Posted by Rick Denney on February 01, 2001 at 23:12:30:
In Reply to: Re: Re: Re: Re: Metallurgy posted by Steve Inman on February 01, 2001 at 22:11:58:
Annealing doesn't change the properties that matter. The only material property that seems to me to be important is stiffness, and that doesn't change with annealing. Density is not changed, but yield strength, malleability, ductility, frangibility, and a whole bunch of other properties adding up to brittleness.
When materials people talk about "softer" and "harder" they really mean "weaker" and "stronger." A steel spring has been heat treated and worked to increase its hardness. Tools have been heat treated and worked to increase their hardness. But an annealed spring would sag the same amount under the same load as a heat-treated and work-hardened spring, if it didn't yield first. If the brass on a tuba is too weak while annealed with withstand its normal stress, it will soon deform, which will relax the stress to lower levels.
For example, let's say a bow would not fit in a ferrule easily. Joe S. would hammer on it until it did, but I might be tempted to force it in there. That would leave the ferrule with a lot of tension (hoop stress) and the bow would be compressed. I put the torch to it to solder it, and get it a bit too hot, and the brass both expands and loses its strength. The result is a wrinkle that suddenly appears in the brass, causing colorful commentary from the moron holding the torch. There was no wrinkle there before the heat (and the annealing), and after the wrinkle, the stress was reduced.
Rick "wondering how freezing has this effect, or anything like it" Denney