First broken blade (heat treat)

Patrice Lemée

Patrice Lemée

Joined
Aug 13, 2002
Messages
5,703
Well, it looks like I won't be passing my JS test anytime soon. ;)
Blade was 1084, 1/8” thick at the spine, convex grind. Heated in a small forge and quenched in Park50 at about 130F. Full quench, horizontal quench tank.
Came out with a very small bend. It snapped right away when I tried to straighten it. I did not even bend it that much. (I use a jig on the vise for straightening).
Should I have done the tempering before trying to get the kinks out?
I know that I should get an oven cause the forge is not that precise for heat treating but I thought 1084 would be more forgiving. Worked better when I use Vegetable oil.

broken1.jpg


broken2.jpg


By the way, is Park 50 suppose to smoke that much?
 
you have to temper first, then unbend just out of the temper, while it's still hot/warm. Straight out of the quench it's very brittle.
Can't help on the smoke issue, I use canola oil and it smokes a bit and I even had a brief flare up for the first time in my last set of blades. Nothing significant but it was the first time I got more than smoke.
 
Parks 50 smokes a fair amount during quench. At least for me.

Don't worry about the breakage. It means nothing as far as the bend test if the blade wasn't tempered yet.

If it broke that easy after hardening and tempering, then you would want to start making adjustments to your heat treat.
 
You do have a small amount of time to straighten it out of the quench, gotta be quick about it tho. I had something similiar to happen recently, is it 1084fg?
 
You should be able to hand straighten the blade within the first 3 or 4 minutes out of the quench. Could be the photo, but the grain looks a little coarse to me.
 
Sorry, LRB, but you should not straighten the blade after quench until it is tempered. You have a short window during the quench when the blade is between 900F and 400F to straighten it.....but once it crosses the Ms it becomes a structure called brittle martensite, and they use the word brittle for a reason. After temper, the structure is called tempered martensite, which has been tempered to make it less brittle.
Any attempt to straighten a fully hardened blade just out of the quench tank and below 400F will result in a blade that looks exactly like Patrice's. If your blades can be straightened in those circumstances, it is likely hat you are using the wrong quench or there is a problem with your HT, and you are forming a considerable amount of coarse pearlite along with the martensite.
 
from the look of the break that blade has been over heated and would have most likely broken anyway. you need to thermal cycle more or do several post forging quenches and then normalize several times. you have to wwatch the heat carefully.
 
Thanks guys.
Next time I will temper first. But I also have to get an oven to be able to do a more precise heat treat. It is the most important part after all.
I also need a bigger quench tank I think. The temp in mine goes up to about 170-180 after quench so I need to cool it down to do another blade. I also think that it may have something to do with the excessive smoking.
 
Sorry about your blade, Patrice...looks like it was going to be cool. I've seen other people straighten blades right out of quench, but it sounds like that's maybe not ideal. I've not tried it either way myself.

I hope you get it sorted out!
 
Stacy, in this case I am sure you are correct, however, what you say does not apply with all steels. 01 has a good 3/4 minute window to hand straighten below the 400° mark. I suppose the simpler steels work differently.
 
LRB... it is the same for ANY steel. We are talking about basic metallurgical facts here. The TTT charts for O1 and 1084 don't differ THAT much.
 
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NO, I'm sorry Rick. That may be, on paper, but I can assure you, 01 has a much more flexable range than what Stacey laid out. Try it before you are so damned sure of yourself. I use an Evenheat oven, Pre soak for 45 minutes at 1250°, ramp to 1485° soaking for 20 mintes, then quench in Parks AAA warmed to 135°. Blade goes in point first, and is moved fore and aft, until I am sure it has cooled below 400° After maybe 45 seconds, I pull it out. If it needs straightening, I have, acually as much as 5 minutes, to a tad more, to get it straight by hand pressure. I don't really give a damn what the charts say about that. I know what I can get away with by working 01 for the last 5+ years. I also know, that 01 will not be as hard in those first few minutes out of quench, as it will be 10 minutes later. I have checked it. Martensite continues to form, at a guess, for the next 15/20 minutes. Probably more. Anybody, with a basic knowledge, knows that martensite is never completed entirely in quench. It continues forming for a while afterwards. This holds true even for 1095, but would be measured in seconds I would guess, rather than minutes. Do you see anything wrong in my HT process? If you you do, I would really like to know what. I always end up with a predictable hardness after temper, and very close to the charts.
 
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Nothing stands out as wrong with your process LRB. It was not my intention to offend... this is supposed to be a discussion, not a pissing match. The charts say what they say. If your experience has lead you to believe otherwise, you have to go with what you know, I guess. I don't have much experience in O1... I'm a simple forge kind of guy using simple steels. I don't really have all that much experience reading TTT charts, either... but it looks as if they all go to brittle martensite in the same range.

Do you have any ideas as to why the alloying in O1 would slow the process?

Rick
 
My guess is retained austenite converting or additional cooling and more martensite? Might indicate a problem with the HT...

