AU463540B2

AU463540B2 - Corrosion-resistant nickel-iron alloy

Info

Publication number: AU463540B2
Application number: AU52027/73A
Authority: AU
Inventors: THOMAS ERNEST EVANS and ANTHONY CHRISTOPHER HART GEORGE NORMAN FLINT
Original assignee: Inco Ltd
Current assignee: Inco Ltd
Priority date: 1972-02-16
Filing date: 1973-02-09
Publication date: 1975-07-31
Also published as: DE2307363A1; GB1412951A; ES411646A1; BE795564A; FR2172318B1; JPS4893524A; SE383901B; CH579637A5; AU5202773A; FR2172318A1; IT980414B; ATA137573A; IL41482A0; NL7301592A; AT328485B; LU67024A1; US3813239A; CA989208A; ZA73610B

Description

5,2 0 2 7 n3

This invention relates to alloys having good

resistance to corrosion in chloride and in acid media combined with

good hot and cold workability and also weldability. There is a

demand for such alloys for a wide range of applications in

the chemical and other industries. Thus parts of chemical

process plant may be exposed on one side to highly corrosive

acid solutions, and on the other to chloride-containing brackish

or sea water used for cooling or heating. For this purpose

effective resistance is required to stress-corrosion cracking

intergranular corrosion, pitting and crevice corrosion.

Resistance to pitting, crevice corrosion and stress-corrosion is also requiree for articles immersed in sea-water, for example,

woven wire rope for mooring cables and the like, which additionally

require high tensile and yield strength, and cable armouring. Of these types of corrosion, crevice corrosion is a

particularly strong form of attach which can occur in metal or alloy parts possessing recesses or pockets where stagnant

liquid can collect. Such recesses may result, for example,

where two parts are joined together or where the part meets a

gasket or washer, etc. and the liquid which collects may be

that in which the part is immersed or a liquid which is being passed through or round the part. Crevice corrosion is

particularly likely to occur in chloride containing environments. Our object in the present invention is to provide an

economical, corrosion-'resistant alloy suitable for these and a

wide range of other uses.

In our Australian Patent Specification No. 429,305 we have described and claimed alloys containing from 30 to

nickel, from 17 to 22% chromium, from 5.5. to 9.25% molybdenum,

463.540

5,2 02 7 n3 from l.to 3.25% niobium with or without up to 2% tantalum, the niobium content plus half the tantalum content being from 1 to 3.25%, and the contents of nickel, molybdenum and the sum of niobium and one-half the tantalum being correlated with one another, from 0 to 0.03% carbon, from 0 to manganese, from 0 to 1% silicon, from 0 to 0.6% titanium, from 0 to 0.6% aluminium, from 0 to 2% vanadium, from 0 to 2% copper, from 0 to 1% tungsten, from 0 to 0.08% magnesium, from 0 to 0.005% boron, from 0 to 0.05% calcium and from 0 to 0.02% zirconium, the-.balance, except for impurities, being iron.. It is stated in this prior specification that low amounts of niobium, e.g. 0.2 or are ineffective for imparting crevice-corrosion resistance, and at least 1.5% niobium is advantageously present. Moreover the copper content of the alloys is preferably no more than 0.75%. We have now surprisingly found that the best combination of workability with resistance to crevice corrosion in chloride media and resistance to corrosion in acids is exhibited by alloys having niobium contents less than 1% and copper contents of 1.4 to 3.5,in which thereis a special correlation of the contents of nickel, copper, chromium and molybdenum. The alloys according to the present invention contain from 33 to 45% nickel, from 1.4 to 3.5% copper, the sum of the nickel and copper contents being at least 35%, from 14.5 to 20.5% chromium and from 8.5 to 9.5% molybdenum with the value of the expression Cr) Mo)] Ni) Cu)] 4 3 A0

5,2027 n3 being from 99 to 107, from 0 to 0.9% niobium, from 0 to 0.05%

carbon, from 0 to 1% manganese, from 0 to 0.605% boron, from 0

to 0.5% silicon, from 0 to 0.8% titanium, from 0 to C.7% aluminium, from 0 to 0.05% magnesium, from 0 to 0.8% zirconium and from 0 to 0.05% calcium, the, balance, except for impurities, being iron.

