Re: Machine Shop

On 3/5/2025 2:46 PM, Frank Krygowski wrote:

On 3/5/2025 1:51 PM, cyclintom wrote:

... instead of actually looking into the science.

 What a weird idea. I took two courses in metallurgy as part of my first engineering degree. I taught basics of metallurgy as part of manufacturing courses at two different schools. I'm betting I'm the only person here who has used a metalloscope (although Andrew might have), I'm sure I've done and observed more heat treating than most here, and I'm sure I've done and taught more physical testing of materials, including testing for modulus of elasticity, elastic limit, yield point, ultimate tensile strength, hardness by at least 3 or 4 different methods, etc.
 Tell us about your education and experience in metallurgy, Tom. Especially, tell us where you were taught that plastically deformed metal can spontaneously return to its undeformed shape, and how that can happen. Nobody here believes you.
 

No, I have not observed metallic structure directly but textbooks are rife with diagrams and micrograph photos along with the text. (cheap at any used bookstore).
This is short and clear:
https://www.slideserve.com/angeni/single-crystal-slip
I think the misunderstanding here is to consider metals as amorphous like liquids and polymers. They are crystalline, with an ordered repeating structure like ice not like water. Permanent deformation exactly describes crystal slip which is a permanent change and can be removed only by remelting (recycling) the material as Nucor does. Or for a small area, heating and cooling only a portion (see link at end).
Because crystal slip inherently makes the material larger by some degree, any reshaping (such as working a dent or straightening a bend) will not and cannot return the piece to exactly the same shape. Close enough for many actual applications, but not perfectly the same by its nature.
Short overview of practical application:
https://www.hotrod.com/how-to/0709rc-straightening-sheetmetal/
--
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971