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Re-ran one of the pieces at 1600F with other 4150 bars stock of varying OD and length and got the same results. Checked hardness after the oven and was getting 32RC while other pieces in the load were consistent and as high as 58RC.

The heat treat operator said that the scale on the two offending pieces was very heavy compared to the rest of the load. Should all the pieces be de-scaled before heading into the tempering furnace.

First off, thanks for all to your replies. Our hardness for this part is 320-340 BHN, after quench (and we do not normally check hardness directly after quench, we did this time because we were having a problem) is 285 BHN. After temper this will obviously be well below our requirement. The bars...

Pieces are set in furnace with equal spacing around each. None of the pieces are set near edge of furnace. I would think that at 1520F convection would overcome or at least minimize hot/cold areas of the furnace, however this is not beyond the realm of possibility. Values are as follows, C-.5...

The piece's is question came from the same heat lot and were heat treated together (in total 6 pieces. Two of the six were returning hardness values below our requirement while the other four were fine. Material certs from vendor where fine and were validated by third party analysis after the...

Having an intermittent issue with hardening 3.5 in OD, varies in length of 4150 steel. Can not find any variables with heat treatment/quenching/tempering process. In furnace at 1520F for 4 hours, oil quenched and then tempered at 1020 for 4 hours. Can get low hardness on pieces from batch that...

Same thing happened to me. I took the job and I do not regret it one bit. I am reminded of that everytime i talke to one of my fellow graduates who are still looking for that perfect job. DP

Flame hardening worm gears, question is how far beyond the lowest part of the last thread is it necessary to flame harden?

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?