after 14 yrs being away from knife making .. and now going back to it ,, i find myself at a loss of memory .. harding 5160 with a propaine forge .. and using chevron 70 quenching oil . i started .. my forge at 10 lbs ,, after warming took it to 5lbs gas .. the forge is a venturi system , no blower , oil 125 degrees , my edge thinkness is 5/32nd thick enough meat to protect the inturnal egde . i have taken to nonmagnetic .. to different temps but all has been non magnetic , and after quenching .. im not getting a heavy scale at all .. and no slate gray ,, a file will cut it .. i have treated the same blades .. 3 times ,, and still the same . my flame at the ovens pipe entrance is blue , so any thoughts .. i was thinking clay coating the blades ,, to retain the carbon any thoughts ... thankyou

I think you need to try a sample of your material in a more aggressive quench than oil, probably tepid/warm water. Do not try this blade, but make a simple "stamp" of metal out of the parent stock.

Did you buy 5160 or is this recycled automobile spring? Some springs are more hardenable than others.

Loosing carbon is a lot harder than I have believed, and has been impressed on me by others (I don't have enough experience on this).

That your forge is running rather rich (low to no scale) should not affect your carbon content, but does account for your lack of scale formation. (I have built a couple burners and forges, I have experienced this)

It sounds like you read your notes from 14 years ago. I am not a bladesmith, so find a grain of salt for my advice.

Phil

You mentioned some big keys here: you heated to non magnetic. That works..as long as you did not let that temp drip from the time you pulled it from heat, went to the magnet and then into the oil. any delay at all will dreop below the right temp to harden. I use a magnet but in maybe a little differnt manner, i kind of have an eye for wot color is right. I check that each and every time. i bring it out and magnet check as soon as I feel i am close to temp..when it does not stick I heat again to the same color, and just a wee bit above. Then in a short motion go right into my oil quench..Do a cold run a couple of times to get that move down before the heat. If you bought new steel and they told you it was wot you wanted. that may not be true. There may have been an error in your order. It has happened before. I have not idea where you are located, but if youi send me a sample piece I will try to harden and then do a rockwell test on it and return. You can find my contacts on my web site,,google richhaleknives. and send me a note about where you got it,,I can likely guess the name of the place but not in here.