Chisel snapped

[Paleo]

I’m making a 14” chisel for stone quarry work made from 7/8 tool steel (according to spark test) with a 7” taper. The first one I made I cut the taper using a band saw and then sanded smooth. I then heated to cherry color quenched the tip and waited until blue moved down and a complete quench in water.

The first time I used it an 1-1/2” of the tip snapped off. Where am I going wrong?

Thanks

[ThomasPowers]

Did you just hold it in water at that spot or did you move it up and down in the water?

If you just held it steady you may have a "water line break" issue.

Else you may have an alloy that shouldn't be hardened in water "tool steel" is rather meaning less as there are hundreds if not thousands of tool steels out there, some harden in water, some in oil and some even harden in air!

[S.Willis]

I agree with Thomas. It sounds like a quench line break.

[Paleo]

Thomas, Thanks for the info on tip quenching,no I did not move it up and down. The "tool steel" I used was from a demolition air hammer's 4 foot chisel cut down. Do you think I should use water,oil for quenching?

Thanks
Paleo

[Rich Hale]

I would use oil and it needs to be tempered afterwards as quenched will likely be wayy too hard..

[ThomasPowers]

Paleo, that still could be anything from 1050 to S7!

With unknow steel you start with the gentlest quench and if that doesn't get hard enough you go harsher, Remember that you may have a decarb layer so when you check it with a file dig in a bit---I "sharpen" the tip a bit to not leave a notch but still get through any decarb.

Even if it's the correct hardness you will probably want to draw a low temper on it to make it tougher.

I'd try oil as a good general first guess (not the gentlest but the air hardening are usually high alloy top dollar metal and so not used a lot)