:-( First time since I started using Parks 50. Broke!

That sucks Rob, heat treating is always causes me the most stress.

The crack looks random, unlike it followed a grinding scratch. How dose the grain look, I don't suppose it got too hot at some point? I guess you win some and you loose some.
 
....The crack looks random, unlike it followed a grinding scratch. How dose the grain look, I don't suppose it got too hot at some point?....

Don't think it got too hot. 1084 - EvenHeat preheated kiln to 1475 and let it stabilize for 15 minutes before putting the blades (2) in. 10 minutes and out. Turco for decarb protection. Grain is nice and fine - not really even visible to the naked eye. After 30 seconds in the P50, I hooked it on a wire and hung it back in the tank to cool while I got the second blade. That's when it went. It goes from spine filework to choil notch, but neither have anything looking like a stress point really.

Trying to remember if I did something to earn some bad Karma.:34:
 
The fracture goes directly from one notch (at the bottom of the plunge) to another (file work at spine), I would look at the bottom of these features to see if there was a stress riser. But first, what steel is it? Indeed, what does the grain look like? How hot did you heat it, and with what equipment? How long did it hang in the quench tank?

I ask all of this because, although it has a reputation for being fast, I have yet to ever crack a blade in #50 that was a shallow hardening alloy for which is was designed. I know this will not be of any consolation, but if the only change you made was the quenchant, you can rest assured that you have reached a new level of hardness not previously obtained, you just need to deal with whatever uneven strain issue that is causing problems. Seriously, I have taught classes where I allowed the students to make ABS test blades with things like black automotive products or peanut oil, but then had them full quench in Parks #50, the latter blades would break and not just easily bend, which allowed them to clearly see the difference between full hardness and mix structures from inadequate quenches. Obtain maximum hardness and then the maker, not the quenchant, is in full control of the final outcome. The first variable I would address is the time hanging in the oil, a sure way to eliminate this problem is to utilize an interrupted quench method, but even without that, quenched blades should be in the temper ASAP after they assume near room temperatures if they obtained maximum hardness.

edited to add: Sorry posted at the same time as you so many questions already answered.
 
Thanks for the response Kevin

Most of what you asked for is in my post above (postings crossed I presume). There is no change in quenchant - been using P50 for a couple years now. I held it in the quench for about 30 seconds - hung a wire through the handle hole and hung it in the tank while I went for the second blade. I heard the tip section hit the bottom of the tank before I had the other blade into the quench.

I'm not a great photographer but

grain.jpg
 
Ouch, forge gremlins strike again. I know that you're more experienced than me at heat treating so I really don't have any insights as to what might have caused this than you do. It's just a shame than it did.

Doug
 
I hear you LRB. While I have only broken and observed a few test samples, I have seen deliberate coarse grain and this doesn't look like it in real life. The blade section is actually only about 1" long, so even the thumbnail represents magnification on my laptop screen. The full pic shown is about 400% larger. I'm hoping the customer will let me hang on to it so I can show it to Kevin in June.

Chasing another possibility .....

plunge.jpg

Putting the pieces together, the fracture starts right where the plunge meets the flat. It certainly didn't follow the plunge, but scratches in the transition area may have been a starting point.
 
Thanks for the response Kevin

Most of what you asked for is in my post above (postings crossed I presume). There is no change in quenchant - been using P50 for a couple years now. I held it in the quench for about 30 seconds - hung a wire through the handle hole and hung it in the tank while I went for the second blade. I heard the tip section hit the bottom of the tank before I had the other blade into the quench.

I'm not a great photographer but

View attachment 47358

Sorry, I misread the title. I thought you meant this is the first one in the #50, and it broke. I was thinking "Oh no, not a very good introduction";) The photo is not detailed enough for any accurate assessment but since it is a spontaneous fracture there is very little chance of there being roughness due to plastic/shear type failure modes, so it does sort of appear to be a bit coarse.
 
EvenHeat preheated kiln to 1475 and let it stabilize for 15 minutes before putting the blades (2) in. 10 minutes and out.

The bold/underlined text is what caught my eye in your initial post. 1475 is at what I consider the very top end for 1084, and 10 minutes is WAY more then I would ever go. From what I can tell in the pics, I have to agree with Kevin that the break occurred from two fileword areas....that leads me to speculate if those areas were left "as filed" finish?

