Inconel 718 vs C3604 Brass: which one fits your part
Inconel 718 is a nickel chromium super alloy that holds strength at high temperature. It is used for turbine, downhole and high temperature parts where creep and oxidation set the limit. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.
It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, food processing is used as the example: surfaces that clean down between production runs.
The short answer
Inconel 718 and C3604 Brass overlap, but they are not interchangeable. Choose Inconel 718 when the requirement is turbine, downhole and high temperature parts where creep and oxidation set the limit; choose C3604 Brass when the requirement is fittings, connectors and turned components where machinability drives the cost.
Side by side
| Point of comparison | Inconel 718 | C3604 Brass |
|---|---|---|
| What it is | a nickel chromium super alloy that holds strength at high temperature | a free cutting brass with lead, the standard choice for turned parts that have to be fast to make |
| Used for | turbine, downhole and high temperature parts where creep and oxidation set the limit | fittings, connectors and turned components where machinability drives the cost |
| Typical tolerance | ±0.02 mm | ±0.01 mm |
| Surface finish | Ra 1.6 µm as machined | Ra 0.8 µm achievable directly from the tool |
| Cost driver | tool consumption and cutting time | material cost is moderate, and the cycle time is the lowest of any metal |
Which one fits your part
Work from the feature that has to work. If the requirement is turbine, downhole and high temperature parts where creep and oxidation set the limit, Inconel 718 is the safer call; if it is fittings, connectors and turned components where machinability drives the cost, C3604 Brass wins on cost or on lead time. Where the drawing does not make it clear, that is the question to settle before quotation rather than after.
A note on specification
Write the drawing so that either route can be considered where the function allows. That keeps the quotation competitive and stops a process being specified where a result should have been.
Applications
Inconel 718 is used for turbine, downhole and high temperature parts where creep and oxidation set the limit, and in practice it appears most often in turbine components, downhole tools, exhaust hardware, high temperature fasteners.
How it fits into a machining route
Inconel 718 is chosen at the drawing stage, and everything downstream follows from it: the tool geometry, the cutting data, the heat treatment and the certificate. Changing the grade later is a different part, not a different quote.The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: tool consumption and cutting time. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.
Standards, documentation and what is issued
The documentation requirement is EN 10204 3.1 with a full melt trace. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.
Dimensional inspection with a certificate review is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.
Frequently asked questions
What tolerance should be specified for Inconel 718?
±0.02 mm is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.
Which material is usually used?
Inconel 718 is the usual choice, supplied against EN 10204 3.1 with a full melt trace.
How is the result verified?
Dimensional inspection with a certificate review, with the results recorded so a repeat order can be compared with the first.
What is the most common mistake?
Planning a lead time as if it were steel.
How long does it take and what does it cost?
A realistic cycle is very slow cutting, a small number of parts per tool, and the cost driver is tool consumption and cutting time.
Related capability
If you are specifying Inconel 718 on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.
Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.
Related entries
These entries sit next to Inconel 718 in the encyclopedia: Duplex 2205 Stainless Steel, 4140 Alloy Steel, Splined Shafts. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
