A Highly Corrosion Resistant and High Strength Alloy for Use in Mineral Processing

Alloy 602CA (UNS N06025) is a wrought nickel alloy with a combination of excellent corrosion resistance and high strength.  These attributes make it ideal for use in high temperature processing of minerals.  One particular application where this alloy is widely used is in fabricating calciner shells.  The UNS N06025 has been used in calciners at continuous operating temperatures up to 1200°C (2192°F) in the processing of a variety of process streams.  Corrosion resistance is achieved by alloying with high chromium levels (25% Cr) in combination with significant aluminum levels (2.2% Al); rare earth elements (Y and Zr) are also added to maintain adherence of the protective scale.  This not only allows long life for the equipment, but also the minerals being processed are not contaminated by scale from alloy, which for example is particularly important when processing high purity alumina used for catalyst substrates.  The high strength is achieved through a unique strengthening mechanism which uses a fine dispersion of primary carbides to achieve essentially a composite structure.  The corrosion resistance of UNS N06025 is compared to other alloys in a variety of high temperature environments and several application examples are also given as a demonstration of the benefits provided by the features of this alloy.