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  1. #1
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    Effects of triple quenching

    There are a lot of different thoughts about whether triple quenching is beneficial to a blade or is it just a waste of time?.

    One such comment I have heard is ..... 'the reason some triple quench is because they didnt get it right the first time around'...... ..there may be some truth in that......Its also possible that triple quenching can do more damage IF you do not get your temperatures spot on....as much as 100F may be the difference between a good blade and a not so good one.


    One of the triple quench theory that I have heard is that triple quenching refines the grain ...........This is what I wanted to investigate for myself in relation to 52100 alloy....results may be different in other alloy steels.


    Effects of thermal cycle procedures on 52100 alloy


    I wanted to see for myself if there was anything in the theory multi quenching itself could improve grain size.

    Using two test samples of 52100, an Even heat oven and peanut oil as a quench medium, I heated both test pieces to 1850 F. This is 300F above the steel manufacturer recommendations for the hardening process (recommended between 1500 and 1550F).

    I chose 1850F because this is what I understand that the carbides in 52100 go into solution and dissolve (have I got that right?).
    Holding the steel at this temperature for 5 minutes, I knew that I would get some grain growth. I then immediately quenched both steels in warm peanut oil to harden. When cooled, I snapped two samples off each piece with a hammer and anvil. The pieces snapped very easily, like glass.

    As expected, on inspection the grain was course, easily seen by the naked eye to look like table salt.

    I then took one test sample thru three separate normalization cycles to 1550 F and held them for 5 minutes each time, allowing to cool to black color in a darkened room before each subsequent cycle. I then heated to 1550 a fourth time and quenched to harden

    The remaining test piece, I did not normalise or anneal at all , but went straight into a triple quench/harden cycle.
    Each time heating to 1550 F, holding for 5 mins then quenching. Allowing to cool below 400 F between each quench again.

    I then snapped both test pieces to compare grain size.

    The first thing that was noticeable was that both test pieces were a lot more difficult to snap. Where else before, I could place it on the anvil, overhang a section and hit with a hammer to shatter like glass, this time I had to secure it in a vice and hit it several times with a lump hammer to get a clean break.

    Results:

    The grain size in BOTH test pieces had been reduced considerably.
    With the naked eye they were both smooth and silky, light gray in color…..and the test piece that was NOT normalized looked finer!

    Using a loupe , under magnification, I could see a slight noticeable difference in the grain size….a view shared by my wife who had no idea which sample was which.

    My conclusion, at this time is that with 52100, it does not seem necessary to go thru a triple normalization cycle to repair the grain size which may have occurred thru over heating……..Going into three quench cycles without any normalizing procedure appears to be as good as a triple normalization cycle , or maybe better.

    What does this mean to my methods?......
    Before this experiment, I have been very carefuly subjecting the 52100 alloy I use to triple normalising cycles...as well as triple quenching/hardening, using my forge as the heat source and relying on colour and magnetic change).

    Now I have an Evenheat oven, I know my critical temperatures are very accurate..........and my experiment suggests to me that grain refines just as well with a triple quenching/hardening cycle compared against triple normalising.....so does this mean that using this method, triple normalising is obsolete?........

    I have always been a firm believer that good normalising techniques greatly help in reducing stresses which results in warpage.....But I also believe that good forging techniques, where during the forging process the heat is constantly reduced till the final few heats are a low glowing red heat in low light (some may call this cold forging?) is beneficial to the steel. In fact, the whole forging process from first putting the steel in the fire to the final blows are in my opinion, a constant thermo cycling of the steel. ...to such an extent that by the time forging is completed, the steel is already de stressed and in a 'normal' state..........I guess I need to do some experiments to test this theory.

    Anyway, I am no expert in any of this...I am only reporting what I found and what I believe to be correct...but if you have any doubts, then experiment yourself and lets compare notes
    Last edited by Kevin; 27-06-05 at 04:04 PM.
    ...formerley known as "coutel".

