Carbon Equivelancy 4150
Carbon Equivelancy 4150
(OP)
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 has acceptable pieces, all of which were done at the same time. Looking at carbon equivelancy, coming up with .88. Contemplating raising the temp to 1600F. Any thoughts?





RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
If correctly done and if it applies to all the pieces (same heat), it eliminates a lean alloy as being the cause.
"When the eagles are silent, the parrots begin to jabber."
Winston Churchill
RE: Carbon Equivelancy 4150
Otherwise, you may wish to go a bit higher with the austenitizing temp, the heat treater's guide recommends 1555F for 4150 grade. A microstructure check may show whether there was sufficient soak, although four hours should work. Also try to determine if the objectionable parts are from a particular side or zone of the furnace, perhaps there are some bad elements or tubes.
Check out your quench temperature, agitation, even send out a sample to your supplier to check quench speed. Possibly some of the acceleration components may have been dragged out.
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
Plugging the numbers into table A2 of SAE J406, gives a DI of 5.13. Using the values for distance in table A10, Jominy hardenability at J4 is 61HRC, @J8=58HRC, @J12=52HRC.
By themselves these appear to be decent values, comparison to typical hardenabililty bands for 4150 (J4=58/65, J8=56/64, J12=53/63) shows that you have a mid- to low-side heat.
I always like using the ASM Heat Treater's Guide. One of the membership perks is that you can get free online access to the Guide.
RE: Carbon Equivelancy 4150
What hardnesses are you obtaining? How are they different than your specification?
I would think 1520F should be adequate, depending on prior microstructure. I don't think I'd want to go much higher for oil quenching. See if a re-treatment at the same temperatures fixes the problem. If it does, it would suggest that incomplete austenitization is the problem. If not, then I'd suspect a quenching problem (are you dealing with an as-forged surface?).
rp
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
If you don't have an OD scale problem, my second guess is a temperature control problem with your austentizing furnace. If you are less than 1475 F in your furnace, you could find that you just aren't fully austenitizing.
rp
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
quenching in agitated oil.
Agitated oil quenched from 1525F
2" Surface, 58 Rc; 1/2 Radius, 57 Rc; Center, 56 Rc.
4" Surface, 47 Rc; 1/2 Radius, 43 Rc; Center, 42 Rc.
Based on Jominy test data you should get a 50-53 Rc
quenching in agitated oil. Water, not recommended, would give you 58 Rc.
Data is from Bethlehem and Republic Brochures
RE: Carbon Equivelancy 4150
Descaling the material prior to the temper will not do any good, since if it is directly responsible, it is affecting the quench, not the temper. A rough turning operation on the OD will eliminate this problem.
Not knowing your end use or volume, this solution may not be pratical, but have you considered just buying some heat treated bar stock? 320/340 BHN in not all that uncommon of a hardness range and while 4150 may not be all that common, 4140/4142/4145 grades are readily available in the heat treated condition.
rp
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
RE: Carbon Equivelancy 4150
I would carefully grind your as quenched sample and check the hardness again on the ground surface.
The hardness you have, Rc 32 is what would be expected if the sample was air cooled from 1600F, normalizing temperature.
What is the condition of the as received bar and what was your checked hardness?
Which anvil are you using on the hardness tester?