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I believe, to technically anneal a piece of low carbon steel you bring it up to critical and slowly cool it.

My experience is you can heat a piece of case hardened steel well below critical and it becomes soft, effectively annealing the spot though probably not technically annealing it.


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Just tossing around some conversation. I believe steel has to be hardened to be annealed. Known low carbon steel may not have the ability to harden in the first place. Thats not a comment about the case that might likely be at least a medium carbon steel, and potentially behave differently than the core.

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Originally Posted By: mc
So Keith explain annealing,


Annealing steel has been defined and explained in the past many times here, but the term is still apparently difficult to comprehend for many people. You could just look it up, but remember that even some sources you'll encounter in a Google search will be incorrect.

A short simple answer is that the steel is brought up a little above the critical temperature, and held at that temperature for a predetermined time... dependant upon the thickness of the steel. This critical temperature is near a point where steel becomes non-magnetic. Then it is VERY SLOWLY cooled at a controlled rate. This process changes the crystalline microstructure of the steel and makes it much softer, more ductile, and more electrically conductive.

In the past, I worked in several different annealing plants where large furnaces were utilized to anneal up to a couple hundred tons at a time. These furnaces had very precise temperature monitoring and control, and atmospheric air was first purged and replaced with an inert gas to prevent scale formation or oxidation. We used catalytic crackers to crack concentrated ammonia to get nitrogen and hydrogen to use for purge gas. Hydrogen is great to keep the steel from discoloring during annealing. It seems counterintuitive to use a highly explosive gas such as hydrogen in a furnace operating at very high temperatures, but it can only burn or explode if oxygen is present in the correct concentration. For such large batches of steel, the heating time often went over 20 hours, followed by a very slow and controlled cooling. The actual times and temps were dependant upon the alloy and thickness of the steel.

Tempering of steel (hardening and then drawing) is another story... also frequently misunderstood.


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craigd, mild steel can be hardened, even though you won't be able to get it to the same Rockwell hardness as the steel you might use to make a knife or spring.

You can even work harden mild steel. Just take a soft piece of mild low carbon steel wire and repeatedly bend it, and it will become hard and brittle, and eventually break. Bending the wire has changed the microstructure and made it much harder. But you can take that work hardened wire, and anneal it to return it to a soft ductile state... if done correctly. Steel mills routinely anneal mild steel because the cold rolling process can make it too hard for the customer requirements, such as steel that is intended for stamping and forming operations.


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keith never ceases to amaze and impress us with his broad knowledge and literary skills....


keep it simple and keep it safe...
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I hear you Keith. I was thinking in terms of hardening by quenching from above the steel's critical temperature. In this example, I believe, the gun part was quench hardened, but only the case. In theory, the base low carbon steel core remains relatively unaffected by the heat treat temperature changes.

Only conversation here, but I think, once a steel yeilds, even if the part hasn't broken, the hardness falls off rapidly. I don't think that type of damage can be corrected and returned to a ductile state that resembles the original wire example. I suppose short of tossing it in a smelter and starting over?

edit to add, ed, ya shud'a spoke up when your budy peed in a no go zone.

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Craig, would respectively question your statement.
Multiple bolt pattern joints depend on bearing yielding so all the bolts pick up the load.
Strength does not change after yielding, might increase from cold work.
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Originally Posted By: Chuckster
....Strength does not change after yielding, might increase from cold work....

Yes Chuck, that is correct. The picture that I had in mind was the strength does increase after yield is exceeded, but failing wire scenario by bending back and forth was past the point of increasing strength?

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