Pitting Resistance Equivalent Number
Pitting resistance equivalent is a value used to estimate the pitting corrosion resistance of stainless steels. It is calculated from the mass fractions of chromium, molybdenum, and nitrogen.
Physical-Chemical Mechanism of Action
The Pitting Resistance Equivalent (PRE) indicates how well a steel resists localized corrosion. It is based on the mass fractions of chromium, molybdenum, and nitrogen in the material. These elements protect the surface against corrosive attack through their chemical composition.
Metallurgical Relevance & Welding Risks
A too low PRE value can cause the steel to rust at certain points (pits). This can impair the service life and mechanical properties of the components. In welding processes, it is important that the PRE value of the weld material is compatible with that of the base material to avoid rust formation.
Workshop Practice & Instructions
To calculate the Pitting Resistance Equivalent (PRE), use the following formula:
PRE = 3.3Cr + 16Mo + 30N
Where Cr is the mass fraction of chromium, Mo that of molybdenum, and N that of nitrogen in %.
Make sure the weld material has a PRE value at least as high as the base material. This prevents rust formation at the weld joints.