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Hi All,


With my very limited experience, I know that if you heat steel to red hot and let it cool naturally, it will be softened or annealed. I also know that if you re-heat it to red hot and quench in either oil or water, you can re-harden it. I've always annealed brass by heating red hot and then immediately quenching in water. It seems to me that to a certain extent the brass tends to get "work" hardened, like copper. But it there a way to reverse the annealing process.





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Heat it and quench it again to soften it.  The only way for a normal person to harden it again is to work harden it.  I wrote a short piece about this which is here:



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Copper and copper alloys, such as brass, can only be hardened by work hardening.  This is usually done by running a sheet between rollers, or it can be done by drawing (pulling a wire through a hole smaller than the diameter of the wire).  Hardening can also be done by beating with a hammer, but the results will be uneven, to say nothing of the resulting uneven thickness.  At some point the material becomes brittle, which may limit the amount of bending possible for your part.  In a rolling plant, the sheets get hard after a few rolls, and so, they need to be heated (tempered) to soften them so the thickness can be reduced some more.


Iron, is also hardenable by working, but the amount is limited.  Hardening cannot be achieved by heating and quenching (rapid cooling) unless the carbon content is greater than 0.12%.  This limit basically defines the difference between iron and steel.  To go beyond this, other elements are added, creating alloys.  On the topic of alloys, brass is an alloy of copper and zinc;  bronze, is an alloy of copper with tin, phosphorus, aluminum, nickle or silicon.  


Aluminum can also be hardened, but this is mostly done by precipitation or solution hardening, where the material is kept at a certain temperature for period of time.   The hardness is designated by a "T" code, as in 6061-T4, which is the most common grade of aluminum.  


We work in brass and copper in models because they are easy to work, easy to solder or braze, and are corrosion resistant.  We could use stainless steels (there are many grades), but they tend to be quite hard, as anyone who has tried to drill and tap a 4-40 thread in stainless knows.  Aluminum has some of the same properties of brass, but it's very hard to join, although I've seen some aluminum "solders'.   Although aluminum is corrosion resistant, it does form a soft oxide layer that comes off easily. 


Probably more than you wanted to know, but now that it's been emptied from my brain, I have room to learn something else....


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