beyond frustrated

samuraistuart

samuraistuart

Joined
Dec 21, 2006
Messages
3,158
You ever get to a point where you just ask yourself, "What the heck do you think you're doing getting involved with this?" I'm there now. I buy a glass kiln, for knife heat treating. Not ideal, but it's got to be better than my paint can forge, right? I had a Cru Forge V knife that I had made and heat treated in my paint can forge. I was IMPRESSED when sanding this stuff. What a b---h! The heat treat came out right, or good enough anyway. But I thought the tip might not be quite as hard as the rest. So I decide to re-do the heat treat, this time in my new kiln. Nothing wrong with that. Now I had done three normalizing cycles in the previous heat treat, and then quenched. Keep that in mind. I did another three, in the new kiln. 1650, 1550, 1450. then 1475 with a hold at temp into parks 50. A file dug right in afterwards. I mean......right in. I thought....decarb.....kept filing away. Not decarb. I could have kept filing that thing to dust.

I pull out my trusty paint can forge and fire her up....put the CruForge V blade in, brought it up past critical, quenched in Parks 50.....file just dug right in.

Pissed does not begin to describe. I don't get this at all. What is that saying, "If it aint broke........."

Just ranting, guys. Feel free to take a swing at me.....I need it.
 
I suspect you may be austentizing too low. AKS lists 1500-1550f for HT.
 
Sorry, Willie....that's not the problem. Like I said...the heat treat in my paint can forge intially went very well.....I was concerned the tip wasn't as hard....hence the re-heat treat in my new kiln. Again.....I tried the kiln (which was my second hardening)......and it was soft. Then I tried my paint can forge again.......the same temps as had used in my previous "succesful" attempt....but now the edge was soft. The temp isn't the problem. AT ALL. Just to clarify.....I had done a good job....but not "perfect". That's why I tried the new kiln.....which didn't produce.....so I went BACK to the SAME thing I had done before that gave me somewhat satisfactory results, with my paint can forge, all steps identical....only this time......soft soft soft soft edge.

Here is what I thought initially....when I open the top opening door (I might modify to a side opening small door)......it sure seems like the rush of cool air (this is a glass kiln...not a proper knife kiln) negates the heat along the thin thin thin edge....so no matter how fast I am into quench....it won't matter.

I bought this thing thinking it was an upgrade to a paint can forge. Now I'm wondering. But here is the thing.....even though I was suspicious of the kiln....using my paint can forge, which is very reliable, gave me the soft edge as well.

Again, is there any way that I over normalized this steel to where it won't harden now? This is baffling me to no end.

Is there a possibility that too many normalizations will cause a blade to not harden properly? 1475 vs 1550 isn't that big of a deal....especially when a file just DIIIIIIIIIIGGGGSSSS in.
 
I think that you might be normalizing at too high a temp. Why not bring your blade up to 1500, take it out of the kiln or forge and let it air cool till the color disappears. Then do it again for a total of 3 times, then do your hardening. Bring the blade up to non magnetic and quench.

Annealing
Heat to 1450°F, hold long enough to make sure temperature is
uniform, slow cool to below 200°F.
Annealed Hardness: About BHN 180

Hardening
Preheat:
Heat to 1200-1250°F (650-675°C) Equalize.
Austenitize:
Heat to 1500-1550°F (820-845°C) Equalize.
Quench in oil.

Temper:
Double temper at 400-500°F recommended.
Approximate hardness after double tempering is shown below.
Actual hardness will depend on hardening temperature and
quench rate.
Temper: 350 400 425 450 500 550 600
HRC: 62 61 59 58 58 56 55
 
One thing I've noticed using a small pottery kiln is that because of having to handle the lid, it's very easy to not get the blade to the quench in time.
This isn't that much of an issue with foil wrapped packets, but with blades resting in a kiln it's a hazard...if you were on the low end of temp, perhaps the quench wasn't really from a high enough temp. How was the color when it went in the oil?

If you're thermal cycling it correctly, it will harden. Just a matter of finding the disconnect....I've sure been there, and when I finally figure it out it's always, "Ooohhh....yeah, I knew that...."