It is essential that the alloy constituents be carefully

correlated in order to achieve the desired combination of

properties. Departure from the defined range with respect to any one of the constituents can detrimentally affect one or more of the properties.

Nickel in an amount of at least 33% is necessary for adequate resistance to crevice corrosion resistance but amounts in excess of 45% unduly increase the cost of the alloys. The nickel content preferably does not exceed 41.5% and more

preferably does not exceed 38%.

Copper imparts resistance to corrosion in acid media and an amount of at least 1.4% must be present for this purpose.

However an amount in excess of 3.5% impairs the hot-workability

of the alloys and preferably the copper contents does not exceed In addition the nickel plus copper content must be at least

for adequate resistance to crevice corrosion. The nickel plus copper content preferably does not exceed 43% and more preferably is from 35.4 to 39.4%.

Chromium imparts corrosion resistance in general to the alloys and at least 14.5% is necessary for this purpose, especially with regard to crevice corrosion resistance. Amounts in excess of 20.5% however detrimentally affect crevice corrosion resistance and additionally have an adverse effect on the 463.54 0

5.2 027/73 workability of the alloys. Preferably the chromium content is

from 17 to 18%.

Molybdenum must be present in an amount of from 8.5 to

for imparting resistance to crevice corrosion and amounts below or above this closely defined range are found to adversely

affect this property. Amounts in excess of 9.5% molybdenum additionally lead to bad workability. Preferably the molybdenum content does not exceed 9.3%.

In addition to the above limitations on the alloy composition,

it is also necessary in order to achieve the desired combination

of properties to correlate the nickel, copper, chromium and

molybdenum contents of the alloys so that the value of the

expression:

Cr) Ni) Cu)]

is from 99 to 107.

Niobium can be optionally present in the alloys in an

amount not exceeding 0.9% to stabilise carbides and minimise

intergranular corrosion in the welded condition and preferably

at least 0.3% niobium is present for this purpose. Carbon can also be present in an amount which,in order to avoid weld decay,

must not exceed 0.05%, and preferably should not exceed 0.03%.

If the carbon content does not exceed 0.03%, the niobium content

is preferably less than 0.7%.

While titanium and aluminium may tend to form oxide

inclusions which may impair the surface quality of sheet rolled

from the alloys, the presence of one or both of these elements

in residual amounts up to 0.8% and up to 0.7% respectively

improves the hot-rolling of the alloys and these elements may.

therefore advantageously be added for this purpose. The residual 463.540

52 0 2 7 n3 titanium content is preferably from 0.2 to 0.7% and the

residual aluminium content is preferably from 0.05 to 0.15%.

Titanium may also act in the alloys as a carbide stabiliser.

Preferred alloys of the invention nominally contain

nickel 17.5% chromium, 9% molybdenum and 1.7% copper with or

without 0.5% niobium and 0.5% titanium and a maximum of 0.03% carbon.

The alloys may be made byair melting, preferably in a basic

lined high-frequency induction furnace, though vacuum-melting

may be used if desired. When air-melting is employed it is preferable to deoxidise the alloys with calcium a suitable

addition being 0.05% as calcium silicide, nickel-calcium or

calcium-aluminium. The retained calcium content should not exceed 0.05% and is advantageously from 0.004 to 0.01%. Silicon may also be employed as a primary. deoxidant in its own right and the silicon

content of the alloys arising from such use or arising from the

addition of calcium silicide should not exceed

Other elements that may be used for deoxidation include titanium, aluminium, magnesium, boron, zirconium and manganese. Like

titanium and aluminium, both magnesium and zirconium tend to form

oxide inclusions which may impair the surface quality of sheet but

magnesium up to 0.05% or zirconium up to 0.8% can be advantageously

used to deoxidise the alloys if they are to be extruded before

further hot-working. If manganese is used, no more than 1 1 should be present in the alloys and if boron is used, no more than 0.005%

should be present.

