Langley Alloys - Inconel 625

Inconel 625 (Alloy 625, UNS N06625, 2.4856) is a nickel-based alloy that provides good levels of strength and excellent corrosion resistance at elevated temperatures. It was developed in the 1960s by Inco (now part of Special Metals Corporation), hence the associated Inconel trademark. The Inconel trademark has become ubiquitous for a family of nickel-chromium alloys, even though versions are now produced by other manufacturers.

Nickel alloys are well-suited to high-temperature applications due to the formation of a stable passive oxide layer that prevents further oxidation of the metal occurring. Adding chromium improves resistance to corrosion but does little to enhance the mechanical properties. In the case of Inconel 625, additions of niobium and manganese are responsible for the uplift in yield strength. It achieves a minimum yield strength of 50ksi (345N/mm2) in diameters greater than 4” (100mm) and 60ksi (415N/mm2) for smaller diameters. The minimum tensile strength is 110ksi (760N/mm2) and 120ksi (830N/mm2) respectively.

Although Inconel 625 does not provide the very high strength levels of Inconel 718 and other precipitation-strengthened alloys, the yield strength is comparable with duplex stainless steels, and just below that of super duplex stainless steels. However, properties are more consistent over a wider temperature range. Impact strength is retained down to cryogenic temperatures (-196degC), whereas there is a transition to brittle fracture for ferritic and austenitic-ferritic duplex stainless steels somewhere between -70 to -50degC. Similarly, their mechanical properties are reasonably consistent up to 650degC. The nickel content ensures continued resistance to oxidation up to nearly 1000degC, so it can be used in non-structural or load-bearing applications.

Although primarily used for applications that exploit its mechanical properties over the wide temperature range, this is ably supported by excellent corrosion resistance in an array of media. With more than 20% chromium and up to 10% molybdenum, Inconel 625 has a pitting resistance equivalent number (PREN) of 45 or more. This ensures high pitting and crevice corrosion resistance. Equipment for the chemical processing industry is a common application for this alloy. Besides its corrosion resistance and tolerance of elevated temperatures, the ease of welding and fabrication are also helpful.

Langley Alloys carries a significant stock of Alloy 625 solid bar, from ½” up to 9” in many incremental sizes. In addition, customers can make use of our in-house first-stage machining to offer near-net shape components. 

Published: 29th September 2020