Ignorant metallurgy question...

Does not work like that

jim reed @ tallahassee


>The properties of O-1 steel require full hardening and then tempering. That's just the pure physics of it.

The hurrier I go

Jim in Burlington On


>The behinder I get. Heating oil to 450 will casuse you to fall way behind:) I seem to recall watching a blacksmithing program where they only quenched high carbon steel for a few seconds so that some of the heat was retained in the steel to temper it. Pretty sure it was a St Roy episode.

Re: Does not work like that

George in Lowell, Mich.


>Denis,

The hardening process involves heating the metal up very hot to allow the carbon molecules to get smaller so they can "dissolve" in the iron molecules. When they are small and dissolved, you quickly cool the steel that is formed and this locks the carbon molecules in this smaller and harder carbon/iron combination. Allowing it to cool slower lets the carbon clump together making a softer combination. This is a huge over simplification, but it explains why you don't want to cool it slower and "skip a step". The tempering step allows the steel that is made to soften slightly and not be nearly as brittle.

I guess the thing is each step is important.

George in comfortable Lowell, Mich.

My take

Adam Cherubini, NJ


>I seem to recall watching a blacksmithing program where they only quenched high carbon steel for a few seconds so that some of the heat was retained in the steel to temper it.

I don't think it works like that.

I look at it this way- You start with annealed metal and you've got one kind of crystal. After heat treating, you've got a completely different crystal. Tempering doesn't change the hardened crystals back to annealed crystals. Only annealing does that.

So the point of hardening is to get all of the really soft crystals to convert into really hard crystals. You don't want to retain any heat because that will allow some hard crystals to slip back into the soft annealed state. That's not the same as tempering.

Tempering fiddles with the hard crystals to make them less brittle.

My understanding of heat treating is very much akin to thinking the stork brings babies. I get the end result part, but I'm fuzzy on the process!

Adam

Actually.....

Todd Hughes


>what was often done was to only quench the last couple inchs toward the cutting edge of the tool leaving the rest of the tool hot and then when you removed it from the quench tank watch it as the heat moved back down toward the edge and then when it got hot enough to "draw The Temper" back to what you wanted you quenched it again to finaly cool everything and you were done.

When I made laminated axes I always did them like this, I would only heat the front part up to about a yellow temp. and the rear would not have any color in it but was of course plenty hot. After quenching the front the front rear would have enough heat left to run the color down toward the edge.With an axe I wanted it to be a blue temperture and as it hit this I would quench it to stop any further heating. I think this works best for larger and more corse edge tools...not how you would want to do a small knife or chisel and of course will only work where you just have to have the cutting edge hard.

As to quenching in hot oil I always heated my quenching oil up with a hot iron rod first befor quenching a knife blade because it will cut down on warping. Don't know how hot it got....I am sure not 450 deg. , probably no more then a couple hundered and you still had to put the blade in the oven to temper it. If the oil was hot enough to temper the steel after hardening it would be to hot to properly cool the steel fast enough to harden it I would think....Todd

Re: I don't know, but I've been told...

William Duffield, on the Cohansey


>...that the optimum temperature for peanut oil (which has the advantage of a high flash point, saving arm hairs for testing edge sharpness, but not blade hardness) for quenching O1 is about 150� F, coincidentally, about the same temperature as you want to keep your glue pot. Thus, I use the same cheap heating vessel* for both tasks, but not at the same time. You definitely do not want to make the mistake of quenching your blades in hide glue. Recent discussions with Dave Anderson indicate the Chester Tool Works follows a similar protocol.

I have no experience and can offer no advise on the optimum oil and temperature to use for tasty Rat-ke-bob. The only experience I have with rats is feeding them to constrictors, and I also have no idea what the typical epicurean python finds tasty about a garlic wharf rat.

* Rival pot-pouri crock pot , with custom modifications. Since it's mostly plastic and therefore subject to melt-down, I remove the can of peanut oil from the warmer before using it for quenching.

An analogy maybe...

John in New Mexico


>Thats like trying to pull into a parking space at 60mph. You can do it, but the results may leave a lot to be desired. That said, why not give it a try? Worst case, reharden and temper normally. Also Wikipedia has some good info on steel metalurgy and the various carbides if you want the gritty details.

John

Not so ignorant

Andrew F in Australia


>Hi Denis,

I'm flat out at work at the moment, but I'll just type in a three minute stream-of-consciousness reply here.

It's a perfectly reasonable and non-ignorant question.

What you are doing there is called martempering or austempering, which is a process often used in industry to make high strength components, such as the steel strap that Gerard Strapping in the US seem to be the main supplier of. (I used to be the metallurgist on Australia's steel strapping line as part of my training as an apprentice engineer.)

What you do is cool the metal down quickly enough to stop it from forming the soft phase, but you don't get the driving force to make the hard, brittle phase (martensite) immediately.

If you hold the steel at the intermediate temperature, (450F is approx 210-230C at a guess, no time to do the conversion) then it will eventually transform to the low temperature, soft phase.

But, if you pull it out of the quench bath after 10 seconds and hold it in boiling water, you create a phase somewhat similar to the tempered martensite, a phase called Bainite.

This is not as hard as tempered martensite, but tougher.

Anyway, I'll get back to work.

Cheers,

Andrew

Oh, and the partial quench and then use the heat in the centre of the bar/tool to provide the heat to temper the outside case - it's common.

The water quench produces an initially martensitic outer core. By leaving the inside of the bar at red heat when you remove it from the quenchant, it then reheats the bar and auto-tempers the steel with no further heat treatment being needed.

It's the standard technique used to make concrete reinforcing bar - gives a tough outer layer and a softer inner core, giving the combination of strength and flexibility that reobar requires.

Bear in mind that the processes I've described need a lot of trial and error to figure out correct parameters.

Quenching and tempering as two stages is a far more repeatable and accurate way of hardening outside of industry.