  2. #2
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    Re: Effects of triple quenching

    Thanks for a very interesting post
    It certainly gives food for thought. The fact that even overheated steel can be salvaged in at least two ways is encouraging to those of us who aren't perfect with our forging.

    One thought I have is what to do with a steel that air hardens? I have found that 01 has an annoying habit of air hardening when you don't want it to. I tend to anneal it before grinding and hardening. I asked Howard about this at Plymouth and he suggested heating in an oven to just below critical, which in effect is like a long high temperature super tempering cycle.

    ps. I know 01 is a pain, but it is so much easier and cheaper to get in England!

    Duncan
    Last edited by Underhay; 27-06-05 at 05:54 PM.

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    Re: Effects of triple quenching

    My O1 and 440F is triple heated, AND triple tempered, and I find that the edge holding is slightly improved, and less likely to chip out.

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    Re: Effects of triple quenching

    I have been playing around with some metalographic gear and thought I would post some photos here.

    Some while ago I had a nice big blade made of O-1, that I was hoping to get heat treated by a well known blade smith so that I could watch and learn, so improving my technique. Things did not work as planned as the smith had never worked with O-1 and was a bit kack handed, only after the blade had been over heated, quenched too fast and left to sit till room temperature did I learn that there was no tempering oven available. As you would expect, the blade cracked at the edge.

    The bits sat for a long time in my draw until I was thinking about the effect of thermal cycles. The broken surfaces, near the edge, had looked like caster sugar, as prime an example to try some grain reduction on as you are likely to find!

    Part of the blade was taken to non-magnetic three times with air cooling in between, then twice more cooling via a hot oil "quench" (Castrol Iloquench No1 @ 75degC) followed by a final quench for hardness.

    A tiny chip was broken from the cycled edge, very smooth grain. The blades were sectioned, polished and etched.


    This shows as clearly as anything that even BAD grain growth can be fixed. The untempered samples tested out as 63Rc for the uncycled piece, and 64Rc for the thermally cycled part. Tempering at 350degF (ramping up to about 400) in my kitchen oven hardly touched this at all, only lowering the hardness by about 2-3 points.

    These hardness figures are interesting as I have had a hard time reproducing them on other blade section. The problem I am encountering with O-1 is the soak time needed to put sufficient carbon into solution. The cutting edge of my last blade came in, tempered, between 59-61Rc, and did not chip on a brass rod, however the rest of the blade, which was all non-magnetic, and fully quenched, came out with hardnesses as low as 35Rc. Examination showed LOTS of undisolved carbides and carbide strings. This blade had been triple normalised, and triple quenched, and had spend more time above non-magnetic than is normally suggested in the "get it hot, check it, heat for 5 more seconds and quench!" instructions.
    Chris

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    Re: Effects of triple quenching

    Quote Originally Posted by C_Claycomb
    , and had spend more time above non-magnetic than is normally suggested in the "get it hot, check it, heat for 5 more seconds and quench!" instructions.

    I cant see the picture Chris.

    Since I did tha little experiment, I have moved on a bit.....

    I soak my brand of 52100 for about an average of 4 mins, depending on the blade size...with a temperature controlled oven its easy to do, and because its so controlled, I doubt very much if I am getting any grain growth in that time..though a microscope may help determine that.

    btw..there is something in the post for you.
    ...formerley known as "coutel".

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    Re: Effects of triple quenching

    Good experiments. Testing is the heart of improvement. Personally I usually thermal cycle several times and with 52100 I use multiple quenches.

    My friend John Davis and I have experimented with multiple quenches on 1084 and 15N-20. Ther results were similar in my shop and John's shop. John has an Evenheat I have a Paragon for a heat source. John has a Wilson Rockwell tester, I have a Chinese Rockwell tester. We used 3 pieces of each steel. We did a single quench, a double quench and a triple quench fallowing all quenches with multiple Rockwell tests. On single quenched 15-N20 and 1084 we found a 5-7 point spread in hardness. With the double quenched material we found a 3-5 point spread in the RC hardness. With triple quenched material we found a 1-3 point spread in RC hardness. Results were very close on the tests performed at two different shops. The steels were in factory out the door condition.

