Why are there more grain boundaries after annealing?

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Discussion Overview

The discussion revolves around the phenomenon of grain boundaries in materials after the annealing process, specifically questioning why there appears to be an increase in grain boundaries following recrystallization, despite the aim of annealing to enhance ductility and reduce strength.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant expresses confusion about the increase in grain boundaries after annealing, questioning how this aligns with the goal of making materials less strong and more ductile.
  • Another participant confirms that after recrystallization, grains become smaller, referencing the Hall-Petch relationship, which suggests that smaller grains can lead to increased strength and ductility compared to work-hardened material.
  • A different participant notes that interstitial stress and dislocation density decrease after annealing, which also affects strength and ductility.
  • One participant mentions that grains grow spontaneously during annealing to reduce grain boundary energy.
  • Another participant states that the outcome depends on the type of annealing used, explaining that in full annealing, small grains are consumed by larger grains, leading to an overall increase in grain size, which may enhance ductility.

Areas of Agreement / Disagreement

Participants express differing views on the implications of grain boundary changes after annealing, with no consensus on the relationship between grain boundaries, strength, and ductility.

Contextual Notes

There are unresolved aspects regarding the specific mechanisms of grain boundary formation and the conditions under which different types of annealing are applied, which may influence the outcomes discussed.

mrhorse09
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I've been confused for a long time and can't figure this out:
In annealing process, after recrystallisation, new "strain-free" grains replaced the strained grains, but it seems there are much more grain boundaries than before the material was annealed? Is this true?
Having more grain boundaries means the materials is stronger but annealing process aims to make the material has less strength and more ductile.

So why is that?
 
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That's true, after recrystallisation, grains will become smaller.and refer to the Hall-Petch relationship,this will make the material has more strength and more ductile.(compared with the material before work hardening)
Annealing process is aimed at make the material softer, so wo can processing it easier
 
The inter stress and the density of dislocation would be decreased after annealing, these are other points affecting the strength and ductile.
 
The grains grow spontaneously to reduce grain boundary energy during anneal.
 
It is depends on what kind of annealing you used. In full annealing, after recrystallization process, it is follow by grains growth, the small grains will be consumed by large grains, then the overall size of grains will be increased, and thus make the steel more ductile, and deformable.
 

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