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PSA: I know everyone says to never quench a file, but I got a perfect chisel edge by dunking it in used motor oil after a 20 minute soak in my old forge. | Blacksmiths - Rigidtalk

nancy418•6mo ago

PSA: I know everyone says to never quench a file, but I got a perfect chisel edge by dunking it in used motor oil after a 20 minute soak in my old forge.

I was trying to make a hardy tool last week and my normal brine quench cracked two blanks, so out of frustration I tried the motor oil trick on a Nicholson file I was reshaping and it came out with zero cracks and a solid bite, so has anyone else had luck with unconventional quenchants for tool steel?

3 comments

3 Comments

the_kai6mo ago

What temperature were you running the forge at before the quench? Used oil has a slower cooling rate, which might explain why it worked where brine failed.

hannah2406mo ago

Hold up, the_kai, I gotta push back on that. Slower cooling from used oil isn't always the fix. If the steel was actually at the right temp, the fast brine quench should have been fine and given a harder edge. The problem might be the steel itself wasn't hot enough to begin with, so the slower oil just barely got it to harden where the brine was too extreme. Used oil working tells me the temp was likely off, not that the oil's speed was the magic answer.

kelly.emma5mo ago

Wait, does that mean the original heat was borderline and the used oil just happened to slow things down enough to squeak by? I feel like @hannah240 is onto something real here. If the steel wasn't soaked long enough or hit the right austenitizing temp, brine would just shock it too fast and cause cracking or soft spots, while used oil gives it that little extra time to actually transform properly. I've seen this happen with cheap 1095 where a guy I know couldn't get it hard no matter what, then he tried a slower oil and boom it worked perfect. So yeah, temp could be the real issue, not the quenchant itself.