steel shrinkage

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Good question. :)
We went over that so fast in metallurgy class that I don't remember the mechanism.
I know guys can shrink metal with a large sponge full of water on red hot steel, like an auto body man shrinking a stretched area of sheet metal and the drive shaft man can shrink the bowed-out side of a drive shaft the same way.
I tried that trick on a auto-dent once... I made the stretched metal bigger not smaller. :/
Alvin in AZ
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On a hail dent, use dry ice. Just in the center when the body is hot hot in the sun. It puckers up and flattens out.
Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member wrote:
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Martin H. Eastburn
I'm only an amateur. And I'm not sure I properly understood your question. But if I did, I believe the answer is: "Yes". The mechanical / blacksmithing term for this is "upset".
Take a straight bar of steel. If you heat a point or ribbon on one side with a torch, as it heats, it will bend in the opposite direction from the heated side.
Upon removing the heat source, as it cools, it will return to straight. As it continues to cool, it will continue to bend, now to the side you heated. Once cool, it will remain there. The ribbon that you heated will be upset i.e. thicker than when you started.
Welders say "the hot side is the short side". Sort of the welding equivalent to the mechanic's chant "righty tighty lefty loosy".
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Sometimes, sometimes not. Shrinkage and distortion are more of an issue when quenching from austenite, and less of an issue in non shrinking grades.
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David Deuchar
Its a complex question because there are a number of phase transformations available to steel as it cool. So due to thermal expansion you get elongation and contraction. If the thermal stresses are larger than the geometry allows and you exceed the yeild strength you'll get distortion. Then depending on how hot you make it and how you cool it you can get phase transformations depending on the composition of the steel. Most of these transformations result in a change in volume as the crystal structure changes. This too can cause distortion.
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|>If you heat steel then let it cool back to the original temperature, |>does it shrink from the original size |>Tom
The proof in the pudding is the tons of metal plants in Red China/Beijing/Taiwan/etc... where they make a great amount of pre/aftermarket items/parts for motors fasteners, scooters, guns (NorInCo) that don't quite fit even when the proper cast/dies are used in the attempt to duplicate the original.
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