Principal Features

A versatile Ni-Cr-Mo alloy with extremely high resistance to HAZ sensitization

HASTELLOY® C-4 alloy (UNS N06455) is the most (microstructurally) stable of the widely used nickel-chromium-molybdenum materials, which are well known for their resistance to many aggressive chemicals, in particular hydrochloric acid, sulfuric acid, and chlorides. This stability means that the alloy can be welded without fear of sensitization, i.e. the nucleation and growth of deleterious, second phase precipitates in the grain boundaries of the weld heat-affected zone (HAZ).

Like other nickel alloys, it is ductile, easy to form and weld, and possesses exceptional resistance to stress corrosion cracking in chloride-bearing solutions (a form of degradation to which the austenitic stainless steels are prone). With its high chromium and molybdenum contents, it is able to withstand both oxidizing and non-oxidizing acids, and is resistant to pitting and crevice attack in the presence of chlorides and other halides.

*Please contact our technical support team if you have technical questions about this alloy.

Nominal Composition

Weight %
Nickel 65 Balance
Cobalt 2 max.
Chromium 16
Molybdenum 16
Iron 3 max.
Manganese 1 max.
Titanium 0.7 max.
Silicon 0.08 max.
Carbon 0.01 max.
Copper 0.5 max.

Thermal Stability (T-T-S Chart)

The above chart illustrates the large difference between the grain boundary precipitation kinetics of C-4 and C-276 alloys. It indicates that C-4 alloy must be held at the most critical temperature (825°C) for 2 hours before grain boundary precipitation is sufficient to cause preferential grain boundary attack of a significant nature, that is to a depth of 0.05 mm in the ASTM G 28A test solution (50% H2SO4 + 42 g/l Fe2(SO4)3 at the boiling point). On the other hand, C-276 alloy is prone to significant grain boundary attack in this boiling solution after just 3 minutes at temperatures in the approximate range 925°C to 1050°C. This means that, during welding, heat input is important in the case of C-276 alloy, but of little consequence in the case of C-4 alloy.

Iso-Corrosion Diagrams

Each of these iso-corrosion diagrams was constructed using numerous corrosion rate values, generated at different acid concentrations and temperatures. The blue line represents those combinations of acid concentration and temperature at which a corrosion rate of 0.1 mm/y (4 mils per year) is expected, based on laboratory tests in reagent grade acids. Below the line, rates under 0.1 mm/y are expected. Similarly, the red line indicates the combinations of acid concentration and temperature at which a corrosion rate of 0.5 mm/y (20 mils per year) is expected. Above the line, rates over 0.5 mm/y are expected. Between the blue and red lines, corrosion rates are expected to fall between 0.1 and 0.5 mm/y.

Comparative 0.1 mm/y Line Plots

To compare the performance of HASTELLOY C-4 alloy with that of other materials, it is useful to plot the 0.1 mm/y lines. In the following graphs, the lines for C-4 alloy are compared with those of two popular, austenitic stainless steels (316L and 254SMO), a lower-molybdenum nickel alloy (625), and C-276 alloy in hydrochloric and sulfuric acids. At hydrochloric acid concentrations above about 5%, C-4 alloy provides a quantum improvement over the stainless steels, and offers greater resistance to higher concentrations of both acids than alloy 625. The concentration limit of 20% hydrochloric acid is the azeotrope, beyond which high temperature corrosion tests are less reliable.

Selected Corrosion Data

Hydrochloric Acid

Conc. 50°F 75°F 100°F 125°F 150°F 175°F 200°F 225°F Boiling
10°C 24°C 38°C 52°C 66°C 79°C 93°C 107°C
1 <0.01 <0.01 <0.01 0.10 0.48
1.5
2 0.01 0.03 1.99
2.5
3 0.02 0.04
3.5
4
4.5
5 <0.01 0.27 0.42 0.98 4.37
7.5
10 0.06 0.19 0.30 0.57 1.11 6.91
15 0.06 0.18 0.39 0.57 1.33 2.33 6.35
20 0.05 0.14 0.27 0.55 1.12 2.19 5.72

All corrosion rates are in millimeters per year (mm/y); to convert to mils (thousandths of an inch) per year, divide by 0.0254.
Data are from Corrosion Laboratory Jobs 2-74 and 73-96.
All tests were performed in reagent grade acids under laboratory conditions; field tests are encouraged prior to industrial use.

