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Paul Checa

Hardening a throwing knife

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I'm making a throwing knife and was wondering at what temp it it the best to heat treat. But I need to know in color of the steel. And then how long do I put in the oven for and at what temp for. Do I have to heat the tip hotter? 

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Your answer varies based on your steel. 

If judging by eye, you need to look for "decalescence". A visible change in atomic configuration that is used as a waypoint to know when it's time to quench. A shadow will form right before you reach the critical temp for quenching. When this shadow has disappeared, you're ready to quench. 

I really need to write some kind of thread on heat treating for beginner's to reference when I have more time. 

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On a throwing knife, especially a mystery steel one, do not attempt to harden and temper it.  Just heat it up to watch for that shadow Zeb mentioned and let it cool in still air.

If you saw the season premiere of Forged in Fire, you would see five out of seven hardened and tempered 1095 throwing knives break.  

In my opinion, your best choice for a thrower is 5160 (most automotive leaf spring) left as-forged and normalized (the shadows/cool in still air thing).  That will give you extreme toughness with little to no risk of breakage.  You can even use plain old mild steel, and when it bends just bend it back straight.  Hardening a throwing knife just greatly increases the chance of breakage and possible injury to you or a bystander.  

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I did use 1095 steel it was what I I had. Andy other recommendation I still have just forged and am waiting to harden. Depending on what advise I get here! Thanks! 

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In that case, just normalize (heat to medium red and let cool) and use it safely!

If you feel you have to harden and temper it, which I do not recommend, follow Zeb's advise, quenching in oil (old deep-fry oil is great!) and temper for two one-hour cycles at 450-500 degrees F (232 - 260 degrees C).  If you have the means to take it to 750 F (400 C) that would be even better.  You want a full spring temper, not hard at all. 1095 tends to be very brittle at best, but if you go for the higher temperature be sure you get there.  There is a zone between 275 and 350 C called the "blue brittle" zone when tempering.  You really don't want it there.  If you are looking for temper colors, the lower end is a light blue and the upper end is gray.  

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Then you'd just get the edge to crack. ;)  You really do not want throwing knives to be hard. They break.  Springy ones can also throw themselves back at you on a bad throw.  

I know, people do it all the time.  In my opinion it's just not a great idea.

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I understand. I was wondering about the 'gotta garden parameter on forged is why I asked.  Now I know make kuni mild to prevent breaking.

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I suspect they insisted on hardening on FiF to see if people knew enough to temper way back.  The guys who didn't break did just that.

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