Carbon Equivelancy 4150

[dpp8]

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?

 

[metengr]

You might want to evaluate how the parts are stacked and loaded in the austenitizing furnace, and during quenching in oil. You might not be getting adequate or consistent oil quenching.

 

[swall]

Couple of questions. Can you explain your use of the term "carbon equivalent"? This usually pertains to welding; I have never heard it associated with heat treating. Second, by batch do you mean furnace load or are you refering to parts made out of the same heat of steel?

 

[dpp8]

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 problem occurred. One suggestion was to check the carbon equivelant, I assume that the alloying elements will have some affect on harden ability and may be an indicator if we are going to have issues hardening this material. Does an CE of .88 indicate anything to you as i have no reference to compare this to?

 

[Metalguy]

"Does an CE of .88 indicate anything to you as i have no reference to compare this to?"

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

 

[dbooker630]

Another way to determine the robustness of the heat is to plug the chemistry values into SAE J406 and calculate Jominy hardenability. If you don't have access to J406 let us know the values for C, Mn, Si, Ni, Cr, Mo, Cu, V.

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.

 

[dpp8]

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, MN-.86, SI-.18, NI-.07, CR-.83, MO-.2, CU-.18, V-.003. Can anyone recommend an ASM manual for heat treating. Already have Heat Treating VOl 4, and Alloy Phase Diagrams Vol 3. Looking for a book that can give formulas for time in oven and temper, any suggestions?

 

[dbooker630]

dpp8,
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.

 

[redpicker]

That chemistry is a bit lean for what I would expect, but it certianly should harden in oil in with a 3.5" OD section.

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

 

[dpp8]

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 are hot rolled more than likely, now work has been performed on them before heat treatment. Can i get a specific name and volume number of the ASM Heat treaters guide?

 

[dbooker630]

#06400G-CC Heat Treater's Guide: Practices and Procedures for Irons and Steels, 2nd edition, 1995 by ASM International. Current price for nonmembers is $251, member price is $201. Call 800-336-5152 for ordering info

 

[redpicker]

If you are only getting 285 BHN as-quenched, my first guess would be that you are dealing with an OD scale problem. Sometimes, particularly with forged bar, there will be a thick OD scale that will prevent the material from being quenched properly. If the OD of the parts has a scale layer greater than 1/32" or so, I'd say that is your problem. An OD turning operation is generally neeeded if this is the case.

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

 

[dpp8]

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.

 

[dbooker630]

I would descale the offending pieces and reaustenitize them; before doing so see if you can check the atmosphere for proper carbon potential/dewpoint as well.

 

[swall]

How are you checking hardness? If you are checking on the round, and the two heavily scaled pieces seem to be where the problem lies, you could have enough decarb to account for the low hardness.

 

[unclesyd]

Looking at mass effect data for 4150 there is an or of magnitude difference in as oil quenched hardness between a 2" round and a 4" round. So you could show some fairly low numbers. Based on Jominy test data you should get a 50-53 Rc
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

 

[redpicker]

As mentioned by swall, a heavy scale can indicate excessive decarburization, which will result in low surface hardness. Typically, for as-rolled bar, you can expect between .015"-.030" of decarb. In excessive cases, maybe twice that. If you are performing a Brinell test, I'd guess you would have to grind about 0.060" to get a wide enough flat to perform the test, so this should not a problem. If, however, they are not grinding deep enough, you can get low hardnesses.

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

 

[dpp8]

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.

 

[dbooker630]

I know that you have reported the cert chemistry; can it be confirmed that the offending pieces are actually 4150? Even a crude spark test might show some differences.

 

[unclesyd]

I have to agree with dbooker630 in that PMI is needed along with a determination that decarburization hasn't occurred on your sample.

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?