Throwing Knife Broke 5160

[DanielJones]

Hi, can someone look at my pictures of this throwing knife I made out of 5160, please? It was a practice piece and had gotten burned some in the coal forge some.  What does the break look like ?  Is it from the burn marks on the side? Thanks for the critique : )

[Joël Mercier]

Looks like it was already cracked. I can't tell much else because we can't see the grain much. 

[Alan Longmire]

I agree, that shadow in the grain on pic 2 says it was cracked to begin with. 

[Geoff Keyes]

Ah, throwing knives.  I hates 'em, I does!  Not that there is anything wrong with throwing stuff at a target.  It's probably the oldest human game.  "Hey, Og, think you can hit that tree from here?  Bet you can't.  Hold my beer and watch this!"

 

What I think about throwers is this.  They should be made out of cheap stuff, since you're going to throw them and if you miss, they are lost (often) and if they are hard and they torque when they hit, they might break.  Further, if they are hard and you hit one already in the target, it might chip or spall and hurt someone.  So I make them out if mild steel, RR spikes make good throwers, as do the big concrete nails (once you normalize them).  If one of my mild throwers bends, a couple of whacks with a piece of wood sets them straight again.

So my first advice is not to use hardenable steel.  5160, BTW, is one of those steels that can act as an air quench steel at times, so it could have hardened even if you weren't trying to.  Second, your second pic shows the problem, both with this piece in particular and with found steel in general.  There was a preexisting crack, that dark shadow proves it.

As forging practice it's fine.  As for throwers, I'm leaning toward screwdrivers as the perfect throwing knife.  You can buy them cheap at garage sales, if the point is damaged touch it up on the grinder.  Get the ones with the bright yellow or green handles for easier recovery.

 

g

[DanielJones]

Thanks for the help looking at them.  Here is one closer pic of the grain.

[Gerald Boggs]

Ah, the fun days of my youth.  I came across the book "Knife throwing; a practical guide"  Sounded like fun, so I bought the Bowie-axe throwing knife.  Built a four foot wide and eight foot tall target out of 2x6's and had a lot of fun learning to throw that knife.  Someone stole it and for whatever reason, I never got around to getting another one.  Don't know what type of steel, but it took quite a beating and never even chipped.

[Charles dP]

Hi Daniel

That grain is a bit course. You want the break to look like fine velvet. That looks like it could have done with one or two more normalisations before the quench. Interestingly the grain on the right of the photo looks courser than on the left. Unless this is just an illusion, I’m not sure why. Uneven heating perhaps?

[Doug Lester]

 

Yes, I think Charles hit the nail on the head.  The grain in course and could have been helped with a couple of normalizations.  It may have contributed to the pre-existing cracks.  You screw up, you learn.

 

Doug