Overheated O1?

C

Chant

Joined
Jan 27, 2006
Messages
279
I have overheated O1 before and had a blade snap - very large, visible grain. That's one of the reasons I shelled out for an evenheat.

Well...my third knife out of the evenheat looks strange to me. Even after double-tempering and regrinding, it has a lizard-skin look to it. Also, after tempering twice at 400, a file still skates across it. The blade I had previously overheated did not look like this, and I'm suprised that I overheated the new one in the oven - I used 1435.

I'm wondering if this lizard skin pattern is more a sign of excessive decarbarization, than of large grain due to overheating. Perhaps I screwed up when watching the clock, and I soaked it too long?

Anyone have any ideas?
 
I have a new oven as well. I have found my biggest change has been in decarb and scale in the oven. I recently thought I botches a clay hardening, but once I took the blade down some with a new 120 grit belt, it now shows the hamon I expected. I also had an 0-1 blade I thought had not hardened correctly as a file was biting. After taking it down a bit, it would not bite. I would try sanding the blade down....also try an etch. Ive found the decarb sections etch far differently and are easilly seen with a quick dip in FECL...

I doubt its your oven...did you do any testing? I did a quick and dirty temp check on my oven by bringing a known steel to just below its magnetic point, testing, bumping it up ten degress and making sure it was non magnetic. I cant picture an oven being so far off as to cause the kind of grain growth you'd need.....

I would bet youre running into the same thing I ran into...a forge had less scale and decarb, plus my soaks and ramp times were much shorter in a forge. That all meant less decarb and scale than I now see with the oven.

Others will chime in, but from my recent learning curve with the oven, what you describe sounds very similar to some of the results I have seen since moving to the oven. Ironic...I was somehow less paranoid when I was using a relatively uncontrolled and wild device....now im using something that will keep my temps within a degree or two and heat treating is all I can think about, haha!
 
Jeff, did you use 1435 F for austenitizing? If so, that is a bit low. You need to be up in the 1475 - 1500 range for proper hardening. Try 1475 with a 10 - 15 minute soak and see what you get. Did you do several normalizing cycles prior to hardening? Go here for some quick specifications.
 
TikTock said:
I was somehow less paranoid when I was using a relatively uncontrolled and wild device....now im using something that will keep my temps within a degree or two and heat treating is all I can think about, haha!
Click to expand...

I'm thinking decarb, but the strange thing is I have ground (60 grit) quite a bit and I still see the pimply "skin". It is bare metal, definitely not scale.

I know what you mean about moving from the torch to the oven. I do have a second pyrometer to check the oven with, and have found that the temps differ all through ramping up, then even out to about the same once the oven has reached and held temp long enough for all the bricks to be evenly heated. It is less exact than I was expecting, though.

BTW, I'm looking forward to seeing (and holding) some of your knives at the HI. Hope your bringing some!
 
Fox said:
Jeff, did you use 1435 F for austenitizing? If so, that is a bit low. You need to be up in the 1475 - 1500 range for proper hardening. Try 1475 with a 10 - 15 minute soak and see what you get. Did you do several normalizing cycles prior to hardening? Go here for some quick specifications.
Click to expand...

Now that you mention it, I normalized twice at 1435, then final heat to 1435 and quench. I've been trying out lower temps with a longer soak - I think (why didn't I make notes!) that I soaked for 20 minutes on this one, twice as long as normal. However, you've reminded me about the two normalizations, each for 10 minutes, so that would make 40 minutes total at 1435. My oven (according to an external pyrometer) can "fly by" target temp by as much as 50 degrees before evening out, so the max temp might have reached 1485 (another reason I'm experimenting with lower temps/longer soaks). Even opening the door to put the blade it can cause large overshoots on temp as the oven tries to get back to target.

I have the feeling the 40 minutes has caused excessive decarb (no foil used or anything). Perhaps if I keep grinding I'll get through the lizard skin.
 
Still there after grinding? Ooof....dunno then....Bring it to the HI and there will be enough experts there that Im sure someone will know or be able to figure it out! I am not a HT expert by any means beyond my own experiences, which are as limited as yours in using an oven....

Did you agitate while quenching? Perhaps you let it sit there too long and the marks are where a vapor barrior formed? I am just throwing things out there now....I think you can rule out overheating if you were at 1435. Even if the oven overshot by a hundred degrees, you wouldnt have extreme grain growth like the marks you describe, i dont think....

You can always just take the edge down to a rough convex final edge. make sure to also take meat off the edge itself. Do the normal brass rod test and cut some wood and do a little chopping and see how the edge holds....

Yeah im bringing at least 5-6 knives...I have 12 in varying stages of completion for a show in about 3 weeks....who knows how many ill actually finish by the show, haha!
 
Try grinding up to 120 grit or even 220 and see what it looks like. It does sound like decarb.
Scott
 
I use Turco on baldes in the oven.It helps control decarb.Raise that temp a bit ,too.
 
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