Nickel-Iron-Chromium Alloys. These materials bridge the gap between the high-nickel austenitic stainless steels and the Ni-Cr-Fe alloys. Their main advantage over the stainless steels is enhanced resistance to environmental cracking. One of the most commonly used NiFe-Cr materials is alloy 825 (N08825), which contains 2.2 wt% Cu to improve its resistance to sulfuric acid. This alloy is used in sulfuric acid, phosphoric acid, seawater, and in downhole oilfield environments.