What is Inconel 625 Grade 2?

Inconel 625 is a nickel-based alloy, also known in the Unified Numbering System (UNS) as N06625, Alloy 625 or DIN 2.4856.

The Two Grades of Inconel 625

According to ASTM B446 it can be supplied in two different conditions:

Grade1

Inconel 625 Grade 1 is the product in Annealed condition. This is the most commonly stocked version, achieving a yield strength of 60ksi (414Mpa) for bars up to 4″ (101.6mm) diameter, and 50ksi (345MPa) for larger bars up to 10″ (254mm) diameter. The tensile strength minimum is 120ksi (827Mpa) and 110ksi (758Mpa) respectively.

Langley Alloys carries significant stock as solid bars between 5/8” (15.875mm) and 10” (254mm) diameter.

Our stock is also certified to API 6A CRA and NACE MR0175 / ISO 15156-3, and also AMS 5666.

Grade 2, 

Inconel  625 Grade 2 is supplied in the Solution Annealed condition. The main difference between Grade 2 and Grade 1 is the annealing temperature. In the case of Grade 1, the minimum annealing temperature is 1600F (871degC), whereas for Grade 2 it is now 2000F (1093degC). A further stabilisation anneal (1800F / 982degC) can be undertaken for the Grade 2 product to increase resistance to sensitisation from exposure at higher temperatures during operation, but is not essential.

By annealing at higher temperatures, the mechanical properties fall slightly compared with Grade 1. Instead of a yield strength of 60ksi/50ksi, it is now 40ksi for all sizes. Similarly, the minimum tensile strength is now 100ksi (690Mpa).

As the annealing temperature for Grade 2 is higher than that for Grade 1, it is possible to simply convert our existing Grade 1 stock to Grade 2 by arranging an additional heat treatment.

The History of Inconel 625

Inconel 625 was launched in 1964 following development by Special Metals Corporation. Inconel 625 achieves reasonably high strength through the addition of molybdenum and niobium to the nickel-chromium base, but nowhere as high as Inconel 718. However, due to the high level of chromium and molybdenum it is corrosion resistant in the most aggressive of environments.

Alloy 625 is certainly one of the more expensive alloys we stock, given its high nickel content (>58%). However, it provides strong performance at temperatures in excess of 800degC.   nb. Special Metals suggest service temperatures from cryogenic up to 980degC for their Inconel 625 product, although mechanical properties do start to drop off more significantly from 650-700degC.

As well as its specific applications at higher temperatures, Alloy 625 is used where high levels of corrosion resistance are also required. Because of its very high level of Molybdenum (8-10%), Inconel 625 Grade 2 has a Pitting Resistance Equivalent Number (PREN) >45.

This is beyond all but the most highly-alloyed grades. In fresh seawater there is virtually no attack, and it can withstand more aggressive oxidising and non-oxidising acids well. For instance, it is one of the few alloys that can be used for the handling or storage of hydrochloric acid (strongly oxidising conditions).

Got any Questions? Get in Touch

For more information about nickel-based alloys, please don’t hesitate to contact us today. We would be happy to answer any questions that you may have regarding specifications and common applications.