2nd thoughts on my HT

[pjelect]

After reading all the posts on quench plates I decided to give them a try. But along with that decision came another question I couldn't find an answer to in the posts.
I have heat treated a lot of ATS-34 and D2 and took them out of the foil and let them cool on a hook. I have a hardness tester and they always come out close to the expected hardness with no noticable warping (blind luck or not paying enough attention?) I sharpened them and tested them but never broke one to see what it looks like inside. Did I make a less then adequate blade by letting them cool a lot slower than a plate quench? Do I have retained austenite to a greater degree with slow cooling? Other than keeping the warping factor down and being able to temper them quicker are there metalurgical reasons to plate quench?
Thanx, Pat

[nate d.]

Pat,

Don't let metallurgy scare you first of all. I've used quench plates with no problems. your first question is subjective and i don't feel comfortable replying to. your second question do i have retained austenite. that question can be answered more conclusively by looking at a TTT curve, or a Time Temperature Transformation curve. this curve is particular to an alloy. YOu mentioned D2 and ATS so you could get a curve for a Stainless and not be to far off in answering that question. If you want help in understanding a TTT diagram rather than me trying to explain it here get a physical metallurgy book and it may have a good description in there. email me and i can recommend a book or if you get to dayton OH we can talk about this, nedozier@utep.edu I know that more than likely (sorry for the wiggle, weasle words i don't paint myself into corners) you have more retained austenite with a slower quench than a faster quench. the metallurgical reasons i use quench plates,
one the plate are more thermally conductive than oil. in other words I can pull more heat out of a blade faster with my plates than with oil. With that said i must place the plates on the hot blade At Near The Same Time!! second i like a hi hardness knife. i'm able to achieve that more consistently with my quench plates. third, i can't screw up my plates prcedure. its stupid proof cause even i can to it and not screw up my HT'ing process. fourth i like that i don't have to get more oil and mess with oil. I like using my plates to cause i don't have to remove the foil from the hot blade i just quench through the foil. I'm unsure about your statement of tempering factor i'm not sure about tempering time differences from one process to another.

[Larrin]

A rule of thumb is to quench as fast as possible. You should be able to quench just about anything in oil that you'll be using with knife making, unless you're going to be using weirdly shaped fantasy knives.

[Andrew Garrett]

"the plate are more thermally conductive than oil. in other words I can pull more heat out of a blade faster with my plates than with oil."

Pat,
I know that 1095 needs a very fast quench. Does the above statement mean that I can quench 1095 or other carbon steels between plates and get a faster quench than I would in oil?

[mete]

You will get a bit higher hardness ,1 or 2 points, with the plate quench compared to air cool. Remember that for some of these alloys they recommend moving air in the quench....I've been trying to get somebody to do experiments with plate quenching oil hardening steels to see if it works.

[RJ Martin]

Pat: As already stated, press quenching will give you a flatter blade, and one with less clean-up work if you leave it in the foil during the quench. It's great for both steels you mentioned.
The thing I never liked about air cooling was all the manipulation of the foil with that red hot, really soft metal in it. Too easy to bend a tip or otherwise ruin a blade. Press quenching is both better and easier. Not too many things in life are like that!

[pjelect]

Nate D, the only reason I mentioned tempering is that it follows that if you can cool a blade faster you coud begin to temper it faster. Question answered though, less retained austinite with faster cooling on air hardening steels.
Better and easier I like, RJ.
Thanks for all your answers, gentlemen.

Who gets credit for this plate quenching process, anyway? Did the steel mfg's come up with it or a knifemaker? Is it a fairly new procedure or am I just coming up to speed on an old process?
Thanx, Pat

[pjelect]

Mete, your reply made me think of another question.

Is my goal to get a blade to the most absolute highest degree of hardness at quench? In other words, if I got a blade to 64-65RC then tempered it back to 59-60RC, will it be a better blade than one quenched at 62-63RC then tempered back to 59-60RC?
Thanx, Pat

[Larrin]

Originally Posted by pjelect

Mete, your reply made me think of another question.

