Flame Hardening and Quench Time

[dpp8]

I am flame hardening 4150 steel that is being quenched in oil and then tempered in an oven. My question is does it matter how long the parts remain in the quench oil, or is there a recomended temperature that the parts should not fall below before they are taken out of the quench oil?

 

[redpicker]

4150 can be rather sensitive to quench cracking, so I wouldn't leave it in the as-quenched condition any longer than I had to. If I could, I'd try an pull it out of the oil after it was below 500F but before it fell below 300F. You'll want to be sure it is below 300F before tempering to insure you get complete transformation. The cooling rate below 500F isn't really that critical, but if you let it get below 300F, your incidence of cracking will go up.

rp