PTFE, PFA, and FEP is further contained as other solid lubricants of the two or more types of solid lubricants. The binder resin contains a PEEK resin having an average particle diameter of 20 m or less as a main component, and the PEEK resin is contained in an amount of 70% or more of a total weight of the binder resin.

A sliding material includes a resin, first particles disposed in the resin and composed of an inorganic material, and second particles disposed in the resin and composed of an inorganic material whose Vickers hardness is higher than a Vickers hardness of the first particles. When a value obtained by dividing a Vickers hardness of the second particles by the Vickers hardness of the first particles is defined as a hardness ratio and when a value obtained by dividing a contained amount of the first particles with respect to the resin by a contained amount of the second particles with respect to the resin is defined as a content ratio, a value obtained by dividing the hardness ratio by the content ratio is greater than or equal to 0.3 and less than or equal to 2.8.

Methods of making improved nanolubricants are providing including dispersing carbon nanoparticles selected from the group consisting of graphene (GN), single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs) in a base fluid, such as POE. The carbon nanoparticles are dispersed by adding the carbon nanoparticles to the base fluid to obtain a mixture and mixing the mixture for about 5 minutes using a magnetic stirrer to obtain a suspension. The resulting suspension is then further dispersed using a bath ultrasonicator for about 60 minutes starting at about 25 C. The temperature may be varied up to about 49 C. and back down to about 25 C. over the course of the 60-minute period.

A sliding material includes a resin, first particles disposed in the resin and composed of an inorganic material, and second particles disposed in the resin and composed of an inorganic material whose Vickers hardness is higher than a Vickers hardness of the first particles. When a value obtained by dividing a Vickers hardness of the second particles by the Vickers hardness of the first particles is defined as a hardness ratio and when a value obtained by dividing a contained amount of the first particles with respect to the resin by a contained amount of the second particles with respect to the resin is defined as a content ratio, a value obtained by dividing the hardness ratio by the content ratio is greater than or equal to 0.3 and less than or equal to 2.8.