Is this true? set me straight.

Fred.Rowe

Fred.Rowe

Knifemaker / Craftsman / Service Provider
Joined
May 2, 2004
Messages
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When you submerge a piece of 1095 in a quench after it has become non magnetic can you remove it after it has dropped below the gate temp of 1100 degrees and still have it harden completley. I was taught that complete transformation doesn't take place until the blades temp drops below 400 degrees but the controling factor is the time it takes to get below the 1100 mark. The faster this happens the harder it gets. That's why you get a difference in hardness obtained with water, oil or brine. Give me some facts, not to technical.
I can be a little slow sometimes.
Thanks Fred
 
Kevin Cashen posted a TTT curve for 1095 recently. If you look at that you will see that you have get down to about 800F before you can safely stop worrying.That means past the pearlite nose. Then you can slow down the cooling rate.But you still have to get down to 400 to start the martensite transformation and still have to get down below 200 to complete it. One of the values of using a commercial quenchant is that some are designed just for this type application .That is fast quench to about 800 then a slower one below that.
 
I think you've got it down about as close as you're going to find as far as general information goes ...there doen't seem to be much data out there on the exact specifics, probably because there are so many different 'recipes' for any particular steel's exact metallurgical content.
The recommended practice for large manufacturers seems to be to experiment with each different batch of a grade of steel they receive to see what exactly works best for that particular steel recipe ...in order to achieve the exact results they need for whatever product they are producing.

With that said, I remember reading somewhere (I can't put my finger on where I read it right now) that once a steel goes below 700 degrees or so during the quenching process, it matters little how it's cooled the rest of the way. In any case, I don't imagine it would affect the hardness more than a fraction of a percent, and I don't imagine that you could even tell the difference without some extensive laboratory testing ...something that seems excessively cost prohibitive for a one person knifemaking operation.

Is what you're referring to 'important'? Yes, if you're making metal parts to rigid performance specifications for industrial use.
But that 'close' of tolerances for a custom made knife, where even the blade variations in size and thickness for each individual knife likely has more effect on the hardening process than what occurs between the temperatures of, say, 900 to 400 degrees, seems ...again, somewhat excessive IMHO.

In other words, is it cost effective to make 50 knives to test for the exact process needed to get the most out of that batch of steel, in both performance and laboratory testing, in order to produce a very few knives with that exact blade design? You'd likely go bankrupt in a week :)
 
The funny thing is, I'd be willing to bet that the large manufacturers of 'cheap' Chinese knives subject their steels and hardening processes to more extensive performance and laboratory testing than any 'custom' knife makers do, or ever will, for that matter :)
 
Hi guys,
I'm talking , rule of thumb, about the process of h.t. not so much the economics part. When I posted the thread, I could not recall the exact temps, only that " getting through the "temperature gate" within the alloted amount of time, for that particular steel" is what dictates [if] the steel gets hard and how hard the steel becomes. Water gets it through the gate quicker, there for harder than say an oil quench. True? or False?

If you are old enough; do you remember the b/w TV cowboy movies
where the smithy held the glowing shoe on the end of his tongs long enough to tell a tall yarn and then and only then, did he toss it into the barrel of water.
Did that shoe harden? ' "he he " :rolleyes:
Imho I think many people are under the impression that hardening takes place at the 400 temp where the final "condition" of the steel appears. Get back with me if you have an opinion on the horse shoe. Fred
 
As far as the shoe goes....they're not supposed ot be hardened :) No benefit from it, and it can actually take away traction because rocks or whatever they're walking on won't have any bite anymore.

As far as the rest of your question. I don't know :D
I've got some charts and stuff I could look at and try to come up with an answer but I loaned them out and haven't gotten them back :o
 
The short answer appears to be 'true', the quenchant affects the hardness. But other factors play into it also ...while water may make the blade a few points 'harder' by cooling it faster, it also increases the probability of warpage and/or stress fractures in the steel ...so there's a tradeoff in there. (Not to mention the fact that the hours that you spent getting to that point with the knife goes down the hopper when the blade cracks).
 
Matt Shade said:
As far as the shoe goes....they're not supposed ot be hardened :) No benefit from it, and it can actually take away traction because rocks or whatever they're walking on won't have any bite anymore.

