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I Forge Iron

Reset process after a fail?

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I've been searching through threads here and elsewhere, and I've found plenty of guides through from start to finish. I'm looking for some guidance on restarting when things didn't work out. I had a go today at heat treating some 5160 blades. First time trying 5160, so these were two practice pieces I had made to make sure I had the full process down before mangling something with more time invested. Propane forge was the heat source and preheated canola oil was the quenchent. The first attempt did not result in a hardened blade (file dug in). I believe my mistake was going too soon after hitting non magnetic and not getting quite hot enough. I reheated, this time holding a little longer past non magnetic and requenched. It hardened this time, but also took a nasty warp. The second blade I gave the extra time past non magnetic on the first go round and it hardened and also did not warp at all. Blades were not the same profile but we're the same thickness (1/8" approximately).

I figure it's always possible that odds just resulted in one warp and one no warp, but I'm wondering if I needed to do something to "reset" after the initial fail. If I had gone all the way back to the beginning of the process and done 3 rounds of normalizing over again would that have reduced the chances of warping?

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You should've annealed or normalized it at least, before hardening again. The first quench may not have hardened it enough but it sure as heck stressed it. If it were going to warp it would've done so normalizing but been soft enough to straighten out without stressing before going back into the hardening cycle.

Having said all that you do know I'm NOT a bladesmith guy. Yes? If one of the real bladesmiths says differently go with their advice.

Frosty The Lucky.

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5160 is the steel I primarily work with when making knives. I've had some knives that warp ( the degree varies) and others that don't. There can be a good deal of stress introduced to the steel when you grind, and so I take each knife through several normalizing heats once it's be worked and ground to the final shape. How much you grind both sides really matters. When I forge I try to count hammer strikes on each side to keep the number even. The same gen idea can be applied to grinding. If you remove more material on one side and unintentionally leave the other side thicker, you are setting the knife up to warp.  If the edge gets wavy and not straight then you ground the edge too thin so you'll have to grind the edge back a bit to thicken it up. 

 When I do my heat treating I like to let the blades "dwell" in the forge and really soak up the heat. If the steel is more evenly heated, I would say it would be less likely to warp. Another thing that I have found to affect warpage is how you quench the steel.  I only move my steel up and down in the quenchant, to me it seems to warp less. I definitely agree with Frosty on normalizing again. If the blade warped then there is still stress that needs to be worked out. I'd recommend when you normalize a blade put it on a wire rack or something, because you want all the surfaces to be exposed to the air so it cools evenly. I put mine on some old wire rabbit cages. I made a batch of 15 knives recently and wasn't thinking when I normalized them and put them on the ground by my forge. When I heat treated them, only 5 came out without warps. How you normalize and and grind effects warpage. 

I don't make a lot of knives but I've made enough mistakes to start figuring it out. 


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