Cast iron, heat treated rings.

[stevehuckss396]

Last metal working meeting we had a guest speaker who talked about heat treating. After the meeting I cornered him and asked about the ring thing. His take is that the rings should be heated to 1100F for 3-4 hours for a good result. He also added that the cast iron should never be heated past 1333F. The rings should be coated with some type of goop to prevent scale or nitrogen can be used in the furnace to prevent scale. 950 - 1000 just isn't hot enough and less than 3 hours isn't long enough. I have tried 950 for 1-1/2 hours and I didn't get a full stress relief. After the 3-4 hours the rings need to cool slowly. It is best to turn off the oven and leave the rings in to cool slowly without opening the door until they are room temperature.

I have seen alot of info here and other places on the web. I just wanted to post this because I believe this to be reliable information. I thought it might help somebody in the future. They say this is the correct way to stress relieve cast iron. If someone asks who they are just tell them...

Dr. John M. Tartaglia is Engineering Manager and Senior Metallurgical Engineer
at Stork Climax Research Services (CRS), a metallurgical engineering, consulting
and testing company located in Wixom, Michigan. At Stork CRS, John is
responsible for managing the engineering department and conducting failure
analysis and metallurgical research in steels, cast irons, aluminum, copper,
magnesium, refractory alloys, and nonmetallic materials for industrial and legal
clients.

 

[steamer]

That jives with what I've read about "Sub-critical stress relieving" of iron.


Dave

 

[doc1955]

I've had 1 year of metallurgy schooling it was a drag. Another way to heat treat them is to seal then in a stainless steel envelope with a little alcohol. In the heat treat oven the alcohol will burn off the oxygen in the envelope and you will not get any scale. It is the same for any steel you need a controlled atmosphere.

 

[Metal Butcher]

Hi Steve. Another very important aspect of stress relieving cast iron rings is 'slow cooling', and the slower the better.

A lot of model engine builders heat their rings cherry red for a few minutes and allow them to cool rapidly in a room temperature environment. This is not a good method but it does produce a few usable rings.

The real 'acid test' is during installation. If a single one cracks, they are not properly annealed.

-MB

 

[stevehuckss396]

Hi Steve. Another very important aspect of stress relieving cast iron rings is 'slow cooling', and the slower the better.

That is correct. I will edit the first post to keep all the info in one place

 

[doc1955]

What we did in the tooling shop where I use to work is just turn the oven off and let everything cool down usually would do our stress reliving in the after noon and let it cool down over night. But yes you definitely want to cool slow if you are stress relieving anything.

I have done the heat to cherry red and let them cool to room temp but I feel in this process we are not so much stress relieving but actually tempering to a certain degree to put some spring into them. I personally have had very good luck with this process.

 

[Rustkolector]

Steve,
In my experience, the correct ring dimensions are as important as the heat treatment. I follow the Trimble method for determining dimensions, especially the radial thickness. My heat treating method is simple: Mount your rings on the Trimble ring fixture (without a cover), and clamp them flat. Coat the exposed rings generously with white silver brazing flux. Put the fixture immediately next to a fire brick back plate on a fire brick harth. Heat slowly and evenly with a pair of propane torches. The flux is an indicator flux and flows clear at about 1100 degrees F. Note the color when it flows, back off on the heat, and try to hold that relative color for about 4-5 miniutes. It will be slightly more orange than dull red color. Cover the ring fixture and harth tightly with any suitable insulation material and allow to cool slowly. Rinse the fixture under hot water and scrub the rings with a brass brush to remove the flux residue. The rings will be gray in color, but should be free of any oxidation damage. Lap the rings to ~.0005" side clearance. Although I usually make spares, rings properly dimensioned, and stress relieved this way will withstand repeated install and removal cycles without undue breakage.

Jeff