oil quench

R

Rey

Well-Known Member
I'm using used vegetable oil turned black now from usage. I will replace it with new peanut oil to quench my farrier rasp files. Question is why do I keep getting those small circles on the blade after quenching. I have to use a course to medium scotchbrite belt to take them off also, the black crust in which heats up the blade and very troublesome to take off. I heat the blade on my forge to non-magnetic then quench, after cooling a bit start taking off the circles and black crust to get it ready for heat treat in small shop oven @ 400 deg. for an hour until I get a hay or light gold color on blade. Afterwards, I lightly hand sand with light motor oil for satin finish. But, at times I have to use an 80 to 100 grit belt to take off those ugly circles. What do I have to do to keep from getting circles upon every quench. Rey in Texas
 
Yeah, it sounds like possible decarb, resulting from too much oxygen. "Too much" being a relative term of course.....
 
Not sure because I cant see the blade but, the black is probably decarb ! but the small circles could be uneven heating . ever try HT at dusk or in the morning before it gets too light. That way you can see any darker spots which are spots that havent gotton hot enough . wait until color is even all over blade before quench . Decarb is easy to remove , just soak in white vinegar for a few hrs , it will come off with light sanding .
 
Will do make sure an even hot surface is on blade before quench. Thanks, gentlemen.
 
Thanks for the good tip with the white vinegar Bubba-san.
I thought that stuff was a pain as well.
 
I can't tell you what causes them exactly, but they are common. I have them on occasion. A little bit of sanding will remove them.
 
Might be over heating as well. I have less problems with the circles now that I have better heat control.
 
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