52100 problem

leifjl

leifjl

Joined
Nov 27, 2011
Messages
789
Heres the story; From my first knife I've H.T. my own blades and never encountered the problem of bacon edge. I've had side to side warping a few times, particularly in the beginning, and one cracked blade, but never had the edge just curl up like it did today. 90% of the time I use either o1 or d2 but I ordered some .110" 52100 to try out, hollow ground it down to an edge thickness of .020" and then went for what was going to be the first of a triple normalization. Brought the piece up to 1650 held for 10 min. then took it out to air cool. When it cooled down I looked at it more closely and noticed some pretty drastic curling, like an 1/8 one way and then an 1/8 the other.

There are too many new variables here for me to safely figure out why this happened this time.
I always take my edges down to .020", even on the o1, so I can't say for certain it was that. But it could be with this steel.
I only just started to hollow grind, this being #2, so maybe I messed that up somehow. Maybe it was too thin to high up into the bevel?

So I'm perplexed. If anyone who has experience with anything I've mentioned any help would be appreciated.

Thanks,
Leif
 
I am relatively new, so take what I say with a grain of salt. I had a "bacon edge" on a very thin O1 blade when I had it lying on its side when in the forge. I thought to myself after it would probably work better with the blade edge up, so gravity doesn't work against me. The other thing I wonder about is grain growth, since the edge was pretty thin. If the edge heated excessively, then the growth has to move the material someplace. I am not experienced with 52100, but I remember reading Kevin Cashen's posts on it, and remember he keeps the heat below 1480f, for heat treating. I assume normalizing would be similar, but someone with more experience can chime in.
 
Nah, I always place edge up.
Now I could be wrong too, but I've seen a lot of normalizing schedules bring the first one up above the normal temp for hardening. I was gonna go 1650,1550 and then 1450 but I got stopped right at 1650.
If anyone also has a normalizing procedure to recommend that'd be great too. I just made an uneducated guess at this one.
 
Grain growth is from grains absorbing their neighbors and is a new formation with less grain in count per given area size due to high heat. To reduce the size it is good to over heat and soak a bit in order to get all the grains the same size, even though large. Then do a series of heats reducing the temps at each, with the last one or two below non-magnetic. These steps make the grain smaller and more in number. When you austentitize for the quench is when not to go above 1480°, but that is for the hypereutectoid steels. Hypoeutectoid, and eutectoid steels do better at around 1500°, for most. Bladsmith or Kevin can you better answers than I of what and why, and maybe an opinion as to the bacon edge.
 
LRB said:
Grain growth is from grains absorbing their neighbors and is a new formation with less grain in count per given area size due to high heat. To reduce the size it is good to over heat and soak a bit in order to get all the grains the same size, even though large. Then do a series of heats reducing the temps at each, with the last one or two below non-magnetic. These steps make the grain smaller and more in number. When you austentitize for the quench is when not to go above 1480°, but that is for the hypereutectoid steels. Hypoeutectoid, and eutectoid steels do better at around 1500°, for most. Bladsmith or Kevin can you better answers than I of what and why, and maybe an opinion as to the bacon edge.
Click to expand...

This is pretty similar to what I've read so far.
 
Try quenching edge up if you dont already. David Boye deals with what you're describing in his book. He also uses very thin hollow grinds on carbon and low alloy steels.
 
It wasn't quenched. I hadn't gotten that far at all. I quench tip first anyway. I think the edge up quench is used when you have downward curve resulting from using an oil quench on a water hardening steel.
 
Ah, that's right. You were normalizing. In any case, Boye describes what you're talking about as a problem on his chef's knives when quenched. He describes the cause as the edge cooling much quicker than the spine, then the spine cooling and sort of wrinkling up the edge. Maybe leaving the grind a little thicker before normalizing would solve the issue, then thin it some more after that step.
 
Too thin! I bet it is too thin behind the bevel as mentioned. Try flexing it with your thumb...
 
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