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KirkL

Experimentation

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I get these hexagonal rods out of the centers of rollers that the maintenance man at work gives me when they need replaced.  In the absence of any better steel (they harden but, just barely) and with a brand new forge all reason was abandoned and I forged a blade just so I could try it.  Here though is the part that I don't get, after forging and quenching (I didn't bother to temper this steel) they are serviceable but after sitting for a while they get harder, not a lot, just a little bit, but enough that I notice a difference.  The process can be speeded up by throwing the thing in the freezer.  I suspect a steel that has retained austenite i.e. past the martensitic start but taking its sweet time to get to martensitic finish.  I forged a thin dagger out of this metal and after hardening could bend it just a little bit by hand but, after a trip through the freezer it would just flex and a week later or so it seemed to take more force to get it to flex.  I know that this is not a premium material to use but, I am curious about what kind of alloy could give these results.  Anyway, here is the knife that I made.  It takes a very good edge and is one of the sharpest knives I have as long as it gets touched up periodicaly.  This is the one everyone goes for to cut those tomatoes and is my wifes favorite.

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Theres another post in this area with a Metallurgy link. On that site they talk about deep cryogenic freezing and stuff. I think you should go there.

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I was hoping to attract the attention of someone with more metallurgical knowledge than myself.  I am puzzled and wanted to hear some speculation about what could be in this steel to make it behave the way I percieve.  My quess is that it is something in the 1040 range as far as carbon but, something else (perhaps maganese?) is causing it to finish the transformation to martensite in weeks not seconds - or with a trip down below room temp.  Granted, I am not following a scientific methodology, everything is just based on how I view it and the reality could be quite different.

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To some extent, all carbon steel retain some austenite and will continue to harden after reaching room temperature. This retained austenite can be tripped to fresh martensite by reheating such as happens during tempering, but it also can happen mechanically by flexing.

 

It is probably more noticeable in your piece because it didn't get that hard to begin with so the increase is more preceptable.

 

Finding out what steel you have may take some research, but it would be helpful in figuring out how to get the most out of it. Recycled steel is not inferior, it is just unknown.

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Don, it seems like I've heard there are labs that for a fee will analyze a piece of scrap steel for the dozen or so (20?) elements of interest to knifemakers. But I don't know who offers such a service, or how much it might cost. Any information you might have about this would be welcome.

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