Heattreating a large batch

You know, a Rockwell tester serves me best to show that the heat treatment went as planned. If I aim for a certain Rc and they hit that hardness I have to assume the heat treat went alright. If it doesn't, something must have went wrong. Some of this CPM steel just doesn't act normal :)
Does a maker that does his own heat treating need one, or at least access to one? In most cases, I think so.
I could tell you a story about 3V and aluminum plates, but I won't :)
 
I've been following this thread a bit, and, here are my thoughts:

Stacking blades, particularly unground blades is perfectly fine. You just have to adjust the soak for the thicker section.

The problem with stacking ground blades in a packet comes when it's time to press quench. You want to press quench the blades in the packet-there is no time for snipping and jerking around getting those blades out, particularly because at the higher temps they sometimes stick to the foil and you'll bend them badly prying them out.

If you have 2 layers of ground blades in a pack, they have to be sitting perfectly on top of one another, ot they'll get deformned during the quench. I have had this happen to blades that shifted in a single layer, and, wouldn't even want to think what would happen if they were stacked.

You can fit as many blades OF THE SAME THICKNESS as you can in a packet that is almost the size of your furnace floor. You need good support, and, you also need to understand that, if something goes wrong, you can lose a lot of blades in a hurry. Also, you can only accurately straighten so many blades before they become too cool to straighten, so, you need to consider that as well.

With practice, 6 is a good number. On chisel grinds, where the tips can't warp more than a very small bit, you can do many more blades.

As to a Rockwell tester, hardness isn't necessarily an indicator of performance, but, like Kit says, it's a sanity check. Particularly if you work with several steels. A tester will show you quickly if your blade is A2 and your cycle was for S30V!!!!!!!!

The tester also lets you adjust tempering cycles to get your hardness exactly where you want it to end up. This takes some practice, but, you can do it if you pay attention and keep good notes.

In my shop, I don't even trust the thermocouples on the furnace. I run a second digital panelmeter with a very accurate thermocouple periodically, so I get a second reading inside the furnace. I have a deep, narrow Paragon that varied 300F over it's length. Yes, 300F variation @ 1750F. I solved that problem with a little low pressure air blown thru the furnace during the cycle. The point is, if I hadn't checked, I would never have known, and, my long japanese blades would not be correctly HT'd.

So, for me, after 10 years of trying things, it's a single layer, press quenched in the foil and Rockwell tested.
 
Hey RJ,
Where along the furnace chamber do you inject the air? I am getting ready to install a gas purge unit on my furnace. Sounds like I can achieve a more even heat and purge at the same time. When foil wrapped I can inject air instead of Argon, for temp evenness. For purge Paragon recommends injection at the far end. But I like the idea of correcting the temp flow even better. Thanks for an idea I didn't know I needed!
Enjoy, Ken
 
Straightening blades before the quench is a difficult concept for me. I see that mentioned here on BF every so often. Is there really that much affordable time available?

For the Rockwell, I put much importance in it and before finally being able to get a couple testers I would travel with my HT'd blade to have it Rockwelled. In those days, not long ago either, I could not practically have them Rockwelled during various steps of the HT procedure. Now that I have in-house capabilty I can enhance my experimentations by testing throughout the HT steps. One very important deficit for me is that I do not have the ability to Rockwell the actual blade as Kit can. The reason is because Kit grinds after HT and I grind before. For Kit all surfaces are flat. Mine are not. I Rockwell just behind ricasso and trust the blade to be similar. I don't like that and feel so far the only trustworthy way around it is for me to someday learn enough about grinding and belts to be able to grind after HT. Back to Rockwell testing, as I believe it variations in HRc value about the area of steel and its extremities can give a picture of how well or not the piece was HT'd. It can help point to problems within the procedure, material or equipment. As just one example, in testing a air quenched blade held point down in the vertical wind tunnel I expect the hardness to be less at the back of tang than at ricasso but it should be reasonably the same at spine, center and belly testing along the tang length.

RL
 
Roger I straighten after the quench and before the temper.
if that clears it up for you:)
if it should happen to need it Kit:)
just do it before it gets cold, with-in a reasonable time
once past the nose and you can handle it with leather gloves..
do it fast:):)

edited to add
if it should happen to need it Kit:)
 
Originally posted by mete
The hardness test gives you the assurance that you have heat treated properly. Relating hardness to edge retention is not all that reliable. The best example is talonite where hardness is low but edge retention is high.
Click to expand...

Agree on the hardness being an assurance mechanism (QA) that the heat treat went right, or that you actually used the right programmed routine (!). Good QA/QC is certainly something I understand the value of, and is part of the reason I'm hesitant to buy a using knife from anyone that doesn't own a Rockwell, or have a good pro do the heat treat for them (and that person uses a Rockwell for QC). (I was of course jesting that eyeballing the color(s) is an accurate method, whether the radiant color at heat or the color of oxidation layers).

Yeah, edge retention isn't easily pinned down, but edge retention characteristics for knife blades do seem to have a couple of pretty good indicators that can be used (at least this is the simple mental model I am working under):

1. resistance to edge roll is (non-linearly) proportional to hardness
2. Resistance to impaction would also seem to be (non-linearly) proportional to hardness also
3. abrasive wear resistance is somewhat (non-linearly) proportional to hard (e.g. > Rc68) carbide content (Moly, tungsten, vanadium carbides) as long as the underlying substrate holding the carbides is suitable.

Maybe the yield strength plays in there somewhere in #1 and #2. Not sure.

Talonite does well with #3, not nearly so well with #1 or #2 relative to harder steels in my (limited compared to some) experience. So hardness would seem to tell a big portion of the story, and hard carbide content helps explain a significant portion of the rest.

Or maybe I'm just drunk and there is a better explanation out there that I haven't heard yet.

Part of the reason I like hard blades is that in normal daily usage, I'm usually using a folder, and using the knife for stuff folders are designed to be used on. And it seems like the majority of the time I'm straightening out rolled edges when a blade goes a bit dull and I need to resharpen (strop, steel, or a mild, very quick resharpen with stones). Sometimes abrasive wear takes it down (carpet, cardboard, or in dirty gritty stuff) and I truly need to re-establish an edge.
 
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