Hello everyone, I accidentally left a 52100 bowie knife in the oven tempering at 450F overnight... I'm curious as to what it has done to the steel. Should I re-harden it? Has anyone accidentally done this too?

From what I have read and experienced long tempering times have a neutral to beneficial effect on the steel.  Though this may not be the case in all situations.

Sharpen it and do some cutting test.  If it seems a little soft then go through the hardening procedures again. 

Don't feel bad, I once left a knife in etchant all night. :blink: yeah, there wasn't much left in the morning. :blink:

Alright thanks guys !

Did you file test it?

The math says tempering for twelve hours at 450F has the same effect as tempering for one hour at 500F. Look up "tempering parameter" if you want to know more.

 

while I wouldn't make it a practice, your mistake isnt going to ruin your knife. how ever if I where you I would still temper that knife for a second time.  typical practice is one hour at temp then alow to reach room temp then back into the oven for another hour. this is because of the posibility of retained austenite.  When you temper steel you are slightly softening the martensite that was produced during hardening. this produces a servicable edge that is not too hard or too soft. You also are transforming a matrix of steel grains that are still untransformed from austenite to martensite. when you temper for the first time you produce more fresh martensite; hard and untempered. this fresh martensite needs to be tempered in a second trip to the oven, especialy in an advanced aloy steel like 52100. this is why some of the more advanced steels get harder after tempering.

I have only used 52100 one time and will likey use more in the future. Do yoiu have any data that shows Rockwell data on some of the steels thatr get harder after tempering? I have never see that happen.

I have only used 52100 one time and will likey use more in the future. Do yoiu have any data that shows Rockwell data on some of the steels thatr get harder after tempering? I have never see that happen.

 

       Rich, there are many steels that Increase in hardness when tempered. some soley because of the transformation of retained austenite and others with carbide forming aloys, like cromium, vanadium, molybdenum, and tungsten, that yeild more carbides at higher temps. for instance M50 was developed as an aerospace/ballbearing steel that starts secondarily hardening at aprox 500 and reaches its peak 64 RC hardness at 985 degrease.