MEMBER ITEMS FOR SALE
Custom Knives | Other Knives | General Items
-------------------------------------------
New Posts | New PhotosAll Photos



Go Back   The Knife Network Forums : Knife Making Discussions > Custom Knife Discussion Boards > Knife Making Discussions > Heat Treating and Metallurgy

Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

Reply
 
Thread Tools Display Modes
  #1  
Old 09-09-2006, 04:01 AM
Bob Warner's Avatar
Bob Warner Bob Warner is offline
Living Legend
 
Join Date: Jun 2002
Location: Royse City, Texas
Posts: 1,820
Stainless heat treat: I need a complete process

I have been reading the forums since 7pm (notice the time of this post) about heat treating stainless (Bob's big adventure).

I can usually put parts of one post with parts of another post and come up with a process, NOT THIS TIME.

I plan on heat treating 440C (inexpensive but good steel, right?). I will build my oven before to long with digital controls.

I need to know a step by step process to heat treat 440C. For grins lets say I want RC58 just to have a standard for this discussion.

Here is why I am asking:

I don't understand what "Snap Temper" means but see it used often.

I am confused when I read about "Air Hardening Steel" being quenched in oil. What kind of oil?

Do I need a fan or quench plates?

If I use plates, the cutting edge will not touch the plates and not cool as fast as the spine. This would leave the spine harder (cooled faster) than the cutting edge right? What is the point of quench pates if this is the case? You RC test the tang right? You don't know what hardness the edge is. How do you know the edge is at RC58?

Can you use foil more than once?
If not. why not?
If so, how do you know it is wore out?

How do you test a 440C blade? Put in a vise and bend the crap out of it or use a hardness tester. If it is RC58 is it automatically good to go? Would you trust it in the hands of a soldier trying to survive by the RC test only?

If you can get RC58 without cryo, WHY cryo? What is the benefit? If it will cut a rope two more times, I would think that learning to sharpen the knife would be a better investment.

Why don't people use argon fed into their ovens (like Geno)? Wouldn't it be cheaper than buying all that foil? From inert gas heat to oil quench would pretty much eliminate scale, right?

So, now that I got that off my chest, does anyone want to share their process?

I can be kinda dense sometimes so something like this is what I am hoping to get:

Step one, take your ugly ^%& knife and wrap it in foil with some paper in it.
Step two, set the oven controller to do (whatever it needs to do, heat to X degrees and hold, then heat to X degrees and hold again ).

"Ding" when it is all done.

Take your ugly ^%& knife out very quickly and throw it in the lake.

Heat it up to X degrees to temper.

Purdy it all up.

Sell it for millions.


Any takers?


__________________



Tumbling down the road at 35 MPH is no fun, TRUST ME!
Reply With Quote
  #2  
Old 09-09-2006, 06:26 AM
nate d. nate d. is offline
Enthusiast
 
Join Date: Nov 2002
Location: OK
Posts: 97
Mr. Bob,

Glad to see you are dong better first of all. I don't know if I can answer all of your questions in one sitting. Today is Sat. but i've got a scheduel unfortunately. Sir, i became a metallurgist in college because no one could answer many/most of my metals questions I have, just like you do, in plain English. Been ther done that got the T-shirt. OK so here goes.

I've never heard of snap temper and don't have time to look it up. i'll come back to that one.

If you want a faster quenching medium you will go to oil instead of quenching in air. there are risks with doing this. let me stop here and tell you that this question would be easier to answer with a Time Temperature temper or TTT curve. this will tell you how fast you have to cool a material to get the desired micristructure or more important properties.

