Nickel mainly, in addition to many other elements some of which include: Chromium, Molybdenum and Niobium. The chemistry of Inconel 625 is as follows:
Chemical composition:
Nickel (plus cobalt) ……………….. 58 % minimum
Chromium ……………………………… 20. 0 – 23.0 %
Iron ……………………………………….. 5.0 % maximum
Molybdenum …………………………… 8.0 – 10.0 %
Columbium (plus Tantalum)……….. 3.15-4.15 %
Carbon …………………………………… 0.10% maximum
Manganese ……………………………… 0.50 % maximum
Sulfur ……………………………………… 0. 015% maximum
Phosphorus………………………………. 0.015% maximum
Silicon……………………………………… 0.50% maximum
Aluminum ………………………………… 0.40% maximum
Titanium……………………………………. 0.40% maximum