What is QPQ processing

QPQ (Quench-Polish-Quench) processing, also known as liquid nitriding, is a surface treatment technique used to improve the hardness, wear resistance, and corrosion resistance of metal components. It involves a combination of quenching, polishing, and post-quenching processes.

The QPQ process typically includes the following steps:

1、Pre-cleaning: Thoroughly clean the metal components to be treated to remove any dirt, grease, or contaminants from their surfaces. This ensures optimal treatment results.

2、Quenching: Immerse the cleaned components in a molten salt bath or salt solution, typically containing sodium cyanide. Raise the bath temperature to a range of approximately 500 to 580 degrees Celsius (932 to 1076 degrees Fahrenheit).

3、Nitriding: Hold the components in the quenching bath for a specified period, during which nitrogen diffuses into the surface layer of the metal. This forms a hard compound layer, primarily composed of iron nitride (Fe3N), which increases the surface hardness and wear resistance.

4、Quenching (again): After the nitriding period, rapidly quench the components in a water or oil bath to cool them down. This step helps stabilize the compound layer and prevent undesired reactions.

5、Polishing: Subject the components to a polishing or finishing process to remove the compound layer from the surface, exposing a clean and smooth surface. This step enhances the aesthetics of the components while maintaining the benefits of the nitrided layer.

The QPQ process creates a diffusion layer on the surface of the metal, providing improved hardness, wear resistance, and corrosion resistance without significantly affecting the core material properties. It is commonly used in various industries, including automotive, aerospace, tooling, and general engineering, to enhance the performance and lifespan of metal components subjected to harsh operating conditions.