quench plates for me are stupid proof, and i use them. i screw up blades when i'm not paying attention and thats <1% of what i've made. I can't get the steps right for oil and never tried air quenching. OK on the next question about hardness, i don't buy that there will be a different hardness from spine to cutting edge. in the case of 440C i think you have like 30 sec. to reduce the temperature to 400C so that is plenty of time for heat to dissipate out of the uncontacted cutting edge. thermal conductivity is a wonderful thing, God is the Master Thermodynamicists. OK better go for now. Sir, i'm up here in OKlahoma city now thank goodness, if you wanna meet up and talk face to face about this.
Reply With Quote
  #3  
Old 09-09-2006, 06:38 AM
RJ Martin RJ Martin is offline
Steel Addict
 
Join Date: Jun 2002
Location: Bridgewater, MA
Posts: 249
Send a message via ICQ to RJ Martin
OK Bob, here you go:

Take your 440C blades and wrap them in SS foil. If you have multiple blades that are the same thickness, you can arrange them in a single layer in a single, larger packet.

I like SS foil because it is reliable and foolproof. It's relatively inexpensive, because I buy it in large rools. And, it continues to protect the blades while they are being quenched.

You need two, flat Aluminum plates, larger than your foil packet, and 1" thick, minumum.
Do not use any paper inside your foil packet. It just causes problems.

Once your blades are wrapped, and the edges are double folded and crimped (use a dowel or some sort of plastic tool handle to crimp them), support them in your furnace on a firebrick(s) that have 2 slots cut into them that will accept your forked tong. So, the blades are lying on their side in a single layer inside the foil pack. Just wanted to clarify that....

Ramp your furnace up to 1875F, as fast as possible. This will likely take between 1.5 and 2 hours, with blades in it. My CRESS furnace can reach 2000F in 1 hour with no load, but, it is faster tnhan most.

Soak your blades for 40 minutes at temperature.

Set up your plates in front of the furnace. One plate on the ground, the other plate standing on edge, next to the first plate, so they make an "L".

After 40 minutes at temp, put on your gloves and open the door. Get your forked tongs under the foil packet, remove it and lay it on the lower plate. Use a "pizza man" move to deftly remove the tongs from under the packet. Drop your tongs and grab the top plate, laying it carefully on top of your packet.

Now, get up and stand on top of the plates. You will hear the foil creaking. this is good.

Depending on how thick your blades are, how many blades you have in the packet, and the size of your plates, your blades will be well below 900F in something like 30-60 seconds.

At this point, you can continue to let them cool, or, do the following:

Remove the top plate and trim the entire perimiter of the foil packet with a pair of sharp scissors. Peel up the top layer of foil (I use bare fingers for this, but, I am kind of crazy!)

If your blades are stuck to the foil, grab the tang of the blade with a gloved hand and peel them off. Check your blade tips and hand straighten if necessary. Lay them back on the plate and re-cover with the top plate. Stand on it again for another minute.

At this point, your plates are warm and your blades are very happy at around 200F. The hard part is done.

Once the blades are cool enough to handle without gloves, do a hardness check, if you have a Rockwell tester. You may need to check more than once, as the martensite is still fresh. If you get 59, great.

If you want to cryo, do so now. Hang your RT blades in string and lower into the dewar. 6 hours is planty, but I use 24.

After the cryo, temper twice @ 325F. You may have to play with this temp a bit to get Rc58. If your blades are under, then you may need to use 1900F for your Austenitizing temp.

If your blades are harder, double temper again, going up 25F in temperature.

Allow the blades to cool to RT in between tempers.

That's it. Full recipe for 440C Heat Treatment.

Now, to your questions:

Snap temper: A quick, 300F temper for 1 hour before cryo treatment. Performed right after quench. Reduces stress in newly formed Martensite to recude the possiblilty of cracking during cryo. I used to do it, not anymore. Never had a blade crack in cryo.

Yes, you can quench air hardening steel in oil. But, it's not going to get any better than the above process.

Use quench plates. No fan is required with my method.

Your edges will be fully hardened, don't worry. Quench plates suck the heat out so fast. It's beautiful.

Your foil will be grey and brittle after a single use. Throw it out. Don't be cheap. You'll ruin blades if you re-use it.