Another thing that occurs to me is that it's very likely that the temp you thought you had in your forge the second time wasn't what you actually had. I thought I was good at judging temp by color until I ran the kiln up to known temperatures...wasn't what I thought!

There's another thing: Surface decarb- you could try grinding off a bit of steel and seeing if you have better hardness underneath.
But really? It's easier to just put that one up on the wall as a reminder of how tricky this stuff is, and just try another one, with all this stuff and Chuck's excellent info in mind.
 
OK, most has been covered, but I'll try and recap.

The temps you got in the forge are just guesses. You don't really know if they were the same.
The temp in the kiln is probably accurate, but you need to check it against a Known source to know. Either use a known pyrometer, or get some temp-stix or temp-cones.

The austenitizing temps you used are a bit low, and you didn't mention the equalizing step at 1200F, but you should have hardening to some degree in what you listed.

I would take it to 1650F , hold for 10 minutes, and quench, followed by a second austenitization at 1550F, hold , and quench.
BTW, you didn't mention the quenchant and volume of it you are using???

Cold air does not "rush in" to a top opening kiln. If the kiln was fully soaked for fifteen minutes or so at the proper temp, the hot refractory lining maintains the heat just fine. You knife will not suddenly cool of when the top is opened. The biggest problem with a top opening kiln is getting the knife out without setting your arms on fire.
 
Thanks, Stacy, for the tip on top loading kiln. I saw the reading go down on the sensor, so assumed that the blades were going all over temp-wise. The last batch came out just fine (52100) so perhaps I'm worrying too much.

Is there a set of conditions that would make CruForge not harden, given proper Aus. temp and quench, short of the steel being seriously burned?
My assumption is, you do your part, and the steel will do its part, but there's always more to it, it seems.
 
Sometimes the file feels like it is biting after the final hardening quench. I've seen where I leave the blade for about an hour and come back, then the file just skates across.
 
I am using an Evenheat front-loading furnace turned on end to harden my tomahawks. I took a lid off an old kiln (rather than hack up the brand-new door), cut a slit in it, and built a little frame that sits on top and suspends the blanks down inside the furnace on a heavy stainless steel filler rod. Works rather well. You might try a setup like that to get around the limits of using a top-load furnace.

 
I don't think there's anything more frustrating than those times that you feel like you did EVERYTHING right, yet the H-T fails.

I had issues with the first couple CruForge V blades I did (this was just recently!) that were all due to decarb. I was using my Paragon kiln, not my salt bath.

One of the blades came out of the Park50 and a triangle file bit into it like mild steel. I was so frustrated/pissed! The ricasso was Rc testing at like 50C (after the first temper).

I hollered at Matt Gregory, as CruForge V has become one of his "pet steels" and he is also very good friend with Dan Farr. They thought my problem was decarb.

I surface ground something like 0.010 of each side of the ricasso and re-tested... it was around 65C (which is even harder than the specs said it should be).



So--- I'm wondering if you are just having the same issue I did...???
 
My first thought was decarb too. Especially if you have done all this heat treating without grinding the steel after. If I test a blade that i know I heat treated properly and a file bits, I just keep filing and after two or three strokes it skates.
 
I neglected to mention dealing with decarb. Grind the blade on the grinder along the edge. I bet it suddenly starts throwing big sparks.
 
Wow guys....you're making my day better, for sure. Thank you. Let me try to address some of these points, and get to the bottom of this. First let me say that when I open the lid on the kiln, it does seem like the edge looses it's heat (goes black) rather quickly, by the time I get it into my 5 gallons of Parks 50. It really really seems that was the case. However, my edge was ground thin. Probably too thin. I'm guessing .015. I had been leaving them too thick, so I may have overcompensated. As far as decarb....that is different than scale, right? After normalizing, I sand off the scale back to bare blade, each cycle. And if decarb is the issue here....my edge was already so thin.....the file was just going to eat that edge right up, if decarb is the issue.

