Heat treating - can somebody please interpret this ?

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faramir

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Oct 30, 2004
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I was lookingfor HT details for L6. I have no experience with HT any steel and only a vague idea as to how the process should go. Woudl anybody be kind enough and check out whether my understanding (below) is correct and chime in with suggestions ?

First of all, the steel in question is L6 as mentioend, source of information is http://www.knives.com/heatreat.html and owen to be used is lab owen (fully calibrated up to 1100 deg C, which is 2000+ degrees F).

A generic question about that particular page first: two temperatures are listed in each step of the process - which one is correct ?

These are the questions about the entire process itself:

Since the chunk of metal i'll be working with is of desired size already i'll skip the forging. I have to anneal the metal first so i heat it up to 1450 (?) F and let it cool slowly - how slow is "slow" ? I don't have wood ash handy anywhere near that owen, can i let the metal cool in air (or inside the owen, gradually reducing temperature) ? How long should the cooling take ?

When i'm done shaping that metal i'll have to harden&temper it. I heat it up again to 1450 F and quickly soak it in (olive ?) oil. What should be the temperature of the oil to begin with and how long am i supposed to soak a 4 mm wide (5/32") sheet of L6 ? What does "soak at full heat for XX minutes" mean ? Full heat of what ? Which "minute" figure is correct in that table ?

Then i have to temper it or it will remain brittle - i heat it up again to desired temperature from "Tempering" table) and let it cool slowly in the air ? Or what ?

I'm such a n00b :D Your help will be greatly appreciated.
 
Where did you get the L6? Without knowing the variety of L6 (or similar alloy) any advice will be ball park figures at best (and it would be a pretty big ball park ;) ). Almost any variety of true L6 will require more than heating and packing in vermiculite to cool. If you have an oven, normalize it and then soak it at 1275F. for an hour, this will work better than trying to give it a traditional anneal.
 
They aren't giving you two different temperatures but a temperature range , just stay within that range....A motor oil or machine oil would be better than olive oil and the oil should be heated to about 135F [57C] .But before you attempt something like heat treating L6 you should spend some time reading about heat treating .Start with my tutorial www.knivesby.com/robert-cella-1.html .
 
You need to get a few definitions down first, the wording is throwing you off :)

Soak: When your heat treating, and it says to soak at a given temperature, it means to hold the steel at that temperature for a given period of time. Kind of like baking the steel, soak at 1400 for two hours, means leave it in the oven at 1400 for two hours. This part fo the process helps dissolve carbon, and austenize the steel, and all that good stuff. Mete's tutuorial will probably explain that much better.

Quench: This is what you use the oil for. Quenching means rapidly cooling the steel, this is what hardens it. Some steels are quenched in water (this is the fastest) , some in oil (medium speed, varies depending on type of oil), and some in air (slowest). The type of steel will dictate how fast you want the quenching medium to be. 1095 for example, doesn't harden deeply as easy as O1. You normally quench 1095 in water or brine, O1 would shatter in water or brine. You quench O1 in oil. It all depends on what your working with.
 
Thanks for great replies guys - and i apologize about the typos (if i had a dime for every typo i make ... i'm blind as a bat, hence the typos). To be quite honest i don't know exactly what kind of steel i'll be dealing with just yet - but i figured if i understood the procedure for L6 i can do the same thing with any other steel listed there. When get it i'll enquire further about exact composition (but it'll be some kind of tool steel, saw blade or such) and then look up the closest match.

Matt, the "soak" part had me really confused - as i'm not a native english speaker "soaking" means something involvng some kind of liquid to me :) This was quite puzzling. The owen can hold the temperature and all (it's a lab owen so it's fine tuned and fortunately just big enough to accomodate a blade blank).

Mete, i'll read your tutorial the first thing in the morning, i haven't recieved the material yet so i'mpreparing myself in theoretical aspects, planning it all out :)

Kevin, that "vermiculite" thing ... can i make it work without it ? I have absolutely no idea what that is anyway (wood ash woudlbe far easier to come by) but if temperature is the only thing that matters- which seems logical - i can get away without it by controlling owen temperature and timing to cool the material down properly ?
 
If you are using L6, you will want the oven. If you are using 1080, 1084, 1095 etc... just heating up and letting it cool in the air will get you by. But if you were to heat it up and put it in wood ash you will do fine. The temperature ranges listed for L6 on that site are fairly low with pretty long soak times.

Carpenter L6:
1500F- 1550F soak 5 minutes per inch of thickness.

