Pitting Resistance Equivalent Number
The PREN value (Pitting Resistance Equivalent Number) indicates how well stainless steel resists pitting corrosion. It is based on the steel's composition. A higher value means more corrosion resistance.
Physicochemical Mechanism of Action
The PREN value is calculated from the contents of chromium (Cr), nickel (Ni) and molybdenum (Mo). These elements protect the steel against corrosion by building a dense protective layer. The more of these elements are present in the steel, the better the corrosion resistance.
Metallurgical Relevance & Welding Risks
A low PREN value can lead to pitting corrosion, especially in damp or salty environments. This can lead to cracks and loss of the mechanical properties of the steel. When welding stainless steels, it is important to choose as high a PREN value as possible to ensure the service life and safety of the parts.
Workshop Practice & Instructions
To determine the PREN value of a stainless steel, use the formula: PREN = 3.3Cr + 30Ni + 16Mo. For critical applications, choose steels with a PREN value of at least 40. When welding, make sure the chemical composition of the filler material does not undercut the PREN value of the base steel.