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