TINK!! Again

K

Kevin Powers

Joined
Jul 23, 2015
Messages
411
Apparently I have a bad habit of torturing myself and I continue to abuse myself by continually cracking 1095 blades. I have gone through sticks of the stuff and have turned out approximately 1 good knife to date. So today I figured let's make a Bowie, never made one of those. I profiled and ground the blade evenly, went up to a trizact a65. Edge was .030" and spine was 1/4". Once the grinding was out of the way I began my thermal cycles. I wrapped the blade in foil and waited for the oven to reach 1300. Opened the door and put the stainless burrito in, edge up. I took the oven up to 1630*f after it stabilized at 1300. Once up to 1630 I took it out and let it cool to black. Back in the oven, this time at 1500 then out to black. 1450, 1400, 1350, 1300 all out to black. I removed the blade from the foil and inspected it thoroughly, no warps, nothing different than when it went in, just now it was darker in color. I cleaned the blade and applied the kiln cement for a hamon. Then the knife went back into the oven. Up to 1475*f, 10 minute soak, into parks. In the parks uninterrupted. Pulled the blade out, straightest knife I've ever quenched. Lost all the mud off the blade in quench and was looking good. Set the blade aside until I could grab it with a bare hand. Went up to the grinder to clean the scale off and see what the hamon fairy delivered to me. Trizact a65 running about half speed on the vfd. Swipe one, looking good. Swipe 2, even better. Swipe 3, tink! No!!!!god, whyyyyy? First time the blade has actually cracked in my hands. I have had them come out of quench fine and then crack 15 minutes later sitting on the bench. So mind you that I'm bare handed, not over heating the blade by any means. Do I think the blade would've cracked if I went straight into temper? No idea. Tons of people that do hamons tell me they grind right after quench to see if they have enough activity, if not reclay and requench. So can anyone shed some light on if something is jumping out at them? I have read and researched this to death and it just keeps killing me.
With this one I'm not even mad and have almost come to expect failure, I almost want to blame the metal but I had success out of this exact piece of material.
Pre thermal
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Plunge
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Clay
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Crack from edge to about 1/2" away from the spine about 1-3/4" away from the plunge.
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Best to temper right away if you keep having this problem. After at least a quick snap temper first at around 350 for an hour, you can then grind and check for a hamon. If you don't like what you see, then you can always re-harden it. May not be as quick as re-heat treating right away, but it's a lot faster and a lot less painful than having it break and making a new knife from scratch. :thumbup: Great looking blade btw, reminds me of the Joe P & Nick Wheeler bowie, sorry it cracked. :( :thumbdn:

~Paul
My YT Channel Lsubslimed
... (It's been quite a while since I've posted any new vids)
 
Bummer!!! I agree, do a snap temper to help prevent Ping! BTW, how'd the hamon turn out? you did etch to see hamon - didn't you?
 
That's a big thickness differential from spine to edge. Perhaps leaving the edge a little thicker could have helped- say, .040 and with no grind scratches crossing the edge. That is, grind or sand the edge out lengthwise first. I agree that a snap temper will likely help.
One thing you could do, to get through this bar of steel if all else fails, is heat treat in the forge and don't let the clayed portion get up above critical. That puts less stress on the blade. That's a good trick to use when water quenching for a hamon.
 
That sucks.... I feel your pain. Break it open and examine the crack. If it is dark, it happened in the kiln or the quench if it is light it cracked after the quench and before the temper. Try to get a clear shot of the grain and post it.
 
I always do a temper before anything else after the quench. Releasing some of the tension in the steel would likely prevent a crack this late out of quench.
 
Yes ,you shouldn't mess with the blade before some temper .300-350 F snap temper at least. There will be very high stresses after quench just wanting to relieve themselves .Grinding , no matter how careful you are ,will add stresses !! You're setting yourself up for doom !
 
I'm by no means an expert, but I've read elsewhere in this subforum that it might not be a bad idea to cover the entire blade with a thin wash of satanite/clay before applying thicker pattern for hamon. I gather that it doesn't slow the quench as much but makes the reaction when blade comes in contact with quenchant less violent and might help to prevent cracking. HTH
 
For hyper-eutectoid shallow hardening steels, quench, cool to room temperature, and them IMEDIATELY temper. If you set it aside, drop it on the floor, or take to the grinder, you greatly invite cracking.
 
Lots of good replies. I know the crack happened after quench because I felt and saw it happen as I was examining the hamon after a clean up grind pass. The only thing that was different about the process yesterday is that it was raining in San Diego. The parks was room temp. I've heard that parks likes to be above 80* today I plan to do basically the same thing but heat the parks and snap temper. I'll report back with my progress.
 
Atlas Knife Company said:
Wow, that's a lot of pre-HT stress relief followed by NO post-HT stress relief. Definitely out of balance.
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The pre heat treat regime does seem a bit excessive. :eek:

Three cycles is typically all that is needed. Normalize above acm (even carbide distribution) cool in air to magnetic, heat below acm (grain refinement) cool to magnetic, quench if desired, once more in the 1400-1450 range, cool to black, quench. Now austentize and quench. I like 1450-1460 for knives where a Hamon is desired. Immediately temper at 375-400 for an hour. Subsequent tempers to walk up to desired RC value.
 
Kevin Powers said:
Lots of good replies. I know the crack happened after quench because I felt and saw it happen as I was examining the hamon after a clean up grind pass. The only thing that was different about the process yesterday is that it was raining in San Diego. The parks was room temp. I've heard that parks likes to be above 80* today I plan to do basically the same thing but heat the parks and snap temper. I'll report back with my progress.
Click to expand...

I would think that a thin layer of clay slip would actually increase the speed of the quench slightly. Just off the top of my head, the clay being blown off would agitate the initial plunge. My physics might be off, but it makes sense to me out of the gate.
 
From how it was explained to me, Rick is correct. It makes a slightly smoother faster quench.
 
Got another profiled and ground. Also picked up a better quench tank. This one holds over 5 gallons but it's big enough to put my blades in level instead of vertically. The blade is in the oven to begin the thermal cycles. This time no foil.
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1650, 1550, 1450, 1400 x2, all cooled to black between. Into oven after clay 1455 10 minute soak after the oven stabilized. Quenched into park, no warps no cracks (fingers crossed) now it's in the kitchen oven at 350. I'll let you know how it all goes after this hour.
 
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