Could it be the "Foil" ?

Robert Dark

Well-Known Member
Scenario..........

CPM 154 finished to 400 grit
Blade double wrapped in H/T foil
Pre-Heat to 1400 F. to equalize - 10 minute hold
Ramp to 1925 F. - Hold for 30 minutes
Quench (while still in the envelopes) between two 1 inch thick X 6 inch X 12 inch (frozen) aluminum plates with compressed air blown between the plates during quench.

Here is the problem....... When I take the blade out of the envelope(s), the envelope wants to slightly stick to the blade in a few places. Then, the blade is sort of "mottled" looking that requires me to either go back to the grinder or start over by hand at 220 grit, then work through the grits again.

Now, I will admit that the H/T foil is some I have had for several years. When I bought it, I didn't pay attention to the temp rating. Could this be the problem, or is my H/T recipe off? I have also had the same problem with S35VN.

As a side note, I have also tried placing a 1/4" square piece of paper towel in the foil pouch on the tang end in order to help consume any oxygen within the pouch. Doesn't seem to make a difference whether I use it or not. The problem still exists.

What "Foil" are you using and where are you getting it? Any suggestions will be appreciated.

Robert
 
This happens to me also but it's not a problem because I'm going to surface gring at 400 grit after heat treat then hand finish. I've heard that you can put talcum powder in the pouch and that will prevent it from sticking.
This may be related to plate quenching,I've never had it happen when air quenching.
 
Hi Robert

We sometimes see the blotches or 'worm tracks' and I can't explain the cause. We also get some occasional foil sticking - maybe one or two out 100.

Most of our customers take the finish a whole lot further before HT - probably between 800 and mirror - and most of the time they can do a final clean up on the buffer or start off with the last grit they used for clean up.

I don't know if any of this will help you but here it is.

We also double wrap and we use only 309SS foil. The blades go in a cold oven (or at least lower than 500F) because we've had envelopes explode when they are put in a hot oven. We don't pause to equalize - simply not necessary with a thin profile object like a knife blade that is probably going to take 40 minutes or more to reach temperature, the middle stays pretty much with the outside temp. (Might be useful if heating fast in a forge.) We also quench in the envelopes between 1" aluminum plates. We don't freeze the plates or blow air, but our plates are big - 12 x 24 so they'll hold a lot of heat. We do use a piece of paper (except on Damascus) and ours is much bigger than yours - about 1" x 2" and maybe a couple pieces on big knives. We get more sticking of foil with thick blades and high temperature formulas so we have used talcum with those with good results.

We also cryo before temper, but that seems beyond the point where your problems are occurring.

Rob!
 
I am going to lean towards the foil temp rating being too low, I've seen some rated at 1800 degrees and some at 2100 or 2140. My current foil is 309 SS rated at 2100 from Enco.
 
I'm glad to hear that I'm not the only one who has had sticking problems, and even the "worm tracks".

Perhaps the "Frozen" plates are a bit of overkill on my part. I will give quenching a try without freezing and see if that helps.

Rob, I tend to agree on the "Pausing to equalize". I can't see where it would make that much difference on a thin blade.

The Talc / Baby Powder is something that I have not tried. I am assuming that you are just lightly dusting both sides of the blade, then sealing it up. I am going to give it a try on the next one.

I am going to order some of the higher temp foil (309SS). Will have to do a little searching to find a decent price on it. They don't give that stuff away.

Thanks for your input gang.

Robert
 
A quick follow-up. I had an individual recommend that I check out a certain company for H/T foil. I did, and found a 50 foot X 20 inch wide roll of 309 (.020 thick - Max Temp. 2100 degrees) on sale. Regular price $229. on sale for $119.

In addition, while I was looking, I decided to check my email. Low-and-behold, there was an email from said company that had a 2 day special (20% off of orders over $99.00). I placed the order with their discount code and even with $10.00 shipping, I am out only $105.00.

Sometimes I guess it just pays to live right.

The wifey was making her bi-weekly run to Wally World, so I asked her to get me a small container of either Baby Powder, or Talc Powder. She comes home with a bottle of Equate Shower and Bath Powder. While I am sure it would make my fanny smell better, I am not sure this is what I need to dust my blades prior to putting them in the 309 foil.

The ingredients are corn starch, talc, sodium bicarb, something else and fragrance. I am afraid that if I use it, the corn starch might turn into syrup. At least with the bicarb, it shouldn't have indigestion, and the fragrance would sure smell better when I cut the pouch open. :)

Robert
 
X2 on the talcum powder. It makes life much easier. I also thoroughly clean the foil and blade with acetone before putting it together and sealing up.
 
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