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

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?

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.

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

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.

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. 

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!

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.. 

 

On 3/13/2019 at 8:43 PM, jlpservicesinc said:

I'd split it to see what the metal has for a story to tell..

Please post pics if you do split it open. 

I'm forging lot of tools out of 4140 (1.7225), never had any problems. quite the contrary 4140 is a steel that forgives some mistreatment. quenchend it in oil and water without any cracks. Maybe too hot (max. light red, better cherry red, do not overheat and wait till it's red!). annealed before?