I was thinking of rigging this oven somehow with a side slit. Leave the lid down at all times, and use a slit cut on the side. There is already a peephole there, just a bit above the floor level inside, I was thinking of cutting a slit that goes from that peep hole down to where I could slide a blade in there and it rest on the inside floor. But I'm leary of doing that.....especially since the foil wrap was mentioned. Does that do a good job of heat retention from the kiln to the quench? I know if I leave my edges a bit thicker, they will retain heat better, but then that means more sanding afterwards.

Ah, yes....Stacy, thanks for the pyrometer recommendation. I did indeed check it, and if the kiln shows 1475, the pyrometer shows about 1490. About 15 degrees hotter. And the blade went into 5 gallons of Parks 50.

Just so everyone knows....this kiln has the elements in the lid itself....not around the sides. And I could be wrong....but it sure seemed like the edge was black by the time I got it into the Parks oil. Lifted it with a wire, and right in...immediately. Fast...no dilly dallying around. But it sure seemed like that is an effort in futility.....the edge being black (but it was thin).

Nick, and the rest of you, I'm with you on the decarb. That was probably it.
 
.015 is way thin. Unless you are using an inert atmosphere or salt pot it will decarb. Yes decarb is different than normal scale. The steel decarburizes when the material is heated above transformation phase. The hotter the faster it decarbs. The heat and atmosphere, esp an oxidizing, will literally suck the carbon right out of the steel. This can make it so the steel will no longer harden ie mild steel. There is no easy way to fix this other than grind it off. Many makers leave .062 thickness while others take down to .031. You may need to do some grinding to reduce the edge to a usable thickness.

Using foil is not really conducive to an oil/water quench blade. Air hardening yes, not a liquid quench though. It would take way too long to remove it from the foil and you will not get a thorough quench leaving it in the foil.

Like others above have recommended, grind back the edge and try the file again. Just remember that the sides of the blade might have decarbed as well so grind enough off sides to get back down to good steel. Could even just file back until you come to hard material or the edge is over .062 thick.

I had a similar problem with W-2 but I did like 6-8 normalizing cycles. It would not harden.. I put it back in the forge and took it back up to 2000f then did 2 normalizing cycles and re hardened. Worked like a charm. Just another possibility.
 
Thanks, Mr Richards. About the foil, I thought of that as well. For an oil quench blade, it would take too long to get out of the foil. I believe the issue was indeed decarb, and I will make sure to leave edges thicker, and deal with thinning them down after heat treat.

I've heard (I may be slightly off here), that too many normalizing cycles will cause an edge to not harden. Not really sure why that is...I forgot the reasoning behind that. Too fine of grain to harden, or something like that. Thanks again to everyone who chimed in. My next knife has edge at .030. I think I'll be good to go there.
 
samuraistuart said:
Thanks, Mr Richards. About the foil, I thought of that as well. For an oil quench blade, it would take too long to get out of the foil. I believe the issue was indeed decarb, and I will make sure to leave edges thicker, and deal with thinning them down after heat treat.

I've heard (I may be slightly off here), that too many normalizing cycles will cause an edge to not harden. Not really sure why that is...I forgot the reasoning behind that. Too fine of grain to harden, or something like that. Thanks again to everyone who chimed in. My next knife has edge at .030. I think I'll be good to go there.
Click to expand...

Stuart,

It is possible to decrease the grain size to the point where it doesn't fully harden and has a lot of retained austenite, but your treatment wouldn't get you remotely close to this and is more a limit that you would have to try really really hard to reach intentionally and you'd have to have really excellent heat control. It sounds like decarb is your problem. I've had a similar experience with Cruforge like some of the other guys. Leave a thicker edge and good luck!

~Luke
 
Thanks for the luck, Luke. There is a lot to learn, isn't there?!? I hear you.....it is possible to get grain size so small that it won't harden well, but I wasn't even close to that limit. The word for the week, for me at least, is DECARB DECARB DECARB!!!!
 
It's probably decarb as mentioned, but if your edge is going black before you're in the quench, it's certainly not going to harden properly.


The issue is still edge thickness regardless, but the blade needs to be staying extremely close to the color it comes out of your kiln, as it goes into the oil. You need to be set up that it doesn't take more than a second or two to get from inside the kiln, to inside the oil.
 
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