Heat treating question- Soak times

Jericoh

Well-Known Member
So my Evenheat furnace looks to ship this Wednesday, so I've been wrapping my head around the whole heat treating thing. One question that has come up that I haven't been able to find an answer to involves soak times. Does the soak time start when the furnace reaches temp, or when the blade reaches temp?

Say I put a blade in the furnace and start her up to 1475. Do I start timing when the furnace reaches 1475? Or when the blade gets to 1475? Say, I'm putting a blade in an already at temp oven. Do I start timing, or wait until the blade is hot? For 1095 it, in theory, should be easy to check when the steel is at temp because of the loss of magnetism, but for something like CPM154CM or Elmax that goes really hot....

Thanks
 

EdCaffreyMS

Forum Owner - Moderator
When you read about soak times for given steels, it generally refers to the time measured from the point when the steel has reached the indicated temp.

Without getting into "this is what I do", I would encourage you to experiment. The old saying of "you can't make a cake, without breaking a few eggs" also applies to heat treating. There are always a number of variables present within each individual environment/shop that may require an individual to deviate from written procedures. What I'm saying is to use the written data as a STARTING POINT, and adjust as necessary based on the results you achieve. Yes, that means that you are going to wreck a few blades while you are "learning" how to heat treat, but that is the price we all pay to learn our craft. No amount of written information nor quality level of heat treat oven can ensure a "good" heat treat.....it's all about the experience of the individual who is using those tools.
 

rob45

Well-Known Member
Say, I'm putting a blade in an already at temp oven. Do I start timing, or wait until the blade is hot?
The very act of opening the oven door means the oven will no longer be at temp, so you have to account for the "recovery time" of your particular oven.
When you get your oven, something that you'll soon notice is the amount of heat loss as soon as that door is opened.
 

Knifemaker.ca

Dealer - Purveyor
You're asking the right questions and that shows a pretty good understanding of the issues even before you start. I personally use anti-scale compound to protect non-air-hardening steels - and I put them in when the oven is at temperature. The 'soak' as has been mentioned, starts when the blade has equalized at the oven temperature. I usually allow 5 to 10 minutes depending on size / number of blades - and then then start counting soak time.

I do stainless in foil envelopes, and putting them in a hot oven usually turns out badly. The air in a well sealed envelope expands so fast it blows the envelope open, and ruins the blade. I put these blades in a cold oven and expansion has time to adjust gradually so as not to compromise the envelope. Heating it this way, the blade is very close to the same temperature as the oven, since they get there together, so for these, the soak starts when the oven gets to temperature.

You may find other things that work for you, but understanding the problem is the best way to developing your answers.

Rob!
 

Jericoh

Well-Known Member
Thanks guys, and holy smokes, Ed Caffrey responded in one of my posts, anyway one other dumb question. How do you tell when a steel like Elmax or CPM154CM has come up to temp? They're gonna be almost 2000 degrees, I haven't found an infrared thermometer that goes that high. I would imagine that with CPM154CM being in the oven for 2 hours there's no way it wouldn't be at temp, but how do you tell? Does each steel have a different point that it looses magnetism or do you go by color or just voodoo?
 

EdCaffreyMS

Forum Owner - Moderator
It's all about time and temp...especially when dealing with steels like CPM154...... with those steels you have to be able to trust the controller on your oven.....and allow for the proper soak times. In general, the less alloys present in a steel, the less soak time is required....as you get into more and more alloys within the steel, it requires more time at a given temp to get everything into "solution". As has been mentioned, your asking intelligent questions, and I have little doubt that you'll have a handle on it fairly quickly.
 

Battle Creek Knives

Well-Known Member
Jericoh,

I would not start with such complicated steels.. do some 5160, 01, 1084 to start and have them RC tested... .

also do NOT expect your kiln to be dead on in temps, some thermocouples have been found to be off bigtime... (ask me how I know).

When I first got my kiln I would bring it to temp as fast as possible, soak the blades as required etc... to only find failure..

now I bring my kiln to temps slowly and let the chamber bake for a good 20 mins before I place blades in...

there are a few methods to try to calibrate your oven, but the most accurate is trial and error..

if I were you to save the frustrations I just currently went through, I'd take 2 small coupons of the desired steel, say 01 for example... HT and quench per specs, only temper one coupon per spec and have them both RC tested..

you may be surprised at the results, you may find your kiln is dead on, and have a good system to run with reliably...

my case however I've found my kiln to be off at least 50*F, I wasn't getting the steel hot enough and the recommended 1475-1500 wasn't doing it per my thermocouple......

good luck.. and be safe :)

btw, it is voodoo and it is best to HT at night with low artificial lighting.. colors do make a difference... (in my very limited experience)
 
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Jericoh

Well-Known Member
Thanks guys. Rob I gotta hit the ground running with this thing. Ive got test blades ready for trying out stuff, but also have 34 knives waiting to be heat treated right after. A mix of 1095, CPM154CM and Elmax.

Here's another dumb question. Say the blade is heat treated and quenched and the as quenched RC is exactly what I want the finished knife to be. Does it still have to be tempered just to end up at the same RC? Is it a stress relieving thing?
 

rob45

Well-Known Member
Yes, the purpose of tempering is to relieve stresses.

I don't know if and how it may alter the hardness, but I do know that tempering should be included as part of the overall heat treating process.
So it's probably best to aim for a target hardness that a known tempering process can provide.

For almost any known steel, there will be a "schedule" with different temperature options to provide the hardness you seek for your application.
Keep in mind that these are targets, not exact results. There are too many variables involved, so it's best to start with a suggested schedule for your steel, and then "tweak it" if need be.
 

Jericoh

Well-Known Member
Gotcha. So even though the blade comes out of the quench at the hardness I want it still needs to be tempered to the same thing so it can be all relaxed. Awesome. I think I'm about ready for launch.
 

Jericoh

Well-Known Member
According to Uddeholm, the lower temp hardening directions the as quenched hardness is 58 which is what I have my blades heat treated to now. If I went with the higher temp directions the quench hardness is 61 or 62 if I'm remembering right.

Oh yeah, this is for Elmax.
 

DJJ

Active Member
Great info.
My Evenheat arrived last week,trying it out this weekend with 1084 and 01.
 
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