Corrosion Guide

Nickel Alloy Groups

1. Commercially-Pure Nickel (Ni)
2. Nickel-Copper (Ni-Cu)
3. Nickel-Chromium (Ni-Cr)
4. Nickel-Molybdenum (Ni-Mo)
5. Nickel-Chromium-Molybdenum (Ni-Cr-Mo)
6. Nickel-Chromium-Iron (Ni-Cr-Fe)
7. Nickel-Iron-Chromium (Ni-Fe-Cr)

The general attributes of each group are listed in the following table, along with the names of some representative alloys:

Group	Examples	Attributes
C-P Nickel	Nickel 200 alloy	Very resistant to caustic alkalis. Useful electrical and magnetic properties.
Ni-Cu	MONEL® alloy 400 alloy	Very resistant to seawater and hydrofluoric acid. Moderately resistant to sulfuric acid. Very resistant to oxidizing acid solutions.
Ni-Cr	HASTELLOY® G-35® alloy
Ni-Mo	HASTELLOY® B-3® alloy	Very resistant to hydrochloric acid and sulfuric acid.
Ni-Cr-Mo	HASTELLOY® C-276 alloy	Resistant to both oxidizing and reducing acid solutions. Very resistant to chloride-induced pitting, crevice attack and stress corrosion cracking.
Ni-Cr-Fe	HASTELLOY® G-30® alloy	Very resistant to oxidizing solutions. Moderately resistant to chloride-induced pitting, crevice attack and stress corrosion cracking.
Ni-Fe-Cr	INCOLOY® alloy 825	Resistant to oxidizing solutions. Some resistance to sulfuric acid and chloride-induced localized attack.

Compositional details of several materials from each group are given in the table below. For completeness, some casting equivalents are included (although their characteristics are generally affected by microstructural inhomogeneity, and elevated residual element contents).

Group	Alloy	UNS No.	Form	Composition wt.% (values denoted with * are maxima, and ** are minima)
				Ni	Cu	Mo	Cr	Fe	W	Mn	Si	C	Al	Ti	Other
Ni	200	N02200	Wrought	99.5	0.1	-	-	0.2	-	0.2	0.2	0.08	-	-	-
	201	N02201	Wrought	99.5	0.1	-	-	0.2	-	0.2	0.2	0.01	-	-	-
	301	N03301	Wrought	96.5	0.1	-	-	0.3	-	0.2	0.5	0.2	4.4	0.6	-
	CZ-100	N02100	Cast	95**	1.25*	-	-	3*	-	1.5*	2*	1*	-	-	-
Ni-Cu	400	N04400	Wrought	66.5	31.5	-	-	1.2	-	1	0.2	0.2	-	-	-
	K-500	N05500	Wrought	66.5	29.5	-	-	1	-	0.8	0.2	0.1	2.7	0.6	-
	M-35-1	N24135	Cast	BAL.	29.5	-	-	3.5*	-	1.5*	1.25*	0.35*	-	-	Nb 0.5*
Ni-Mo	B-2	N10665	Wrought	69	0.5*	28	1*	2*	0.5*	1*	0.1*	0.01*	-	-	-
	B-3®	N10675	Wrought	65**	0.2*	28.5	1.5	1.5	3*	3*	0.1*	0.01*	0.5*	-	-
	N-7M	N30007	Cast	BAL.	-	31.5	1*	3*	-	1*	1*	0.07*	-	-	-
	N-12MV	N30012	Cast	BAL.	-	28	1*	5	-	1*	1*	0.12*	-	-	Co 2.5*, V 0.4
Ni-Cr	600	N06600	Wrought	76	0.2	-	15.5	8	-	0.5	0.2	0.08	-	-	-
	625	N06625	Wrought	61	-	9	21.5	2.5	-	0.2	0.2	0.05	0.2	0.2	Nb + Ta 3.6
	690	N06690	Wrought	58**	0.5*	-	29	9	-	0.5*	0.5*	0.05*	-	-	-
	725	N07725	Wrought	57	-	8	21	7.5	-	0.35*	0.2*	0.03*	0.35*	1.5	Nb 3.5
	G-35®	N06035	Wrought	58	0.3*	8.1	33.2	2*	0.6*	0.5*	0.6*	0.05*	0.4*	-	-
	ALLCORR	N06110	Wrought	BAL.	-	10	31	-	2	-	-	0.02	0.25	0.25	Nb 0.4
Ni-Cr- Mo	C-4	N06455	Wrought	65	0.5*	16	16	3*	-	1*	0.08*	0.01*	-	0.7*	-
	C-22®	N06022	Wrought	56	0.5*	13	22	3	3	0.5*	0.08*	0.01*	-	-	V 0.35*
	C-22HS®	-	Wrought	61	0.5*	17	21	2*	1*	0.8*	0.08*	0.01*	0.5*	-	-
	C-276	N10276	Wrought	57	0.5*	16	16	5	4	1*	0.08*	0.01*	-	-	V 0.35*
	C-2000®	N06200	Wrought	59	1.6	16	23	3*	-	0.5*	0.08*	0.01*	0.5*	-	-
	59	N06059	Wrought	BAL.	-	16	23	1.5*	-	0.5*	0.1*	0.01*	0.25	-	-
	686	N06686	Wrought	BAL.	-	16	21	5*	3.7	0.75*	0.08*	0.01*	-	0.15	-
	CW-2M	N26455	Cast	BAL.	-	16.25	16.25	2*	1*	1*	0.8*	0.02*	-	-	-
	CW-6M	N30107	Cast	BAL.	-	18.5	18.5	3*	-	1*	1*	0.07*	-	-	-
	CW- 12MW	N30002	Cast	BAL.	-	17	16.5	6	4.5	1*	1*	0.12*	-	-	V 0.3
	CX-2MW	N26022	Cast	BAL.	-	13.5	21.5	4	3	1*	0.8*	0.02*	-	-	V 0.35*
Ni-Cr-Fe	G-3	N06985	Wrought	44	2	7	22	19.5	1.5*	1*	1*	0.015*	-	-	Co 5*, Nb 0.5*
	G-30®	N06030	Wrought	43	2	5.5	30	15	2.5	1.5*	0.8*	0.03*	-	-	Co 5*, Nb 0.8
	G-50®	N06950	Wrought	50**	0.5*	9	20	17	1*	1*	1*	0.02*	0.4*		Co 2.5*, Nb 0.5*
Ni-Fe-Cr	825	N08825	Wrought	42	2.2	3	21.5	30	-	0.5	0.2	0.05*	0.1	0.9	-
	925	N09925	Wrought	44	2.2	3	21	22**	-	1*	0.5*	0.03*	0.3	2.2	Nb 0.5*