Speaking strictly for myself, time and experience has taught me that the closer you go to the "upper range" of a given steel, the shorter any "soak time". If you're intent on soaking, go to the lower end of the austinizing temp for the given steel. I'll use 52100 as an example....if I'm near the upper end of it's austenizing range, I allow NO soak at all. If I want to soak, I'll back off on the temp (usually all the way to the lower end of the austenizing range).

It might sound trival, but again, based on my experiences, upper range austenizing, and soaking are usually reciepies for disaster.
 
Thanks Ed and Kevin and everyone. Good learning going on here. Looking for ways to improve my process.

First, Kevin's website shows 1500F for austenizing 1084, so I thought I'd already dropped temps a bit. What temp do you guys generally use for 1084? Would I still get full hardness out of 1450F?

Second, is so called "soak". When I put blades in the kiln, it takes the kiln a little over a minute to recover temperature. (As you know kilns are much slower than forges.) I'm under no impression that the blade heats all the way through that fast. I have peeked on occasion at the 5 minute mark and there are still those elusive dark shadows suggesting incomplete through heat. Guessing that full through heat on a blade of about 3/16 takes 6 or 7 minutes, I have been allowing for a 3 minute "soak" at temperature. That was my logic and I'd like your input on times in the kiln? Should I be quenching as soon as those shadows are gone? (6-7 minutes?)

Third, my quench tank is agitated to help break vapour jacket. I don't imagine that's a problem, but mention it because its not common outside of professional HT shops.

This is the first break out of maybe a thousand blades through the P50. I guess that's not bad, but I'd really like it to be the last too. Kevin and Ed, I hope to have the blade to show you in person at Jim Clow's hammer-in in June. Any suggestions will be valued. Dissenting opinions also welcome.

Rob!
 
Well, the verdict is in - or at least mostly. The grain on magnified observation is very fine. The break goes from choil to one of the spine filework low spots. Apparently, it appears that the fracture began at the choil and progressed to the spine. The file lines were a bit more coarse at the choil. I have heat treated blades with much coarser grinding than this spot on the choil. Anyhow, I sure didn't see it coming. Thanks for all the input everyone. Hope it helped others as much as it did me.

I often opine that extreme circumstance makes for bad policy. This unusual outcome was indeed extreme circumstance. It won't lead me to process changes just yet - but it will lead me to some experimentation - on my own test blades.

Rob!
 
I can't find any error in your procedure, the only thing i'm noticing from the pic is that the bottom of the notches make sharp 90° angles to the blade planes, and that is scary ;)
I usually feel more confortable to break all the sharp corners before the ht (spine, edge, riacsso and tang included)...then sand everything sharp again after when needed.
 
Thanks Stezann. I generally don't get much say in pre-ht form, because theses are customer knives for the most part, I gotta say judging from the ones that have survived, I didn't see it coming with this one. I was fortunate enough to have a metallurgist I greatly respect look at the blade and the break and he saw fine grain, suggesting I not change my process. It hasn't happened since, and while I don't like the word never.... :)

The break was humbling and the maker was very understanding.

Since we've revived the thread, I have to say the post that's given me the most pause here was Ed Caffrey. I have huge respect for the man and his pursuit of excellence in the craft. Many makers start counting their soak (if any) when the kiln recovers to set temperature. I don't believe the blade equalizes as fast as the air around the thermocouple, and I can see shadows in the blade for as much as 6 or 7 minutes after I put the cold blade in the hot oven. For me, that means I'm soaking 3 - 4 minutes - and maybe that's too long. (or not :) ) I'd like to emulate Ed - maybe not in everything he does, but in his dedication to finding out what works. This forum is always invaluable in that pursuit.

Thanks
 
Glad you got to have such skilled eyes look at the knife. I had a bird and trout 15N20 blade a little earlier this year cause me all kinds of frustration. It looked great, but upon testing, the edge wouldn't hold for any time at all.... It was the first knife I heat treated in my new salt pot and I thought I'd done everything right.

After several conversations and subsequent tests, I found the steel I used to be good, so it had to be in my process. When I put the blade into the molten salts, I gave it about a 20 count before hardening (for some reason thinking it wouldn't need long at all...). Best I could figure was that this short amount of time (even with such a thin piece of steel) wasn't enough to get to full Austenizing temp. Another piece of the same steel in the pot for longer snapped in the vise easily after being quenched. I made some more and left them in the salt for longer and had no problem.

The lousy thing for you (vs my situation) is it was my first go with the new equipment and far from it for you... It would be interesting to have 3 or 4 of the same blades to test some different temps and times with and see what the results are. Glad you haven't had the same bad result since and here's to hoping you don't have any more ;).

Jeremy
 
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