Hey all
My wife and i compete in knife throwing. I am looking at making some throwing knives. The ones we use are 4" x 16" x .25
Any recommendations on steel to use? If i use a high carbon steel. How hard is it to cut on the Crossfire? Anything i should think about.
Thanks for the help
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Should cut the same. I can’t tell a difference between Ar500 and plain mild steel when cutting with the plasma.
Aim for medium carbon steel unless you guys are throwing in places where they’re unlikely to hit anything that isn’t the endgrain target. Medium carbon steels will hold up well without being likely to chip or crack if you have a dinger or ricochet into something hard.
Something like 1070-1080 would be cheap and hold up to a lot of abuse as long as you harden and then temper them back into the low to mid 50’s Rc. The micro cracking along the plasma cut edge wouldn’t be as bad as it would with high carbon steel or alloys, and the heat affected zone should be easier to grind off when you start shaping them.
If price and effort to process isn’t much of a concern here are some suggestions for alloys. Things like CruForgeV, 15N20, 5160 and AEB-L are all good choices too so long as you have someone who can harden them properly if you don’t have the resources to do it.
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Lots of great info. We dont throw into end grain. Thats why i am thinking a harder steel. Will 8 need to harden the steel no matter what after cutting?
Do yoy temper the steel after cutting?
Yes, you’ll have to heat treat, because you’ll have to grind the steel so it will be a knife and not just a knife shaped object. Whatever case hardening that happens from cutting will be removed in that process.
A fair number of small machine shops/tool and die shops have heat treating ovens. So do many trade schools with a machine tool program. Some guys practice and can heat treat a knife from 1080 halfway decently in a blacksmithing forge. You may be surprised how many places may be nearby that can heat treat them for you.
Throwing into side grain I’d probably still try 1080 and heat treat just a little harder. If you find a place that can heat treat whatever you give them, maybe try 52100 and stay in the 56-59Rc range after tempering.
If you’ve been throwing mild steel knives, or lesser quality hardened steels, you’ll probably be shocked how tough 52100 is, and how long it will stay sharp. It’s not a super steel like CPM-3V, but it’s still darn tough when heat treated properly.
Also, I didn’t mention it, but I probably should. You’re likely going to get the material in bars, not sheets, so if you’re going to use the plasma to cut them, be prepared for that. It’s not that sheets are unavailable, it’s that they’re cost prohibitive unless you’re making a boat load of knives, in which case get the best steel you can afford and send them to Peter’s Heat Treating in Pennsylvania for hardening. They do small batch jobs, all the way up to production runs for big companies, and can handle basically any steel you send them.
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Does the heat of the plasma affect the heat treating down the road?
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Not as long as they heat treat it properly. Usually there is an annealing or normalizing step as part of the heat treating process, and that will basically “reset” the grain structure of the steel.
The microcracking at the cut (in the heat affected zone) is a big deal though. That really has to be ground out while shaping the blade or it can propagate cracks.
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Sounds like Henry has a very strong background in metallurgy. Is price a driver for you? Do you have easy access to a small forge or oven? I had a friend who made a lot of knives out of old leaf springs and wheel bearing races. The steel used in the springs is tough the bearing races are hard. Make the blank out of the spring and hammer weld the bearing material where you want the harder steel.
I’m not sure if you’d need to flatten the leaf spring before cutting the blank on your table.
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Here is just such a post where Tin did a similar cutting:
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I find metallurgy very interesting, but besides some classes at the local community college on it and lots of independent reading and some test projects when I got into knife making, it’s not something I claim to be an all around expert about. Most of the steels I liked to play with were all CPM steels which needed vacuum ovens and cryo treatments to properly harden, and the cost to buy that equipment meant I sent almost all my blades out for heat treating besides some of the prototypes where I cobbled together some oddball ideas to prevent oxidation at high temps without the proper gear along with a dry ice and antifreeze cryo treatment, and was able to get decent enough results in the supersteels.
Composition and it’s effect on the steel, being able to read and understand heat treating datasheets, and application are where my knowledge base is the strongest.
I’ve got a cheap forge at home now and some steels that should be hardenable in it, like 15N20, CruForgeV, and 1095. My goal is to see if I can forge something usable and then work my way up to making a Damascus knife, just for funsies.
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Thanks everyone. I am not sure how fancy i need to get with metals and tempering. Mainly just trying to keep them from snapping. Maybe not having the metal tempered will make that better.
Plasma cutting will create a heat effected zone that will need to be ground away if you want to maintain the integrity of the edge. I’ve been making knives for about 5 years and my go it is 1095. You can forge it, grind it, and heat treat it with simple vegetable oil. I just machined a couple knives out of 1095 with my MR-1 last week. It machines really well.
For heat treating get the steel red hot and check with a magnet. When it gets hot enough it will no longer be magnetic. Then you dip it in the oil. (DO NOT MOVE SIDE TO SIDE IN THE OIL) work the blade up an down until it stops smoking. Then place in the oven at 450 to 500 degrees for 2 hours. If not it will be like glass.
here is a quick video my me machining a knife out of 1095 on my MR-1 Beck's Armory LLC on Instagram: "Getting these new parts dialed in #cnc #langmuiresystems @langmuirsystems #mr1 #diycnc"
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If it turns out you love knife making you’ll need some knife making tools like a 2x72 belt grinder. I happen to be a belt grinder manufacturer. 
here is my website. http://becksarmory.com/
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Richard is highly recommended for belt grinders and tooling.
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Not tempering it is probably a good choice for a throwing knife, but you should still anneal it. I’d think as long as the tip doesn’t bend you’re good. You may have to sharpen it a bit more often.
Just a point on heat treatment process for steel. Like @MrHaNkBoT mentioned. When heat treating steel you typically anneal it first, which relieves the thermal stress from cutting the blank and takes it to is softest/ toughest condition. Annealing is followed by tempering.
For the 10xx series steels it’s pretty simple ; heat it red hot and let it cool slowly. If you’re heating in an oven( or forge) you typically just shut it off and come back a day later. Most steel behaves pretty much the same but a few of the more exotic metals have more complex processes…
A lot of people like case hardening after forming because it only makes the outer few thousands of an inch hard preserving the toughness in the interior or the part. Best of both worlds.
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I love it when a new topic pops up and we hear from new people with all sorts of specialized knowledge. It’s just fun to watch and learn.
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Great video. In this you are machining the blade. I am hoping to cut it out of sheet metal with the Crossfire. Do you think the 1095 will still work?
I am debating if i want to go with something hardened. I am wondering if hardened will break easier. Not worried about it holding an edge.
When i get into cutting these out i will make sure to post some stuff
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Partially correct. Between the annealing and tempering steps is the hardening cycle. Tempering is used to bring the hardness down and increase the toughness of the steel after hardening it.
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