DET anneal and Subc...
 
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DET anneal and Subcritical Anneal

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Active Member Apprentice Bladesmith (5yr)
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Hopefully I can get some clarification here about a couple spherodizing annealing methods that I have both done and read about.  I have read many examples on the various forums about subcritical anneal in order to spherodize the existing pearlite after our normalization and grain refining steps.

However according to documentation from Knife Steel Nerds a subcritical anneal requires a "long" period of time to be done properly.  The micrographs he uses as an example show pearlite even after 21 hours at the subcritical temperature.  The steel became fully spheroidzed after 200 hours.  The was for 1040.

His recommendation is for Divorced Eutectoid Transformation/ Transformation Anneal.  If I understand it correctly (big IF), DET anneal works primarily for hypereutectoid steels because at just above the critical temperature, carbides that have not gone into solution prevent grain growth and sperodizes the steel, the steel is held for a relatively short amount of time; 30 minutes or so, and slow cooled in vermiculite.  This seems to result in sperodized carbides.  This strikes me as similar to the suggestions to heat and slow cool in ashes or vermiculite suggestions that I have commonly read about in blacksmithing forums.

 

So, assuming the information above is mostly sound, my main questions are:

Does subcritical annealing have any significant benefit at shorter period of times, say 2 hours, at the subcritical temperature?  If so, it a subcritical anneal more effective on simple steels as opposed to richer alloys?

Does the DET anneal have any significant drawbacks for the higher carbon steels that we typically use?

Is it mainly just different methods to get to a similar place?

 

I mostly want to understand the difference and be able to determine which is preferred and when.

 
Posted : 23/01/2023 1:37 pm
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