Why Does Heated Wire Remain Elongated After Cooling?

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Discussion Overview

The discussion revolves around the phenomenon of a heated iron-chromium-aluminium wire that remains elongated after cooling. Participants explore the concepts of thermal expansion, creep, and the effects of tension and cooling methods on the wire's behavior.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether the elongation of the wire after cooling could be attributed to thermal expansion.
  • Another suggests that the wire likely stretched while hot and may have become thinner as a result.
  • A participant raises the possibility that significant tension on the wire could lead to creep, indicating a need for more information about the conditions under which it was fixed.
  • It is noted that creep is a common occurrence in steel at elevated temperatures, particularly at 1000K and 1200K, and that the initial metallurgical state of the wire could influence its behavior.
  • One participant proposes that observing the wire's behavior during subsequent heating could provide insights into its creep characteristics.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the causes of the wire's elongation, particularly concerning the roles of thermal expansion and creep. The discussion remains unresolved as no consensus is reached.

Contextual Notes

Participants note that the wire's initial metallurgical state and the conditions of cooling may significantly influence the observed elongation, but these factors remain unspecified.

130mikep
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thermal expansion of wire??

hi I've got this 3mm iron-chromium-aluminium wire fixed at both ends, heated to approx 1000k (max 1200K) and suspended horizontally approx 1metre long.

the wire it would appear has been extended by about 8mm, similar to what would be expected when its hot, only it stays this long when brought back down to room temperature!

so my question is: why?! lol

could it really be creep?

thanks, mike
 
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The wire probably stretched while it was hot and sagging down. If the wire stretched then it must also have gotten thinner.
 


Was it fixed under significant tension? If it was, then yes, it could be creep.

Otherwise, it may depend on how it was cooled.
 


Creeping is absolutely normal for steel at 1000K, much more at 1200K. Even over a short time with a moderate load.

Then, if your wire was new, you can have glowed it from some initial metallurgical state, like cold drawn. To decide what effect it was, just observe if the wire creeps further next time.
 

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