The composition and classification of nickel alloy

TAGS: Nickel alloys | nickel | alloy |

The following is a simplistic categorisation of the various nickel alloy types.

• Wrought Nickel

  Pure nickel UNS N02200 is used in the chemical industry for its corrosion resistance - particularly to alkalis. It is also used for its properties in shielding against electromagnetic interference and in transducers.

• Nickel-Iron Alloys

  These are used as soft magnetic materials, as glass-to-metal seals and as materials with defined thermal expansion properties.
  

  Invar® (UNS K93600), with 36% nickel and the remainder iron, is unique in having an almost zero coefficient of thermal expansion around room temperature. This makes it valuable where high dimensional stability is required, such as in precision measuring instruments and thermostat rods. It is also used at cryogenic temperatures because of its very low thermal expansion rates.
  

  Alloys containing 72-83% nickel have the best soft magnetic properties and are used in transformers, inductors, magnetic amplifiers, magnetic shields and memory storage devices.

• Nickel-Copper Alloys

  These are highly resistant to corrosion by alkaline solutions, non-oxidizing salts and seawater. The best-known is Alloy 400.

• Nickel-Molybdenum Alloys

  These are highly resistant to reducing acids in the absence of oxidizing ions, such as ferric and cupric or dissolved oxygen. The best-known is Alloy B-2.

• Nickel-Chromium Alloys

  These are characterised by their high resistance to corrosion at both normal and high temperatures (resistance to scaling), good high-temperature strength and high electrical resistance. There are three main groups of alloys:

  • Ni-Cr (and also Ni-Cr-Fe) alloys with high electrical resistance for heating elements, such as 70-30 (UNS N06008) and C-Grade (UNS N06004)

  • Ni-Cr alloys (with Fe and other alloying elements) with good corrosion resistance. The best-known are Alloy 600 (UNS N06600) and Alloy 601 (UNS N06601)

  • Ni-Cr alloys with high-temperature strength and creep resistance, mostly age-hardenable, such as Alloy X-750 (UNS N07750)

• Nickel-Chromium-Iron Alloys

  There are basically two groups of alloys:

  • Ni – Cr – Fe alloys with excellent strength at high temperature and the ability to resist oxidation, carburisation and other types of high-temperature corrosion. The best-known is alloy 800 (UNS N08800) and its variants 800H (UNS N08810) and 800HT (UNS N08811). (Recently, these alloys were classified as stainless steels reflecting their high Fe content)

  • Ni – Cr – Fe (with Mo and Cu) alloys with excellent corrosion resistance in specific applications. Probably the best-known is alloy 825 (UNS N08825), which offers exceptional resistance to sulphuric acid. Alloy G-3 (UNS N06985) offers exceptional corrosion resistance to commercial phosphoric acids as well as many complex solutions containing highly oxidizing acids.

• Nickel-Chromium-Molybdenum Alloys

  These are highly corrosion-resistant, of which Alloy C-276 (N10276) is the best-known. They offer exceptional resistance to reducing acids such as hydrochloric and sulphuric. There are a number of variants based on this composition, which have modified the Cr and Mo levels and, in some cases, added Cu or W in order to extend the corrosion resistance to conditions that are more oxidising or more reducing. These include Alloy C-22 (N06022), Alloy 59 (N08059), Alloy C-2000 (UNS N06200), and Alloy 686 (N06686).

• Nickel-Chromium-Cobalt Alloys

  The addition of cobalt and molybdenum imparts solid-solution strengthening and high levels of creep-rupture strength to alloy 617 (UNS N06617). The addition of cobalt to HR-160 (N12160) provides outstanding resistance to various forms of high-temperature corrosion attacks, such as sulphidation and chloride attack in both reducing and oxidizing atmospheres.

• Nickel-Titanium Alloys

  55% nickel-titanium alloy (UNS N01555) (also known as Nitinol) has shape-memory properties. When formed at one temperature and then deformed at a lower one, it regains its original form when reheated. The transition temperatures can be adjusted through careful control of the composition. Medical devices and specialised connectors are two of specific the applications. The same alloy can also undergo considerable elastic deformation and still return to its original shape (super-elastic property). This property has been exploited for applications as diverse as spectacle frames and shock absorbers that provide earthquake resistance in historic stone buildings.

 

Nominal composition of various nickel alloys:

Alloy name	UNS	% Ni	% Cr	% Fe	% Mo	% Cu	% Co	% Other
200	N02200	99 min
Invar	K93600	36		64
400	N04400	65	32
B-2	N10665	68		2	28
70-30	N06008	70	30
C-Grade	N06006	60	16	bal
600	N06600	76	16	8
601	N06601	60	23	bal				Al - 1.3
X-750	N07750	70	15	7				Ti - 2.5 Al - 0.7 Nb - 1.0
825	N08825	42	21	25	3	2
G-3	N06985	bal	22	20	7	2
800	N08800	32	21	45				W - 3.5
C-276	N10276	bal	15	5	16
C-22	N06022	bal	21	4	13
59	N06059	bal	23	1.5 max	16
C-2000	N06200	bal	23	3 max	16	1.6
686	N06686	bal	21	2 max	16			W - 3.7
617	N06617	44.5 min	22	3 max	9		12
HR-160	N12160	bal	28	3.5 max			30	Si - 2.75
Nitinol	N01555	55						Ti - 45

 

 

Alloy Type	UNS	%Cr	%Ni	%Mo	%Cu	%Fe
304L	S30403	18	8	-	-	bal	Most common stainless steel used for potable water treatment and food contact.
316L	S31603	16	10	2.1	-	bal	Addition of Mo provides greater resistance to chlorides and acidic solutions. Used in coastal regions, in water treatment and in the chemical processing industry.
2205	S32205	22	5.7	3.1	-	bal	Even greater corrosion resistance than 316L. Can be used in place of 316L, but its greater strength can mean weight reduction. May be  substituted for 316L if it fails in service.
2507	S32750	25	7	4	-	bal	Even greater corrosion resistance than 2205. Useful corrosion resistance to seawater.
254 SMO	S31254	20	18	6.1	-	bal	Corrosion resistance similar to 2507, also possessing useful corrosion resistance to seawater.
Alloy 20	N08020	20	33	2.1	3.2	bal	Cu bearing stainless steel with useful corrosion resistance to all concentrations of sulphuric acid.
310S	S31008	25	20	-	-	bal	High chromium stainless steel with excellent resistance to high-temperature oxidation.
800H	N08810	20	32	-	-	bal	Stainless steel with excellent high-temperature strength and useful resistance to high-temperature oxidation.
625	N06625	21	bal	9	-	3	Well-known nickel alloy with excellent high-temperature strength and outstanding aqueous corrosion resistance.
C-276	N10276	15	bal	16	-	5	One of the best-known nickel alloys with excellent corrosion resistance to reducing acids.
600	N06600	16	76	-	-	8	Useful resistance to high-temperature corrosion and caustic solutions.
Alloy 400	N04400	-	65	-	32	-	Most common uses are in marine and chemical processing.