QPQ

QPQ is an abbreviation for a multi-stage metal surface treatment known as Quench – Polish – Quench. It is a modern chemical-heat process used on steel to significantly increase surface hardness, wear resistance, and corrosion protection. QPQ is applied to high-stress weapon parts, tools, and machinery components — in airsoft, for example, on outer barrels, gear sets, or pistol slides like the one shown below.

The QPQ surface treatment process

The QPQ procedure consists of three repeating phases:

First “Quench” – the part is submerged in a salt bath (nitrocarburizing), where nitrogen and carbon atoms diffuse into the metal structure.
Polish – mechanical polishing smooths the surface, improving appearance and precision.
Second “Quench” – followed by a second salt bath treatment, which stabilizes the hardened surface layer and enhances corrosion resistance.

The process creates an extremely hard nitrocarburized layer on the surface, comparable to nitriding but with improved corrosion protection.

Benefits of QPQ treatment

Extremely hard surface – significantly increases part lifespan.
High wear resistance – ideal for moving components.
Excellent corrosion protection – superior to phosphate or blued finishes.
Smooth surface – reduced friction for smoother cycling.
Uniform matte black finish – attractive non-reflective appearance.

QPQ is valued in professional firearms and high-performance airsoft parts for its balance of affordability, durability, and corrosion resistance. On quality barrels, slides, or gear sets it offers long service life even under demanding use.