    Phase two we did three thermocycles on both steels then quenched and tested. After three thermal cycles and a quench we had 2-4 points difference. After two quenchs on this multiple thermal cycled steel 1-2 points difference. After three quenchs 1-2 points difference.

    I thermal cycle everything I make into a knife. I multiple quench most everything I make into a knife. It is a stressful process in particular if the blade is a complex mosaic material; I sometimes just quench once. All the blades I finish are Rockwell tested; this gives me the confidence to send them out the door...Take Care...Ed Schempp

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    Re: Effects of triple quenching

    Ed, great to see you here!

    How do you guys deal with de-carb when using your oven's for cycling? I have only ever used an oven (ok, it was a lab type furnace) once, and the O-1 had flakes coming off it like you wouldn't believe, it looked like we were laying sheets of news paper on the hot blade. In my pathetic one brick set up I get less, but still enough on multiple cycles that i have to grind quite a bit off to get back to hard steel.

    Speaking of hard. Something I have wanted to know for a long time. How do people mount their blades to hardness test them? The Vickers tester I use needs the sample to be parallel to the test bed, so the indenter comes in at right angles. Does the Rockwell tester cope with testing on a bevel better?

    My next test will be to give my blade a really good soak, such as I can, to get as much carbon into solution as possible, ignore grain growth then quench, followed up with cycles to refine the grain. I am coming to think that the cycles, be they just zipping back and forth through the critial temp, or quenching to get martensite, are the easy part with O-1. Getting complete solution is much harder. I really couldn't believe just how little carbide had disolved during cycling alone.

    Kevin, I didn't post a picture of that last blade yet, will do so in the next week I hope.
    Chris

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    Re: Effects of triple quenching

    hi folks,
    I'm not as experienced or as technical as you gents .

    I use a small 2 foot diameter side blow coke powered forge for my heating or I stock remove with a little forging as it does seem to make a difference to the balance of the blade.

    I have had quite a few problems with O1 recently when using the magnetic/ non-magnetic indicator 'method' , so much so that last year I spent some time corrosponding with Brian Goode as to why couldn't harden my O1 or get it to keep a decent edge.

    the last 5 or 6 knives I have made I have gone back to my old method of heating to a bright red heat and quenching in cold oil and doing this 3 times , I then clean up the blade adn run an oxy acetylene or propane torch along the back until I get a dark brown edge along the cutting edge, that is then quenched.

    I have found that this passes the 'Wayne Goddard Brass rod test' and will actualy shave brass rod, bUt, if put in a vice and bent with a steel pipe on the handle will bend to about 30 degrees before snapping.

    what would you all say is happening to the grain of the steel with the way I'm doing it?
    I thought maybe I'm getting a 'graduated grain throught the steel with the way i'm doing it?
    A man without a Knife is like a Fish without Water

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    Re: Effects of triple quenching

    Scale is from oxidation and there is a limited amount of decarbonization in the oxidation. The electric ovens are pertty much neutral atmosphere; the oxidation occurs when the piece is removed and exposed to air.

    There are alot of ways to skin a cat. Test your efforts and that is your best information.

    As I'm doing mainly folders I heat treat before grinding so I have a parallel surface to Rockwell test. The grinding of the blade removes my Rockwell marks...Ed

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    Re: Effects of triple quenching

    Welcome Ed...
    It is good to hear that you Ht before grinding. I read Wayne Clay's commnets a long time back about that way of doing things, and so I did about fifty blades that way, and apart from using more belts, it is seemingly more accurate. I just had to watch for overheating the steel and destroying the HT value...
    HT is safer using a flat piece of steel, in regards to warping...
    My blades are now ground first, then vacuum HTed and sub zeroed...and I use less belts and water paper...

