Oil Quenching Air Hardening Steel?

69_knives

69_knives

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Nov 20, 2008
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I've had this idea running around in the back of my mind that I'd like to make a knife or three out of M4 and I read about oil quenching it to get maximum hardness out of it.

My question is do you quench it with the foil on or do you have to remove the foil?
 
I haven't done M4, but assuming it is similar to M2, you're going to want to pull it out of the foil, and you're going to want to pull it out of the oil as soon as it stops glowing.
 
That's what I thought. I can't even imagine how one would remove a glowing red blade from a foil packet. About the only thing I can imagine is some dude (me) playing hot potato with a red hot foil packet.
 
One of my friends have made a test recently to oil quench an AEB-L knife. He puts the knife in a SS rectangular profile and puts a piece of paper in it then covers both ends with fireclay. Before quench he gently hits one end of glowing profile and clay just pops out. Removes the knife and quenches in oil. The knife came out with no decarb and a very thin oxide layer and as hard as it can be...

Emre
 
Air hardening steels have been oil quenched and even brine quenched !
Emre's solution to removing the blade from protective stainless steel seems to be excellent !
 
I leave enough room in the foil pack to cut off with shears and reach in with pliers and pull the blade out, holding the other end of the pack with pliers. I like to take my blades out for plate quench although most people just plate quench in the foil.
 
Actually most air hardening steels can be oil quenched and when oil quenched the performance and the stain resistance is a little better than air hardened ones. Especially some semi-SS steels like D2 will benefit from oil quenching. Also for poor guys like us without the sub-zero equipment it is better to quench as fast as it can be and austenize as low as it can be...

Emre
 
Rossi Knives said:
Why not just air harden it?
Click to expand...

Because with complex steel there is more to it than just getting "under the nose".

Steel manufacturers frequently recommend an interrupted oil quench (or salt quench) for HSS to optimize its properties.

Carbon movement is time and temperature dependant. Carbon is leaking out of the austenite on the way down, and will combine with alloying elements to form carbides rather than staying in place in the soon-to-be-martensite.

A rapid quench will reduce this carbon leak - achieving two things. A more carbon rich martensite, and more free alloying elements, which can be a good thing. And, through a mechanism that I don't understand, it will also result in less retained austenite.

According to the 5th edition of "Tool Steels", high speed steel in industry is frequently about 20% RA. That is after three high temperature tempers.

A property that is important to us, but less important to tool makers, is fine edge stability. A nice homogenous micro structure with hard martensite, little RA, and an optimum carbide structure and fine even grain will have the best edge stability. A rapid quench helps some steels achieve some of these properties (though no effect on grain size or primary carbides). Cryo as part of the quench, and avoiding the secondary hardening hump are frequently helpful as well, though I'm not sure about M4.

HSS is generally fairly low in carbon, and high in alloys. Its hardness in the secondary hardening hump comes not from martensite hardness, but from the formation of carbides which increase the overall hardness of the microstructure (though probably reduce edge stability).

M4 is about 1.4% carbon, which would usually be considered very carbon rich - but not when you consider the very high vanadium, tungsten and moly content. These will gobble up most of that carbon. So even with its 1.4% carbon, M4 is probably still fairly carbon lean because all the alloying. There is also something like 4 or 5 % chrome. A rapid quench will prevent that chrome from gobbling up what is left of the carbon on the way down.

So, it seems reasonable to me that oil quenched M4 will have harder (stronger) martensite, less carbide volume, and less RA and more free chrome (corrosion resistance), though I'm unsure how one would go about cryo and tempering to maximize the effect.

... my .02 on oil quenching air-quench steels...
 
Thank you, Nathan; bookmarked and printed! I enjoy reading and rereading your posts on steel and HT and can only hope that some of it has sunk in when the time comes for me to draw on it.
 
Very interesting and makes perfect sense. Nathan, have you ever oil quenched any D2 and if so what kind of results did you get. I have been very happy with my plate quench and cyro, but, now you got me wondering. I think on the next batch I will quench one in oil and then go with the same cryo and temper as the rest and see what happens. I got a break from the job I was on and did a coupe D2 hunters and a W2 bowie with a harmon. I am a knife maker again.
 
ib2v4u said:
I am a knife maker again.
Click to expand...

Yay! Good to hear that Jim. :)

Yes, I have oil quenched D2, with good results. However, I have found that plate quenching D2 also gives good results. Both are much faster than an air quench or positive pressure atmosphere quench. I couldn't tell a difference in the finished blade.

HSS, and ATS34 / 154CM steels which are very borderline air quench steels - oil is probably worth the bother, I don't know.

The quench should be interrupted before Ms or you'll risk unnecessary warping. HSS should be pulled as soon as it turns black.
 
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