If you want to test your blades beyond Rockwell testing, sharpen them up and CUT with them. Pry, chop, whatever. Hell, break one off in a vise if you don't trust it. The broken surface should be a fine grey surface that looks like really smooth velvet. If you want, send one to Crucible and pay them to analyze it. You'll get a nice report with micrographs and a full workup. Worth the $$!

Argon is an alternative to foil. If you like the idea, do it. But, how do you get 20 individual blades in and out of the furnace at the same time with Argon?
I can do that with my foil pack!!

Cryo helps convert retained Austenite to Martensite. Many high alloy steels won't achieve complete conversion when quenched to RT, because the alloying additions lower the Martensite finish temperature (Mf) to below RT. Can you make a great knife without cryo? Sure. But, cryo is kind of an "equalizer" in the HT process. It can get you to a better finished product even if some aspects of your HT are a little off.


Bob: I hope this helps. Good luck!

RJ Martin


__________________
Stay Sharp,

RJ Martin
Knifemaker
www.rjmartinknives.com
Reply With Quote
  #4  
Old 09-09-2006, 07:54 AM
SVanderkolff's Avatar
SVanderkolff SVanderkolff is offline
Moderator
 
Join Date: Jun 2002
Location: Mildmay, Ontario, Canada
Posts: 2,472
Bob
First thing that took me a while to get my head around was how forgiving 440C is. One of the reasons you will find an almost infinite variety of HT methods for the steel is that the steel will harden nicely in a wide range of procedures. SO here is mine

Prepare the blade - here is choice #1 do you want to hand sand to almost final finish before HT or after, I go to 800 grit and polish before HT
Wrap in foil - yes you can use it again if you have been careful the fist time, I have had no problems with reusing. Do not put paper in the bag. A little too much and the expands and gets leaks
place it in the kiln in a set of slotted holders spine down. I have two sets of slotted ceramics so I can stand multiple blades in my kiln. I have never had any luck with more than one blade per package.
Ramp the kiln to 1900 and hold for 5 to 10 minutes. The steel is so thin that it will be a consistent temp in that short a time.
Grab some good gloves and a long pair of tongs, remove the package from the kiln and place it on the quench plate and put second plate on top. Wiat 1 minute then take off the top quench plate and carefully cut one end off the foil pack , preferable the butt end of the knife end. Use a pair of needle nosed pliers to remove the blade and put it back between the quench plates. Let it sit for a few minutes until cool enough to touch. Into the toaster oven at 400 for 1 hour. test withthe rockwell tester. I hit 58 to 60 every time. Buff off the colour added by theHT and you are ready to start the handle.

Hope that helps
Steve


__________________
Stephen Vanderkolff
Please come on over and check out my website. http://www.vanderkolffknives.com/
Thanks
Reply With Quote
  #5  
Old 09-09-2006, 09:07 AM
tbark44 tbark44 is offline
Member
 
Join Date: May 2006
Posts: 22
If you triple package the blades in the foil you have No discoloration but you need to add time to 25 min , the outer foil pack is destroyed but the 2 inner foil packs can be reused without any problems , Name of the game is to Keep the air away from the steel , I quench mine in olive oil the temper 2 times for 2 hr's each time allowing it to compleatly cool in the oven , T
Reply With Quote
  #6  
Old 09-09-2006, 10:17 AM
RJ Martin RJ Martin is offline
Steel Addict
 
Join Date: Jun 2002
Location: Bridgewater, MA
Posts: 249
Send a message via ICQ to RJ Martin
Bob: Keep the soak time to at least 30 minutes.


__________________
Stay Sharp,

RJ Martin
Knifemaker
www.rjmartinknives.com
Reply With Quote
  #7  
Old 09-09-2006, 10:33 AM
SVanderkolff's Avatar
SVanderkolff SVanderkolff is offline
Moderator
 
Join Date: Jun 2002
Location: Mildmay, Ontario, Canada
Posts: 2,472
HOW DARE YO DISAGREE WITH ME!!!!!!!!

