Surface pitting after heat treat

[Doc Shipley]

I heat treated a 1084 blade the other night in an electric oven, soaked at 1500F for about 10 minutes and quenched in McMasters 11-second oil at 140F. I forgot to throw the chunk of charcoal into the oven when I put the blade in, and it came out of the quench pretty badly pitted. It sanded out OK and I haven't found any internal pitting or evidence of cracking or delaminating, so I ASSumed it was just surface decarb.

But, I decided I'd rather ask than assume. Should I be worried about the pitting? Have I ruined the blade?

Doc

PS - I'm pretty sure I didn't overheat it. I checked the PID's accuracy by bringing the oven up to 1400, putting in a piece of scrap 1084 for about 10 minutes, and testing with a magnet. Still magnetic. Turned the temp up to 1420 and the coupon went non-magnetic. That's close enough for me.

 

[Stacy E. Apelt - Bladesmith]

First off, keep the charcoal for the barbie. It won't do anything to control pitting and decarb in an open oven.

What you saw was probably normal surface artifacts from small particles on the blade surface. They get hot and burn up, leaving behind a shallow pit. Sand to at least 220 grit ( I like 400) and clean every blade well. Coating the blade with a thin coat of satanite works wonders. Mix it about like thin pancake batter. Coat the blade with a wash of this and dry with a hair dryer.

Back to the surface pits for a moment. When you grind, all sorts of stuff gets shoved into the blade surface. Tiny bits of silicon carbide from the belts, metal shavings and little balls of steel rolled up (and virtually welded to the surface) by filing and belt friction, dirt,etc.. When the blade surface gets heated, these small particles heat first, and become little burning spots on the surface. They can cause anything from minor dark spots to pits.

 

[sunshadow]

I will have to disagree with Stacy on this one, i have been using charcoal in and enclosed electric kiln for atmosphere control (not a burnout kiln which is vented, but a lab kiln which only has a 3/16 probe hole in the door) and I have seen a dramatic diference in scale and decarb between using the charcoal (wood charcoal not briquettes) and not using it. If the charcoal lasts for the entire HT and only flares up when you open the door it is most likely consuming most of the available oxygen in the kiln

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[Doc Shipley]

First off, keep the charcoal for the barbie. It won't do anything to control pitting and decarb in an open oven.

What you saw was probably normal surface artifacts from small particles on the blade surface. They get hot and burn up, leaving behind a shallow pit. Sand to at least 220 grit ( I like 400) and clean every blade well. Coating the blade with a thin coat of satanite works wonders. Mix it about like thin pancake batter. Coat the blade with a wash of this and dry with a hair dryer.

So the damage is only as deep as the pits?


Doc