Blades not magnetic after quench?

G

gixxer

Joined
Sep 21, 2006
Messages
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I am sure it is a simple answer, but not for me. I HT'ed my own blade for the first time, cooked it, plate quenched it (CPM154) and the foil welded to the blade. I have the high temp foil, so I know I did not bust temp on that. Anyhow I was thinking I could slap it on the ol SG and be done in 5 min and right into cryo. Nope. Sucker would not stick to the magnetic chuck. How do I fix that? No, the chuck is not broke, and yes it did hold my blades before HT.

ended up grinding the foil off, now I have 60 grit scratches to put up with after I temper it tomorrow out of cryo.

Any suggestions?
 
r-winter said:
after heat treating steel is not supposed to stick to magnets that is a GOOD thing.
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Well, apparently every knife I own is junk then :rolleyes: ;)

At a certain critical temperature DURING the heat-treating process, yes, blade steel becomes non-magnetic. That's not what gixxer is talking is talking about.

It's an interesting question and I look forward to hearning the answer. I don't know why the foil would weld to the blade either. :confused:
 
HT foil itself is non-magnetic. How thick is the foil on the side you're placing on your chuck?
 
Austenite is non-magnetic .Foil is austenitic steel and steels above the critical temperature are also non-magnetic. [actually above the curie temp]
Ferrite and martensite are magnetic .
You probably have cheap magnets on your SG !
 
When I first started to heat treat I had a box furnace without PID. I was treating 440C and burnt the foil onto the blade. I was taking the blade way up past my intended temp. The blades after tempering also were not magnetic.. I chalked it up to experience and junked the blades. I can tell you they were extremely hard and BRITTLE.

Ken
 
mete said:
You probably have cheap magnets on your SG !
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I had stripped off what I could, and the blade still would not stick. My magnet is a Brown & Sharpe, I figger that is pretty good...

ken erickson said:
When I first started to heat treat I had a box furnace without PID. I was treating 440C and burnt the foil onto the blade. I was taking the blade way up past my intended temp. The blades after tempering also were not magnetic.. I chalked it up to experience and junked the blades. I can tell you they were extremely hard and BRITTLE.
Ken
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My furnace is PID controlled, it held to within 1deg +- at 1975 (or what the PID calls "1975").
 
Some guys do not put a thing in their envelope except the clean blade, which is what I did and they have never had a problem with the foil. Some put a piece of paper in there to soak up the oxygen but would they do the same thing to keep the foil from sticking to the blade? I even heard one guy putting a hair of WD40 in his pack to keep the foil from sticking.
 
was the blade/foil still hot when you put it on the magnet, because the heat can ruin magnets
 
Stainless steel becomes less magnetic the harder it becomes. I normally use a bit of super glue to help hold my stainless blades to the magnet when I need to surface grind them.
 
Retained austenite in the high ranges?????
Was it more magnetic after the cryo and two temper cycles?
 
I would like to know the folks thoughts on the foil welding to the blade . Is it possible that the direct heat from the elements caused certain areas of the blade to get hotter than the desired soak temperatures ?? I have read something about this before which has me wondering if it would not be a good idea to shield the blade from the elements direct heat . My thought was to sacrifice a couple of pieces of steel to place in the blade holding fixture on each side to shield the blade .

Any thoughts on this ??
 
bladsmth said:
Retained austenite in the high ranges?????
Was it more magnetic after the cryo and two temper cycles?
Click to expand...
I do not know how much RA there is/was. t only took me maybe 5sec to get the blade in the plates and locked down. Used compressed air around the edges too.
Blade is coming out of cryo as soon as I get done typing this, and I am gonna try again.

ONeill said:
Is it possible that the direct heat from the elements caused certain areas of the blade to get hotter than the desired soak temperatures ?? I have read something about this before which has me wondering if it would not be a good idea to shield the blade from the elements direct heat . My thought was to sacrifice a couple of pieces of steel to place in the blade holding fixture on each side to shield the blade .

Any thoughts on this ??
Click to expand...

you could create a muffle, would not hurt things. Even a couple of firebricks sliced thin stood up like walls surrounding the knife with space for air to circulate(maybe) would even up the temp hitting it. No need for a top unless you have elements in the roof of the oven.

I do not think my tip was getting cooked too hard, the very tip and the edges all around were not stuck. My oven is long enough that the tip is further away from the back wall element compared to the sides. the blade is maybe 7" overall and I had it closer to the oven door.
 
I used to have this prob fairly often with 440c, called Paul Bos and he said get everything acetone clean including the foil. I'm not sure this is what took care of the prob because I would air quench long enough to cut the packet open (in my case blades and springs) go to plates more for getting dead flat than a quench and then cryo. A couple of weeks ago I tried the speed deal to the plates, under 5 sec. to plates that were in the freezer I'm guessing the quench was so fast the blades came out as white as when I put them in the foil, 0 color. I drew them at 950 for the blades and came out with an Rc of 63-64 and seemingly a finer grain structure and the steel ground more like cpm, or 13c26. I did a few tests after that and no matter how fine the grain or the way it felt under the belt I'm with the cryo for the long haul. I've never had a blade that didn't get what I perceive to be fully hardened with the LN, or dry ice method and on a ground blade I beleive more wear resistance. Maybe use the plates after getting the blade out of the foil and rely on the freeze?
Ken.
 
One question that I have not read is, was it magnetic before HT?? And it the Blade hard? I have used double sided carpet tape on my surface grinder chuck to hold difficult materials. It is very accurate and easier to remove than superglue.
 
The annealed stock was magnetic, I surface ground it to a higher finish before I cooked it. it was magnetic after temper.
 
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