Crucible L6:

1500/1550F(815/845C),

(a hold of 10 minutes should work for a blade in an oven)

I would go with 1500F for 5 to 10 minutes after the blade has reached temperature. I have never needed the 1550F. temperature but 1450F is low for the L6 I have worked with and 1400F would barely be able to harden it.
 
You would be well advised to read a good bit on heat treating in general before you try it.Steel at 1500 degrees and hot (and flammable) oil can be very dangerous if you don't know what you are doing.Lastly the device to heat the steel is an OVEN, not owen.
Study this subject more before you start heating the metal.Good luck.
SA
 
The word is oven indeed, my bad :) I just looked it up because it looked odd to me. I will most certainly do RTFM before i get on with it.

One more question: can non-flammable substance (brine bath) replace the oil or is this steel-specific ?
 
The safety concerns with oil unfortunately will not be part of most knifemaking or metallurgical texts. I draw upon the fire science portion of my firefighter training when teaching oil quenching. If your blade is the correct temp and the oil is heated to a proper 130-150F. flame-up is very avoidable. Just get all of the hot steel below the surface of the oil and keep it there. Fire needs several things to burn, two if which are fuel and oxygen. The liquid cannot burn, only the vapors of the liquid, combined with oxygen burns.

If your quench tank is small, after around 3 blades, you oil will have heated to the point of not being very efficient in the cooling, but more importantly, it will have come much closer to the vapor point and flash point, so it might be best to let things cool before proceeding. If it does flash, don't panic, just leave the blade right were it is at (it will be safe there, your hand won't :eek: ) and cover the quench tank until the flames are gone.

All of these points are why it is so important to consider vapor points of the oils used. The same thing that make them fire hazards will create a vapor jacket around your blade and keep it from cooling properly. Quench oils have been specifically made with this in mind. Convection, conduction, vapor points, viscosity, thermal extraction rates etc... Quenching in liqud mediums is a very complex subject, that one could fill entire books with all by itself.
 
How does one go about partial (edge) quenching then ? In inert atmosphere ? I can sort out the safety part pretty well (lab has that closed-thingy where chemicals can be mixed safely behind the glass and all and fire extinguisher is close by). After readingseveral HT resources i was under the impression that with knives (~5" blade) it makes sense to make the blade part harder and the spine softer.

Since this is a first for me i'll undoubtedly have to settle for "close enough" a result, perfection takes decades of experience which i lack.
 
faramir said:
How does one go about partial (edge) quenching then ? In inert atmosphere ? I can sort out the safety part pretty well (lab has that closed-thingy where chemicals can be mixed safely behind the glass and all and fire extinguisher is close by). After readingseveral HT resources i was under the impression that with knives (~5" blade) it makes sense to make the blade part harder and the spine softer.

Since this is a first for me i'll undoubtedly have to settle for "close enough" a result, perfection takes decades of experience which i lack.
Click to expand...

When one only quenches the edge, and the spine is up to temperature as well, a flash fire on the oil is often unavoidable, this is just one of many reason that I have not had much use for that technique for some time now.

It is important to mention a very critical point about letting the oil flash. If you are using old automotive waste to begin with, this really doesn't matter, but if you have a good clean quenching oil and you allow it to flash, you are destroying the cooling quenching properties pretty quickly. Oxidation and thermal breakdown of the oil is something to be avoided if you wnat to quench with it for any ammount of time. A good oil should be nice and clear, I have been using my #50 for some time now and I can see the blade cooling under the surface as well now as the day I first poured it.

I may step in it here, but making blades with pearlitic spines only makes sense if you rely on the literature currently popular in knifemaking. I would encourage you to expand your research and find out more about what a soft spine can and cannot do for a knife blade. Many years back it was suggested to me that I think outside the knifemaking box (while still entirely inside the metallurgical box) and now the only time I do a differential quench is when a customer requests it for visual effect. I am not knocking anybodies way of making knives here, I am just asking why it necesarrily "makes sense" that it is better to do it this way, so far I haven't been given any reason that "makes sense" ;).
 
Kevin,I'm with you.I find a diferential temper is more reliable than a diferential quench.I can soften any part of a blade to the degree needed,and still have the best edge possible.
SA
 
mete you said
"A motor oil or machine oil would be better than olive oil and the oil should be heated to about 135F [57C] ."

can you elaborate on that some? I thought the thinner olive oil would cool faster. :confused:

edit: i also thought motor oil had bad things for the body in it when heated (carcanagenics or something like that).
 
Motor oil can be found with various viscocities from 10 and up. They also have antioxidants which will minimize oxidizing which is a major way oils break down.A proper quenching oil is of course the best.As far as bad things for the body ,burned olive oil has bad stuff too and it's terrible for the taste buds !!
 
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