Some examples of alloys according to the invention will now be given. EXAMPLE 1 A forging ingot 80 mm in diameter and weighing 11.5 kg was cast from an alloy containing 33.5% nickel, 17.Ichromium, 8.8% molybdenum, 4635 4 0

5.2 02 7 n3 1.95% copper, 0.48% niobium, 0.035% carbon, 0.27% manganese,

0.27% silicon, 0.48% titanium, 0.47% aluminium, 0.005% calcium,

the balance, apart from impurities, being iron (Alloy No. 1).

The alloy was prepared by vacuum induction melti:, in-cluding a

final step of deoxidation with calcium. The ingot was forged at

11500C to 20 mm thick plate and then hot-rolled to 3 mm plate.

After surface grinding to remove oxidation scale, the plate was

annealed for one hour at 1150°C, descaled in potassium permanganate/

sodium hydroxide solution, and cold-rolled to 1 mm thick sheet.

After cold-rolling the sheet material was again annealed for one

hour at 1150 C. Samples cut from the annealed sheet were

immersed in boiling aqueous solutions of sulphuric and phosphoric

acids for five periods each of 20 hours duration. The average

corrosion rates, calculated from the loss in weight of the samples,

were equivalent to 0.18 mm penetration per year in boiling acid. sulphuric acid and 0.25 mm per year in boiling 75% phosphoric EXAMPLE 2

A 3 kg extrusion ingot cast from the same alloy as in Example 1

was extruded from 50 mm diameter to 16 mm diameter, centreless diameter ground to 8.6 mm diameter and cold drawn to wire 0.25 mm in

with anneals at 1150°C at various stages during the cold reduction.

The cold reduction obtained in the last pass was in excess of

The tensile strength of the 0.25 mm diameter wire in the as-drawn 2 condition was 1780 MN/m.

EXAMPLE 3

A 55 kg heat of an alloy containing 34.5% nickel, 17.7% chromium,

8.6% molybdenum, 1.75% copper, 0.47% niobium, 0.016.% carbon,

0.23% manganese, 0.25% silicon, 0.25% titanium, 0.004% calcium,

4 3.5 4 0

5.2 0 2 7 M3 the balance, apart from impurities being iron (Alloy No. 2).was

prepared by vacuum induction melting, cast to ingots and processed

to 1 mm thick sheet by procedures similar to those described in

Example 1. Crevice corrosion tests were performed by placing

samples 50 mm x 25 mm, cut from the annealed sheet material,

horizontally between two watch glasses so that the convex surfaces

of the watch glasses were in contact with the flat surfaces of the

sample, thus forming crevices near.the points of contact. The

specimen assemblies were immersed in 1% ferric chloride solution

and held therein at a temperature of 600°C for 40 hours. This

test is a searching one and will produce severe corrosion in the

crevice areas of materials susceptible to this form of attack.

Of six identical samples of the alloy tested, four remained

completely free from attack in the crevice regions, while in the

other two cases only a very slight amount of crevice corrosion

occurred, amounting to less than 10 mg loss in weight.

EXAMPLE 4

Pour &lleyo UZo.3 to 6))having the composition shown in

the Table were vacuum melted, cast as 3 kg ingots 50 mm in

diameter, and extruded in mild steel cans at 1200°C to 16 mm

square bar. The bars were heat treated at 12000°C for 4 hour

and quenched in water. The remains of the mild steel cans were

then removed by pickling. Crevice corrosion tests were then

carried out on specimens of this material. Each specimen was

of uniform size and consisted of two parts, the first of which

was a cylindrical sleeve and the second had a narrowed piston-

shaped portion and dimensioned to fit closely within

the first part. The second part

additionally possessed a shcilder on which the first part could 8- 4 3.540

5.2 0 2 7 n3 rest, the shoulder being so shaped that a crevice was formed between the shoulder and the first part. When the two parts were fitted together, the specimenwas essentially cylindrical exter- nally, its diameter being 1 2 .7mm and its length being 45 mm. Each specimen was immersed in 10% ferric chloride s-;luton at for 18 hours. Each specimen was weighed before and after

immersion and the loss in weight is shown in the Table.

