Alloy 214, 2.4646, UNS N07214, Haynes® 214 - nickel alloy

Alloy 214, 2.4646, NiCr16Al, UNS N07214 - nickel alloy

Alloy 214, 2.4646, Haynes® 214 – description

Alloy 214 is a Ni-Cr-Al-Fe alloy offering the highest oxidation resistance in temperature above 950°C of any nickel or cobalt based alloys.

Up to 900°C, alloy 214 shows similar oxidation resistance to the other top heat-resistant nickel and cobalt alloys. However, above 950°C, while most alloys become more susceptible, alloy 214 gets even more resistant. The cause is the high chromium and aluminium content with the presence of yttrium. The chromium present in most alloys improves oxidation resistance below 950°C, but above this temperature the protective coating it forms begins to dissolve. Alloy 214, thanks to high aluminum content, forms above 950°C a much harder protective scale of aluminium oxides. Yttrium in turn improves its adhesion and prevents spalling. It all results in an unparalelled oxidation resistance above 950°C.

The high aluminium content has its drawbacks - in the temperature range 540-950°C the alloy is hard and not very ductile due to the precipitation of intermetallic gamma prime phases (Ni₃Al). This is particularly evident at 700-760°C, when the elongation falls down to 15%!

Applications

Mainly used in oxidising environments above 955°C.

Haynes® 214, alloy 214 - physical and mechanical properties

Room temperature physical properties:

• Density: 8.05 g/cm³
• Specific heat capacity: 452 J/kg⋅K
• Thermal conductivity: 12 W/m⋅K
• Linear expansion coefficient: 13.3 μm/m⋅K
• Young's Modulus: 218 GPa
• Melting temperature: 1355-1400 °C

High-temperature Coefficient of thermal expansion:

• 20-200°C: 13.3 μm/m⋅K
• 20-300°C: 13.6 μm/m⋅K
• 20-400°C: 14.1 μm/m⋅K
• 20-500°C: 14.6 μm/m⋅K
• 20-600°C: 15.2 μm/m⋅K
• 20-700°C: 15.8 μm/m⋅K
• 20-800°C: 16.6 μm/m⋅K
• 20-900°C: 17.6 μm/m⋅K
• 20-1000°C: 18.6 μm/m⋅K
• 20-1100°C: 17.79 μm/m⋅K

High-temperature Specific heat capacity:

• 20°C: 452 J/kg⋅K
• 200°C: 493 J/kg⋅K
• 400°C: 538 J/kg⋅K
• 600°C: 611 J/kg⋅K
• 800°C: 705 J/kg⋅K
• 900°C: 728 J/kg⋅K
• 1000°C: 742 J/kg⋅K
• 1100°C: 749 J/kg⋅K
• 1200°C: 753 J/kg⋅K

High-temperature Thermal conductivity:

• 20°C: 12.0 W/m · K
• 200°C: 14.2 W/m · K
• 400°C: 18.4 W/m · K
• 600°C: 23.9 W/m · K
• 800°C: 29.7 W/m · K
• 900°C: 31.4 W/m · K
• 1000°C: 32.7 W/m · K
• 1100°C: 34.0 W/m · K
• 1200°C: 36.7 W/m · K

High-temperature Electrical resistivity:

• 20°C: 1.359 μΩ·m
• 200°C: 1.369 μΩ·m
• 400°C: 1.377 μΩ·m
• 600°C: 1.368 μΩ·m
• 800°C: 1.382 μΩ·m
• 900°C: 1.249 μΩ·m
• 1000°C: 1.216 μΩ·m
• 1050°C: 1.209 μΩ·m
• 1100°C: 1.210 μΩ·m
• 1150°C: 1.219 μΩ·m
• 1200°C: 1.229 μΩ·m

High-temperature Dynamic modulus of elasticity:

• 20°C: 218 GPa
• 200°C: 204 GPa
• 400°C: 190 GPa
• 600°C: 177 GPa
• 800°C: 162 GPa
• 900°C: 151 GPa
• 1000°C: 137 GPa

Tensile properties of Haynes® 214 cold-rolled sheets:

• Room temperature
  • Yield strength: 605 MPa
  • Tensile strength: 995 MPa
  • Elongation: 36.8 %
• 540°C:
  • Yield strength: 545 MPa
  • Tensile strength: 865 MPa
  • Elongation: 40.4 %
• 650°C:
  • Yield strength: 565 MPa
  • Tensile strength: 815 MPa
  • Elongation: 25.5 %
• 760°C:
  • Yield strength: 645 MPa
  • Tensile strength: 705 MPa
  • Elongation: 16.3 %
• 870°C:
  • Yield strength: 310 MPa
  • Tensile strength: 400 MPa
  • Elongation: 15.4 %
• 980°C:
  • Yield strength: 54 MPa
  • Tensile strength: 105 MPa
  • Elongation: 61.3 %
• 1095°C:
  • Yield strength: 27 MPa
  • Tensile strength: 58 MPa
  • Elongation: 61 %
• 1150°C:
  • Yield strength: 12 MPa
  • Tensile strength: 32 MPa
  • Elongation: 89.2 %
• 1205°C:
  • Yield strength: 9 MPa
  • Tensile strength: 30 MPa
  • Elongation: 74.8 %

