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It's back in the mainstream.......ugh


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This could also go in the Fiery Beards humor thread, but I figured I  would post it here in case anyone starts thinking about doing this.

 

So there I was sitting at my table at Blade when this couple comes up and he starts talking knife making. I always entertain discussions about the art, especially with younger makers, but this guy really set me off.

He wants to show me his work and share his processes. OK. I'm game. Then he starts telling me about multiple quenching cycles for 1095 and I'm like, huh? Didn't we go through that 15 years ago? So I ask him why he does this and he says "grain refinement" looking at me like he doesn't believe I already know. When I ask to what end? He replies edge retention and increased toughness.

I kind of lost it. Then he drops the name of someone who is a fairly well known and respected individual and says he learned it from that guy.

 

Because I like all you guys, I'll share his other secret about the double quench on 1095. It seems that if you leave the edge at 60 thousandths, and the spine over a 1/4", you will get 1095 to auto-hamon!

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Well, I don't know about double quenching as a valuable addition to a heat treatment regime if it is defined as simply bringing the steel above the transition temperature then rapidly cooling it and repeating that exact process again.  However I have had a teacher I respect greatly advocate a method using two quenches to produce something that could be termed "grain refinement".  As I understand it the theory goes something like this:

  1. After forging and rough grinding the blade, the grain sizes throughout can be highly irregular.  A standard normalizing and stress relief heat treatment program prior to the quench may not keep the steel above the austentizing temperature in the first part of the cycle long enough for the grain sizes to homogenize prior to being shrunk down by the successively lower heating during the balance of the normalizing/stress relief cycle.
  2. He suggests in this case that an initial heating and soak well above the transformation temperature to intentionally grow the grain to a relatively common size, then initial quench to lock the boundaries as a first step.  This is followed by a conventional full normalizing/stress relief regime to reduce the newly homogenous grains prior to the final quench and temper.

To date I have not tried this technique, but I see it as being more effective than a simple double quench.  I wouldn't be shocked if adding spheroidal annealing between forging and rough grinding accomplished a similar thing. 

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I once saw a demo by a master smith where he advocated quenching after every few heats into oil to keep the carbon in.... Theres such a staggering amount of bad advice and practice out there regardless of whether you're a beginner or ABS master smith apparently. I actually imagine we're probably talking about the same guy 

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I wonder if that's the same ABS Mastersmith who told me with a straight face that the one and only source of 1084 in the world is Hitachi, and it is only found in sway bars from Toyota?

 

A lot of the apparent bull is well meaning, but a garbled understanding of the metallurgy. Multiple quenches do refine the grain, but no better (and far more stressfully!) than simple normalizing.  

 

Also, a lot depends on the alloy in question.  The things you can do to get the best blade performance from O-1, for example, would ruin 1095.  Or at least, not be helpful in any way.  

 

But, that's why this subforum is here, and thanks to having actual metallurgists offering the real story from time to time, it's the best place to learn this stuff. 

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2 hours ago, Alan Longmire said:

But, that's why this subforum is here,

It is also why one particular thread above this one is pinned.

tripple quenching vs tripple normalising - Metallurgy and other enigmas - Bladesmith's Forum Board (bladesmithsforum.com)

 

The Verhoven study referenced in the final post is readily available online too: http://hybridburners.com/documents/verhoeven.pdf

 

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