Sulfuric Acid

Conc. 75°F 100°F 125°F 150°F 175°F 200°F 225°F 250°F 275°F 300°F 350°F Boiling
24°C 38°C 52°C 66°C 79°C 93°C 107°C 121°C 135°C 149°C 177°C
1
2
3
4
5 0.01 0.02 0.41
10 <0.01 0.01 0.03 0.19 0.43
20 0.01 0.05 0.38 0.89
30 <0.01 0.02 0.07 0.54 1.85
40 <0.01 0.03 0.38 0.87 3.63
50 0.02 0.01 0.03 0.63 0.99 9.96
60 0.03 0.15 0.67 1.24
70 0.04 0.06 0.14 0.46 0.94
80 0.04 0.13 1.10 2.47
90 0.04 0.05 0.19 0.71 2.63
96

All corrosion rates are in millimeters per year (mm/y); to convert to mils (thousandths of an inch) per year, divide by 0.0254.
Data are from Corrosion Laboratory Jobs 19-73, 24-94, and 68-96.
All tests were performed in reagent grade acids under laboratory conditions; field tests are encouraged prior to industrial use.

 Reagent Grade Solutions, mm/y

Chemical Conc. 100°F 125°F 150°F 175°F 200°F Boiling
38°C 52°C 66°C 79°C 93°C
Hydrobromic Acid 2.5 <0.01 <0.01 0.08
5 <0.01 0.01 0.76
7.5 0.03 0.18 0.76
10 <0.01 0.37 0.53
15 <0.01 0.24 0.37 0.56
20 0.15 0.24 0.35 0.51
30 0.10 0.16 0.23 0.41 0.67
40 0.11 0.17 0.28 0.44
Hydrochloric Acid 1 <0.01 <0.01 <0.01 0.10 0.48
2 0.01 0.03 1.99
3 0.02 0.04
5 <0.01 0.27 0.42 0.98
10 0.19 0.30 0.57 1.11
15 0.18 0.39 0.57 1.33
20 0.14 0.27 0.55 1.12
Hydrofluoric Acid* 5 0.59
Sulfuric Acid 10 <0.01 0.01 0.03 0.19 0.43
20 0.01 0.05 0.38 0.89
30 <0.01 0.02 0.07 0.54 1.85
40 <0.01 0.03 0.38 0.87
50 0.02 0.01 0.03 0.63 0.99
60 0.03 0.15 0.67 1.24
70 0.04 0.06 0.14 0.46 0.94
80 0.04 0.13 1.10 2.47
90 0.04 0.05 0.19 0.71 2.63

Resistance to Pitting and Crevice Corrosion

HASTELLOY C-4 alloy exhibits high resistance to chloride-induced pitting and crevice attack, forms of corrosion to which the austenitic stainless steels are particularly prone. To assess the resistance of alloys to pitting and crevice attack, it is customary to measure their Critical Pitting Temperatures and Critical Crevice Temperatures in acidified 6 wt.% ferric chloride, in accordance with the procedures defined in ASTM Standard G 48. These values represent the lowest temperatures at which pitting and crevice attack are encountered in this solution, within 72 hours. For comparison, the values for 316L, 254SMO, 625, and C-4 alloys are as follows:

Alloy Critical Pitting Temperature Critical Crevice Temperature
°F °C °F °C
316L 59 15 32 0
254SMO 140 60 86 30
625 212 100 104 40
C-4 212 100 122 50

Other chloride-bearing environments, notably Green Death (11.5% H2SO4 + 1.2% HCl + 1% FeCl3 + 1% CuCl2) and Yellow Death (4% NaCl + 0.1% Fe2(SO4)3 + 0.021M HCl), have been used to compare the resistance of various alloys to pitting (using tests of 24 hours duration). In Green Death, the lowest temperature at which pitting has been observed in C-4 alloy is 85°C. In Yellow Death, C-4 alloy has not exhibited pitting at temperatures up to 120°C (the maximum to which C-4 alloy has been exposed).

Resistance to Stress Corrosion Cracking

One of the chief attributes of the nickel alloys is their resistance to chloride-induced stress corrosion cracking. A common solution for assessing the resistance of materials to this extremely destructive form of attack is boiling 45% magnesium chloride (ASTM Standard G 36), typically with stressed U-bend samples. As is evident from the following results, the two nickel alloys, C-4 and 625, are much more resistant to this form of attack than the comparative, austenitic stainless steels. The tests were stopped after 1,008 hours (six weeks).

Alloy Time to Cracking
316L 2 h
254SMO 24 h
625 No Cracking in 1,008 h
C-4 No Cracking in 1,008 h

