Home / HAYNES® HR-235® alloy

Principal FeaturesNominal CompositionMetal DustingCarburization ResistanceOxidation ResistanceWeld Solidification Cracking ResistancePhysical PropertiesTensile PropertiesCreep and Stress Rupture StrengthHardness and Grain SizeHeat TreatmentWeldingSpecifications and CodesAlloy Brochure

Principal Features

HAYNES® HR-235® alloy (UNS N06235) is a nickel-chromium-molybdenum-copper material with outstanding resistance to metal dusting. It has no deliberate addition of iron, an element which is detrimental to the performance of alloys under metal dusting conditions. It is resistant to creep-rupture at temperatures under which metal dusting is normally encountered. Having a low silicon and aluminum content, HR-235® alloy is resistant to weld solidification and strain-age cracking. This is an improvement over other alloys intended for metal dusting resistance. It is also available as a filler wire with matching composition.

Applications:

  • Petrochemical plants
  • Syngas production
  • Synthesis of ammonia, methanol, LNG, H2
  • Microchannel High Temperature Reactors
  • High carbon containing gases
  • Direct reduction of iron ores
  • Carbon fiber production
  • Gas-to-liquids (GTL) plants
  • Steam-methane-reforming process

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

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Nominal Composition

Weight %
Nickel Balance
Chromium 31
Molybdenum 5.6
Copper 3.8
Iron 1.5 max
Niobium 1.0 max
Aluminum 0.4 max
Manganese 0.65 max
Silicon 0.6 max
Titanium 0.5 max
Carbon 0.06 max

Metal Dusting

HAYNES® HR-235® alloy has been tested alongside competitive materials in a controlled atmosphere, thermal cycling rig. The reaction gas was H2 + 68% CO + 6% H2O, the carbon activity of which was 2.9 at the reaction temperature. The cycling operation, which was controlled automatically, comprised 45 minutes at the reaction temperature of 1256°F (680°C), followed by a cooling period of 15 minutes, during which the samples rapidly reached a temperature of about 194°F (90°C). The samples were tested for 1,200 (one hour) cycles, with the following results. The formation of filamentary carbon deposits with metallic nanoparticles (coking) is an indicator of the onset of surface damage (pitting).

Alloy Approximate Number of Cycles to Coking Form of Coke
601 48 Grain boundary deposits, pits
602CA 48 Adherent coke, no metal visible
617 48 Numerous small pits, grain boundary deposits
693 24 Numerous small pits
696 100 Attack on grain boundaries
HR-235® 400 Grain boundary deposits, minor pits

Carburization Resistance

In addition to its high resistance to metal dusting, HAYNES® HR-235® alloy also withstands carburization, a degradation process which occurs at lower carbon activities and which negatively affects many metallic materials, as shown in the following chart. The test involved a gas mixture of Ar – 5% H2 – 2% C3H6 at 1800°F (982°C), with a carbon activity of 1; the test duration was 215 h.

Internal Carburization in Ar– 5% H2 – 2% C3H6 at 1800°F (982ºC)

The samples for 800HT, X, and 556® alloys experienced through thickness carburization, hence the values for these three materials would have been greater, had the samples been thicker.

Oxidation Resistance

HAYNES® HR-235® alloy also exhibits good oxidation resistance, as indicated in the following chart. The test was performed in flowing air (55.5 cm3/s) for 1,008 h, with an air cool to room temperature every 168 h.

Measurement of High Temperature Corrosion Attack

To assess the extent of attack (internal and external) of materials caused by oxidation, the following measurements are taken, using metallographic techniques, where A is the original thickness of the sample.

Weld Solidification Cracking Resistance

HAYNES® HR-235® alloy is resistant to weld solidification cracking, as measured by the VARESTRAINT weldability test. Materials with significant silicon contents, such as HR-160® alloy, are prone to this form of cracking, as a result of their wider melting ranges. Having a low silicon and aluminum content, HR-235® alloy is resistant to weld solidification and strain-age cracking. This is an improvement over other alloys intended for metal dusting resistance.  It is also available as a filler wire with matching composition. For more information, visit our Welding and Fabrication Brochure.

