Pitting resistance equivalent number
The WAK value indicates how resistant a stainless steel is to pitting. It is based on the mass fraction of chromium, molybdenum, and nitrogen.
Physical-Chemical Mechanism of Action
The PREN value (pitting resistance equivalent number) is calculated from the mass fractions of chromium (C), molybdenum (Mo), and nitrogen (N) in steel. These elements create a stabilized austenitic structure that increases the pitting resistance of the material.
Metallurgical Relevance & Welding Risks
A too low PREN can lead to pitting, especially at high temperatures and under mechanical load. This can cause cracks and failure in the workpiece. A too high PREN increases toughness, which may be desirable for certain applications, but might result in too low formability.
Workshop Practice & Instructions
To determine the PREN of a steel, use the following formula: PREN = (C + Mo) x 1000 + N x 500. A PREN of at least 25 is sufficient for many applications. For especially harsh environments, choose a PREN of at least 40.