As far as the rest of your question. I don't know :D
I've got some charts and stuff I could look at and try to come up with an answer but I loaned them out and haven't gotten them back :o
Click to expand...
Now that sounds reasonable to me, about the shoes. You wouldn't want those big critters skating around willy nilly. I am not a horse person, obviously!
Thanks Fred
If those charts come back your way, post something on the subject.
 
The following applys to flintlock frizzen hardening as well as knives.
I manufacture flintlocks to go on early rifles and I do my own heat treating. Early on I found that frizzens quenched in heated motor oil or cooking oil did not spark well so I finally bought some commercial quenching oil and that got the frizzens just that little bit harder and now they spark VERY well. By the way frizzens are 1095 steel. The last time I bought quenching oil I bought a 5 gal pail and it sure didn't brake the buget so I don't think any one can use cost as a reason to take chances on questionable heat treat practices.
 
I don't think this question can be answered correctly without being specific especially with 1095 because it is a shallow hardening steel. Shallow hardening meaning it is difficult to get optimal results because of the limited time you have to cool the metal, not that it won't harden.

According to the TTT curves I have, the TTT nose is just above 1000°, Ms is at 420°, M90 is 240°, and Mf is a bit below room temperature. Continuous cooling curves would work better to answer this question, but I don't have any of those. TTT curves are pretty much Isothermal, but give critical information.

Now if you were to interupt the quench at 800° (assuming you missed the nose of the curve and have pure Austenite) and did slow cooling after that, in about 4 seconds you are going to cross into the region where the austenite will start changing into ferrite and carbides. Continued slow cooling will ultimately transform all of the autenite into ferrite and carbides.

The main things are to miss the nose of the TTT curve and then to get below the Ms temp within about two minutes. That will allow you to transform the austenite into martensite. If that does not happen then you will have retained austenite and probably ferite and carbides mixed in with your martensite. All of those things are not desirable.

Whether you quench in oil or water, the TTT curve stays the same and as long as you miss the nose and cool to below Ms fast enough the resulting hardness will be the same.
 
Here is a TTT curve for 1086/1095. Just note that the time scale is logorithmic.

1095TTT.jpg
 
Whether you quench in oil or water, the TTT curve stays the same and as long as you miss the nose and cool to below Ms fast enough the resulting hardness will be the same.
Click to expand...

So why do you say there isn't a different curve for different quenchants and/or different 'recipes' of 1095? It only stands to reason that there would be. Where does it state that all 1095 follows this exact pattern under all circumstances?
 
For instance, here's another TTT curve; Note how it's referred to as the "ideal" curve ...not the 'do all end all' curve.

"Figure 1. Ideal TTT-curve for 0,65% carbon steel depicting time interval required for beginning, 50% and 100% transformation of austenite at a constant temperature A= Austenite F= Ferrite P = Pearlite B = Bainite"

art14-p1.gif


"The TTT-curve is most useful in presenting an overall picture of the transformation behaviour of austenite. This enables the metallurgist to interpret the response of steel to any specified heat-treatment, to plan practical heat-treatment operations and to control limited hardening or softening and the time of soaking.

The decomposition of austenite occurs according to three separate but sometimes overlapping mechanisms and results in three different reaction products: pearlitic, bainitic, martensitic."

Source:http://www.key-to-steel.com/Articles/Art17.htm
 
jiminy said:
So why do you say there isn't a different curve for different quenchants and/or different 'recipes' of 1095? It only stands to reason that there would be. Where does it state that all 1095 follows this exact pattern under all circumstances?
Click to expand...

1095 is what we and the industry calls the alloy of steel. The name is derived from a specification (i.e. AISI 1095). The standard/specification calls out ranges/tolerances of the alloy's chemical make up. Alloys that are within the called out ranges are considered to be 1095. There can be be an infinite number of alloys that would still be called 1095.

Through emperical testing they derive the TTT curves for the alloy. The TTT curve is for the range of chemistries that the 1095 specification covers. There will not be one for each variable or quenchant. You can also see the curve i posted is also for 1086. So one curve is good for two alloys.

Now talking from experience from working in the Automotive industry for 10 years, we rely on standards and specifications. One place I worked made door beams for side impact occupant safety. They heat treated 50 miles of steel tubing per day for the products they made. The steel was certified coming in the door to garauntee that it's chemical composition was within spec. By no means did they change their processing variables and tune them for each lot or chemical variation that was within the called out standards. A certain sample size was tested to make sure the process was running as it should. The testing was not based upon which lot the steel came from, but it was a set number of pieces per shift. This would set up statistical conformation of their heat treating process. It did not matter what the tube's OD or wall thickness was, it was all heat treated the same way.

