Alloy B2, 2.4617, UNS N10665, Hastelloy® B2 - Ni-Mo alloy

Alloy B2, 2.4617, UNS N10665, Hastelloy® B2 - nickel alloy according to ASTM B366, DIN 17750

Alloy B2, 2.4617, Hastelloy® B2 – description

Alloy B-2 is a Ni-Mo alloy, unique in that it contains basically no chromium, an element common to nearly all other corrosion-resistant alloys. The high nickel and molybdenum content gives it superior resistance to hydrochloric acid and other reducing environments, such as high temperature, including applications in the as-welded condition. Without chromium, however, this alloy is vulnerable to corrosion attack in reducing acids contaminated with even traceable amounts of oxidizing salts, like ferric chloride. It is an improved version of Alloy B (which was susceptible to intergranular corrosion attack in weld heat-affected zone), with lower carbon and iron contents. Hastelloy® B-3 and Nicrofer 6628 are very similar to Alloy B-2, but were developed some 20 years later and provide a better level of thermal stability.

Selected standards describing the alloy:

• ASTM B 333, ASME SB-333 - Sheets and plates
• ASTM B 626, ASME SB-626 - Welded pipes
• ASTM B 622, ASME SB-622 - Seamless pipes
• ASTM B 366, ASME SB-366 - Welded fittings
• DIN 17750 - Sheets and plates

Applications

Alloy B-2 is used mostly in chemical processing for equipment handling hydrochloric acid (all concentrations and temperatures), sulfuric acid, acetic acid, and phosphoric acid. It is also used in high-temperature applications when a low coefficient of thermal expansion is required.

In oxidizing gases, such as the air, the alloy B2 can be used up to 540°C. In reducing gases or vacuum, the alloy can be used from 815°C to substantially higher temperatures. Exposure to temperatures ranging 540-815°C should be avoided in any environment, as it results in forming of intermetallic phases Ni₃Mo and Ni₄Mo. Precipitation of these compounds reduces the ductility of the alloy.

Alloy B2, Hastelloy® B-2 - physical and mechanical properties

Room temperature physical properties:

• Density: 9.22 g/cm³
• Specific heat capacity: 373 J/kg⋅K
• Thermal conductivity: 11.1 W/m⋅K
• Coefficient of thermal expansion: 10.3 μm/m⋅K
• Melting temperature: 1300-1350 C

Coefficient of thermal expansion and temperature (linear):

• 20-93°C: 10.3 μm/m⋅K
• 20-204°C: 10.8 μm/m⋅K
• 20-316°C: 11.2 μm/m⋅K
• 20-427°C: 11.5 μm/m⋅K
• 20-538°C: 11.7 μm/m⋅K

Specific heat and temperature:

• 20°C: 373 J/kg⋅K
• 200°C: 406 J/kg⋅K
• 400°C: 431 J/kg⋅K
• 600°C: 456 J/kg⋅K

Thermal conductivity and temperature:

• 20°C: 11.1 W/m·K
• 100°C: 12.2 W/m·K
• 200°C: 13.4 W/m·K
• 300°C: 14.6 W/m·K
• 400°C: 16.0 W/m·K
• 500°C: 17.3 W/m·K
• 600°C: 18.7 W/m·K

Thermal diffusivity and temperature:

• 0°C: 3.2 10^-6⋅m²/s
• 100°C: 3.4 10^-6⋅m²/s
• 200°C: 3.6 10^-6⋅m²/s
• 300°C: 3.8 10^-6⋅m²/s
• 400°C: 4.0 10^-6⋅m²/s
• 500°C: 4.2 10^-6⋅m²/s
• 600°C: 4.5 10^-6⋅m²/s

Electrical resistivity and temperature:

• 0°C: 1.37 μΩ·m
• 100°C: 1.38 μΩ·m
• 200°C: 1.38 μΩ·m
• 300°C: 1.39 μΩ·m
• 400°C: 1.39 μΩ·m
• 500°C: 1.41 μΩ·m
• 600°C: 1.46 μΩ·m

