Alloy 625 (UNS N06625)


Alloy 625 is an austenitic nickel-base superalloy with excellent resistance to oxidation and corrosion over a broad range of conditions, including jet engine and chemical process applications.  The outstanding strength and toughness of Alloy 625, at temperatures ranging from cryogenic to 2000˚F (1093˚C), are derived primarily from the solid solution strengthening of columbium and molybdenum in a nickel-chromium matrix.

Alloy 625 can be used for parts requiring both corrosion and oxidation resistance up to 2000ºF (1093˚C).  AMS 5666 requires a minimum yield strength of 60,000 psi at room temperature for bars under 4 inches in diameter.  Mechanical properties for bars 4 inches in diameter and larger are to be agreed upon by purchaser and vendor.  This alloy is exceptionally resistant to crevice corrosion and stress corrosion cracking and to chemical attack in both highly oxidizing to moderately reducing conditions.  Alloy 625 is virtually immune to corrosion in marine environments and is used extensively in the hot section of jet engines and in high temperature corrosive environments in the chemical processing industry. The alloy has outstanding resistance to creep and stress rupture up to 1200ºF (649˚C), and oxidation and scaling resistance up to 2000ºF (1093˚C).

Chemical Composition

Chemical Composition (wt%) limits as specified in ASTM B446*

Carbon 0.10 Silicon 0.50
Chromium 20.00-23.00 Phosporous 0.015
Nickel 58.00 min Sulfur 0.015
Molybdenum 8.00-10.00 Aluminum 0.40
Iron 5.00 Columbium+Tantalum 3.15-4.15
Titanium 0.40 Cobalt 1.00
Manganese 0.50    

*Maximum, unless range is indicated

Physical Properties

Physical properties for 625

Density, lb/in3 0.305
Modulus of Elasticity, psi 29.8 x 106
Coefficient of Thermal Expansion, 68-212˚F, /˚F 7.1 x 10-6
Thermal Conductivity, Btu/ft hr ˚F 6.3
Specific Heat, Btu/lb ˚F 0.098
Electrical Resistivity, Microhm-in 50.7

Mechanical Properties

Mechanical property requirements for heat treated bar product as specified in ASTM B446

Property Grade 1 Grade 2 Grade 3
Yield Strength, min. (ksi) 60 50 40
Tensile Strength, min. (ksi) 120 110 100
Elongation, min. (%) 30 25 30


Typical standards for 625

AMS 5666
AMS 5665