Foil wrap failure

L

LRB

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Feb 28, 2006
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HTed 4 A2 blades earlier today. They were foil wrapped with a paper towel inside the envelopes. The envelopes were double rolled with pressed flat seams. Plate quenched with 1" aluminum blocks. First two came out fine, second two showed discoloration on each end, and the discolored areas were soft. Easily cut with a 40 RC rated file. Obviously the envelopes leaked and allowed air contact on the ends. What is the recommended method for seaming these envelopes? This is my first experience with foil, and plate quenching.
 
If significant air had gotten into the pack you should have scale not just discoloration .It would take time and high temperature to decarb enough to get such a low hardness.Have you tried to grind off the soft layer ?
 
I have used a roller (that comes with the stainless steel wrap roll ..i buy 2 feet x 100 feet at a time) ...same thing as a roller you would use to do wallpaper with. it's plastic. I generally use that on the long side of the envelope. I fold over twice....3 is recommended, but kinda overkill. then folding over twice on the ends, i use a HAMMER and hammer the envelope shut to as flat as I can get it.

NO NEED FOR PAPER TOWEL INSIDE! :) Or paper anything. Eventually it will cause the envelope to expand. Degrease your blades well and if you get all the air out you can, the steel should be the same color as when you put it into the envelope. Especially if you're plate quenching (which i don't do as it can use some undesired things going on)...can keep the blade straight but...the blade can also warp left to right or right to left causing a curve..generally on 1/8" stuff or thinner. Plate quenching also does not guarantee a straight blade. if your crimps are thicker than the blade itself, then you might get some warping.

I prefer to take the blades out of the kiln, wait till all the visible red heat is gone...then cut open the foil packet, check for straightness and then hang to still air cool. will still achieve hardnesses of 65-66 prior to temper. temper twice at 500 for two hours and you'll get about 60-61 assuming your austenizing temperatures of course. if the blade is warped, then i use my vise with some aluminum jaws and with the jaws opened about 1/2" inch, i put light pressure to bend it to straight.

any discoloration in the steel is caused by oil left on the blade. No biggy...you can sand it off.

When you have flaking of the steel, then that's BAD.

if you had a hole in the envelope, you'd have some decarb for sure. try grinding it down .001 or .002 and test again with
the file.

while i was writing this, METE apparently beat me to it!
 
The colors started about 1" back from the point. Maybe 1/2" at the tangs. Went from neutral at the point to a darkesh blue where it stopped. The colors were in a radius shape. The rest of the blade was a faint gray. The gray was hard, the colors were not. The blades were pre heated at 1350° for 45 minutes, then ramped up to 1775° for 45 minutes. This was done in an Evenheat oven, the blades resting in shallow slots in a fire brick. The point area is pretty thin for the last 1/2", so I would have go back as well as in to remove any decarb, and in using my 65 RC rated file, it seems pretty soft for a good depth. Beyond .002. I cut in that much just testing them. I am going to rerun them tomorrow, and see what happens. Any suggestions beyond that, or just any suggestions at all, would be gratefully appreciated.
 
LRB said:
The colors started about 1" back from the point. Maybe 1/2" at the tangs. Went from neutral at the point to a darkesh blue where it stopped. The colors were in a radius shape. The rest of the blade was a faint gray. The gray was hard, the colors were not. The blades were pre heated at 1350° for 45 minutes, then ramped up to 1775° for 45 minutes. This was done in an Evenheat oven, the blades resting in shallow slots in a fire brick. The point area is pretty thin for the last 1/2", so I would have go back as well as in to remove any decarb, and in using my 65 RC rated file, it seems pretty soft for a good depth. Beyond .002. I cut in that much just testing them. I am going to rerun them tomorrow, and see what happens. Any suggestions beyond that, or just any suggestions at all, would be gratefully appreciated.
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The colors are fine. Again, from oil that was on the blade..even the slightest bit will give that neat coloring effect. Gray is also normal as well. Again, what you don't want it flaking/decarb.

Are you saying you got decarb/flaking of the steel? Is the blade already tempered?
 
Got no flaking that I noticed, just the colors. The soft/hard is almost a perfect border with the colors. The faint gray of the rest of the blade will not yield to my 65RC rated file, but the colors cut with ease. They are not tempered.
 
LRB said:
Got no flaking that I noticed, just the colors. The soft/hard is almost a perfect border with the colors. The faint gray of the rest of the blade will not yield to my 65RC rated file, but the colors cut with ease. They are not tempered.
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How odd. The colors should be really no different compared to the gray areas. Either one the file should not bite into prior to being tempered. This is an question for Kevin Cashen or mete!

I'm sure if you ran the HT again, wrapped the envelope good and well, it should solve the problem.
 
There's something missing here.
As it's you're first try at foil and plate quench some questions. If you've excluded most of the air [paper not necessary] double fold and sealed the seams ,that should be enough. 1" thick Al plates will do fine. Did you use some pressure ? Did you plate quench [oven to plates] quickly ? Any possibility of mixed steel ? Compare with spark test.
 