The TTT curves are setting your heat treating process and if the steel you are using satisfies the standard that that TTT curve was derived for, you are good to go. Yes there are going to be some slight differences in the hardened steel, but I doubt there are many knife makers out there that would be able to quantify the differences that you would see from the varying chemical compositions. That is the whole idea behind standards and specifications.

The TTT curve is the TTT curve. Like Fitzo said, it is all on how you remove the heat from the steel. To transform the austenite to martensite in 1095 it has to be cooled according to the curve for 1095. It is that plain and simple, no questions, no arguments. It can be colled faster, but not slower.

It is independant on what you use to quench the steel. If you use water it can cool it quicker than oil, but if you use the proper oil you can get the same as quenched hardenss as you do with a water quench.

The TTT curves are also independant of blade shape and thickness. If you are quenching an extremely thick blade and the outside gets to martensite, but the center doesn't, the steel is still following the TTT curve. You just did not remove the heat fast enough to form martensite in the center of the cross section. No unique TTT curve is needed to tell you how to cool a 1 inch thick blade or a 1/16 thick blade in oil or water or air. Martensite is formed or it is not and for martensite to be formed the steel needs to be cooled according to the TTT curve.

I guess I don't completely understand what point you are trying to make either. 1095 is 1095 whether it has 90 points of carbon or 103 and is different and will have a different TTT curve than the TTT curve you displayed for 1065 steel. Each alloy has its own TTT curve, there is not one "master curve" for all steels.
 
Awww, come on Fitzo, it was just getting good. ;)

I would rather discuss this than the thread about that U2 regrind blade from Cliff Stamp. :D

This is good information and one of the rare times that I stick my neck out. I personally think there are too many myths and vodoo about heat treating. Plus it is the most important part about making a knife IMO, so i make it a personal goal to get good info out there about what it takes to do proper heat treating. I don't claim to know it all, but what I will tell you what I do know.
 
You made a comment earlier about rate of cooling below 700F being unimportant.
Click to expand...

No, I believe what I said was that, off the top of my head, the rate of cooling below 700 or so degrees matters little.
i.e.
"With that said, I remember reading somewhere (I can't put my finger on where I read it right now) that once a steel goes below 700 degrees or so during the quenching process, it matters little how it's cooled the rest of the way. In any case, I don't imagine it would affect the hardness more than a fraction of a percent, and I don't imagine that you could even tell the difference without some extensive laboratory testing"

So ...what's the problem? It was a generalization for carbon steels ..not specifically 1095 steel ...nor meant to be taken as 'gospel'.

Did you notice that Sean's curve specified not only a carbon and manganese percentage but a specific grain size and austenitizing temperature? That seems pretty specific to me, not at all generic.
Click to expand...

Yeah, I saw that. But everyone knows that recipes of types of steel vary widely in their exact makeup, and this chart is just for one specific 'recipe'. So all that proves is that the chart is the "ideal" curve for that particular recipe of steel. Not by any means the only chart for 1095 steel. And since different quenchants pull heat from the steel at different rates, then it stands to reason that the hardness would indeed be influenced by (not only the exact makeup of the steel, but also) what quenchant was used (and how it was used) ...thats the point. In other words, if you quench 1095 in water it would be harder than if you quench it in oil ...which was one of the the 'points' of the original post.

Whether you quench in oil or water, the TTT curve stays the same
Click to expand...
That's the statement I don't agree with.
 
Again, that may be the "ideal" chart for 1095 ...a baseline chart, if you will. But one you change the metalurgical content of the steel, then it stands to reason that the curve for that recipe of steel would change also.

If you've got tolerances that can fall anywhere between 1086 and 1095 steel, using the same hardening process, I wouldn't exactly call said tolerances 'tight'. Nor would I expect that a part for a car door would need to be that tight.
 
OK, I think I understand where the mis-communication is. If you use a quenchant that cannot remove the heat fast enough then you can not meet the TTT curve and you will not have complete transformation to martensite.

But, the TTT is independant on the quenchant. The TTT curve is telling you at what Time and Temperature the steel needs to be cooled at to get the various microstructures. If your quenchant is too slow, you final hardness will be lower.
 
Well, I apologize for having deleted my post and making things confusing. :(

You guys can carry it on any way you want. I'll stay completely off this. Sorry.
 
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