Cobalt Alloy Groups

There are relatively few wrought, corrosion- and wear-resistant, cobalt-based alloys. On the other hand, there are many cast, wear-resistant, cobalt-based alloys (closely associated with the STELLITE® tradename) that, despite their high carbon contents, possess a modicum of resistance to aqueous corrosion. This manual is concerned with the former materials. However, the cast alloys will be referred to often, since they provide a well-known frame of reference.

There are essentially three types of wrought, cobalt alloys used to resist aqueous corrosion. All contain high levels (20 wt.% or more) of chromium, and significant molybdenum and/or tungsten contents.

First are those derived from the cast, tungsten-bearing, high-carbon alloys, exemplified by HAYNES® 6B alloy (also known as STELLITE® 6B alloy). With a 1 wt.% carbon content, this alloy can be hot worked, but cannot be cold worked. Wrought processing enables the breaking down of large carbide particles (within the cast, ingot structure) into a discontinuous dispersion of equiaxed carbide particles; this results in enhanced ductility, increased resistance to corrosion, and excellent resistance to low stress abrasion, relative to compositionally-similar, cast and weld overlay materials.

Second are those tungsten-bearing, low-carbon, wrought materials designed for high temperature service, but whose resistance to aqueous corrosion is so high that they have found use in low temperature applications also.  The primary example is HAYNES® 25 alloy, which is approved for biomedical use.

Third are those molybdenum-bearing alloys with carbon contents of about 0.35 wt.% or less, and designed to excel in both corrosive solutions and systems subject to wear. The prime example is ULTIMET® alloy, which exhibits a unique blend of properties, including high resistance to aqueous corrosion and wear, relatively high ductility, and excellent weldability.

The nominal compositions of several wrought, corrosion-resistant, cobalt alloys are given in the following table, along with those of several cast, cobalt alloys, for comparison.

Group	Alloy	UNS No.	Form	Composition, wt.% (values denoted with * are maxima)
				Co	Ni	Cr	Mo	W	C	Fe	Si	Mn	Other
Tungsten-Bearing High-Carbon	6B	R30016	Wrought	58	2.5	30	1.5*	4	1	3*	0.7	1.4	-
	1	R30001	Cast	BAL	1.5	30	0.5	13	2.5	3*	1.3	0.5	-
		W73001**	Weld Overlay
	6	R30006	Cast	BAL	3*	29	1.5*	4.5	1.2	3*	1.5*	1*	-
		W73006**	Weld Overlay
	12	R30012	Cast	BAL	3*	29.5	1*	8.25	1.5	3*	1.2	1*	-
		W73012**	Weld Overlay
Tungsten-Bearing Low-Carbon	25	R30605	Wrought	51	10	20	1*	15	0.1	3*	0.4*	1.5	-
Molybdenum-Bearing Low-Carbon	ULTIMET®	R31233	Wrought	54	9	26	5	2	0.06	3	0.3	0.8	N 0.08
	F75	R30075	Cast	BAL	1*	28.5	6	0.2*	0.35*	0.75*	1*	1*	Al 0.3* B 0.01* N 0.25*

**Welding filler metal designations, with slight compositional modifications