Strength Test of a Coiled Ring
An assertion was made that this was so, and that not only would it be strong, but that a coiled ring that had been heated and flattened would be stronger than a coiled ring that had not been heated or flattened (untreated).
I doubted this assertion, so I put it to the test.
The image below shows the first test ring. This ring is a coil of 18GA mild steel wire, with a 3/8" ID. It has been wound approximately 2 times, as you can see. It has not been heated, and it has not been flattened. Note that I positioned the cut ends facing upward. This was consistant on all rings tested.
The ring was then put under load. I accomplished this by adding rings to the bucket. I added a clump of rings, handful by handful, until the ring failed. Below you can see the failed ring.
The images below show the amount of rings needed to cause the unheated, unflattened ring coil to fail. The tape measure is approximately 2" deep in rings.
Next, I constructed a coiled ring, identical to the first coiled ring, except that I heated this ring to yellow heat, dropped it in my flattening fixture, and quickly flattened it before it could cool. The images below show either side of the resulting ring:
I then attached the bucket, with the same amount of rings that caused the unflattened, unheated ring to fail. The heated, flattened coil did not fail, and supported the load easily:
Then constructed a third ring, that had been coiled approximately 2 times and flattened, but not heated at all. It also supported the load easily. Note that the ring ends are spread apart slightly. This occured during flattening. Before flattening, the ring ends matched up (2 complete revolutions of coil).
Next, I continued adding rings to the weight vehicle until the unheated, flattened ring coil failed:
Here you can see the amount of rings (roughly 5" deep)needed to cause failure of the unheated, but flattened, ring coil. This is over twice the amount of weight needed to fail the unheated, unflattened ring coil:
Then I attached the heated and flattened ring coil to the weight vehicle, with the same amount of weight that failed the unheated, flattened ring coil. This heated, flattened ring also failed, under the same load.
However, because the ring coil that was both flattened and heated failed under the same load as the ring coil that was only flattened, we cannot deduce that a flattened ring which has been heated is stronger than a flattened coil that has not.
In other words, heating of the flattened ring coil does not make it stronger. In fact, it is possible that heating the flattened ring coil makes it weaker. However, this test did not check that possibility. Instead, as the above description shows, a load was found which would fail the unheated flattened coil, and that same load was applied to the heated flattened coil. It failed too, but it is possible that the heated ring might have failed under less weight load.
However, given that the deformed shape of both the heated and unheated flattened failed rings are roughly the same, it is my guesstimate that the rings are roughly equivalent in strength.
This result does not surprise me, as all of the rings were made of annealed black wire. Heating one of the rings would likely only anneal it further since I did not follow up with a quench - that was not one of the original conditions. However, it is unlikely quenching would add significant hardness, either, as the wire is low carbon steel.