# Tool hardening & annealing - understanding what happens at a moleculear level



## Planeman40 (Nov 3, 2010)

We all have occasions where we would like to make a special cutting tool but are put off by not understanding how to properly harden the edge. Here is a quick video that illustrates what is going on at a molecular level when you quench and anneal.






One other thing. Many have problems obtaining that proverbial "straw" color when annealing. The secret is: (1) polish the hardened tool end to be hardened, and (2) *DON'T* hold the tool end in the torch flame to anneal! Apply the flame further up the shaft of the tool a short way away from the edge to be hardened. Then watch as *the heat travels up the tool shaft toward the sharp edge*. When the polished sharp edge becomes "straw" colored, remove the heat.


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## Redoak49 (Dec 15, 2012)

While this is a nice explanation of dislocations and what happens if you heat certain pure metals, it has little application to heat treating steels to harden them. He shows a bunch of steel balls all the same size. When you have an iron alloy with carbon different things are happening in the matrix. When you heat it up high enough, almost everything goes into solution. When you quench, you trap carbon in the crystal matrix and form martensite. If you cool much more slowly, you allow the carbon to diffuse, move, and form different crystal structures such as pearlite , bainite and some others.

With high carbon steels you will also form very hard carbide particles scattered in the matrix.I


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## waho6o9 (May 6, 2011)

Fascinating thread, thank you!


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## Planeman40 (Nov 3, 2010)

Readoak49, you are correct about the carbon molecules and other possible added substances, however I believe this is beyond most woodworkers who just need to have a basic understanding of what is happening, enough to successfully harden a steel edge. Thanks for your post. I hope other knowledgeable members will add more.


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