quenchent

[topknot876]

hey fellas
have any of u guys ever used bacon grease to quench blades ?

[Lin Rhea]

No.
I'm not saying it would not work for some steels. It probably would.

You can get the same result with vegetable oil without it going rancid.

[kbaknife]

Do you understand WHY? we quench a blade?

[topknot876]

yea its to harden the steel... I just remember reading some where that old school knife makers used animal lard like bacon grease to harden blades and I was wondering if anyone had experience with using fat as a quenchent

[Bobby Urban]

There is a LOT of voodoo magic sauce information out there about quenching oils but in my truly humble opinion the two replys above are from a journeyman and master smiths respectively. Forgive me if you are both master smiths now. But suffice it to say their advice is better than voodoo.

Take it with a smile. Most do here and we are grateful for it.

[Ray Hammond]

I personally use unicorn urine laced with eyelashes and mane hair from My Little Pony....but always face the quenchant North South in order to line up the molecules properly.  

While I'm doing that I enjoy a bacon sammich.

tsk tsk, Karl. tsk tsk.

They used to bleed people out when they had a fever too.  I don't think that's in as high a favor as it used to be.

All joking aside, there are quenchant oils available which work together with known steels to produce predictable results.  Why would you go to all the effort involved in making a knife like object and then try to harden it using an unreliable material like animal fats?

[kbaknife]

Originally posted by Ray Hammond:


They used to bleed people out when they had a fever too.  

And they used to blow smoke - somewhere?

Seriously, when thinking about the 'quenching' process, I often think of it in the reverse when explaining it to beginning knife makers.
Think of it not so much as what we are trying to make the steel do, as thinking of it as what we are trying to NOT let the steel do.
When we  have heated it so the steel's matrix is in the condition of austenite - (what's often referred to as critical) - and we simply let it air cool, it reverts to the soft condition of pearlite - which is worthless as a working knife. Now, it begins that reversion as it approaches about 900 degrees,and sometimes much sooner, and once it starts reverting to pearlite, it's too late.
That's where it's going, and you can't stop it.
And it uses that heat and time as energy to make this transformation.
We QUENCH steel to suck the heat out of it from that 1500+/- temperature range and QUICKLY get it past that 900 degree window and below, so the steel can't head off in the direction of pearlite.
We have robbed it of its time and energy it needs to make that pearlite condition transformation.
Now, since everything in the universe has to be in some sort of condition, the steel matrix is forced to convert to the next possible condition that it can, and in most cases that condition is martensite, which we want.
The idea of quenchant is that it must be capable of removing up to 600+ degrees of heat/energy in a brief couple seconds of time.
That's one of those confusions that run amok in the heat treating arena, is that people often think they only have a second or so to get their steel in the quenchant. You have as much time as you need to get it there without letting it cool too much as to endanger the martensite transformation.
The critical couple of seconds is in the quenchant's ability to extract heat fast enough to jump over the pearlite 'window' of time and get the steel to convert to its next possible condition - martensite.
Anything that's in a solid condition like bacon fat and unicorn ear wax won't do it.
The quenchant needs to be able to absorb that heat without igniting and it needs to be able to circulate around the steel and get that temp dropped many, many hundreds of degrees in only a few seconds.
That's where liquid mediums come in.
Lots of things happen in only a few seconds, and sometimes milliseconds, which is where the commercial quenchants come in that have added ingredients to give the liquid combustion retardants/inhibitors, vapor jacket inhibitors, etc., so as to allow efficient temperature extraction and circulating abilities without starting fires!!
There are a lot of different steel types that have different qualities, times, conversion rates, etc., other than the scenario I listed here. So matching the quenchant's speed to the steel's needs is critical.
The times and transformation rates I use here are simply illustration for the topic. These aren't chiseled in stone but simply to give a basic understanding of what we're doing.

[Bladepeek]

Karl, I studied metalurgy for a bit before I switched to electronics. That is beyond a doubt the best explanation of the quenching process I have ever heard (or, in this case, read).

