Nickel alloys readily with chromium, iron and molybdenum to form a wide range of high-performance alloys. These exhibit outstanding corrosion resistance, excellent high-temperature strength and unique properties such as shape memory and low coefficient of expansion.
Nickel-chromium alloys are known as Nichrome (Nickel–Chromium–sometimes also iron, NiFeCr) and typically contain 80% nickel by weight. These are commonly used in a variety of applications due to their good corrosion resistance, especially to oxidizing environments.
The most common of these is the 17-4 PH nickel-chromium alloy, which is commonly used in chemical processing equipment such as those for ethylene pyrolysis, hydrocarbon cracking and diphenol production. This alloy is particularly well-suited to use in conditions with reducing media because of the alloy’s high level of chromium, which helps resist pitting and crevice corrosion.
These alloys are also characterised by their exceptional resistance to stress-corrosion cracking in petrochemical environments. This is primarily because the high levels of chromium help to prevent precipitation of d ferrite, which can lead to cracking at grain boundaries. These characteristics make this alloy well-suited to use in petrochemical plants where components are exposed to corrosive attack from 1100 to 1800 deg C.