Tensile properties of Haynes® 214 hot-rolled sheets:

• Room temperature
  • Yield strength: 565 MPa
  • Tensile strength: 960 MPa
  • Elongation: 42.8 %
• 540°C:
  • Yield strength: 495 MPa
  • Tensile strength: 825 MPa
  • Elongation: 47.8 %
• 650°C:
  • Yield strength: 525 MPa
  • Tensile strength: 790 MPa
  • Elongation: 33 %
• 760°C:
  • Yield strength: 505 MPa
  • Tensile strength: 670 MPa
  • Elongation: 23.1 %
• 870°C:
  • Yield strength: 345 MPa
  • Tensile strength: 460 MPa
  • Elongation: 33.6 %
• 980°C:
  • Yield strength: 58 MPa
  • Tensile strength: 115 MPa
  • Elongation: 86.4 %
• 1095°C:
  • Yield strength: 29 MPa
  • Tensile strength: 62 MPa
  • Elongation: 88.6 %
• 1150°C:
  • Yield strength: 14 MPa
  • Tensile strength: 46 MPa
  • Elongation: 99.4 %
• 1205°C:
  • Yield strength: 10 MPa
  • Tensile strength: 34 MPa
  • Elongation: 91.5 %

Note the deterioration of ductility at approximately 760°C.

Stress rupture strength:

• 760°C, 100h: 235 MPa
• 760°C, 1000h: 165 MPa
• 760°C, 10 000h: 115 MPa
• 815°C, 100h: 145 MPa
• 815°C, 1000h: 100 MPa
• 815°C, 10 000h: 69 MPa
• 870°C, 100h: 91 MPa
• 870°C, 1000h: 54 MPa
• 870°C, 10 000h: 31 MPa
• 925°C, 100h: 45 MPa
• 925°C, 1000h: 27 MPa
• 925°C, 10 000h: 16 MPa
• 980°C, 100h: 17 MPa
• 980°C, 1000h: 12 MPa
• 980°C, 10 000h: 8,3 MPa
• 1040°C, 100h: 14 MPa
• 1040°C, 1000h: 8,3 MPa
• 1040°C, 10 000h: 5,2 MPa
• 1095°C, 100h: 9,7 MPa
• 1095°C, 1000h: 6,3 MPa
• 1095°C, 10 000h: 4,1 MPa
• 1150°C, 100h: 6,9 MPa
• 1150°C, 1000h: 4,7 MPa
• 1150°C, 10 000h: 3 MPa
• 1200°C, 100h: 5,3 MPa
• 1200°C, 1000h: 3,4 MPa
• 1200°C, 10 000h: 2,3 MPa

0.5% creep-rupture strength of Haynes® 214 sheet:

• 760°C, 100h: 179 MPa
• 760°C, 1000h: 121 MPa
• 760°C, 10 000h: 77 MPa
• 815°C, 100h: 103 MPa
• 815°C, 1000h: 61 MPa
• 870°C, 100h: 52 MPa
• 870°C, 1000h: 31 MPa
• 925°C, 100h: 26 MPa
• 925°C, 1000h: 14 MPa
• 980°C, 100h: 8,3 MPa
• 980°C, 1000h: 5,2 MPa
• 1040°C, 100h: 5,1 MPa
• 1040°C, 1000h: 3,3 MPa
• 1095°C, 100h: 3,8 MPa
• 1095°C, 1000h: 2,2 MPa
• 1150°C, 100h: 2,4 MPa

Corrosion behaviour

High-temperature oxidation - superior resistance of all wrought alloys. At temperatures above 955°C alloy 214 produces an extremely oxygen-resistant protective Al₂O₃ scale, a property unique to this alloy. Below 955°C the alloy develops an somewhat less protective scale which is a mixture of chromium and aluminum oxides.

1008h long static oxidation test results:

• 980°C:
  • Metal loss: 0.0025 mm
  • Average metal affected: 0.005 mm
• 1095°C:
  • Metal loss: 0.0025 mm
  • Average metal affected: 0.0025 mm
• 1150°C:
  • Metal loss: 0.005 mm
  • Average metal affected: 0.0075 mm
• 1205°C:
  • Metal loss: 0.005 mm
  • Average metal affected: 0.018 mm

The alloy has very high resistance to cyclic oxidation, with heating and cooling cycles that better represent the real conditions in processing plants. Based on tests, it is extrapolated that in flowing air at 1095°C in 25-hour cycles, the corrosion rate is 0.2 mm/year. For 168-hour cycles, the rate is 0.025mm/year.

