Ovako develops new index to predict steel corrosion resistance
Ovako has introduced a new method, the Corrosion Resistance Index (CRI), to predict the performance of steels alloyed with aluminum. This index complements the traditional PREN method.
Steel company Ovako has developed a new method to assess the corrosion resistance of its specialty steels, including Hybrid Steel®, designed for high-temperature applications. The traditional PREN (pitting resistance equivalent number) index is not suitable for these aluminum-alloyed steels because it does not account for aluminum's positive contribution to corrosion resistance.
Ovako's new Corrosion Resistance Index (CRI) incorporates the effect of aluminum. The new formula, CRI = Cr + 3.3Mo + 16N + 5.2Al, can predict steel performance in aggressive environments, which is crucial for demanding applications such as high-performance bearings and fuel injectors.
Traditional stainless steels typically contain at least 10.5% chromium. However, Ovako's Hybrid Steel has a lower chromium content (around 5%) with an addition of aluminum (around 2%). This lower chromium level renders traditional PREN formulas less accurate for these materials.
Through a research program, Ovako tested various alloys to identify aluminum's effect. The findings indicated that aluminum enhances the corrosion resistance of chromium-containing steel. However, the new CRI index is only valid when the chromium content exceeds 4 wt% and the ratio of chromium to aluminum is above 1. Furthermore, the index is applicable in low-chloride environments.
The development of the CRI index allows for more precise evaluation and optimization of Ovako's steel solutions to meet customer needs, promoting the use of sustainable and high-performance materials in industry.