| From: ChrisS
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| Date: 18-Dec-14 |
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My older son is building a knife from file for his brother. After his work, the blade is too brittle and tip broke off easily.
He is not on leatherwall but would really appreciate some direction to correct this.
Here are the steps he took....What went wrong and can he fix it?
Steps: 1. Heated old file in propane forge to glowing and hammered on anvil to shape. He did this several times to shape it. Then slowly cooled it.
2. Hand filed blade, and drilled hole in tang.
3. Heated it to glowing and quenched in oil.
4. Finally, he heated in oven 550deg for 1.5 hours to temper it. Slowly cooled.
If he can fix the blade he will make a tanto tip and finish it out. Any advice greatly appreciated. Thanks, Chris
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| From: HD RIDER
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| Date: 18-Dec-14 |
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Lots of how to videos on utube .very helpful
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| From: Les Bishop
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| Date: 18-Dec-14 |
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I believe the knife blade is still to hard and brittle may require another tempering
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| From: woodinhand
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| Date: 18-Dec-14 |
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Just finished these rasp knives up. When I heat treat I heat until non-magnetic then another minute or so, immediately into oil, keep moving in oil until it cools down so you can handle it. I temper at 300 for 2.5 hrs. You need to get to non- magnetic, I don't know how hot glowing is. Good luck, Carl
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| From: JamesV
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| Date: 18-Dec-14 |
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Wood..............
Those are some good looking knives, very nice workmanship
James
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| From: Ghost308
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| Date: 18-Dec-14 |
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Sounds like he might have put a fracture in the metal from hammering on it, once it's heated until it's non-magnetic it needs to cool down very slowly , then it can be shaped with a new file or even cut on a band-saw. When it is time to harden the blade heat it until it is non-magnetic again then quench tip and blade in oil first then the rest of the blade. Temper it starting at 500 for an hour and work your way down 100 per hour until your down to below 200.
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| From: THRC
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| Date: 18-Dec-14 |
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I never beat a file knife, just ground to shape. Polished the steel to bright (to see color) then heated to blue and air-cool to work the steel; then heated blade only to red with torch and edge first into USED Diesel crankcase oil to carburize, and polish the blade, reheat with torch until spine and tang is blue, body of blade is straw, and edge is bright, then Immediately back edge first into the crankcase oil.
Crazy system, only had a cutting torch and a grinder to work with, been using these blades with no ill effects or dulling for the last 30 years or so...... it makes a Rockwell 45 spine and a 55 edge, just about perfect for me.
TinHorn
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| From: ChrisS
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| Date: 18-Dec-14 |
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Thanks all for the advice! I have shared your comments with him.
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| From: MGF
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| Date: 19-Dec-14 |
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His "temper (550 for 1 1/2 hours) should have made it plenty soft...too soft for my tasts.
My guess is that it cracked during the hardening (the quench) or shortly after.
Immediately after quenching the blade should be full hard...maybe glass hard. It has to be treated gently at this stage and tempered as soon as possible.
Sometimes you can hear them crack when they crack in the quench.
There are a number of things that can cause it...blade geometry or maybe enlarged grain structure from the way it was forged. I'm not a metallurgist so I don't know if I want to try to explain all that but you want to forge at progressively lower heats as the forging nears completion and finish with a normalization or anneal.
The idea is to relieve forged in stress and reduce grain size.
Forging high carbon steel is a little trickier than mild steel. It has to be worked at the right temperatures...not too hat and not too cold.
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