Physical Properties

Physical Property British Units Metric Units
Density RT
0.312 lb/in3
RT
8.64 g/cm3
Electrical Resistivity RT 49.1 μohm.in RT 1.25 μohm.m
200°F 49.1 μohm.in 100°C 1.25 μohm.m
400°F 49.6 μohm.in 200°C 1.26 μohm.m
600°F 50.0 μohm.in 300°C 1.27 μohm.m
800°F 50.5 μohm.in 400°C 1.28 μohm.m
1000°F 51.3 μohm.in 500°C 1.29 μohm.m
600°C 1.32 μohm.m
Thermal Conductivity RT
70 Btu.in/h.ft2.°F
RT 10.1 W/m.°C
200°F
79 Btu.in/h.ft2.°F
100°C 11.4 W/m.°C
400°F
92 Btu.in/h.ft2.°F
200°C 13.2 W/m.°C
600°F
105 Btu.in/h.ft2.°F
300°C 15.0 W/m.°C
800°F
119 Btu.in/h.ft2.°F
400°C 16.7 W/m.°C
1000°F
133 Btu.in/h.ft2.°F
500°C 18.4 W/m.°C
600°C 20.5 W/m.°C
Mean Coefficient of Thermal Expansion 68-200°F 6.0 μin/in.°F 24-100°C 10.9 μm/m.°C
68-400°F 6.6 μin/in.°F 24-200°C 11.8 μm/m.°C
68-600°F 7.0 μin/in.°F 24-300°C 12.5 μm/m.°C
68-800°F 7.2 μin/in.°F 24-400°C 12.9 μm/m.°C
68-1000°F 7.4 μin/in.°F 24-500°C 13.2 μm/m.°C
68-1200°F 7.5 μin/in.°F 24-600°C 13.4 μm/m.°C
Specific Heat 32°F 0.097 Btu/lb.°F 0°C 406 J/kg.°C
200ºF 0.102 Btu/lb.°F 100°C 427 J/kg.°C
400ºF 0.107 Btu/lb.°F 200°C 448 J/kg.°C
600ºF 0.111 Btu/lb.°F 300°C 465 J/kg.°C
800ºF 0.115 Btu/lb.°F 400°C 477 J/kg.°C
1000ºF 0.118 Btu/lb.°F 500°C 490 J/kg.°C
600°C 502 J/kg.°C
Dynamic Modulus of Elasticity RT
30.8 x 106psi
RT 212 GPa
200°F
30.2 x 106psi
100°C 208 GPa
400°F
29.3 x 106psi
200°C 202 GPa
600°F
28.3 x 106psi
300°C 196 GPa
800°F
27.3 x 106psi
400°C 190 GPa
1000°F
26.2 x 106psi
500°C 183 GPa
1200°F
25.0 x 106psi
600°C 176 GPa

RT= Room Temperature

Impact Strength

Test Temperature Impact Strength
°F °C ft-lbf J
RT RT 281 381
-320 -196 215 292

Limited data
Impact strengths were generated using Charpy V-notch samples, machined from mill annealed plate.

Tensile Strength and Elongation

Form Test Temperature Thickness 0.2% OffsetYield Strength Ultimate TensileStrength Elongation
°F °C in mm ksi MPa ksi MPa %
Sheet RT RT 0.065 1.7 60.3 416 111.4 768 52
Sheet 400 204 0.065 1.7 58.5 403 102.4 706 49
Sheet 600 316 0.065 1.7 53.8 371 97.9 675 52
Sheet 800 427 0.065 1.7 46.4 320 95.2 656 64
Sheet RT RT 0.125 3.2 61.0 421 116.2 801 54
Sheet 400 204 0.125 3.2 46.4 320 98.3 678 54
Sheet 600 316 0.125 3.2 43.9 303 97.5 672 59
Sheet 800 427 0.125 3.2 43.9 303 93.4 644 62
Sheet 1000 538 0.125 3.2 43.4 299 93.5 645 55
Sheet RT RT 0.156 4.0 53.0 365 113.5 783 55
Sheet 400 204 0.156 4.0 39.9 275 99.9 689 55
Sheet 600 316 0.156 4.0 36.1 249 95.3 657 61
Sheet 800 427 0.156 4.0 36.2 250 95.1 656 68
Plate RT RT 0.250 6.3 48.8 336 111.3 767 58
Plate 400 204 0.250 6.3 42.8 295 104.0 717 54
Plate 600 316 0.250 6.3 40.8 281 103.3 712 55
Plate 800 427 0.250 6.3 37.0 255 99.0 683 60
Plate RT RT 0.375 9.5 51.6 356 114.7 791 59
Plate 400 204 0.375 9.5 43.6 301 105.4 727 56
Plate 600 316 0.375 9.5 39.1 270 102.1 704 59
Plate 800 427 0.375 9.5 37.4 258 96.3 657 62
Plate 1000 538 0.375 9.5 33.0 228 93.3 643 52
Plate RT RT 0.500 12.7 48.6 335 116.8 805 63
Plate 400 204 0.500 12.7 38.3 264 105.2 725 61
Plate 600 316 0.500 12.7 35.8 247 102.5 707 65
Plate 800 427 0.500 12.7 34.2 236 99.8 688 66
Plate 1000 538 0.500 12.7 29.8 205 92.1 635 71

RT= Room Temperature

Hardness

Form Hardness, HRBW Typical ASTM Grain Size
Sheet 92 6 – 7.5
Plate 90 4 – 6

All samples tested in solution-annealed condition.