Is my goal to get a blade to the most absolute highest degree of hardness at quench? In other words, if I got a blade to 64-65RC then tempered it back to 59-60RC, will it be a better blade than one quenched at 62-63RC then tempered back to 59-60RC?
Thanx, Pat

The hardness as quenched should be controlled by the austenitizing temperature, not the speed of the quench. And to answer your question, no, you don't necessarily want the highest hardness you can get. The reason you get higher hardness with faster quenches is because more austenite is converted to martensite. Austenite = bad.

[Kevin R. Cashen]

You want the most complete conversion from austnenite to martensite that you can get, without precipitation of fine pearlite, whatever the hardness may be. Going beyond this in quench speed can be overkill in that you will invite warping or cracking, without the ability to cool the part entirely even.

Although it is done far too often, controlling the hardness with the heating and quenching operation would be accomplished by mixing the martensite with either retained austenite (in richer alloys), or fine pearlite (in simple carbon steels), niether would be desireable for top performance. Complete conversion to the desired microstructure and then tempering to whatever hardness you desire should yield the best results.

[Larrin]

Originally Posted by Kevin R. Cashen

Although it is done far too often, controlling the hardness with the heating and quenching operation would be accomplished by mixing the martensite with either retained austenite (in richer alloys), or fine pearlite (in simple carbon steels), niether would be desireable for top performance. Complete conversion to the desired microstructure and then tempering to whatever hardness you desire should yield the best results.

Actually, you're wrong. Lower austenitizing temperatures yield lower hardness because less carbon goes in to solution, more goes towards forming carbides, not because of more retained austenite.

[Kevin R. Cashen]

Don't be too quick to say "your wrong" , at what point did I say the lower austenitizing temps result in retained austenite? In fact at what point did I mention lower austenitizing temps at all?

Indeed higher temps may result in austenite stabilization, with the steels chemistry being a high concern. Incomplete soaks will indeed result in leftover ferrite/cementite or carbides, that is what I was saying, but slowing your quench down with carbon steels will give a lower hardness from skidding through that nasty nose on the TTT curve. My point was that a knife that saw complete conversion to martensite and then was drawn back to a desired lower hardness in the temper will give better results.

Be careful not to let the desire for "aha gotcha!" drive you to misread too much of what one may write.

[Larrin]

Originally Posted by Kevin R. Cashen

Don't be too quick to say "your wrong" , at what point did I say the lower austenitizing temps result in retained austenite? In fact at what point did I mention lower austenitizing temps at all?

Indeed higher temps may result in austenite stabilization, with the steels chemistry being a high concern. Incomplete soaks will indeed result in leftover ferrite/cementite or carbides, that is what I was saying, but slowing your quench down with carbon steels will give a lower hardness from skidding through that nasty nose on the TTT curve. My point was that a knife that saw complete conversion to martensite and then was drawn back to a desired lower hardness in the temper will give better results.

Be careful not to let the desire for "aha gotcha!" drive you to misread too much of what one may write.

There wasn't any "aha gotcha!" about it, though it may look like it by how little that I said. From what I read in your post, you said that you shouldn't waste your time with heating and quenching temperatures. When using that sentence on top of what I said, you're basically saying you should disregard my comments on austenitizing temperature. Austenitizing temperature is very misunderstood.

[Kevin R. Cashen]

The austenitizing time and temperature are perhaps the most critical operations one will ever do in the creation of a blade, I could never and would never want to give the impression that any ammount of care given to them would be a waste of time. I wouldn't have spent so many years of my life acquiring the tools and any knowledge I can on the pursuit of accurate control of it if I thought otherwise. Adjusting the hardness level down with them I believe would be a bad habit to get into, when one has so much more control with tempering a nice homogeneous microstructure.

[mete]

That has always been standard practice and good practice in heat treating.