Anyways, can you tell me why it needs a longer soak time. I always figured that since we were dealing with at most 1/4" thick steel it would not need much soak to heat the whole thing through. Is there some benefit to holding the temp for a while?
Thanks
Steve


__________________
Stephen Vanderkolff
Please come on over and check out my website. http://www.vanderkolffknives.com/
Thanks
Reply With Quote
  #8  
Old 09-09-2006, 11:36 AM
Bob Warner's Avatar
Bob Warner Bob Warner is offline
Living Legend
 
Join Date: Jun 2002
Location: Royse City, Texas
Posts: 1,820
Thanks RJ and Steve.

RJ, I am curious what your forks look like that you remove the blades with.

Is there a length of time between hardening and tempering that is critical? I was hoping to use the oven for tempering as well but would have to let it cool down first. Is this a problem because it could take a while to cool down.

Would there be an advantage to freezing the quench plates?

Would it be advantagous to get thicker than one in aluminum plates or will one inch be good enough for all applications?

Will the method need to change in any way for 1/4" steel -vs- 1/8" steel? It seems the quench plate time would be longer.

On the Bob Loveless video he sends his blades out for heat treat. They come back black. Does the place he gets them done not worry about scale?

RJ, your description says that you hardness test after the blade comes out of the quench plates. If I get 59 I would not have to temper? The blade is good to go?

Thanks


__________________



Tumbling down the road at 35 MPH is no fun, TRUST ME!
Reply With Quote
  #9  
Old 09-09-2006, 12:06 PM
SVanderkolff's Avatar
SVanderkolff SVanderkolff is offline
Moderator
 
Join Date: Jun 2002
Location: Mildmay, Ontario, Canada
Posts: 2,472
Bob
You will definetely have to temper. I just finished a small blade and forgot to temper. RC was 61. I went to pressure fit the guard and shattered the stub tang. I forgot to temper.

My quench plates are 2 1/2" thick each and they still get warm after a big blade. Thicker is definetely better.

BTW, why are yu switching to stainless. It would sem to me that you would know well how to harden the steels you were working before. The onlydiference would be shaping through grinding versus through pounding.

SO, why switch from the steels you are comfortable with???

Steve


__________________
Stephen Vanderkolff
Please come on over and check out my website. http://www.vanderkolffknives.com/
Thanks
Reply With Quote
  #10  
Old 09-09-2006, 12:23 PM
RJ Martin RJ Martin is offline
Steel Addict
 
Join Date: Jun 2002
Location: Bridgewater, MA
Posts: 249
Send a message via ICQ to RJ Martin
Steve: It's not just about reaching the temperature-In that respect, just a few minutes soak is fine. You need to give the various alloying additions time to come into solution, and distribute themselves properly, in preparation for the quench
.
I find this to be a big mis-conception in knife heat treatment. People read about grain growth and get nervous, and the result is that they don't achieve what their steel is capable of WRT microstructure.

If you have an accurate furnace, and stay approximately in the center of the recommended heat treat temperature for your steel, there is little danger of problems from over soaking. There are problems from undersoaking that will show up in performance, but, not necessarily in terms of hardness. So, you may get the right hardness, but not have the best microstructure. (large carbides instead of small ones).

I don't use 440C anymore, so, I consulted my Crucible handbook for their recommended process. Their soak time is 30-45 minutes. Generally. the higher Austenitizing temperature gets the lower soak time, and vice versa. So, for the middle range, I recommended 40 minutes. This is close to what my old heat treater used to do my 440C blades at.

BOB: You can temper 440C right in your kitchen oven. Just monitor the temperature with an oven thermometer-some ovens are off about 50 degrees. Keep records, so you can learn what works with your setup.

Don't freeze your quench plates, it may warp your blades. Plus, it's not necessary. Aluminum plates cool your blades far faster than air, which is what 440C was made to harden with. You'll get a great quench rate with RT plates.

