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I Forge Iron

Left knife in oven....

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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.
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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.

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