A method is shown for constructing portions of a sucker rod pump of the type having a steel plunger with an exterior cylindrical wall and a barrel with a cylindrical bore. A chromium case if formed on the cylindrical bore to a selected depth for receiving the plunger in sliding contact. The chromium case is formed by forming a base electrolyte bath including water, chromic acid, a sulfate component, an alkyl sulphonic acid, and an anion of molybdenum. The bore is then exposed to the aqueous electrolyte bath at a current density and at a plating temperature sufficient to form a chromium deposit of desired thickness on the bore.