I was making a couple of what should have been simple punches from an old SDS chipping bit I got at the flea market.  One tool worked out just fine.  The other split... I think while I was doing a partial quench in water while tempering.

 

Can you see the longitudinal split in the pics?  About 2 1/2" up from the point there is a band of oxidation colors and from there to the butt is a split.  I'm somewhat well read in heat treating.  That about wraps up a description of my experience.  So I had hardened the whole tool knowing that I should probably try an oil quench, but I didn't have oil, so I opted for water.  Then thinking I'd soften the striking end and temper the business end, I heated the butt watching for the oxidation colors to run toward the tip.  When I started to notice a change in color forward the tip, I quenched about 2 1/2" of the tip in water and held the butt above water w/ some tongs.  I'm thinking this is when it split but I'm not sure.  The split is from the water line up to the butt, but not below the water line.

 

Comments?  Cause?

what kind of steel is it? If you are using water when you need oil, it is not good. Cracking from cooling too fast, little if anything to do with tempering. its from the hardening.

Cracks are almost always from quenching rather than tempering---though they may show up during tempering...

Good Morning,

 

You don't know about it's previous life. You bought a used breaker bit.

Sometimes this happens. If your process worked on one piece and not the other, it may not be a problem with your process.

I reforge thousands of bits, sometimes they break like that.

SDS bits are probably 1045 or something close. There should not be a problem quenching the tip in water.

 

Neil

Thanks for your comments.

I'm kinda new to heat treating, but from what I've read it's best to not hold the piece in one place but to move it vertically a bit as well as swirling around to prevent a sudden demarcation line where the metal is quenched.  Anyone else have a take on that?

I'm kinda new to heat treating, but from what I've read it's best to not hold the piece in one place but to move it vertically a bit as well as swirling around to prevent a sudden demarcation line where the metal is quenched. Anyone else have a take on that?

Ive never hardned anything, but ive read posts by the phoenix blade master (Rich Hale) but side to side movement can warp blades when quenching.

no swirling it will twist the metal. only up and down to break the vapor jacket.

The steel is a crap shoot; you're guessing at Tom Cats. If you don't have oil, sometimes heating the water to luke warm by stirring with a hot piece of metal may help.

 

Sayings and Cornpone

"Have you swept your swarf today?"  [possible bumper sticker to be peddled at conferences]

Did you run the piece through a normalization cycle after forging and before going through the heat-treat process?  

 

Mystery metal very rarely ends up cheaper than buying new stock.  WIthout knowing the alloy, you can't possibly know how to heat treat it properly and then you went with the fastest quench you could find simply because it's the only thing you had handy.  That's a recipe for disaster if ever there was one.

It looks to me like that crack is coming from the key way in the top of the tool. This is a common way for cracks to start since key ways often have a sharp corner between the bottom and side. My bet is that the crack is the result of quenching the entire tool. Differential tempering could have been the trigger for the crack form, but had you only quenched the working end it likely would have worked out.