Quench polish quench is a specialized type of nitrocarburizing case hardening

Case hardening

Case hardening or surface hardening is the process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy...

 that increases corrosion resistance, originally developed by the Kolene Company. The name refers to the three steps involved: nitrocarburizing, polishing, and post-oxidizing.

This process is usually used when two or more of the following properties are required in a workpiece: wear resistance, corrosion resistance, lubricity

Lubricity

Lubricity is the measure of the reduction in friction of a lubricant. The study of lubrication and mechanism wear is called tribology.-Measurement of lubricity:...

, or fatigue strength. However, it is also used when superior corrosion resistance is required. Common applications are piston rods for shock absorber

Shock absorber

A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...

s, cylinders and rods for hydraulic systems, pump

Pump

A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

s, axle

Axle

An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle...

s, spindle

Spindle (tool)

In machine tools, a spindle is a rotating axis of the machine, which often has a shaft at its heart. The shaft itself is called a spindle, but also, in shop-floor practice, the word often is used metonymically to refer to the entire rotary unit, including not only the shaft itself, but its bearings...

s, and valve

Valve

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

s.

Process

The process starts with a standard salt bath nitrocarburizing cycle, which produces a layer of ε iron nitride. Next, the workpiece is mechanically polished; typical polishing processes include vibratory finishing

Vibratory finishing

Vibratory finishing is a type of mass finishing manufacturing process used to deburr, radius, descale, burnish, clean, and brighten a large number of relatively small workpieces....

, lapping

Lapping

Lapping is a machining operation, in which two surfaces are rubbed together with an abrasive between them, by hand movement or by way of a machine.This can take two forms...

, and centerless grinding

Centerless grinding

Centerless grinding is a method of material removal through grinding, similar to centered grinding except for the absence of the spindle. It has high throughput, i.e. a large number of parts can be manufactured in a short time....

. Finally, the workpiece is re-immersed into the salt quench bath for 20 to 30 minutes, rinsed, and oil dipped. This last step optimizes the corrosion resistance by creating a 3 to 4 micrometre thick layer of iron oxide

Iron oxide

Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...

. It also gives the workpiece a black finish.

Corrosion resistance

The two charts below compare the corrosion resistance of QPQ to other common corrosion resistance coatings.