How do you heat treat 440C?

C

cjwb2012

Joined
Dec 7, 2013
Messages
27
Hey guys!

I'm just wondering how all the pro's heat treat their 440C SS? I have a chefs knife I will be heat treating in a few days. Its 440C from NJ Steel Baron and I want to make sure I'm on the right track. I have an Evenheat kiln I do my heat treating in and have wrapped the blade in a few layers of foil and added a small scrap of paper. The blade has a flat grind(dime thick edge) and is sanded to 320 grit. I plan on heating to 1880-1900 and holding for about 15-20 minutes and quenching in warm oil. Do I need to hold the blade at at a lower temp say 1400-1500 for any time or just go right to hardening temp to hold?

Thanks for any advice.

-Rob
 
Here are a few searches:
http://www.crucible.com/eselector/general/generalpart2.html
http://www.bladeforums.com/forums/showthread.php/463148-Heat-Treating-440C-Stainless

Here is my HT specs for 440C:
The blade must be enclosed in a stainless foil packet to keep all oxygen away from the blade.
Pre-heat at 1400F ( 760C) and hold for 10 minutes.
Raise temperature to austenitize at 1900F (1040C) and hold for 30 minutes.
Air cool or use aluminum quench plates. ( quench plates are best to prevent warp)
Cool in water to room temperature.
Immediately chill to at least -95F (-70C) for 30 minutes.
Allow to warm to room temperature.
Temper at 375F (190C) for two hours, cool in water to room temperature, and repeat the temper for a second two hours.
 
OK great. Thanks for the links. I have seen both of those links but they didn't quite answer my question and some even began leading me down the wrong path...(1950F for an hour) but now you have clarified what I need to do so thanks! I have the blades enclosed in 2 layers and are hopefully air tight. Crimped the ends with pliers and added a scrap of paper. Ill have to invest in some quench plates for now oil will have to work.
 
Also, is the "foil" you are referring to stainless steel HT foil? Two layers is not needed if it is HT foil. Ten layers won't work if it is any other type of foil.
 
Just finished the HT and the blade turned out great. There is a tiny bit of warpage but nothing I cant easily remove.
Preheated at 1400 for 10 min
Ramped up to 1900 and held for 30 min
Air quenched
Now its tempering at 375 for 2 hours....
There is a tiny bit of warpage but nothing I cant easily remove.

Bladsmth- Yes I used SS HT foil(2000F). Last time I used 1 layer it did not seal properly(Blade came out black). I'm sure I just didn't have the ends crimped well enough. Do you recommend adding any bits of paper. Like I said I did add some and the blade came out nice and clean.

Centennial - I did not end up using oil. I have a few knifemaking books and they both have oil as a method of quenching 440C (The Complete Bladesmith pg.24 and Step by Step Knifemaking pg. 264 - David Boye). Luckily I did exactly what bladsmth suggested and the blade turned out great. Point taken -No oil. Maybe I need to find more updated books.

Anyone else heat treating 440C a different way and getting good results feel free to share!

Thanks for the help gents! When I get her all done Ill throw up some pics.
 
I plan on buying some aluminum plates. When I use those I have read to leave the blade in the SS foil. Do I need to use compressed air to help cool or will the plates alone suffice? Thanks!
 
Just clamp the foil packet between the plates and let it sit for a few minutes. No need for air. Make sure the foil packet is large enough so the folds are away from the blade to assure a good fit with the plates. I pound my seams with a hard rubber mallet to get a good seal and leave about 1" of space around the blade.
 
Awesome thanks again!

Bladsmth - Ill be down your way for the next few weeks. Teaching a class to some Navy guys in VA Beach(Little Creek)

Anyhow, thanks again for all your help.
 
Shoot me an email about when you will be in town. My buddy has a BBQ shop where we get together with other makers from time to time ( Megallon's Gourmet BB, just up form the Amphib Base on Little Creek Rd.), and I live only a few more minutes away.
 
bladsmth said:
Pre-heat at 1400F ( 760C) and hold for 10 minutes.
Raise temperature to austenitize at 1900F (1040C) and hold for 30 minutes.
Click to expand...

Stacy do you alter either of these times in relationship to the thickness of the steel, say 3/16 vs 1/8 ?
 
No, I don't alter these times.

The HT process for stainless steels is a time dependent thing. Longer wouldn't hurt, but shorter may give poor results. Forget the things in industrial charts about 1 hour per inch and such. There is still a minimum. In stainless and high alloy steels, 30 minutes is a minimum. The 10 minute equalization at 1400 is to let the stresses out and allow the blade to fully convert to austenite before the steel is raised to the higher temperatures where the carbides will dissolve. Again, ten minutes is a minimum.

BTW, one place where newer folks go wrong is in HOW they time these steps. The time starts when the temperature reaches the target and is stable. A programmable PID should already do this, but when doing it manually, remember that the time starts at temperature, and not one second before.

I recall a person with a small jewelry kiln doing a stainless HT. He did not wrap the blade, and since the oven took over an hour to get up to 1900°F, he took the blade out once it got there. Suffice to say that varying from the accepted standard procedures did not get him good results.
 
bladsmth said:
Forget the things in industrial charts about 1 hour per inch and such.
Click to expand...

I assumed that had to do with the thickness not the length, I have never seen a 1 inch thick knife ;0)

One more question if you don't mind, how do you chill the blade to -95F ?
 
Last edited:
Sounds good. Ill shoot you an email when I get down there. Thanks!

Jone- I've read you could use dry Ice and acetone? Not sure what temp that will reach like I said its just what I've read.
 
Dry ice and denatured alcohol is the normal combination for sub-zero treatment to finish the quench. It reaches about -100F.
 
Welcome to Bladeforums. You may not have noticed that this is a year and a half old thread. Resurrecting old threads with a new question isn't usually a good idea. Posting a new thread is better.

To your answer, there is a lot more going on than just Rc hardness in the quench. The cryo (or at least sub-zero) step is part of the quench. Tempering is also part of the HT process. Skipping either can affect the steel.

Give us some info on what you will be making and how you will HT it and we can help more.
 
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