  11. #11
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    Re: Effects of triple quenching

    Quote Originally Posted by Wayne D

    the last 5 or 6 knives I have made I have gone back to my old method of heating to a bright red heat and quenching in cold oil and doing this 3 times , I then clean up the blade adn run an oxy acetylene or propane torch along the back until I get a dark brown edge along the cutting edge, that is then quenched.

    I have found that this passes the 'Wayne Goddard Brass rod test' and will actualy shave brass rod, bUt, if put in a vice and bent with a steel pipe on the handle will bend to about 30 degrees before snapping.

    what would you all say is happening to the grain of the steel with the way I'm doing it?
    I thought maybe I'm getting a 'graduated grain throught the steel with the way i'm doing it?
    No definitive answers from me, but a suggestion or two.

    The way your tempering (with a oxy acet torch along the spine) works, but rather than temper once, try it three times, and clean up the temper colors on the blade each time to clean metal, and take it thru the temper color you desire each time.

    Tempering this way, needs to take time, the slower the better...and maybe even consider placing just the edge in some water now and again. Concentrate on getting the spine area a purple or blue each time.

    The disadvantage of tempering just once with a torch MAY be that you are only tempering the outer steel and not the inner core, so it stays brittle.

    Try tempering it three times as I suggested, and you should be able to get the blade to bend to 90, and maybe even spring back some..if thats what your aiming for.

    Shaving brass shouldnt be too difficult for most blades, shaving a mild steel wire nail is imo, a better test.
    ...formerley known as "coutel".

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    Re: Effects of triple quenching

    Shaving hardened steel is a much better test, neh? Let's go for the whole hog.

    Sorry Kevin I couldn't resist.

    My Rockwell tester does not do well on tapered pieces, aka, knife edges. So, I made some tapered shims that match the blade bevel angles. It's not perfect cause sometimes the shims slide away and every time that happens the test isn't accurate. Point testing is better when the surface does not allow the diamond to slide.
    Once in a while you can get shown the light, in the strangest of places, if you look at it right...

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    Re: Effects of triple quenching

    Tempering this way, needs to take time, the slower the better...and maybe even consider placing just the edge in some water now and again. Concentrate on getting the spine area a purple or blue each time.
    with the width of my blades I usualy get the spine to purple/blue as the edge gets the right colour, so I'll have a go with the '3 tempers' you suggest and see what happens .

    thanks
    A man without a Knife is like a Fish without Water

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    Re: Effects of triple quenching

    Very very interesting. Hi newby from the US. Since you guys are really into testing it seems like I've found someone that might be able to give me real test results rather than guesses. My big question is in 01 and oil quench, seems several makers says edge quench for several seconds and then put whole blade under oil- others just says stick blade straight in and move around.. Does the edge quench method really make a somewhat less hard back ? or does plunging whole knife in work just as well since the thinner blade edge will cool quicker anyways ?? hope this is clear. I really don't care if my hunting knife will bend, just that its as hard as practical without being brittle, I just use for field dressing and skinning so want kinfe that will stay sharp longer but not chip out if I hit a bone when quartering or seperating joints.
    Richard Grantham TX USA

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    Re: Effects of triple quenching

    hello everyone,
    well to start, i agree with Ed, experimentation is everything.
    I can say from my own testing that o-1 will pass the edge retention and 90 deg. flex test with one hardening cycle. Both edge quench and torch draw are acceptable, I usually follow with two cycles of 400 F to temper.
    I cannot speak to many other steels, but I have always been under the impression, particularly with the thin cross section of a blade that critical temperature, even over a short period of time would dissolve the carbides. That said, normalisation and annealing procedures require heat work over time of a completely different time scale, so perhaps those multiple heats to critical do have cumulative effect. I believe there was a long thread on Knife Forums on this subject that may shed some light.

 

 

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