No possibility of mixed steel, unless from the original source. Did not move in a frantic rush from oven to plates, but tried to waste no time getting there. I had a helper. I removed the blade from the oven, close the oven door, take three steps back, turn and set the blade on bottom plate, my buddy wearing gloves then set the top plate on and put it all in a vise. I cranked the vise down snug. Wait maybe 3 to 4 minutes and remove. Blades warm, but comfortably handled without gloves. 65 rc test file will not cut the faint gray area of blades, but digs right in where the blue coloring starts nearing the point.
 
How uniform is the heat in the oven ? Where is the thermocouple located in regard to the blades. Have you calibrated the thermocouple ? Exactly how are the blades located in the oven ?
 
mete said:
How uniform is the heat in the oven ? Where is the thermocouple located in regard to the blades. Have you calibrated the thermocouple ? Exactly how are the blades located in the oven ?
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I have had poor results with the blades laying on the floor of my oven. It seems to have a cold floor. I made a slotted light weight fire brick so they are sitting on edge and about one inch off the floor. Helped my warping problem too.
 
Blades sit in 3/8" deep slots in a full size fire brick directly under the thermocouple. I have been doing the A2 coated with the paint on anti scale, and forced air with good success except for maybe .002/.003 decarb, and slight warpage. Since I found some aluminum blocks, I thought I'd try the foil. Out of the foil and blocks, there is no warp, no decarb that I can tell. Only those colors and softness in the colors only. Main blade body is clean, faintly gray, and hard. Cannot make a scratch in it. Thermocouple has not been recently calibrated, but works very well for 01, and the A2 when HTed as I was originally doing, instead of the plate quench.
 
I'm running out of ideas !
What thickness did you start with ! What was it sold as ? Precision ground ? decarb free ?
About the only thing I can think of at this point is that the material you bought didn't have all the decarb removed and some spots have decarb and some don't ! Perhaps the color differences are due to oxidation differences with different cabon levels.
 
The steel was bought as A2, 3/32" PG decarb free. First two out of the oven were fine. The last two both had the same identical problems. When I take blades from the oven, I close the door back ASAP. There would have been maybe a lapse of 8 to 10 minutes per blade, between extractions. Could it be that the oven did not have enough time to put the necessary heat back into the point areas which would have cooled more and faster than the main blade bodies, due to the temp drop when opening the door? Maybe I did not allow enough time for the blades to come back up evenly? I have only recently been working with the A2 and these higher temps. My oven is an Evenheat Rampmaster 2, 220 volt, 22.5" depth.
 
That was gona be my WAG if your taking them out one at a time and plate quenching, opening the door grabbing another, closing the door etc etc maybe the temp dropped to low for the last couple. Heck I don't have a clue as I'm just learning HT on stainless myself but I was gona post a similar question of how many can you HT at one time or what is the correct process of HT mulitple SS blades. I'm sure someone here can help.
 
You're talking about HRc 40 !! That's not something you would expect from just a drop in temperature in the oven. So I'll still go with the decarb in the steel as you received it !
 
Not to argue Mete', but what are the odds that the two blades are going to have decarb almost equall in amount, and just at each end? The two looked like brothers.
At any rate, I plan to run them again this morning. 2 new ones, and the 2 failures. All in fresh foil with no paper inside. We shall see, unless you have any suggestions you think I should try.
 
If it was me personally, based on what I've reseached and read, when I do multiple knife blanks of air cooled SS I will foil wrap them all together. Take them out as one unit, snip open a end and slide them out on a wire mesh where they can all air cool as this would be fine if you stopped here. But then I'd take them one at a time from the off the wire mesh and plate quench just to hurry up the cooling process. Atleast thats my plan. Sure would love to hear how the pros HT or do multiple SS knife blanks on a single oven firing.
 
I would say opening the door, taking out a blade and closing the door should not drop temperature enough to affect anything. If you were leaving the door opening for quite awhile and the temperature dropped significantly, then maybe.

Why is it taking 8-10 minutes between blades? That seems like a LONG time. Perhaps your last two, the oven had cooled down enough to do this.
seems like you'd take it out of the oven, put it between the plates and move on. should not take 8-10 minutes between blades. Try doing this faster and getting them out of the oven asap. My other thought is, the areas where they were softer, the plates maybe didn't have any contact compared to the rest of the blade which had full contact

Last night I heat treated 12 blades and the cycle ran, i took them all out one another another, layed them on the floor of the garage, opened one packet at a time, checked for straightness, corrected some with warps (18" overall ones) and then moved to the next one. I have noticed with A2, that you can straighten them for a looooooong window of time. even if the blade is warm, or almost at room temperature, you can still tweek it and it will not snap. Unless maybe 1/16" stuff.
 
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