Patrice - if the blade is behaving more brittle out of quench with the Parks 50 - I'd see that as evidence that the Parks 50 is working properly and you may have had structures other than martensite in your blades before. Untempered (tetragonal) martensite is supposed to be brittle. It converts to tempered (cubic) martensite at perhaps 400 deg.

You can straighten a blade around the 500 degree mark during the quench. At this temperature you're well under the nose and can safely air cool - but you're still largely austenitic, so you can straighten your work. This is the best time to do this.

Some metals get harder after a few minutes, aluminum for example. And PH steels too I guess. This is precipitation hardening. O1 - to my knowledge (and I've worked a bunch of it) does not behave this way. However, it will be more prone to retain austenite than simple steels and I'm sure the Mf is lower than simple steels - so perhaps you're seeing it go from something like M70% to M90% as it cools from something like 120 (very warm) to room temp? Otherwise, conventional metallurgical wisdom says the martensite conversion is temperature dependent and instantaneous, not a diffusion process where time is a factor.
 
Rick, sorry if I was a bit testy, but that is the way with 01. 01 requires a slower quench than simple steels, and I would have to assume that is because of the alloys. 01 really doesn't require AAA for a good quench, but I use it because it is more predictable, and I feel that I owe my customers the best I can give. Kevin Cashen would have to give you the whys, but 01 continues the formation of martensite for a good while after quench, and is quite pliable for a few minutes after. I would bet that I could bend it to 45° without damage, straight out of quench, and depending on length, and the temp below 400°. I believe it would bend as much as 20°, after cooling to where you could hold it with bare hands, but would very soon harden to where it would break.
 
Hi Patrice

sorry to see the blade go bad...
- you woulda have to have pulled the blade out of the quench before it hit MS temp... and tweak it with some thick gloves on...
-myself i like it after the temper when the blades hot ...it'll move abit for minor re-adjusting

i have to tell you... that a heat treat oven would make your life a heck of alot easier... trust me... the evenheat i have is easy to work with and no sweat at all... .. you can make sure all your normalize temps are on the ball and bring that grain right down..
... no more fussing with a pyrometer and a propane forge... and running the blade in and out to even up the heat...

i know i know... it costs some bucks... but i'll tell you ...it's worth it...it'll save you from pulling your hair out ;)

Greg



Patrice Lemée;8960119 said:
Thanks guys.
Next time I will temper first. But I also have to get an oven to be able to do a more precise heat treat. It is the most important part after all.
I also need a bigger quench tank I think. The temp in mine goes up to about 170-180 after quench so I need to cool it down to do another blade. I also think that it may have something to do with the excessive smoking.
Click to expand...
 
Hi Patrice,
I too know you have a few precious minutes to tweak the blade back to straight after the quench. I've done it many times with gloves on. If you can handle the blade without gloves its very risky. By the looks of your blade I think it needed more grain reduction by thermal cycling aka normalizing. Your Parks 50 is a fast quench oil and may have contributed to brittleness. A slower oil would have been a better choice.
 
I will save my pesos for a oven and try everything else except the straightening while hot. With me it is an accident waiting to happen. :(

Thanks for the additional info guys.
 
Intersting discussion, why not have a practice heat treat with some thin strips of O1 ? I know it wont be exactly the same as a blade due to the geometry differences, but it will give you a feel of how bendy or not the steel is immediatly after quench!

Generally, Ive found there is a striaghtening 'window' when the blade can just about be held with thick gloves, bottle usually goes at about 1 min though :)
 
I do not wish to get into any argument with anyone who has a process that works for them , but there are two different things being discussed.

One - the OP was asking for advice on a problem he had with 1084.He wanted to know if he should have tempered the blade first. One answerer told him of his personal observations with O-1, saying that bending an untempered blade is fine for 3-4 minutes. That is like someone saying, " I ate a mushroom with spots on it, will I die?" and someone answering, " NO, I ate an apple today , and I am fine."
Also,time is relative when cooling is concerned. Three-four minutes near the winter solstice...in Quebec... may be a lot more temperature drop than three-four December minutes in Florida. The only difference in using temperature instead of time between Florida and Quebec is that 400F in Florida is 200C in Quebec.

Two - Patrice is a new maker with very simple equipment. LRB is a professional with lots of equipment and experience. Telling him what will work in his shop as a fact, despite metallurgy, is going to have a lot of new makers try it, and possibly fail.

On a forum such as this, read by people worldwide and of greatly different equipment and experience, we have to be careful what we post. Some person will be self-learning knifemaking and read a comment and have no metallurgical knowledge to understand if it will work in all circumstances ,or in just one circumstance. That is why I explain the metallurgical process in my advice whenever it would be helpful. Just saying, It worked for me, without any reason why it worked doesn't really aid a new smith in his learning.

To reiterate what I recommend to all new makers ( and old ones) - Straighten post-quench immediately after the blade drops below 900F, doing all straightening above 400F. Do not try and bend any amount below 400F at all (and quit immediately if you feel the blade stiffen). Postpone any further straightening until after the full temper cycles. Then additional straightening can be done at the tempering heat (usually 350F-400F). Re-warm the blade as needed to complete the straightening process.
 
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