Checking my learning curve (more advice requested)



OK, it's been a few years, but here's how I remember the next bit (please please please feel free to correct me):
When the metal is cold worked, these planes slide along each other. They slide until they either reach the end of the grain (where the planes don't match up) or until they hit an impurity large enough to stop them--like a carbon atom. Then it takes a slightly larger force to start the slide along the next available plane. You get enough work into the metal, and you run out of available room for the crystal planes to slide, and it gets brittle.
If you anneal the metal at this point, two things happen: You let all the tension flow out of the crystal planes, as it is much easier to get the atoms to flow over each other at this point and realign to however they need to be for minimum stored energy, and the grains tend to seperate into smaller grains along the larger stress disruptions in the crystal, up to a point. As you keep adding heat, the planes tend to realign to each other and you get bigger grains again.
When you work the metal hot, this doesn't matter nearlty so much, since it's so much easier for the atoms within the crystal to slide over each other that the strain never really builds up.
But for simple carbon steels, this is why some people like to do a little cold work, to deliberately build up some stress to toughen up the metal (use up some of the slide in the crystal planes) and why smaller grain structure can give better properties--it gives less room for the crsytals to "run" when subjected to stress.
I'm not sure how useful that is, but I always found it fascinating, at least! --Glenn Lyford
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Yes. :)

Wow! :)
That was cool. :)
Glenn, was "dislocations" a word you might have been looking for?
Alvin in AZ
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Quite likely! As I said, it's been a while. :) --Glenn Lyford
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Metallurgy math...
1 + 1 = 4
2% of an alloy does "X". 2% of a different alloy also does "X". 1/2% of each alloy together does "X" too. That's a total of 1% alloy doing "X".
Half as much total "expensive" alloy and get the same results. :)
No wonder steels have a list of alloys as long as your arm, huh? ...and that's just the beginning, just the "money angle". :)
O1's a good example of cheap. :)
Mn based to get oil hardening properties, instead of having to use more expensive Cr. O1's got a little of W -and- Cr in it to control the grain size and it just takes a little of each "together" to get the job done. Mn isn't one of the better grain size reducers, but Mn is cheap(!) and makes for a relatively strong and easy to work steel. :)

Face centered cubic (FCC) and body centered cubic (BCC) are the two crystal patterns described there.
I never bothered to keep track of which one was which, because why would it really mattrer? :/ But realized during class one day, FCC is hot-ass austenite and you can "feel that on your face". ;)
Ok so, austenitic stainless steel ain't always hot. :/ What of it? ;)

Mn Si Ni and Co (and who knows what else) substitute for the "about same sized" iron atoms.
You'll see them described as "ferrite strengtheners" as a result.
Cold, hot, quenched, annealed or whatever, they strengthen the iron (ferrite) by "solid solution". Nothing like C P B and N.

Cool, it's my "first metallurgy book" and still the best, IMO :)
On the metallurgy NG, "books for beginners" is asked for ever so often and I always check out the "competition"... so far Allen's got 'em hammered. :) And MT&P's price, clinche's it tight. ;)

Cool. :)
Alvin in AZ and usenet's #1 steel-metallurgy-parrot :)
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