heat treat foil question

[BCROB]

........I received some info from a knife-maker and I'm interested in opinions please.

when he uses foil for stainless and when finished heat treat he removes the blade from the oven..........snips the foil.........removes blade from pkg.....then returns to oven to reheat the blade back to required temp that was lost fiddling around with removing foil etc........is this normal procedure ? is this a no-no ? or can this be avoided by simply speeding up the unwrapping time ?
understanding obviously that oven to quench time is critical am curious in your thoughts

until recently all my knives have been shipped for HT so this is all new to me............
up til now thank-you all for the emails and pm's to this point !!

cheers

[Ray Rogers]

Never used foil myself and I'm not metallurgist enough to anticipate all the wrinkles that might accrue to that process. A lot will depend on what steel he's using. If it's an air hardening steel then I think it would be OK to take the foil off, put the blade on a cooling rack, and not bother putting it back in the oven.

For oil quenching steel that process might be a problem but, again, would be partly defendant on what steel it was. If it was me, I think I'd wrap the blade tightly enough to minimize any air inside the envelope and then quench the whole thing instead of trying to get the foil off. If there's no insulating gas layer inside the foil then it shouldn't matter.

Or, I'd work out a way to cut the foil off very quickly and then quench rather than going back to the oven. All this is about foil but there are other ways to skin that cat ...

[BCROB]

Originally Posted by Ray Rogers

Never used foil myself and I'm not metallurgist enough to anticipate all the wrinkles that might accrue to that process. A lot will depend on what steel he's using. If it's an air hardening steel then I think it would be OK to take the foil off, put the blade on a cooling rack, and not bother putting it back in the oven.

For oil quenching steel that process might be a problem but, again, would be partly defendant on what steel it was. If it was me, I think I'd wrap the blade tightly enough to minimize any air inside the envelope and then quench the whole thing instead of trying to get the foil off. If there's no insulating gas layer inside the foil then it shouldn't matter.

Or, I'd work out a way to cut the foil off very quickly and then quench rather than going back to the oven. All this is about foil but there are other ways to skin that cat ...

..............oil quenching steel Ray

[nate d.]

This is no complicated. it is dependent on the alloy being used. There is something called a TTT curve, or time temperature transformation curve. the decision to how one goes about removal of an austenitized piece of metal to quenching is alloy dependent on that curve. I love these curves, they tell you a lot of nifty things in my opinion. Get one of these TTT curves for your alloy or a close neighbor alloy and walk through the information presented step by step and slowly and see what you can and can't live with.
in closing bottomline: removal of foil and reinserting blade is not a smart idea. that will grow the oxide layer which them most likely be taken off. doesn't make sense to me to set yourself back like that. also i've heat treated Stainless and not had any problems obtaining 62 HRC taking knives out of the foil straightening them and them plate quenching.

[BCROB]

Originally Posted by nate d.

also i've heat treated Stainless and not had any problems obtaining 62 HRC taking knives out of the foil straightening them and them plate quenching.

good to know , thanks for your input

[bob levine]

When using foil I always wrap the blade in colored newsprint. This does two things. First when the temp reaches 451 the paper burns up excluding any air which is an oxidant. Second the newsprint which is basically carbon. replaces carbon burned off by the heating of the steel to hardening temps You wind up with a blade that is free of any scale.