FC-0205 vs FC-0208 vs FC-0808: Choosing the Right Iron-Copper PM Grade

The FC series - iron-copper-carbon PM alloys defined in MPIF Standard 35 - is the most widely used alloy family in structural powder metallurgy. FC grades are the default starting point for most industrial and automotive PM structural parts: gears, hubs, cams, brackets, and valve bodies. Their popularity comes from the combination of adequate mechanical properties, good dimensional stability, and relatively low cost.

Three grades cover the majority of FC applications: FC-0205, FC-0208, and FC-0808. They share the same base (iron + copper + carbon) but differ in copper and carbon levels in ways that meaningfully change their behavior in production and in service.

Composition

The MPIF grade code encodes nominal composition: FC-[Cu%/2 digits][C%/2 digits].

Carbon is the primary hardening element. Copper improves strength and dimensional stability by solid-solution strengthening and by resisting sintering shrinkage. More copper also improves machinability.

Mechanical Properties (As-Sintered)

Representative property ranges at ~6.8 - .0 g/cm3:

These are representative ranges from MPIF Standard 35 and published supplier data. Actual values depend on density, sintering conditions, and carbon control. Always verify with supplier material data sheets for the specific process.

Key observations:

• FC-0205 is softer and more ductile - better for parts subject to impact or press-fit deformation without cracking
• FC-0208 is the general-purpose workhorse: strength and hardness adequate for most structural parts, with acceptable machinability
• FC-0808 is the strongest as-sintered grade of the three, with better machinability than FC-0208 at equivalent strength due to the copper content

Heat-Treated Properties

All three grades are heat treatable, but the available hardness range differs with carbon content:

For through-hardened applications requiring HRC > 45, the FN-series (iron-nickel) grades with better hardenability are usually the right step up from FC. FC grades have limited through-hardening depth in sections above ~8 - 0 mm.

For case carburizing, FC-0205 is often preferred over FC-0208 because the lower base carbon provides more clean "headroom" for carbon uptake during carburizing without over-carburizing the case. A carburized FC-0205 achieves a hard, high-carbon case while the core remains tougher than an FC-0208 case-hardened equivalent.

Dimensional Stability During Sintering

Copper content has a notable effect on sintering dimensional change:

• FC-0205 and FC-0208 (2% Cu): Moderate shrinkage (~0.5 - .0% linear) during sintering. Predictable and consistent in well-controlled furnaces.
• FC-0808 (8% Cu): Copper at higher levels creates a transient liquid phase during sintering (copper melts at 1085 deg C; sintering temperature for FC grades is typically 1120 - 150 deg C). This liquid-phase sintering effect can cause dimensional growth or greater scatter than low-copper grades if not controlled. FC-0808 requires more careful process control to achieve tight dimensional tolerances.

For parts with tight sintering tolerances, FC-0205 and FC-0208 are generally easier to control. FC-0808 may require tighter furnace temperature and atmosphere control to achieve comparable dimensional scatter.

Machinability

Copper significantly improves the machinability of iron-based PM. The soft copper phase in the matrix lubricates cutting tools and provides a more continuous cutting path than pore-interrupted iron:

FC-0808's 8% copper content provides noticeably better machinability than the 2% copper grades. If a PM part has multiple secondary machining operations (cross-holes, threads, turned ODs), FC-0808 reduces tool wear and machining time, which can partially offset its higher copper cost.

Cost Comparison

Copper is more expensive than iron. The cost differential between grades (per kg of alloy, at typical production volumes):

• FC-0205 and FC-0208: similar cost (same 2% copper; minor difference in graphite addition)
• FC-0808: higher cost - approximately 10 - 0% more per kg than FC-0205/FC-0208 (copper premium and higher total alloy percentage)

This cost difference is meaningful at high volumes. If FC-0208 meets the mechanical and machinability requirements, specifying FC-0808 for its machinability advantage may not be justified unless the secondary machining cost savings are demonstrably larger than the powder cost premium.

Grade-by-Grade Application Guidance

FC-0205: When to Choose It

FC-0205's lower carbon content makes it the preferred choice when:

• Ductility or impact resistance is important. Parts that will be press-fitted, staked, or subjected to occasional shock loads benefit from FC-0205's higher elongation and impact strength vs. FC-0208.
• Case carburizing is planned. Starting from 0.5% carbon gives cleaner headroom for carburizing to a high-carbon case.
• The application is light structural loading where the moderate UTS of FC-0205 is adequate and the cost of FC-0208 properties is not required.

Typical applications: lightly loaded cams, bearing housings, structural inserts where assembly operations involve deformation.

FC-0208: When to Choose It

FC-0208 is the most widely specified structural PM grade for good reason: it offers the best overall balance of properties, dimensional stability, and cost. Choose it when:

• General structural gears, hubs, and cams with moderate load requirements
• No specific driver favors FC-0205 or FC-0808 - this is the default
• Heat treatment (Q&T) is planned to achieve HRC 30 - 4
• Good dimensional control is required, with straightforward sintering process control

Typical applications: automotive auxiliary gears (oil pump rotors, balance shaft sprockets), industrial drive gears, cam rings, structural hubs and flanges.

FC-0808: When to Choose It

FC-0808's higher copper content gives it the best combination of as-sintered strength and machinability in the FC family. Choose it when:

• High secondary machining content: The part has multiple cross-holes, tapped holes, turned features, or milled slots where improved machinability reduces cost enough to offset the copper premium.
• Maximum as-sintered strength without heat treatment: If heat treatment is not planned and strength requirements push toward the upper end of what the FC family can deliver as-sintered, FC-0808 delivers more strength than FC-0208.
• Good copper brazing compatibility is needed: High copper in the base alloy makes the part more compatible with copper-braze assembly operations (sinter-braze or separate braze cycle).

Typical applications: hydraulic manifold bodies requiring machined ports and threads, heavily machined pump housings, complex structural parts with high secondary operation content.

Quick Selection Summary

If you are specifying a PM structural part and are unsure which FC grade is appropriate, contact our engineering team. We can match the grade to your loading, machining, and heat treatment requirements.