Air hardening steel?

G

Gossman Knives

Edged Toolmaker
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Apr 9, 2004
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This is probably a stupid question but when you air harden a steel are you simply taking it out of the HT oven/furnace and letting the outside air cool it or do you need a source of forced air to cool it quickly?
On a different note instead of starting a new thread, what are the key ingredients that make a steel stainless? Thanks
Scott
 
Chromium levels are what determines a SS, I think, Scott. Levels above 12% are considered SS's I think.. Thus, D2 @ 12% is considered "near SS".

I've done a lot of SS. After experimenting with oil quenching, still air (not good), forced air, and plate quenching, I prefer the plate quench. Nowadays I slap the blade in between the quench plates, tighten them down, and then blast compressor air in the little gap. Good hardnesses!
 
Thanks Mike. I thought the chromium was the ingredient but wasn't sure. I've been oil hardening D2 with excellent results but I'm always wanting to try different things. I have an air compressor, what are the plates you are referring to?
Scott
 
Razorback - Knives said:
Thanks Mike. I thought the chromium was the ingredient but wasn't sure. I've been oil hardening D2 with excellent results but I'm always wanting to try different things. I have an air compressor, what are the plates you are referring to?
Scott
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I have two 6x12x1 aluminum plates hooked into a horizontally mounted "quick-close" woodworking vise. I prop it open, lay the blade in the foil packet on the bottom plate, quickly close the other plate on top, tighten a bit, and blow air in between. I have one friend who lays one plate on the floor, puts the blade in, puts the other plate on top and stands on it....

It's not that they necessarily work better than oil. It's just less messy and you don't have to take the chance of either bending the blade ripping it out of the bag to quench or dropping 1900F steel on yer foot. :eek:

After hardening, I cryo, then temper. Others procedures may differ...
 
fitzo said:
I have two 6x12x1 aluminum plates hooked into a horizontally mounted "quick-close" woodworking vise. I prop it open, lay the blade in the foil packet on the bottom plate, quickly close the other plate on top, tighten a bit, and blow air in between. I have one friend who lays one plate on the floor, puts the blade in, puts the other plate on top and stands on it....

It's not that they necessarily work better than oil. It's just less messy and you don't have to take the chance of either bending the blade ripping it out of the bag to quench or dropping 1900F steel on yer foot. :eek:

After hardening, I cryo, then temper. Others procedures may differ...
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That sounds simple enough. I know about getting the blade out of the foil:rolleyes: but I need larger tongs because the flame up burns the hair off my arm when I quench.:eek: :D
Scott
 
Razorback - Knives said:
That sounds simple enough. I know about getting the blade out of the foil:rolleyes: but I need larger tongs because the flame up burns the hair off my arm when I quench.:eek: :D
Scott
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You don't shave your quenching arm?? :eek: ;)

I use long plain-jaw blacksmith tongs. :)
 
Since stainless steel requires higher hardening temperatures [1900-2000F ] oxidation and decarburization are more of a problem. Therefore you use foil to protect it.While you could use air, especially moving air it's difficult to remove the blade from the foil. Plate quenching eliminates this and insures no warping also. ...Why do bladesmiths have an obsession to remove arm hair ?They all shave it off or burn it off !!
 
And then if you're making damascus or forging, it seems you always end up with a little less eyebrow and beard, too! :D

In the hurry before a show, I never had ANY hair left on my left arm, and usually very little left on my left lower leg. I cut myself too much trying to shave hair with my off hand! :D

"Non-knife people" always ooh and aah when you blow on the blade and little hairs fly up into the air!!!
 
41357524-M-1.jpg
 
Yeah, just like that. Except, naturally, my aluminum's not that big! ;) :rolleyes:
 
I oil quenched D2 for years with good results, but have been plate quenching for the last year and a half. I don't see much difference, if any, with the results, but plate quenching in the foil is much less hectic. You get a cleaner end result with the plates. I use 7/8" X 8" X 14" plates of 6160 Al(?) with good success. Look on Ebay.

The 12% Cr is the old definition. The newer version I got from online tech sites (I will look up which one later) is that the steel has to have at least 10% Cr left over after Carbide formation to form a transparent layer of CrO on the outside of the steel which gives it the stainless qualities. With the high C content, D2 is not quite as near SS as you might think from the 12% definition.

Here in the high desert though, D2 seems to be pretty close to stainless. You have to really abuse it to get it to rust.
 
shgeo said:
The 12% Cr is the old definition. The newer version I got from online tech sites (I will look up which one later) is that the steel has to have at least 10% Cr left over after Carbide formation to form a transparent layer of CrO on the outside of the steel which gives it the stainless qualities. With the high C content, D2 is not quite as near SS as you might think from the 12% definition.

Here in the high desert though, D2 seems to be pretty close to stainless. You have to really abuse it to get it to rust.
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Thanks Steve for that info. One other question, when you blow air on the blade, how do you guys do it? Along the edge or along the spine?
Scott
 
Scott,

Use the yellow pages and find a metals supplier. Typically, they'll have or can get within a couple days what you need. Mine is 12"x4"x1.25". It was free because... well actually it wasn't free, but it was leftover from a job I did for someone.

I use mostly air-hardening steels now. I try to blow compressed air between the plates to blow out a lot of hotness. I'm kind of anal about it, but it seems to do a great job. After cryo, the steels are usually still wicked hard...














hey...











...pssst!











Kinda like IG's head! SHHHHH! :eek: :p :foot: :D
 
Scott, if you have access to a scrap yard, check there. Copper would remove heat even a little faster. Silver would be the best! Yeah, right!

Anyway, the stuff I bought through MSC was over $80 for a square foot of 1". That's awfully expensive, but we can't go into the local scrap yards because of "liabilty insurance issues".

Hopefully you can find something a whole bunch cheaper. If you go to a local supplier like Jeff suggested, don't forget to ask to look in their drop bin first.
 
Terry_Dodson said:
What are the air hardening steels yall use the most? A2, D2, any others? Are these forgeable also?
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I use A2 and D2. Mostly D2. I know that Larry Nowicki forges D2 quite a bit. Not sure about A2 but can't see why not.
Scott
 
Air hardening steels can be forged, but at least in the case of D2, it does what's called red shorting. Get it too hot or too many times and it'll crumble. It also hardens as it cools, so has to be forged hot and for shorter periods. It can be done, but it takes alot of skill. There's better steels for forging, IMO.
 
Terry, if you're looking for something different to forge, try O-1. It makes good knives. Forges hard and slow. Air hardens a little bit, so it'll give you a taste of forging alloy steels.
 
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