4 fi 54 0

5.2 02 7n3

a, U) 0 W 0 %D0 0

:2

t- Ln

o 0

'0 t

o 0

cu cui o 0 o; 0 13 o 0

0 0

Cu

LA 0

LA LAN

0 z

463.54 0

5,2 0 2 7 n3

Comparison of Alloy No 3 whose composition is within the invention with Alloy Nos. 4 and 5 whose composition is outside the invention clearly demonstrates the superiority

of the alloys of the invention in terms of resistance to crevice corrosion. This comparison emphasises the careful control of the molybdenum content necessary to achieve the

desired properties.

The alloys can be readily hot and cold-worked. Thus they can be extruded, rolled or forged for example, at 1150 0 C,

coldrolled to sheet or strip, cold-drawn to wiere and cold-headed.

For optimum cold ductility hot-worked material should be

annealed at about 1150 C, e.g. for about one hour. It is not necessary to water-quench from the annealing temperature, but

very slow cooling such as furnace cooling should be avoided

to minimise the risk of structural instability.

The alloys can readily be welded by the metal-inert gas and tungsten-inert gas techniques.

Articles and parts which may advantageously be made from the alloys include plate heat exchangers, tubular heat

exchangers, marine wire rope, cable armouring, fasteners,

evaporators, e.g. for phosphoric acid or chloride solutions, pulp and paper bleaching plant, and surgical implants. The alloys are also useful for forming overlays on objects which

may be subject to crevice corrosion, e.g. on tube plates,

valve seats and variably pitch propellers.

All the percentages in this specification and claims are by weight.

4 63. 5 4 Q

Claims

5,202 7 n3 The claims defining the invention are as follows: 1. An alloy containing from 33 to 45% nickel, from 1.4 to

copper, the sum of the nickel and copper contents being at

least 35%, from 14.5 to 20.5% chromium and from 8.5 to

molybdenum, with the value of the expression:

Cr) Mo)] Ni) Cu)]

being from 99 to 107, from 0 to 0.9% niobium, from 0 to 0.05%

carbon, from 0 to 1% manganese, from 0 to 0.005% boron,

from 0 to 0.5% silicon, from 0 to 0.8% titanium, from 0 to

0.7% aluminium, from 0 to 0.05% magnesium, from 0 to 0.8%

zirconium and from 0 to 0.05% calcium, the balance, except

for impurities, being iron.
2. An alloy according to claim 1 in which the nickel content does not exceed 41.5%, the copper content does not exceed

and the sum of the nickel and copper contents does not

exceed 43%.
3. An alloy according to claim 2 containing no more than 38% nickel.
4. An alloy according to claim 2 or claim 3 in which the sum

of the nickel and copper contents is from 35.4 to 39.4%.

An alloy according to any one of claims 2 to 4 containing

from 17 to 18% chromium.

6. An alloy according to any one of claims 2 to 5 containing

no more than 9.3% molybdenum.

463.540

7. 2 0 2 7 n3 An alloy according to any cne of claims 2 to 6

cor.taining at least 0.3% niobium.

An alloy according to any one oi claims 2 to 7 containing no more than 0.03;, carbon. 9. An alloy according to any one of claims 2 to 8

ccntaining from 0.2 to 0.7% titanium.

An alloy accordircng to any one of claims 2 to 9

containing from 0.05 to 0.15% aluminium. 11. An alloy according to claim 1 containing nickel, 17.5% chromium, 9% molybdenum, 1.7% copper, niobium, 0.5% titanium and no more than 0.03% carbon.

12. An alloy having substantially the composition of either Alloy No. 1 or Alloy No. 2 herein. 13. An alloy having substantially the composition

of Alloy No. 3 herein.

DATED: 3rd July, 1975.

PHILLIPS ORMONDE AND FITZPATRICK Attorneys for INTERNATIONAL NICKEL LIMITED

0®

4 3.540