As to thickness, I like 2" thick. The thicker the better, really, particularly for larger, thicker blades and multiple batches.
With thinner plates, you can cool them down after use in the kitchen sink, or outside with a garden hose, if you're doing multiple batches of blades.

No, you have to temper-it's critical to make your blades tough enough to resist chipping. You'll probably get 60/61 at quench, but, it's important to know the hardness so you can adjust your tempering temperature. If you got 59, for example, I'd still temper twice at 300F. I'd rather have a softer blade that was tempered than a harder, untempered blade.

Your blades will probably get grey and possibly develop some colors from the thin oxide layer caused by the air burning up during HT. Sharp edged and points can occasionally puncture your foil, which will cause some dark grey scale locally. You can help prevent this by nesting your blades in the packet, alternating the tip direction (left, right, etc.) and lightly rounding the tips off.


__________________
Stay Sharp,

RJ Martin
Knifemaker
www.rjmartinknives.com
Reply With Quote
  #11  
Old 09-09-2006, 01:02 PM
mete's Avatar
mete mete is offline
Master
 
Join Date: Sep 2004
Location: NY State
Posts: 777
Soaking - you're starting with a structure of ferrite with spheres of carbide . The carbides must be dissolved and the carbon diffused throughout the matrix. Unless those carbides are dissolved as much as possible [you can't dissolve all of it] and the the carbon diffused uniformly throughout the matrix you will never achieve the properties that the steel is capable of. The more complex the alloy the more difficult it is to dissolve and diffuse the carbides.There seems to be a fear of grain growth but the very alloying elements that require long soaks also greatly retard grain growth....If you guys weren't so cheap you'd get a vacuum furnace and make it much easier !!
Reply With Quote
  #12  
Old 09-09-2006, 02:16 PM
AcridSaint AcridSaint is offline
Guru
 
Join Date: Jan 2004
Location: North Carolina
Posts: 1,144
I didn't see a really clear explanation on why your edge won't be harder Bob, so I wanted to touch on that. As mentioned in the earlier posts, physics is doing iit's best to help you out with that one. Heat transfer allows the metal to evenly distribute the heat and it is much faster in air hardening steels (to the best of my knowledge). The reason that aluminum and copper cool so fast is because they have a high heat transfer rate, that's why we see them being used as heat sinks when air isn't enough. Basically, the aluminum is going to move the heat away from the blade relatively evenly and quickly, so long as it's touching the majority of it. The air hardening steel is going to do the rest of the work.

That's my newbie understanding of air hardening steels and plate quenching. I will now prepare for lambasting from more experienced makers


__________________
Cap Hayes

See my knives @ knives.caphayes.com

This quote pains me:
-- "Strategically placed blood grooves control blood spray in covert deanimation activities." --
Reply With Quote
  #13  
Old 09-09-2006, 06:21 PM
RJ Martin RJ Martin is offline
Steel Addict
 
Join Date: Jun 2002
Location: Bridgewater, MA
Posts: 249
Send a message via ICQ to RJ Martin
Mete: Didn't I just say that, but in layman's terms <G>. THANKS for the not too complicated explaination.
And, no, I don't want a vacuum furnace unless it's got positive pressure nitrogen quench. My quench plates do just fine and are faster!

Bob: forgot to tell you about the "fork" It's 1/4" or 5/16" Dia round stock, bent into a "U" with the tines about 3-4" apart. Weld a "T" handle to the bottom of the "U" and you're all set. Legs of the "U" are about 18" long, or longer if your furnace is deep.

AcridSaint: What you said, plus the thermal gradiant that keeps the heat in the blade moving up into the spine.

