Nickel alloys can offer enhanced corrosion resistance, toughness, strength at high and low temperatures, and interesting magnetic, thermal and electronic properties compared with other metals. Due to their higher nickel content compared with stainless steels, they can be appreciably more expensive, but find uses in more demanding applications from gas turbines to chemical plants and oil & gas industry components.

Nickel-Copper alloys such as Alloy 400 and Alloy K-500 (Special Metals Corporation’s family of Nickel-Copper alloys is known as Monel®) are based predominantly on nickel, copper, with smaller additions of manganese and iron. They are used where a higher strength is required compared to pure nickel, and resist corrosion in a wide range of environments. They can be fabricated readily by hot- and cold-working, machining, and welding. Nickel-Copper alloys find wide application in oil refining and marine applications where long corrosion-free life is required. Because of good thermal conductivity of nickel copper alloys, they are frequently are used for heat exchangers where sea water is one of the fluids concerned.

Nickel-Iron-Chromium alloys such as Alloy 825 (Special Metals Corporation’s family of Nickel-Iron-Chrome alloys is known as Incoloy®) were developed to provide a more cost-effective solution for applications requiring high-temperature and corrosion resistance – achieved by lowering the nickel content. Selectively alloying with other elements can greatly improve their performance in certain environments. For instance, Alloy 825 also contains molybdenum and copper to improve resistance to strongly reducing environments, such as those containing sulphuric and phosphoric acids.

Nickel-Chromium superalloys such as Alloy 625 and Alloy 718 (Special Metals Corporation’s family of Nickel-Chromium alloys is known as Inconel®) are typically used in high-temperature applications. When heated, they form a thick and stable passivating oxide layer protecting the surface from further attack. These alloys retain their strength over a wide temperature range, particularly at elevated temperatures where aluminium and steel would otherwise succumb to creep failure. Varying levels of high-temperature strength can be developed by solid solution strengthening or precipitation strengthening (with niobium additions).

AlloyCommon NameRelated SpecificationsTensile StrengthProof TestElongation
BritishEuropeanUnited StatesN/mm2 (ksi)N/mm2 (ksi)(%)
Alloy 725 UNS N07725 ASTM B637
UNS N07725
1137 (165) 827 (125) 20
Alloy 400 UNS N04400 BS 3076 NA13
2.4360
ASTM A164
UNS N04400, N04405
QQ - N - 281
483 (70) 172 (25) 35
Alloy 825 UNS N08825 BS 3076 NA16
2.4858
ASTM B425
UNS N08825
590 (85) 220 (32) 30
Alloy 718 UNS N07718 2.4668
ASTM B637
UNS N07718
API 6A 718
1138 (165) 965 (140) 20
Alloy 625 UNS N06625 BS 3076 NA21
2.4856
ASTM B564
B466
UNS N06625
830 (120) 415 (60) 30
Alloy 825 HS110 UNS N08825 110ksi BS 3076 NA16
2.4858
ASTM B425
UNS N08825
793 (115) 758 (110) 30
Alloy 825 (Tube) UNS N08825 BS 3076 NA16
2.4858
ASTM B425
UNS N00825
518 (75) 241 (35) 30
Alloy K-500 UNS N05500 965 (140) 724 (105) 20
Alloy 925 UNS N09925 UNS N09925
ASTM B805
API 6A CRA
NACE MR0175-3
965 (140) 758 - 965 (110 - 140) 18
Note: Monel®, Incoloy® and Inconel® are registered trademarks owned by Special Metals Corporation

Alloy 725:

Alloy 725 is a nickel-chromium alloy with significant additions of molybdenum, niobium and titanium, supplied in the hot worked, annealed and age-hardened condition. It is age-hardened to achieve extremely high strength, approximately twice that of Alloy 625 in the annealed condition, through the precipitation of ϒ” phase during a controlled heat treatment process. As this high strength is achieved by ageing rather than cold working, it retains excellent ductility and toughness, and this approach is useful for large or non-uniform sections that cannot be strengthened through cold working.

