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Heat loss between kiln and quench

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Posts: 5
Active Member Apprentice Bladesmith
Topic starter
 

Should I be at all concerned about heat loss between removing the blade from my heat treat oven and moving it 3 feet to the quench tank?  Would it be prudent to ramp the temperature up 50 degrees, or so, after soaking at critical to make up for any heat loss?

Thanks,
Matt

 
Posted : 17/03/2023 3:47 pm
Ed Caffrey
Posts: 748
Prominent Member Master Bladesmith
 

Congratulations!  I can't count the number of times younger/inexperienced Bladesmiths have asked for my help with the question "Why is my steel not hardening?"  Although it's possible that many things COULD be contributing factors, experience has taught me to to ask the question.... "Where is your quench tank in relationship to your heat source?"  

  Several years ago, I went around and around with one individual who told me "I cannot get ANY of my blades to fully harden!".   Of course when you ask someone to take you through their process, it's always a very rough outline of what they do, and rarely every in the detail needed.  

  After several calls from him, it finally it came down to me telling him...."Now, I need you to take me STEP BY STEP through your process including EVERY detail of what you do, and how you do it."  He did, and when he got to...."I heat the blade in the forge, and once it's to temp, I take it to my quench tank and quench it".......STOP!   "Where exactly is your quench tank in relationship to your forge?"   The reply:  "Oh, it's just on the other side of the shop."  Turns out "the other side of the shop" was about 30 feet away, through a door, and under an open overhang.  Long story short, my best guess is IF he was heating just to critical temp, the blade(s) was easily a few HUNDRED degrees too cold when he got the to quench tank.

  Which brings me to the moral/conclusion of my story.....  For ANY operation with steel, that requires a specific temp, the steel must be at that temperature when the associated/required action occurs/takes place. 

  So, IMO, the answer is "YES!".  What you've hit upon is the "art" portion of Bladesmithing.  Knowing that the steel must be at a specific temp when the actions occurs is only the beginning.  The rest is figuring out just how much above the specific temp you need to go when heating, to overcome all those unique factors IN YOUR shop, that contribute to how rapidly the steel cools....without overheating the steel enough to cause damage.   

Great question!  And good on ya for asking it! 😉    

Ed Caffrey, ABS MS
"The Montana Bladesmith"
www.CaffreyKnives.net

 
Posted : 17/03/2023 5:39 pm
Matthew Parkinson
Posts: 540
Honorable Member Journeyman Bladesmith (5yr)
 

move the tank don't up the temp .. air is a quench medium just very slow. 

MP 

 
Posted : 18/03/2023 7:28 am
Kevin R. Cashen
Posts: 118
Estimable Member Admin
 

What Matt said.  Absolutely do not bump up your temp, I would rather be under temp than over temp.  As Matt said, air is a good insulator, but you do not want your quench on the other side of the room from your heat source.   Not many folks get the opportunity to look into what is actually going on at the point of transformation on the way up and the way down, I have been fortunate enough to study it quite well over the years and just this last December worked with John Verhoeven and Tim Zowada studying the air cool from critical quite closely in ways not done before.

The first thing to realize is that the “critical temperature” on the way up is not the same at all on the way down.  This is why they have the separate designations of Ac1 and Ar1 on the charts, since Ac1 can be as much as 100°F different from Ar1.  The easiest way to see this, is heat a piece of steel to decalescence and look at the color where the magnet stops sticking.  Then allow the steel to air cool and make note of the color where the magnet will stick again.  You will be shocked at how the steel will be dull red to almost black, in some circumstances, before the magnet will stick again.  This is the same transformation on the way up, but in reverse when the steel recrystallizes to make pearlite.

This is not to say that it is a good idea to let the steel cool this much, because there are all kinds of other phases that can come out of solution before you make enough pearlite to pull on the magnet and so it is best to be closer to your soak temperature of you want best results.  If you get lower hardness readings quenching three feet from your kiln I would look for decarb first and then your soak time/temperature.  If you are walking twelve feet from the heat source to your quench, then I would move that up on the list and get that quench tank next to the heat source.   

This post was modified 1 year ago by Kevin R. Cashen
 
Posted : 18/03/2023 11:05 am
Posts: 5
Active Member Apprentice Bladesmith
Topic starter
 

Great info. Thanks, gentlemen!

 
Posted : 18/03/2023 6:52 pm
Kevin Stinson
Posts: 130
Estimable Member Apprentice Bladesmith
 

Posted by: Michael Samdahl

Here is a cheap gauge that I find works well.

I have that and am wondering What do you have it set for?

Posted by: Kevin R. Cashen

This is not to say that it is a good idea to let the steel cool this much

Is 3 steps too far? i currently don't own a kiln and HT with my forge and dont like the idea of my forge being that close to my quench oil unless i am quenching something really small like a scalpel and then i fill a small bread pan with oil and bring that over to quench in. i have dont super accurate readings for hardness but i tend to skate a 60-62 Rockwell file once i temper. sharing a picture as i know you need a certain amount of oil for it to work effectively but its a tiny blade 

 
Posted : 04/04/2023 11:37 am
Posts: 8
Active Member Apprentice Bladesmith (5yr)
 

Having your quench tank to the side of the forge takes it away from directed heat coming out of the forge.

As for the radiant heat from the sides shouldn’t be that concerning(not to be ignored either). This is especially true if forging in an open air environment(outside, very large shop with high ceilings,etc). Smaller spaces may likely require shielding and heightened level of awareness and precautions.

If the radiant heat is still concerning for you. You could make a barrier next to the forge(about a foot away) between it and the quench tank. It should reflect and absorb much of the radiant heat from the side of you forge. Much the same way heat shielding is used in automotive industry for exhaust and engine heat. It can be as simple a wire oven rack wrapped in aluminum foil held in a standing position between the two.

 
Posted : 06/04/2024 12:35 pm
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