Physical Properties

Physical Property British Units Physical Property
Density RT
0.295 lb/in3
 RT
8.16 g/cm3
Melting Range 2401-2437ºF 1316-1356ºC
Electrical Resistivity RT 48.4 μohm-in RT 1.23 μohm-m
200°F 48.8 μohm-in 100°C 1.24 μohm-m
400°F 49.2 μohm-in 200°C 1.25 μohm-m
600°F 49.6 μohm-in 300°C 1.26 μohm-m
800°F 50.4 μohm-in 400°C 1.27 μohm-m
1000°F 50.8 μohm-in 500°C 1.29 μohm-m
1200°F 50.4 μohm-in 600°C 1.29 μohm-m
1400°F 50.4 μohm-in 700°C 1.28 μohm-m
1600°F 50.4 μohm-in 800°C 1.28 μohm-m
1800°F 50.4 μohm-in 900°C 1.28 μohm-m
2000°F 51.2 μohm-in 1000°C 1.28 μohm-m
Thermal Conductivity RT

70 BTU.in/h.ft2.°F

 RT 10.0 W/m.°C
200°F

77 BTU.in/h.ft2.°F

 100°C 11.0 W/m.°C
400°F

89 BTU.in/h.ft2.°F

 200°C 12.5 W/m.°C
600°F

101 BTU.in/h.ft2.°F

 300°C 14.2 W/m.°C
800°F

114 BTU.in/h.ft2.°F

 400°C 15.8 W/m.°C
1000°F

125 BTU.in/h.ft2.°F

 500°C 17.3 W/m.°C
1200°F

137 BTU.in/h.ft2.°F

 600°C 18.9 W/m.°C
1400°F

150 BTU.in/h.ft2.°F

 700°C 20.6 W/m.°C
1600°F

153 BTU.in/h.ft2.°F

 800°C 21.6 W/m.°C
1800°F

164 BTU.in/h.ft2.°F

 900°C 22.3 W/m.°C
2000°F

174 BTU.in/h.ft2.°F

 1000°C 23.5 W/m.°C
Mean Coefficient of Thermal Expansion 70-200°F 6.8 μin/in.°F 25-100°C 12.3 μm/m.°C
70-400°F 7.1 μin/in.°F 25-200°C 12.8 μm/m.°C
70-600°F 7.4 μin/in.°F 25-300°C 13.2 μm/m.°C
70-800°F 7.5 μin/in.°F 25-400°C 13.5 μm/m.°C
70-1000°F 7.7 μin/in.°F 25-500°C 13.8 μm/m.°C
70-1200°F 8.1 μin/in.°F 25-600°C 14.2 μm/m.°C
70-1400°F 8.4 μin/in.°F 25-700°C 14.7 μm/m.°C
70-1600°F 8.7 μin/in.°F 25-800°C 15.2 μm/m.°C
70-1800°F 9.0 μin/in.°F 25-900°C 15.7 μm/m.°C
70-2000°F 9.3 μin/in.°F 25-1000°C 16.2 μm/m.°C
Thermal Diffusivity RT
0.108 ft2/h
 RT
0.0279 cm2/s
200°F
0.116 ft2/h
 100°C
0.0299 cm2/s
400°F
0.127 ft2/h
 200°C
0.0328 cm2/s
600°F
0.139 ft2/h
 300°C
0.0356 cm2/s
800°F
0.151 ft2/h
 400°C
0.0382 cm2/s
1000°F
0.162 ft2/h
 500°C
0.0408 cm2/s
1200°F
0.173 ft2/h
 600°C
0.0434 cm2/s
1400°F
0.183 ft2/h
 700°C
0.0459 cm2/s
1600°F
0.182 ft2/h
 800°C
0.0470 cm2/s
1800°F
0.191 ft2/h
 900°C
0.0475 cm2/s
2000°F
0.200 ft2/h
 1000°C
0.0495 cm2/s
Specific Heat RT 0.105 BTU/lb.°F RT 440 J/kg.°C
200°F 0.109 BTU/lb.°F 100°C 456 J/kg.°C
400°F 0.114 BTU/lb.°F 200°C 477 J/kg.°C
600°F 0.119 BTU/lb.°F 300°C 494 J/kg.°C
800°F 0.124 BTU/lb.°F 400°C 511 J/kg.°C
1000°F 0.133 BTU/lb.°F 500°C 532 J/kg.°C
1200°F 0.148 BTU/lb.°F 600°C 611 J/kg.°C
1400°F 0.146 BTU/lb.°F 700°C 620 J/kg.°C
1600°F 0.152 BTU/lb.°F 800°C 615 J/kg.°C
1800°F 0.152 BTU/lb.°F 900°C 641 J/kg.°C
2000°F 0.153 BTU/lb.°F 1000°C 624 J/kg.°C
Dynamic Modulus of Elasticity RT
29.0 x 106psi
 RT 200 GPa
200°F
28.5 x 106psi
 100°C 196 GPa
400°F
27.6 x 106psi
 200°C 191 GPa
600°F
26.7 x 106psi
 300°C 184 GPa
800°F
25.9 x 106psi
 400°C 180 GPa
1000°F
25.0 x 106psi
 500°C 174 GPa
1200°F
23.9 x 106psi
 600°C 168 GPa
1400°F
23.0 x 106psi
 700°C 162 GPa
1600°F
21.3 x 106psi
 800°C 154 GPa
- - 900°C 144 GPa

