What is the difference between Inconel 625 Grade 1 and Grade 2?
What is Inconel 625 Grade 2?
Nickel Alloys
Inconel 625 is a nickel-based alloy also known as N06625, Alloy 625, or DIN 2.4856 in the Unified Numbering System (UNS).
Two Grades of Inconel 625
According to ASTM B446, it can be supplied in two different tempers:
Grade 1
Inconel 625 Grade 1 is the product in the annealed condition. This is the most common stock version, with a yield strength of 60ksi (414MPa) for bars up to 4 inches (101.6mm) in diameter and 50ksi (345MPa) for larger bars up to 10 inches (254mm) in diameter. Tensile strengths are a minimum of 120ksi (827Mpa) and 110ksi (758Mpa), respectively.
GNEE group carries a large inventory of solid bar in diameters between 5/8 inch (15.875 mm) and 10 inches (254 mm).
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. For Grade 1, the minimum annealing temperature was 1600F (871 degrees Celsius), while for Grade 2 it is now 2000F (1093 degrees Celsius). Grade 2 products can be given a further stabilization anneal (1800F / 982 degrees Celsius) to improve resistance to sensitivity from exposure to higher temperatures during operation, but this is not required.
By annealing at the higher temperature, the mechanical properties are slightly reduced compared to Grade 1. The yield strength is no longer 60ksi/50ksi, it is now 40ksi for all sizes. Likewise, the minimum tensile strength is now 100ksi (690Mpa).
Since Grade 2 has a higher annealing temperature than Grade 1, our existing Grade 1 inventory can be converted to Grade 2 simply by scheduling additional heat treatments.
History of Inconel 625
Inconel 625 achieves comparable strength by adding molybdenum and niobium to the nickel-chromium base, but nowhere near as much as Inconel 718. However, it is corrosion resistant in the harshest environments due to its high chromium and molybdenum content.
Alloy 625 is certainly one of the pricier alloys in our inventory due to its high nickel content (>58%). However, it still provides excellent performance at temperatures in excess of 800 degrees Celsius. Note: Special Metals recommends service temperatures for its Inconel 625 products from cryogenic to 980 degrees Celsius, although mechanical properties begin to decline significantly at 650-700 degrees Celsius.
In addition to specific applications at higher temperatures, Alloy 625 is used where a high level of corrosion resistance is required. Due to its very high molybdenum content (8-10%), Inconel 625 Grade 2 has a Pitting Resistance Equivalent Number (PREN) >45.
This exceeds all but the highest alloyed grades. Corrosion is virtually non-existent in brackish water, and it resists more aggressive oxidizing and non-oxidizing acids very well. For example, it is one of the few alloys that can be used to handle or store hydrochloric acid (a strongly oxidizing condition).