[kbaknife]

I have to keep things simple in my head to have any form of success at all.
I'm thrilled you found it understandable.
I hope others do, too.
Even simple metallurgy is complex

[The Gopher]

Karl has explained that to me in person before but I didn't take good enough notes, now I printed it off! Thanks Karl!

[kbaknife]

One of these days we'll get some one-on-one time in the shop and I look forward to it.


 

Originally posted by The Gopher:
Karl has explained that to me in person before but I didn't take good enough notes, now I printed it off! Thanks Karl!

[mater]

Karl, can you explain why preheated oil is a benefit? I cant seem to get my mind to grasp it.

[kbaknife]

Originally posted by mater:
Karl, can you explain why preheated oil is a benefit? I cant seem to get my mind to grasp it.

Easy - when we heat oil it becomes a little thinner and moves around and circulates better!
The more it moves around and remains in contact with the steel, the more heat it can absorb from the steel faster!
If it's cool, it' sort of sluggish. Sort of like pouring maple syrup on ice cream.
It needs to be able to move around and when it's cooler it can't.
You really need to imagine ONE THOUSAND FIVE HUNDRED DEGREE!! steel hitting a container of fluid! Man! That stuff just wants to turn into vapor.
Think about that a moment.
And if it turns into vapor, then it's not even in contact with the steel, so the blade just cools down slowly and begins its conversion to pearlite.
Lots of guys wonder why they have difficulties when quenching into grocery store oils and that's why. The liquids they're using instantly convert to a vapor and create what is called a "vapor jacket" around the steel and no accelerated cooling that is needed is taking place. By the time the vapor jacket collapses and comes into contact with the steel, it has already dropped below where it can head off into pearlite.
It's too late.
Those oils just lack the necessary additives you find in commercial oils.
They're for french fries - not blades.  
Now, that all depends on the oil type.
The Parks #50 that a lot of us use has additives that allow it to absorb heat from steel while at room temperature at the same rate as H20/brine - which is amazingly fast.
That's one of the reasons we use it on shallow hardening steels which require heat removal in only a few seconds. It really doesn't need to be heated much more than about 80 degrees.
The faster steels like W1, W2, 1095 need to get below the pearlite window of time in just a few seconds, so there aren't really a long list of oils that will work for those.
However, once we get into the deeper hardening steels like L6, 5160, O1 that have more alloy and a longer amount of time to get into the martensite start conversion range, we can use oils that extract heat a bit slower, which there are more of.
I use something that is called Texaco A, which is no longer produced. It's a really slow oil, and to get the best out of it, I need to warm it up to about 130 degrees to get it to circulate a bit faster for even the slow steels.
There is a great company called Great Lakes Oil that makes a Texaco A equivalent that I have heard good reports about.
Now, when guys use non-industry oils like mineral oil and vegetable-type seed oils that are mostly made for cooking, and also lack the additives to make them really perform well, the best thing to do is warm them up to increase heat reduction speed.
It's a shade-tree method of making sub-standard oils work.
That said, mineral oil is a better option for the deep hardening steels than things like seed oil.
Truth is, if you just heat up 5160 to 1525 degrees and let it air cool, you'll get enough hardening that it'll kill a drill bit.
So warming up non-commercial oils will work for hardening.
The down side of this is that 5160 has enough alloy that to get the best alloy/carbon solution it requires a considerable soak time in a controlled oven.
I've proven again and again how superior 5160 s when austenized with a soak time in an oven to a forge.
The rules of all of this stuff are pretty basic.
There are no real heat treating secrets. Short-cuts are just that. Short-cuts. That doesn't mean they're better, and usually to the contrary.
I've been using my same Parks #50 and Texaco A for years.
Years.
The only way those things really break down is if you catch them on fire, and that almost never happens because of the flame retardants they possess.
They're a little pricey when you first buy them, but when you consider how long they last, and how much better you can make your knives, then it's foolish to not invest in some.
In a movie by Tim Hancock, who a lot of people think walks on water, I heard him make the comment, "Don't you owe your customers the best knife you can possibly make?"

[Thadbow]

Very well explained Karl, Thank You!

[TrackerNy]

Karl, best write up on quenching I've read. Thanks.