Dynamic modulus of elasticity of solutioned and quenched Hastelloy® B-2 13mm thick plate:

• 20°C: 217 GPa
• 315°C: 202 GPa
• 425°C: 196 GPa
• 540°C: 189 GPa

Tensile properties of sheets and plates, 1.3 to 3.0 mm thick, solutioned and quenched, made of Hastelloy® B-2:

• Room temperature
  • Yield strength: 525 MPa
  • Tensile strength: 965 MPa
  • Elongation: 53 %
  • Hardness HRC: 22
• 400°C
  • Yield strength: 450 MPa
  • Tensile strength: 885 MPa
  • Elongation: 50 %
• 600°C
  • Yield strength: 425 MPa
  • Tensile strength: 860 MPa
  • Elongation: 49 %
• 800°C
  • Yield strength: 415 MPa
  • Tensile strength: 860 MPa
  • Elongation: 51 %

Tensile properties of sheets and plates, 2.5 to 9.0 mm thick, solutioned and quenched, made of Hastelloy® B-2:

• Room temperature
  • Yield strength: 415 MPa
  • Tensile strength: 895 MPa
  • Elongation: 61 %
  • Hardness HRC: 95
• 400°C
  • Yield strength: 350 MPa
  • Tensile strength: 850 MPa
  • Elongation: 59 %
• 600°C
  • Yield strength: 325 MPa
  • Tensile strength: 820 MPa
  • Elongation: 60 %
• 800°C
  • Yield strength: 310 MPa
  • Tensile strength: 805 MPa
  • Elongation: 60 %

Tensile properties of plates, 9 to 50 mm thick, solutioned and quenched, made of Hastelloy® B-2:

• Room temperature
  • Yield strength: 405 MPa
  • Tensile strength: 905 MPa
  • Elongation: 61 %
  • Hardness HRC: 94
• 400°C
  • Yield strength: 360 MPa
  • Tensile strength: 870 MPa
  • Elongation: 60 %
• 600°C
  • Yield strength: 340 MPa
  • Tensile strength: 840 MPa
  • Elongation: 60 %
• 800°C
  • Yield strength: 315 MPa
  • Tensile strength: 820 MPa
  • Elongation: 61 %

Typical room temperature mechanical properties of 2.4617 according to DIN 17750:

• Yield strength: >340 MPa
• Tensile strength: >750 MPa
• Elongation: >40%
• Hardness HBW: <240

Exposure of the allloy B-2 to the temperature ranging from 540 to -815°C makes it very brittle:

• Room temperature elongation: > 40%
• Elongation after being exposed to 760°C for 10 minutes: < 5%

Corrosion behaviour

Alloy B-2 has exceptional resistance to reducing environments, excellent resistance to pitting, stress-corrosion cracking, and crevice corrosion resistance. It has good oxidation resistance, and in oxidizing environments is should not be used above 540°C. It has superior resistance to hydrochloric acid, aluminum chloride and exceptional resistance to hydrogen chloride gas, sulfuric acid, acetic acid and phosphoric acid. It is resistant to knife-line and weld heat-affected zone corrosion attack, thus it is suitable for most chemical process applications in the as-weld condition.

Reducing acids - superior resistance. Highest resistance to hydrochloric acid among all nickel alloys. Average corrosion rates in boiling solutions:

• Acetic acid CH₃COOH, 10%: <0.02 mm/year
• 30%: <0.01 mm/year
• 50%: <0.01 mm/year
• 70%: <0.01 mm/year
• 99%: <0.01 mm/year
• Formic acid CH₂O₂, 10%: <0.01 mm/year
• 20%: <0.02 mm/year
• 30%: <0.02 mm/year
• 40%: <0.02 mm/year
• 60%: <0.02 mm/year
• 89%: <0.02 mm/year
• Hydrochloric acid HCl, 1%: 0.02 mm/year
• 2%: 0.08 mm/year
• 5%: 0.13 mm/year
• 10%: 0.18 mm/year
• 15%: 0.28 mm/year
• 20%: 0.38 mm/year
• Phosphoric acid H₃PO₄, 10%: 0.05 mm/year
• 30%: 0.08 mm/year
• 50%: 0.15 mm/year
• 85%: 0.63 mm/year
• Sulfuric acid H₂SO₄, 2%: <0.02 mm/year
• 5%: 0.08 mm/year
• 10%: 0.05 mm/year
• 20%: <0.02 mm/year
• 30%: <0.02 mm/year
• 40%: <0.03 mm/year
• 50%: 0.03 mm/year
• 50%: 0.03 mm/year (the piece was aged 48h at 540°C)
• 60%: 0.05 mm/year (the piece was aged 48h at 540°C)
• 70%: 0.23 mm/year (the piece was aged 48h at 540°C)

High-temperature hydrochloric acid HCl - tests show rather small metal loss:

• HCl 300 h; 400°C: 0.75 mg/cm²
• HCl 1000 h; 400°C: 0.76 mg/cm²
• HCl 100 h; 500°C: 2.10 mg/cm²
• HCl 300 h; 500°C: 2.65 mg/cm²
• HCl 1000 h; 500°C: 5.87 mg/cm²
• HCl 100 h; 600°C: 12.93 mg/cm²
• HCl 300 h; 600°C: 62.3 mg/cm²
• HCl 96 h; 700°C: 126.4 mg/cm²

Iron and copper salts greatly accelerate corrosion and can form when hydrochloric acid comes into contact with iron or copper, hence Alloy B2 should not be used where iron or copper comes into contact with hydrochloric acid. Corrosion rates increase with higher concentration of Fe:

• 20%, 10ppm Fe³⁺ : ~1.2 mm/year
• 20%, 100ppm Fe³⁺ : ~10.0 mm/year
• 20%, 800ppm Fe³⁺ : ~70.0 mm/year

Resistance to other agents:

• Hydrofluoric acid HF, 20%, 70°C: 0.38 mm/year

Weldability

Basic data: Weldability group 44 (ISO 15608), brazing P-number 112 (ASME section IX).

Selection of welding consumables:

• Filler metals: ERNiMo-7

Postweld heat treatment is not required for the majority of applications, as the alloy does not show any knife-line or HAZ attack. Welding only slightly reduces the corrosion resistance of alloy B2 in a reducing environment. For example, a 20% boiling formic acid solution causes corrosion at a rate of 0.38mm/year for non-welded parts and 0.51mm/year for TIG-welded parts. Additionally, a 50% boiling sulphuric acid solution causes corrosion at a rate of 0.03mm/year for non-welded components and 0.05mm/year for TIG-welded components. To maximize the postweld corrosion resistance apply heat treatment described below.

Heat treatment

Soft annealing should be done in 1095-1185°C for 5-10 min (continuous annealing) or 60 min (batch annealing). The piece should be quenched in water or rapidly cooled in air.

Alloy B2 precipitates harmful intermetallic phases Ni₃Mo and Ni₄Mo when subjected to the temperature ranging from 540 to 815°C, even if the exposure time ranges from 10 to 15 minutes. Therefore both heating and cooling should be as rapid as possible. Charge the treated piece to the furnace that is at the annealing temperature already and use furnaces with large temperature capacity.

Replacements, equivalents and other designations:

Alloy B2, Hastelloy® B-2, EMVAC HB 2 ACO, Alloy B-2, 00Ni70Mo28, H10665, NiMo28, 2.4617, C-NiMo31, NW0665, SNi1066, EP495-VI, N70M-VI, ASTM B 333, ASME SB-333, ASTM B 335, ASME SB-335, ASTM B 366, ASME SB-366, ASTM B 642, ASME SB-462, ASTM SA 494, ASME SA494, ASTM B 564, ASME SB-564, ASTM B 619, ASME SB-619, ASTM B 622, ASME SB-622, ERNiMo-7