Alloy 801, UNS N08801, Incoloy 801® - Nickel Alloy

Alloy 801, UNS N08801, Incoloy® 801 - nickel alloy according to AMS 5552, ASTM B 163 etc.

Alloy 801, N08801, Incoloy 801 – description

Alloy 801 (UNS N08801) is an iron-nickel-chromium alloy with titanium alloying addition. It is very similar to Alloy 800 with a higher titanium content, optimized for resistance to stress corrosion cracking in polythionic acid environments. Apart from this, it is heat-resistant, corrosion-resistant in seawater, fairly resistant to stress corrosion cracking, organic acids, and nitric acid.

Applications

Used in applications featuring polythionic acid, for example hydrodesulfurizers in petrochemical processing.

Physical and Tensile Properties

Room temperature physical properties:

• Density: 7.94 g/cm³
• Liquidus Temperature: 1385 °C
• Solidus Temperature: 1355 °C
• Coefficient of Thermal Expansion 20-540°C: 17.3 μm/m⋅K
• Specific Heat Capacity: 452 J/kg⋅K
• Thermal Conductivity: 12.4 W/m · K
• Electrical Conductivity: 1.7 % IACS
• Electrical Resistivity: 1.012 μΩ·m

Stress Rupture Strength of Incoloy 801:

• 650°C: 100h; 250 MPa
• 730°C: 100h; 145 MPa
• 815°C: 100h; 62 MPa

High-Temperature Mechanical Properties of alloy 801 bars:

• 20°C:
  • Yield strength: 385 MPa
  • Tensile strength: 785 MPa
  • Elongation: 30 %
• 540°C:
  • Yield strength: 310 MPa
  • Tensile strength: 660 MPa
  • Elongation: 28 %
• 760°C:
  • Yield strength: 290 MPa
  • Tensile strength: 325 MPa
  • Elongation: 55 %

Mechanical Properties of Tubes according to ASTM B 407:

• Yield Strength: >170 MPa
• Tensile Strength: >450 MPa
• Elongation: 30%

Corrosion Resistance

Polythionic acid solutions: Alloy 801's titanium stabilization helps to avoid chromium depletion at grain boundaries, significantly reducing its susceptibility to intergranular SCC in polythionic acid environments compared to Alloy 800 and Alloy 600, which lacks this protective mechanism. Sensitization of Alloy 800 and Alloy 600 in 650 °C for 4 hours makes it susceptible to intergranular stress corrosion cracking in polythionic acid solutions. The susceptibility is related to the existence of chromium-depleted region along grain boundaries, caused by the intergranular precipitation of chromium carbides. Titanium stabilization in Alloy 801 prevents chromium from binding with carbon, thus maintaining a higher chromium concentraton at the grain boundaries.

Hydrogen Environmental Embrittlement susceptibility assesment according to NASA: HEE Index 0.87 (high embrittlement category); Degradation type: Internal Hydrogen Embrittlemen, a result mostly of an unintentional introduction of hydrogen into the alloy during forming or finishing operations, for example acid pickling, electroplating, corrosive and cathodic charging.

Heat Treatment, Working and Machining

Manual spinning parameters: max hardness 88 HRB, max thickness 0.94 mm.

Best machined in the cold-drawn or cold-drawn and stress-relieved conditions. Machining parameters with high-speed steel tools are as follows:

• In the cold-drawn state:

  • Roughing: speed of 15 m/min with a feed rate of 0.25 mm/rev
  • Finishing machining: speed of 18 m/min with a feed rate of 0.13 mm/rev

• In the cold-drawn and tempered state:

  • Preliminary machining: speed of 8 m/min with a feed rate of 0.76 mm/rev
  • Finishing machining: speed of 10 m/min with a feed rate of 0.2 mm/rev

Weldability

Decent weldability. Significant titanium addition may increase the sensitivity of the weld to hot cracking.

We deliver this steel alloy as:

• Plates, strips and sheets according to AMS 5552
• Comdenser and heat exchanger tube according to ASTM B 163 / ASME SB-163
• Seamless pipes according to ASTM B 407 / ASME SB-407; ASTM B 829 / ASME SB-829