HRBW = Hardness Rockwell “B”, Tungsten Indentor.

Welding and Fabrication

HASTELLOY® C-4® alloy is very amenable to the Gas Metal Arc (GMA/MIG), Gas Tungsten Arc (GTA/TIG), and Shielded Metal Arc (SMA/Stick) welding processes. For matching filler metals (i.e. solid wires and coated electrodes) that are available for these processes, and welding guidelines, please click here.

Wrought products of HASTELLOY® C-4®alloy are supplied in the Mill Annealed (MA) condition, unless otherwise specified. This solution annealing procedure has been designed to optimize the alloy’s corrosion resistance and ductility. Following all hot forming operations, the material should be re-annealed, to restore optimum properties. The alloy should also be re-annealed after any cold forming operations that result in an outer fiber elongation of 7% or more. The annealing temperature for HASTELLOY® C-4® alloy is 1066°C (1950°F), and water quenching is advised (rapid air cooling is feasible with structures thinner than 10 mm (0.375 in). A hold time at the annealing temperature of 10 to 30 minutes is recommended, depending on the thickness of the structure (thicker structures need the full 30 minutes). For more details concerning the heat treatment of HASTELLOY® C-4® alloy alloy, please click here.

HASTELLOY® C-4® alloy can be hot forged, hot rolled, hot upset, hot extruded, and hot formed. However, it is more sensitive to strain and strain rates than the austenitic stainless steels, and the hot working temperature range is quite narrow. For example, the recommended start temperature for hot forging is 1177°C (2150°F) and the recommended finish temperature is 954°C (1750°F). Moderate reductions and frequent re-heating provide the best results, as described here. This reference also provides guidelines for cold forming, spinning, drop hammering, punching, and shearing. The alloy is stiffer than most austenitic stainless steels, and more energy is required during cold forming. Also, HASTELLOY® C-4® alloy work hardens more readily than most austenitic stainless steels, and may require several stages of cold work, with intermediate anneals.

While cold work does not usually affect the resistance of HASTELLOY® C-4® alloy to general corrosion, and to chloride-induced pitting and crevice attack, it can affect resistance to stress corrosion cracking. For optimum corrosion performance, therefore, the re-annealing of cold worked parts (following an outer fiber elongation of 7% or more) is important.

Specifications and Codes

Specifications

HASTELLOY® C-4 alloy (N06455, W86445)
Sheet, Plate & Strip SB 575/B 575P= 43
Billet,  Rod & Bar SB 574/B 574P= 43
Coated Electrodes SFA 5.11/ A 5.11 (ENiCrMo-7)F=43
Bare Welding Rods & Wire SFA 5.14/ A 5.14 (ERNiCrMo-7)F= 43
Seamless Pipe & Tube SB 622/B 622P= 43
Welded Pipe & Tube SB 619/B 619P= 43
Fittings SB 366/B 366P= 43
Forgings
DIN 17744 No. 2.4610 NiMo16Cr16Ti
TÜV Werkstoffblatt 424Kennblatt 2666.02Kennblatt 2667.02Kennblatt 2665.02
Others NACE

Codes

HASTELLOY® C-4 alloy (N06455, W86455)
ASME Section l
Section lll Class 1
Class 2
Class 3
Section Vlll Div. 1 800°F (427°C)1
Div. 2 800°F (427°C)2
Section Xll 800°F (427°C)2
B16.5 800°F (427°C)3
B16.34 800ºF (427°C)4
B31.1
B31.3 800°F (427°C)1
VdTÜV (doc #) 752°F (400ºC)5, #424

1Plate, Sheet, Bar, fittings, welded pipe/tube, seamless pipe/tube
2Plate, Sheet, Bar, welded pipe/tube, seamless pipe/tube
3Plate, Forgings, fittings
4Plate, Bar, Forgings, seamless pipe/tube
5Plate, Sheet, Bar, Forgings, seamless pipe/tube

Disclaimer

Haynes International makes all reasonable efforts to ensure the accuracy and correctness of the data displayed on this site but makes no representations or warranties as to the data’s accuracy, correctness or reliability. All data are for general information only and not for providing design advice. Alloy properties disclosed here are based on work conducted principally by Haynes International, Inc. and occasionally supplemented by information from the open literature and, as such, are indicative only of the results of such tests and should not be considered guaranteed maximums or minimums.  It is the responsibility of the user to test specific alloys under actual service conditions to determine their suitability for a particular purpose.

For specific concentrations of elements present in a particular product and a discussion of the potential health affects thereof, refer to the Safety Data Sheets supplied by Haynes International, Inc.  All trademarks are owned by Haynes International, Inc., unless otherwise indicated.

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