Description

Alloy 718 is a nickel – chromium alloy which can be heat treated to give high strength, good corrosion resistance, ease of formability and which can be welded with good resistance to strain age cracking. Inconel 718

The alloy can be used at temperatures up to 700C. Alloy 718 was initially developed for the aerospace industry but its excellent strength and corrosion resistance were recognised by the oil industry and it is now widely used in this field also.

The majority of alloy 718 is vacuum induction melted (VIM) followed by vacuum arc remelting (VAR) or electro-slag remelting (ESR). However some material is electric arc melted, argon oxygen degassed (AOD) followed by double VAR. The major alloying elements are molybdenum, niobium + tantalum, aluminium and titanium. These give the alloy a combination of high strength and good corrosion resistance when the alloy is precipitation hardened.

The heat treatment of alloy 718 differs depending on its application. This is because the aerospace material requires maximum strength for operation at high temperature whereas the oil patch material is limited to a maximum hardness in order to ensure it is resistant to stress corrosion cracking.