Super duplex pitting resistance equivalent number
The superduplex pitting resistance equivalent is a calculation parameter that estimates the pitting resistance of high-alloy steels in chloride-rich environments. It takes into account the mass fractions of chromium, molybdenum, and nitrogen.
Physical-Chemical Mechanism of Action
The superduplex pitting resistance equivalent (SPRE) is a mathematical index based on the content of chromium (Cr), molybdenum (Mo), and nitrogen (N) in high-alloy steels. These elements protect the steel surface from corrosion by chloride ions by forming a dense chromium-rich layer.
Metallurgical Relevance & Welding Risks
A too low SPRE value can make the steel more susceptible to pitting in chloride-rich media. This can lead to cracking and loss of strength. A too high SPRE value makes the weld seam robust but possibly too hard and prone to hot cracking.
Workshop Practice & Instructions
To calculate the SPRE value, the following formula is used:
• SPRE = 10Cr + Mo + N
Where Cr, Mo, and N are the mass fractions in % of the respective elements. A SPRE value of at least 35 is recommended for good pitting resistance in chloride-rich media. When welding such steels, it is important to ensure proper cooling measures to maintain the microstructure and surface condition.