Alloy 400:

Alloy 400 is a nickel-copper single-phase alloy most commonly supplied in hot worked and annealed condition. Although the grade can be tempered or cold worked to increase its properties, in its standard annealed condition it is easy to form and fabricate with no requirements for additional heat treatments to re-balance the alloy. It retains excellent mechanical properties at sub-zero temperatures. Strength and hardness increase with only a slight loss of ductility and impact resistance.

Alloy 825:

Alloy 825 is a nickel-iron-chromium alloy with additions of molybdenum, copper and titanium (NiCr21Mo), supplied in the hot worked and annealed condition. It achieves good mechanical properties from cryogenic to medium-high temperatures (5400C) and can be significantly strengthened through cold working.

The high nickel content ensures resistance to stress corrosion cracking, combined with molybdenum and copper to strongly resist reducing environments such as sulphuric and phosphoric acids, chromium to resist oxidising environments such as nitric acid, titanium to inhibit intergranular corrosion, and overall resistance to pitting and crevice corrosion.

Alloy 718:

Alloy 718 is a high-strength, corrosion-resistant nickel chromium alloy supplied in the hot worked, solution annealed and age hardened condition. The addition of Nb, Ti, Al and Ni form a series of precipitates during the controlled solution annealing and ageing process steps, resulting in a significant increase in strength and hardness compared with alternative nickel alloys. These tensile and creep rupture properties are maintained from cryogenic to elevated temperatures, making it suitable for applications between -250oC – 750oC.

Alloy 625:

Alloy 625 is a nickel-chromium-molybdenum-niobium alloy (NiCr22Mo9Nb), supplied in the hot worked and annealed condition. It achieves high-strength levels from the solid solution effects of Molybdenum and Niobium (Colombium) from room temperature up to 800°C.

It is particularly useful in situations where oxidation resistance and avoidance of pitting is required. In the annealed condition, it is fully austenitic and is suitable for machining. It provides excellent corrosion resistance in a wide variety of severe corrosive environments due to its high alloy content.

Alloy 825 HS110:

Alloy 825 HS110 is a high strength nickel-iron-chromium alloy with additions of molybdenum, copper and titanium (NiCr21Mo), supplied in the hot worked, annealed and cold worked condition. Controlled cold working ensures that the product achieves significantly increased yield strengths over the annealed product, whilst retaining good ductility and toughness.

 

Alloy 825 (Tube):

Alloy 825 is a nickel-iron-chromium alloy with additions of molybdenum, copper and titanium (NiCr21Mo), supplied in the hot worked and annealed condition. It achieves good mechanical properties from cryogenic to medium-high temperatures (5400C) and can be significantly strengthened through cold working.

The high nickel content ensures resistance to stress corrosion cracking, combined with molybdenum and copper to strongly resist reducing environments such as sulphuric and phosphoric acids, chromium to resist oxidising environments such as nitric acid, titanium to inhibit intergranular corrosion, and overall resistance to pitting and crevice corrosion.

Alloy K-500:

Alloy K-500 is a precipitation-hardenable nickel-copper alloy.  Although Langley Alloys supply Alloy K-500 in all conditions, we predominantly supply material in the Hot Worked and Precipitation Treated condition, which offers the optimum combination of high strength and ductility across the size range. The increased properties are obtained by adding aluminium and titanium to the nickel-copper base, and by heating under controlled conditions so that particles of ‘ϒ’ Ni3 (Ti, Al) are precipitated throughout the matrix. The thermal processing used to effect precipitation is commonly called age hardening or ageing.

Alloy 925:

Alloy 925 is a precipitation-hardenable Nickel-Iron-Chromium Alloy with additions of Molybdenum, Copper, Titanium and Aluminium, supplied in the solution annealed and aged condition. The Titanium and Aluminium are specifically added to give a strengthening of the alloy during ageing, as Ni3(Al, Ti) gamma (‘ϒ’) prime precipitates form throughout the alloy matrix and greatly increases the hardness and strength in a similar way to Alloys K-500, 718 and 725.