Dynamic oxidation resistance in high-velocity combustion gas stream test results (samples were cycled to less than 260°C once every 30 min):

• 500h, 1090°C:
  • Metal loss: 0.013 mm
  • Average metal affected: 0.046 mm
• 1000h, 980°C
  • Metal loss: 0.01 mm
  • Average metal affected: 0.031 mm

Results of field test in a natural gas-fired furnace. The test took 113 days at 1090-1230°C with frequent cycles to 540°C:

• Metal loss: 0.013 mm
• Maximum metal affected: 0.11 mm

Results of field test in a natural gas-fired tube at 1010°C for 3000h:

• Metal loss: 0.003 mm
• Maximum metal affected: 0.025 mm
• Oxidation rate: 0.076 mm

Please note, that alloy 214 was significantly better than all the other alloys tested in every oxidation test mentioned above.

High-temperature carburization - superior resistance. 24 test in Ar-5H₂-5CO-5CH₄ at 1090°C showed low carbon absorption of only 3,4 mg/cm². This was the best result of all the alloys taking part in the study. In fact, the next best performer, alloy 600, absorbed 3 time more carbon than alloy 214.

High-temperature nitridation - good resistance at temperatures below 950°C and excellent resistance at temperatures above 950°C, provided that even a small amount of oxidising agents are present which can cause the formation of a protective aluminium oxide scale.

This is confirmed by the following comparison of test results. In each, alloy 214 was exposed to ammonia for 168h. Note the beneficial effect of the higher temperatures:

• 650°C
  • Nitrogen absorption: 1.5 mg/cm²
  • Depth of nitride penetration: 0.04 mm
• 980°C
  • Nitrogen absorption: 0.3 mg/cm²
  • Depth of nitride penetration: 0.04 mm
• 1090°C
  • Nitrogen absorption: 0.2 mg/cm²
  • Depth of nitride penetration: 0.02 mm

Halogenation - excellent resistance, when oxidising agents and very high temperature enable the alloy to produce protective oxide scale.

Total depth of attack in Ar-20O₂-0.25Cl₂ after 400h of testing:

• 700°C: 0.010 mm
• 800°C: 0.061 mm
• 850°C: 0.066 mm
• 900°C: 0.150 mm
• 1000°C: 0.051 mm

Weldability

Alloy 214 forms gamma prime phase precipitates (Ni₃Al), which harden the alloy. Stress caused by welding combined by mechanical deformation caused by the precipitation may cause cracking. Please adhere to following good practice.

• Base metal should be solution-annealed and rapid-quenched
• Minimize heat input and restraint
• Keep the surface clean
• Maintain interpass temperature of 84°C max.

Postweld annealing may be needed depending on the part thickness and complexity. If parts will be in service at temperatures below 950°C, postweld annealing is suggested. The procedure: heat to 1000-1100°C for 5 min, then cool in air or in water.

Selection of welding consumables:

• Hastelloy® X (Electrode); Haynes® 230-W, Hastelloy® S, Hastelloy® W (Filler metal)
• Joining with 0-9% Ni steel: Haynes® 556 (Filler metal)

Heat treatment, working and machining

Recommended working and heat treatment parameters:

• Hot working: 1200-980 °C
• Soft annealing: 1065-1120 °C

Hot working procedure - during the heat up, if the piece hast both large and small cross-sections, equilibrate it at about 870°C. The best overall results seem to be achieved by working from a furnace temperature near 1150°C. Stop the operation when the piece reaches 980°C. Perform soft annealing.

Alloy 214 can be cold worked, though subsequent soft annealing is required. Cold working promotes high-temperature ductility.

Soft annealing procedure - all cold or hot-worked parts should be annealed and rapidly cooled in order to restore the best balance of properties. if the hot working is not yet fully complete, the piece is allowed to air cool to ambient temperature after annealing.

Optimum creep and stress rupture properties can be achieved by increasing the treating temperature and by increasing hot working temperature and scope. This leads, however, to reduced ductility in the intermediate temperature range of 650-950°C and increases the tendency of strain age cracking to occur during welding.

Optimum weldability can be achieved be decreasing the treatment and work temperatures as well as the scope of working. Rapid cooling after the treatment is substantial.

Increased room temperature hardness, strength and difficulty of machining is to be expected, when a product is stress relieved at temperatures below 1065°C or slow cooled. It is the result of gamma prime precipitation.

We deliver this steel alloy as strips, plates and sheets.

Replacements, equivalents and other designations:

Haynes® 214, alloy 214, 2.4646, NiCr16Al, N07214