Heat Treating W1, Still too brittle

[hathegkla]

so, I made a new set of bo-shuriken (darts) yesterday out of some 5/16 square bar. after tempering I tested them out and one of them snapped in half. I know W1 is really high carbon for any throwing weapon but it was cheap and has worked for me in the past. I'm wondering what temperature I should be tempering them at for throwing? I tempered them at 550F (3 times for 1 hour each), the chart I'm using says they should be betwen 55 and 59RC. I'm guessing this is waaaay too hard?

The other 5 I made are ok so I've got the kiln heating up to 650F right now, should I go higher? I'm looking for something springy and not necessarily rock hard, I just want them to be hard enough so they don't get dinged up so quick.

the thing is I have a set of larger spikes (same diameter) that I've been throwing for a year now with no problems, the only thing I did differently is I hardened them at 1550F, this time I hardened them at 1450 (both times I used water), maybe I didn't fully harden them the first time?. I have fast oil but figured it didn't matter since I wasn't making a knife.

so to recap here's my recipe:

5/16" square barstock (7 inches long)
heated in the kiln to 1450F and quenched in water (no visible cracks after hardening)
immediately triple tempered at 550F for one hour each time.

I think after this set I'll probably go back to using mild steel, I case hardened a few last year and they came out really nice.

 

[NickWheeler]

I'm certainly no throwing dart/throwing knife expert... or anything anywhere close, but I have used a lot of W1 over the years and your recipe seems sound. I'm surprised you had one snap. My recommendation would be to keep that recipe, but draw the body of each dart back a little with a torch.

 

[hathegkla]

drawing with a torch sounds like a good idea, at least that way only the tip will be brittle. The only other thing that I thought of is checking my kiln, it seems to work fine at high temperatures but at temperatures as low as 550f it might not be accurate. the last set I made (that seem indestructible) I tempered in my kitchen oven.

 

[Fred.Rowe]

You might try normalizing the darts after they are shaped, then just harden the first inch behind the tip.

Throwing darts are a lot of fun; I never mastered it.

Fred

 

[hathegkla]

so I have a small update. I threw them in the kiln at 650 with a hardened "test piece" of the same metal (same heat treatment just no prior annealing) the test piece snapped when I hit it with a hammer, after an hour at 650 the test piece held up to getting beaten with a hammer the only problem is the darts seem a little soft, I noticed some gouges in the surface after throwing them at each other. this could be due to surface decarb (all I do after hardening/annealing is give them a once over with a wire brush). but the good news is they won't break now.