RJ Martin


__________________
Stay Sharp,

RJ Martin
Knifemaker
www.rjmartinknives.com
Reply With Quote
  #14  
Old 09-09-2006, 08:16 PM
nate d. nate d. is offline
Enthusiast
 
Join Date: Nov 2002
Location: OK
Posts: 97
Talking

Stainless foil is used and is oxidized away grabbing up most of the oxygen in the furnace environment. This prevents the blade from being as oxidized as much. I do like to put paper inside the envelope to further reduce oxidation of the steel.

the foil is so oxidized and brittle you can't reuse the envelopes.

Why cryo. at room temperature the transformation to Martensite is not 100% complete, but we can drive the transformation or reaction closer to completion by lowering the temperature. this does work. I can take a blade that is hardened and raise its hardness 2 points by cryo treating. I've done some piddling around with cryo treating and watching the microstructure and i can't see any difference in the microstructure of a HRC60 blade and that of a HRC63 blade, in the as hardened state. So thats cryo, use it on Stainless and most knife materials, it will do good things for you. ok this next thing is gonna piss some folks off but here goes. you don't have to leave the blade at cryo temperatures but a short period of time. I mean when it reaches the temperature of the liquid you have it in then another couple of minutes and its done. the reaction is instantaneous and does not take hours to complete. I dont' know about how it improves the edge retention of a blade. I haven't really looked into that, i just know that harder it is the longer the edge is held and the more deer and i cut up before resharpening my device.

OK my process.

finish to >240 grit finish

put the blade in a SS envelope. if you don't you will really have to work at getting the oxide off and cleaning up the blade. I fold my seams over twice and put paper on both sides of the blade. I put double sided tape on the blade put the paper to the tape and slide it all into the envelope. very little oxide in the blade upon completion.

ramp the funace up to 1900 degrees F and hold for 40 minutes, So all the carbides are going into solution here.

quench between plates bigger than your knife blade otherwise you may have warpage issues. Aluminum works copper is great, ive got plates made of steel. they all work good. Here we've frozen the carbides into little particles throughout the blade.
I do not take the knife out of the envelope i put it all between the plates and quench.

Take the knife out of the foil and dunk in LIN. allow the blade to stay in there till no more bubbles are coming off the blade and the LIN is no longer boiling off. a couple of minutes. complete the martensitic reaction.

Pull out of there and allow to come to room temperature.

now temper at some temperature above 300F. Otherwise you are gonna see a rise in hardness and not a decrease in hardness. I stress relieve my blades at 325F for 30 minutes and get about 63 HRC out of them consistently. OK so there you go.
Reply With Quote
  #15  
Old 09-09-2006, 09:42 PM
Larrin Larrin is offline
Steel Addict
 
Join Date: Jun 2004
Posts: 278
Quote:
Originally Posted by nate d.
Stainless foil is used and is oxidized away grabbing up most of the oxygen in the furnace environment. This prevents the blade from being as oxidized as much. I do like to put paper inside the envelope to further reduce oxidation of the steel.
Putting paper does not reduce oxidation, it can only increase it. If it burns up, that just creates carbon dioxide, which is an oxidizer for stainless steels. If you ever pull out a knife and find that the foil is puffed out, this is from the buring up of the paper. The foil is designed to suck out the oxidizers, and it does it just fine, as long as you wrap your foil right. I was talking to a knifemaker the other day (who will not be named) who had been heat treating with paper for a long time, but suddenly was having problems with his heat treat, every time the foil would be puffed out. So to "correct it", he was adding more and more paper, and guess what? It kept getting worse and worse. When he heat treated without paper, he couldn't believe what the knife looked like after quenching, he figured it was just supposed to come out looking a little tarnished, this thing looked like aluminum. Imagine that.

The moral of the story: do not use paper in your foil packets.
Reply With Quote
Reply

Tags
blade, forge, forging, knife, knife making, knives


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 07:44 PM.




KNIFENETWORK.COM
Copyright © 2000
? CKK Industries, Inc. ? All Rights Reserved
Powered by ...

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
The Knife Network : All Rights Reserved