Are Iron Copper Carbon Alloys Always the Ideal Powder Metal Materials?.

Posted by Horizon Technology - August 07, 2018

If you’ve sought powder metallurgy services before, chances are you’ve bought components made from iron-copper-carbon powder. Purchasers have long considered it the standard for powder metal materials.

In reality, iron-copper-carbon is the Walmart of materials.

Try instead thinking of Iron-copper-carbon (ICC) as merely a starting point for powder. Sometimes it works fine; sometimes it’s just not adequate and you need to explore the dozens of other possibilities out there.

Here’s some background on ICC and the downfalls of stubbornly sticking to it for every product:

Why Iron-Copper-Carbon Is Most Popular Among Powder Metal Materials

Of all powder metal parts produced in North America, about 50% are made of iron-copper-carbon powder. This is a marriage of convenience, if anything.

In the U.S. auto industry, certain “mega programs” consume tons and tons of products each year. Many of their designs consist of ICC parts:

  • Connecting rods for autos
  • Main bearing caps for the bottoms of engines
  • Transmission carriers
  • Powder forged connecting rods for engines

Because material cost is the dominant factor in the auto industry, saving a few pennies per pound with ICC is significant for auto companies. In most of those “mega program” applications, the strength and mechanical property requirements can be met by cheap ICC powders in their sintered condition.

There’s also the ease of processing to consider in ICC’s popularity. Manufacturing with ICC powder tends to be pretty forgiving if you undersinter, oversinter, etc. In other words, they can be less sensitive than advanced materials.

Here’s a practical example: Almost every North American engine has a powder forged connecting rods. So someone who’s making 60 million connecting rods a year is more likely to be looking for a material that’s easy to handle and, well, idiotproof.

For these reasons, ICC has been the dominant powdered metal for many years and probably will continue to be. But to maximize your project’s potential, you have to understand what ICC offers and what its potential disadvantages are.

Disadvantages of Iron-Copper-Carbon

Albert Einstein once said, ““What is right is not always popular, and what is popular is not always right.” Here are the problems with a one-size-fits-all approach with powder metallurgy:

1. Brittleness

ICC parts that require heat treatment can run into issues. When you heat treat ICC, you risk making a brittle part.

That localized fragility can practically turn your component into “tear along the dotted line” perforated paper.

As such, engineers tend to not specify ICC for heat-treated applications where you want high strength or material hardness. There’s a reason most auto parts are not heat treated.

2. Too Much Porosity

ICCs are known for forming high-porosity parts. How? The loss of density through sintering big particles.

ICCs use pure elemental copper. During sintering, the copper melts and diffuses into the iron, creating an alloy.

Most coppers are the same particle size as iron. This can leave a large hole in your part. Of course, most powder metal parts have holes, but when you have particles this big particles melting, you’re left with a hole that’s significantly larger than you wanted. So that section of your part will have high porosity

Another example: Imagine your copper surface sits on a gear. Once the copper melts, that gear is running on something that’s lower density than you want.

A similar problem occurs when you have parts rubbing against each other when they shouldn’t be. This can result in a large collapse around the large copper particles due to excessive stress.

3. Dimensional Instability

Iron-copper material tends to “grow” during sintering. A part that starts out with a 1” diameter could grow to 1.005”, leading to density loss.

When you press and sinter an ICC component, you have to be extra careful the size comes out the same every time. This is especially true if you have tight tolerances. An ICC can be sensitive to even minor variations in copper or carbon content.

Alternatives

All that stuff we just talked about? That’s what most traditional companies offer. But Horizon provides alternatives using higher-performance materials.

More complex applications with need for high-end properties may benefit from:

  • Iron-nickel mixes
  • Pre-alloy materials

The difference between ICC and other more advanced materials is like the difference between the soft magnetic composite alternatives we refer to as 1P, 3P, and 5P material processes. This article on 1P, 3P, and 5P powder metal gives a good description of these alternatives.

ICCs are akin to the 1P composite in that they’re baseline materials. They might work for some applications, but others demand higher performance.

Thus, in conventional pressed and sintered PM applications, each application needs to be custom designed to meet its own unique set of engineering requirements.

Some advantages to 3P, 5P, and other advanced materials:

  • They’re more predictable for heat treating. As such, you minimize the risk of your part turning out brittle.
  • Your parts will enjoy reduced loss of density through sintering. In some cases, rather than your component growing from 1” diameter to 1.005”, you might see a 0.5% decrease in diameter, So in this example, you’re actually gaining density!
  • Large holes won’t develop in your part’s microstructure, so there will be fewer potential sites for failure on the part.

ICC Parts = Commodity Parts

(DYK? only _% of total Horizon sales come from projects using iron-copper-carbon parts. In fact, only two of our current customers use ICC.)

Iron-copper carbon powder is general reserved for commodity projects like the ones described above. While sometimes useful in high-volume, low-complexity projects, there’s a reason we rarely use ICC at Horizon.

If you want to get serious about turning up the quality in auto, engine, and other applications, consider stepping back and re-examining your material choice. The most convenient way to shop isn’t always the best one.

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Topics: Materials


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