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I made this little top fuller, and it cracked on quench.  Oil quench, pre-heated oil.  Grumpy.

Given the the crack runs in front and behind the eye, I'm thinking I probably drifted it too cold.

Any competing opinions?

Paul

fuller.jpg

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I must admit that makes a great show piece to students about quenching issues!   I have 4 pieces of a bowie knife that I show my new students: old buggy spring, quenched in warm vegetable oil but was a tad soft for a blade so I tried it in water and "TINK".  Got parks 50 for the rerun.

And unless there was a stress concentrator seeing that run right down the middle of both sides makes me think of a temperature issue.  What type of oil?

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Sub-optimal vegetable oil - the bucket of left-over frying oil that always seems to accumulate in my kitchen.  Pre-warmed to "hot-to-hold".  Very scientific.

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I see as odd is the fact it cracked long wise not to the short side of the drift

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Reflecting some more, I also rushed my way through the heat on the way to quench - I bet I pulled it too soon and the core want’t all the way up.  So many variables.

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Sad to see a good tool crack. I have had a lengthwise quench failure in a hammer exactly like this when I quenched 4140 in water. It may well be that the quench was too aggressive. When you heat a quench oil, it reduces the viscosity and greatly accelerates the convective stage of the quench. Contrary to intuition, hot oil typically quenches more aggressively than cold oil. 

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That makes sense.  If I couple that with a bit of differential heating prior to quenching, and working too cold, I can see a whole cascade of failures.  Onwards!

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I'd split it to see what the metal has for a story to tell..  from a close up external it looks like chunky grain size.. 

And/or  defect in the metal itself since it propagated again nearly identically on the other side of the eye.. 

Hard to say without further investigation.. 

 

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