Inconel 625 vs. 718 bolts: Which Is Best for Your Application?

Inconel fasteners are commonly used for extreme environments and come in various “flavors” depending on the needs of the application. This brief paper will give you a quick comparison of the two most popular grades, Inconel 625 and Inconel 718 to help you choose the best material.

Key Differences 625 vs. 718
Inconel 625
o Better general corrosion resistance
o Long-term high temperature stability

Inconel 718
o Precipitation hardened
o 2x’s stronger than Inconel 625

Inconel 625
Inconel 625 screws possess considerable amounts of nickel, chromium, and molybdenum making it not only strong at high temperatures but also resistant to corrosion, oxidation and carburization. One of its most notable characteristics is its ability to prevent stress, pitting and crevice corrosion cracking even when exposed to chloride ions.

Benefits
o Outstanding resistance to pitting, crevice corrosion
o Almost 100% resistance to chloride induced stress corrosion cracking
o High resistance to oxidation at elevated temperatures up to 1050°C
o Good resistance to acids, such as nitric, phosphoric, sulfuric and hydrochloric, as well as to alkalis
o Easily welded by standard shop fabrication practices
o Greater longevity at high temperatures than Inconel 718

Usage Examples
Oil and gas production where hydrogen sulfide and elementary sulfur are present, marine applications including propeller blades, submarine propulsion and other naval applications

Inconel 718
Similar to its sister 625, Inconel 718 is an age hardened version of alloy 625. Aging (or precipitation hardening) produces precipitates in the molecular structure that pins the grains of the metal in place. As a result, materials usually become significantly stronger. In the case of Inconel, 718 has exceptional strength with a yield strength that is about 2x’s stronger than 625!

Benefits
o Super high strength: min ultimate tensile strength of 185ksi/min yield strength of 150ksi
o Good corrosion resistance to sour gas, HCl, H2SO4
o Outstanding weldability

Usage Examples
Gas turbine and jet engines, cryogenic storage tanks, downhole oil & gas and nuclear engineering applications.