Testing a knife

KenH

Well-Known Member
I broke a ceramic sheath until I figured the problem. DO NOT allow ceramic to be in direct flame! Also, keep temperature below 2400F, better 2300F, and I've not broke a ceramic sheath since. Best I understand the ceramic will handle 2300F ok, but starts getting "iffy" around 2400F. Direct flame can be over 3,000F.
 

Drew Riley

Well-Known Member
Couple of things:

Someone mentioned it earlier, but you definitely want to let your oven soak (empty) for a while before you start heat treating. I have a home built oven that normally gets up to temp in about 30 minutes or so, but I like to let it soak empty for 45 minutes to an hour (after reaching temp) before adding my steel. I've noticed the temperature fluctuation stabilizes pretty significantly after soaking.

As far as checking oven temps, a good sanity check is simply to dip your oven's TC into a cup full ice water. That is, fill a cup full of ice and cold water, stir, and let sit for a couple of minutes. Stir it again, and drop your TC in. It should read 0C/32F. If it reads a little higher or lower, then there's a chance that you need to calibrate.
 

Andre Grobler

Well-Known Member
One thing alluded to above, but not expressly stated... if you dont have it in the oven for long enough, the steel is not austenitized fully, now for 1080, it is unlikely to be an issue - the moment the steel is up to temperature... but it is really possible, unless the thermocouple sits against the knife, that your knife is not at the oven temperature for the first ten minutes after you put it in an open air, electric furnace... I have pieces of O1 in the oven for 15min, 20 min and 25 min at 800C, and the 15min total oven time had what appeared to be extremely large "grain" and the grain appeared progressively finer as the time in the oven went up... (that shortest time in the oven one would be the second from bottom piece, this was 5mm thick O1) Now in a gas forge, there would on the balance of probabilities be no such issue, salt pots neither... electric furnaces that can keep their elements on at an idle... Put a piece in the furnace at the same temp, and put it right against the thermocouple, and record the time it takes to get up to temp again, and that would be the time it takes for the steel to get close to starting to soak. Putting it further from the thermocouple would make the steel take longer to get up to temp, because the oven is not ramping hard, so apply caution. c6_fbtt_s15s18s19s17c.jpg
 
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