Tensile Properties

HAYNES® HR-235® Solution Annealed Plate

Temperature Yield Strength 0.2% Offset Ultimate Tensile Strength Elongation
°F °C ksi MPa ksi MPa %
RT RT 48.8 337 106.9 737 58
1000 538 29.5 203 81.6 562 63
1200 649 28.7 198 72.7 501 61
1400 760 27.7 191 56.5 389 67
1600 871 22.4 154 31.3 216 72
1800 982 11.3 78 16.4 113 72

Creep and Stress Rupture Strength

HR-235® Solution Annealed Plate*

Temperature Creep Approximate Initial Stress to Produce Specified Creep in:
°F °C % 100 h 1000 h
ksi MPa ksi MPa
1000 538 1 57 393 45 310
Rupture 81 558 58 400
1100 593 1 40 276 30 207
Rupture 56 386 38 262
1200 649 1 27 186 19 131
Rupture 38 262 24 165
1300 704 1 17 117 11 76
Rupture 25 172 15 103
1400 760 1 10 69 6 41
Rupture 16 110 9 62
1500 816 1 6 41 4 28
Rupture 10 69 6 41
1600 871 1 4 28 2 14
Rupture 6 41 4 28
1700 927 1 2 14 1 7
Rupture 4 28 2 14

*Preliminary data

Hardness and Grain Size

HAYNES® HR-235® Alloy

Form Solution Annealed Room Temperature Hardness Typical ASTM Grain Size
Sheet 87 HRBW 2 - 4
Plate 85 HRBW 2 - 4

HRBW = Hardness Rockwell “B”, Tungsten Indentor.

Heat Treatment

Wrought HAYNES® HR-235® alloy is furnished in the solution heat treated condition, unless otherwise specified. The alloy is normally solution heat-treated at 2050-2150°F (1121-1177°C) at a time to commensurate with thickness and rapidly cooled or water quenched for optimal properties.

Welding

HAYNES® HR-235® alloy is readily weldable by Gas Tungsten Arc (GTAW) and Gas Metal Arc (GMAW) welding processes. For sheet welds and plate root passes, GTAW is suggested. For plate welds, GMAW is preferred. For GMAW, the pulsed spray transfer mode (GMAW-P) is highly suggested. The GMAW-P transfer mode is a stable, low spatter spray transfer at average current levels significantly below that for conventional spray transfer. This results in low-to-moderate weld heat input, which is important to maintain the material properties of Ni-base alloys.  Submerged arc welding (SAW) is not recommended as this process is characterized by high heat input to the base metal and slow cooling of the weld. The welding characteristics of HR-235® alloy are comparable to the highly weldable “C-type” alloys and the same general welding guidelines apply. Compared to other metal dusting resistant Ni-base alloys, HR-235® alloy exhibits excellent weldability. For further welding details, please click here for the Welding and Fabrication guide, which contains general welding guidelines applicable to HR-235® alloy.

Heat Treatment

Wrought forms of HR-235® alloy are furnished in the solution annealed condition, unless otherwise specified, and should be welded in this condition. Welding of cold-worked materials is strongly discouraged, since it accelerates precipitation of secondary phases and induces residual stresses. As such, a full solution anneal in the range of 2100-2150°F (1149-1177°C), depending on specific requirements, followed by rapid air cool or water quench is suggested. Water quenching is recommended when annealing heavy section components and cold-worked structures prior to welding.

