May have been via cold working.

 

 

http://metals.about.com/od/metallurgy/fl/What-is-Cold-Working.htm

Cold working refers to the process of strengthening a metal by plastic deformation. Also referred to as work hardening, the metal working technique involves subjecting metal to mechanical stress so as to cause a permanent change to the metal's crystalline structure.

The process gets its name because it is conducted at temperatures below the metal's recrystallization point and mechanical stress, not heat, is used to affect change. The technique is most commonly applied to steel, aluminum, and copper.

When these metals are cold worked permanent defects change their crystalline makeup. These defects reduce the ability of crystals to move within the metal structure and the metal becomes more resistant to further deformation.

The resulting metal product has improved tensile strength and hardness, but less ductility. Cold rolling and cold drawing of steel also improve surface finish. The major cold-working methods can be classified as squeezing or rolling, bending, shearing and drawing.

Thanks - yes that is a process that would have been noted early on. I've noted that myself but never knew the reason why. If you take a piece of soft copper wire and twist it a straight hardened section will develop along the length of the wire. This hardened section can't be bent by hand even though the wire started off very flexible.

@ Endy0816 - Thanks for that term "cold working".

Thanks - yes that is a process that would have been noted early on. I've noted that myself but never knew the reason why. If you take a piece of soft copper wire and twist it a straight hardened section will develop along the length of the wire. This hardened section can't be bent by hand even though the wire started off very flexible.

@ Endy0816 - Thanks for that term "cold working".

I now remember what it was that I used to twist. It actually was iron paper clips. They start off bendable but if you twist the two ends in opposite rotations the middle section becomes very hard and quite brittle.

Cold working practical demonstration.

Edited June 22, 20169 yr by Robittybob1

That is after the metal has been extracted from the ore.