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 I have been trying to harden a knife I forged out of leaf spring steel and I have heat treated it in vegetable oil while above non-magnetic and won't harden. I have done this several times. Then I decided to try to harden it in water so I got it non-magnetic and didn't want it to shatter or warp so I just dipped the edge in the water and after little bit dunked the whole thing. I have no idea why my knife won't harden. Last night I finally thought I had hardened it is vegetable oil the file seemed to skate across (I am not experienced) and I tempered it in the at 350 for 30mins then 400 for 30mins (All in the same hour) and today did 350 for 20mins and 400 for 40mins and had a slight straw color along the edge that convinced me it was ok. But I go to file a design in the spine of the knife today and the file just digs in and is easy to make the design. Any tips? I know if I dunk the whole thing in water when hot it will warp so I really don't know what to do. 

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playing around wont help  either dunk it ot dont,  if oil doesnt work then use brine,  temperatures and methods are explained in the HT sticky, if it wont harden in water then its not hardenable steel, could have been case harden or work hardened steels.

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In 37 years of smithing I have run across 1 leaf spring that wouldn't harden. It was a strain hardened low carbon steel.

It is also possible to decarburize a blade through excessive time in the forge especially with an oxidizing fire.

The later is very much more likely with people who try to forge a blade before they master basic smithing.

Does a piece of the original material that hasn't been forged harden using the same technique?

What temperature did you have it before quenching it? (Above non-magnetic?)

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I've had one coil spring blade that did not appear to harden in oil or water.  After 4 quench attempts it had developed a fairly significant warp, so I figured I'd straighten it cold because it hadn't hardened anyway.  Long story short, it snapped with moderate pressure.  It turns out it had a much thicker decarb layer than I'd ever seen before and there was hard steel under it.  This may or may not be true for your piece.   If you don't mind a slightly shorter blade and a little extra grinding you can clamp it in a vise with a half inch or so of the tip sticking up and then hit it with a hammer.  If it snaps off you have hardened steel. That will also allow you to see the grain structure if it breaks.  If you can hammer it 90 degrees and it doesn't crack or break then it definitely did not harden in a manner suitable for a blade.

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Yes Thomas I tried too harden and another piece of this same steel but it has been forged a little bit before I quench the in water and the file skates right across the surface.  I think I will just dump the entire thing in water real quick and if that doesn't harden it  I don't think it will be able to be  Hardened.

Thanks for the help guys

 

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If the parent stock hardens in oil or water then it sounds much like my experience.  I hardened a piece of the spring I had cut the blade stock from and it skated a file like glass.  On my blade a file bit in easily on the surface, which is what made me think it didn't harden at first.  Something different could be going on with your situation, but I wouldn't be surprised if you have hardened steel a millimeter or so under the surface.

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From what you say you diffretially heat treated the blade when you quenched the edge only before cooling the whole knife

 

if this is true then the spine of the blade should be soft while the edge is hard

 

du

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Yes, Du I did do that but I figured too that the edge would be hard but I have a softish anvil and lightly TAPPED the edge on the corner of the anvil and it dented the edge so I got another manufactured 1095 knife (kabar) that I have and HIT it on the corner of the anvil and the kabar cut my anvil instead of the edge of the blade. Anyway I tried to dunk the entire knife in water to quench and ended up cracking in three places. I do think I had a thick layer of decarb and I didn't try to grind through it so I will do that next time I have no experience so I am not disappointed I just learned a ton in a couple of days. 

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