NI · superalloy
Nickel Superalloy Inconel 738 (cast, vacuum melted)
A cast nickel superalloy for turbine blades, supplied as a casting rather than bar. The cast skin is abrasive and hard, and the alloy work-hardens like 718.
Quoting this material
- Typical lead time
- 25–40 working days
- Condition
- Investment cast, then solution treated and aged
- Achievable finish
- Ra 3.2 µm (as cast) typical · Ra 0.8 µm best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
A cast nickel superalloy for turbine blades, supplied as a casting rather than bar. The cast skin is abrasive and hard, and the alloy work-hardens like 718.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength (cast) | ~1,000 | MPa |
| Creep resistance | To 980 | °C |
| Hardness (cast, aged) | ~380 | HB |
| Casting form | Investment, vacuum melted | - |
| Thermal conductivity | 11.1 | W/m·K |
| Weldability | Poor (repair only, controlled) | - |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Investment cast, then solution treated and aged
Heat treatment
Solution treat and age after casting. The whole point of the alloy is creep and oxidation resistance at 850–980 °C in a cast form, which a wrought alloy cannot match at that temperature.
Achievable surface finish
Ra 3.2 µm (as cast)
Ra 0.8 µm
Cast surfaces are usually machined only where a fit or a seal is needed; the rest of the blade stays as cast.
Tooling and cutting parameters
Cutting speed
- 15–35 m/min (carbide)
Feed
- 0.05–0.12 mm/rev turning · 0.04–0.08 mm/tooth milling
Tooling
- Fine-grain carbide, tough substrate; remove the cast skin with a ceramic or a dedicated roughing grade
Coolant
- High-pressure flood, and the casting skin will consume the first tool
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Turbine blades and vanes
- Industrial gas turbine hot section
- Aerospace engine hot components
- Power generation turbine parts
- High-temperature cast structural parts
DFM notes for this grade
- Machining a casting means starting from a shape you did not design: the stock allowance varies, so the first operation is to establish a datum from the casting, not to a nominal size
- The as-cast skin is abrasive and often decades-hardened at the surface; expect the first tool to be consumed removing it
- Repair welding is limited and controlled - a casting with a defect is usually replaced rather than repaired in a job shop
Questions buyers ask
- Why is a turbine blade cast rather than machined from bar?
- Because the properties needed at 900 °C cannot be produced in a wrought bar, and the internal cooling passages of a modern blade cannot be machined. Casting gives the shape and the creep resistance; machining only produces the root and tip fits.
- What does a shop actually machine on a turbine blade?
- The root fixing - the fir-tree or dovetail that locates the blade in the disc - and the tip. Those are the tolerance-critical features; the aerofoil and the cooling holes are produced by the casting and the subsequent processes.
Grades we would quote instead
Inconel 718
1/10The bottom of our scale and the reason the scale exists.
Waspaloy
1/10A precipitation-hardened nickel alloy for turbine discs: harder than 718 at temperature and comparable to machine, which is to say slowly and with planned tool consumption.
Hastelloy X
2/10A nickel-chromium-iron-molybdenum alloy for high-temperature structural service.