Base Metal Preparation

The joint surface and adjacent area should be thoroughly cleaned before welding. All grease, oil, crayon marks, sulfur compounds, and other foreign matter should be removed. Contact with copper or copper-bearing materials in the joint area should be avoided. It is preferable, but not necessary, that the alloy be in the solution-annealed condition when welded.

Filler Metal Selection

For GTAW and GMAW, HR-235® bare filler wire is suggested. For dissimilar metal welds involving HR-235® alloy, please consult with Haynes International for suggested filler metals.

Preheating, Interpass Temperatures, and Postweld Heat Treatment

Preheat is not required and is generally specified as room temperature. Preheat should not be used if the base metal to be welded is above 32°F (0°C). To minimize the precipitation of second phases in regions affected by the heat of welding, a maximum interpass temperature of 200°F (93°C) is recommended for HR-235® alloy. Auxiliary cooling methods may be used between weld passes, as needed, providing that such methods do not introduce contaminants. Post-weld heat treatment is not normally required or suggested for HR-235® alloy. Heat treatment of welded fabrications may be required for other reasons, such as stress relief.

Tensile Properties of Welded Material

Transverse Tensile – GTAW Welded Sheet

Temperature 0.2% Yield Strength Ultimate Tensile Strength Elongation
°F °C ksi MPa ksi MPa %
RT RT 88.1 607 105.3 726 30
200 93 43.6 300 94.0 648 43
400 204 43.1 297 99.5 686 42
600 316 38.8 268 82.6 570 26
800 427 35.3 243 76.5 527 27
1000 538 37.6 259 86.1 594 38
1200 649 32.8 226 65.1 449 25
1400 760 28.2 194 54.3 374 22
1600 871 22.1 152 29.6 204 31
1800 982 11.0 76 15.9 110 34
2000 1093 5.3 37 7.7 53 37

Transverse Tensile – GTAW Welded Plate

Temperature 0.2% Yield Strength Ultimate Tensile Strength Elongation
°F °C ksi MPa ksi MPa %
RT RT 65.3 450 112.3 774 51
200 93 56.2 387 89.8 619 19
400 204 48.2 332 96.4 665 41
600 316 45.6 314 90.0 621 40
800 427 42.3 292 89.1 614 44
1000 538 44.1 304 74.2 512 23
1200 649 38.1 263 73.5 507 30
1400 760 37.1 256 60.8 419 13
1600 871 23.9 165 33.1 228 25
1800 982 12.3 85 17.9 123 17
2000 1093 7.2 50 9.8 68 19

AWM (All Weld Metal) Tensile – GTAW

Temperature 0.2% Yield Strength Ultimate Tensile Strength Elongation Reduction of Area
°F °C ksi MPa ksi MPa % %
RT RT 80.0 552 115.3 795 26 30
200 93 69.2 477 101.2 698 31 32
400 204 66.7 460 98.3 678 27 27
600 316 67.0 462 94.4 651 26 35
800 427 63.0 434 89.9 620 30 30
1000 538 58.9 406 82.5 569 29 37
1200 649 52.0 359 71.6 494 22 31
1400 760 48.3 333 64.8 447 16 24
1600 871 26.3 181 36.3 250 21 23
1800 982 15.3 105 20.7 143 15 10
2000 1093 9.1 63 12.0 83 20 15

Specifications and Codes

Specifications

HAYNES® HR-235® alloy (N06235)
Sheet, Plate & Strip ASTM B168 
Billet, Rod & Bar ASTM B166
Coated Electrodes -
Bare Welding Rods & Wire -
Seamless Pipe & Tube ASTM B167
Welded Pipe & Tube ASTM B619 ASTM B626 
Fittings ASTM B366
Forgings -
DIN -
TÜV - 
Others -

Codes

HR-235® alloy (N06235)
ASME Section l -
Section lll Class 1 -
Class 2 -
Class 3 -
Section Vlll Div. 1
1600°F (870°C)1
Div. 2 -
Section Xll -
B16.5 -
B16.34 -
B31.1 -
B31.1 -
VdTÜV (doc #) -

1ASME Code Case 3058: Plate, Sheet, Strip, Bar, Rod, Fittings, Seamless Pipe/Tube, Welded Pipe/Tube

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