What Is ASTM B670 Inconel 718 Coil?
ASTM B670 is the standard specification for precipitation-hardening nickel-chromium-iron alloy (UNS N07718) sheets, plates and strips. Inconel 718 coils manufactured to this standard are designed for high-temperature environments up to about 704°C (1300°F) and are used in applications requiring high creep rupture strength, such as jet engines and gas turbines. The alloy is nonmagnetic and possesses excellent oxidation and corrosion resistance, making it suitable for components that must resist creep, stress rupture and oxidation simultaneously.
Coil Types Available
Hot-rolled coil: produced by hot rolling of the slab or billet, typically used where a thicker gauge and lower cost are acceptable, and often specified as ASME SB670 material for code applications.
Cold-rolled coil: produced by cold rolling the hot-rolled and pickled strip, offering tighter thickness tolerance and a better surface finish for precision components.
Coil sheet: cut-to-length sheets supplied from coil, combining the manufacturing economy of coil with the convenience of sheet formats for stamping and forming.
Specifications and Dimensions
Typical coil specifications cover ASTM B670 and ASME SB670, with thickness from about 0.03 mm to 3 mm, roll width of 3 mm and above, and surface treatments including hot rolled, cold rolled, satin and coated finishes. The exact dimensions and condition should be confirmed against the project requirement, since coil width, gauge and temper affect both formability and final component properties.
Chemical Composition of Inconel 718 Coil
The composition of Inconel 718 coil per typical specification is: nickel 50.00-55.00%, chromium 17.00-21.00%, carbon 0.08% max, manganese 0.35% max, silicon 0.35% max, sulfur 0.015% max and copper 0.30% max, with iron as balance and niobium, molybdenum, titanium and aluminum added for precipitation strengthening. The equivalent grade designation is W.Nr 2.4668, and the UNS number is N07718.
Mechanical Properties
Typical mechanical values for Inconel 718 coil include a density of about 8.2 g/cm3, a melting point around 1350°C, minimum tensile strength of about 930 MPa, yield strength around 482 MPa and elongation of about 45% in the applicable condition. Note that properties vary with heat treatment and delivery condition, so the material certificate should be reviewed for each lot.
Machining Considerations
Inconel 718 has poor thermal conductivity and is prone to rapid strain hardening, which results in demanding machining behavior and surface finish challenges. Rigid setups, sharp tooling, controlled speeds and generous cooling are required to machine the alloy economically. Despite this difficulty, the alloy remains one of the most widely specified superalloys because of its strength, weldability and resistance to strain-age cracking.
Application Industries
Inconel 718 coils are used in petrochemical, shipbuilding, power generation, automotive, pharmaceutical, oilfield drilling platforms, gasket, filter, hose and clamp, metal tower packing and turbine industries. In these sectors the combination of high creep rupture strength, oxidation resistance and corrosion resistance in thin sheet and strip form supports both structural and sealing applications.
FAQ
Q: What standard covers Inconel 718 coil?
A: ASTM B670 is the common specification for Alloy 718 sheet, plate and strip, with ASME SB670 as the pressure-vessel code counterpart.
Q: What temperature can Inconel 718 coil withstand?
A: ASTM B670 Inconel 718 products are designed for high-temperature service up to about 704°C (1300°F), where creep rupture strength is the governing requirement.
Q: Is Inconel 718 coil magnetic?
A: No. Inconel 718 is generally nonmagnetic, which is useful for instrumentation and precision components near magnetic fields.
Q: Why is Inconel 718 difficult to machine?
A: The alloy has poor thermal conductivity and work-hardens rapidly during cutting, leading to poor machinability and surface finish unless rigid setups and controlled parameters are used.
Q: What is the difference between hot-rolled and cold-rolled 718 coil?
A: Hot-rolled coil offers thicker gauge and lower cost, while cold-rolled coil provides tighter tolerance and better surface finish for precision stamping and forming.
Q: What are the equivalent designations for Inconel 718?
A: Inconel 718 is UNS N07718 and W.Nr 2.4668, with nickel 50-55% and chromium 17-21% as the principal elements.
