4130 Hardenability

[PermanentCharpy]

I am having parts manufactured from AISI 4130 (80KSI Yield). The parts are 9.00" OD x 4.50" ID X 20.00" LNG (approximately, with some internal details, threads etc). The shop making these didn't quote for heat treating after roughout, which I have now requested. I am having a bit of friction with management on whether I actually need to heat treat after roughout, and not just buy material on the hard side to guarantee sufficient hardness (my range req'd is 207 - 237 HBW). This should be fine based on the Jominy curves I have looked at for 4130 - 230 HBW on the surface should probably get around the required minimum of 207 HBW at the core. This is not what I am used to doing, and have typically heat treated anything above the LRS after roughout to guarantee through hardness.

 

[jmec87]

You are very likely ok without heat treating after rough out. Other manufacturers have made many similar parts without a roughout operation.

Based on your description, the remaining material ID is within 2.25" of the heat treated OD - it might be slightly softer, but probably not significantly. Unless your design is right at the edge (i.e. 79KSI yield strength at any point would result in failure), you are probably fine. Consider the strength your design actually requires, not just whether you will achieve the specified min yield at all locations in the material.

 

[EdStainless]

You can likely do this pre-heat treated, but the microstructure will not be uniform. The ID surface will not be tempered matensite, it will some mixed structure.
You are trying to do it the correct way.
The Jominy curves that I have from Timken don't go 2.25" deep, and they show values below 20HRC at 2" deep as quenched.

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P.E. Metallurgy, consulting work welcomed

 

[mfgenggear]

MattSci01 (Materials)(OP)20 May 21 11:25
Quote: I am having parts manufactured from AISI 4130 (80KSI Yield). The parts are 9.00" OD x 4.50" ID X 20.00" LNG (approximately, with some internal details, threads etc). The shop making these didn't quote for heat treating after roughout, which I have now requested. I am having a bit of friction with management on whether I actually need to heat treat after roughout, and not just buy material on the hard side to guarantee sufficient hardness (my range req'd is 207 - 237 HBW). This should be fine based on the Jominy curves I have looked at for 4130 - 230 HBW on the surface should probably get around the required minimum of 207 HBW at the core. This is not what I am used to doing, and have typically heat treated anything above the LRS after roughout to guarantee through hardness.: Unquote
Matt
This unusually soft for a shaft, You are the Engineer, did you do a free body diagram, and can you live with the stress & strain. , 4130 at 9 " dia will be dead soft at the core, this is from my own experience.
I would process to rough out the parts leaving .060" per surface, normalize, harden and temper to obtain uniform hardness to the final hardness requirements. 4130 will not harden uniform beyond approximately 3 inches diameter.
and for better machinability, soft material does not machine properly bad finish, harder to hold tolerances, and addition if the material is not properly conditioned,
if there are any close tolerances, it can stress relieve after machining (distort) and move.
more information what is the application of the shaft.

 

[PermanentCharpy]

This is in fact not shaft, it is a pressure vessel that is intended for to be a spool piece in a pipeline. A major concern for me with hardness (ie Yield) is that Post-Weld Heat Treatment will be performed, resulting in a loss of hardness.

In terms of design and strength, this is close to the edge even with the 80K Yield being assumed uniform.

 

[jmec87]

A major concern for me with hardness (ie Yield) is that Post-Weld Heat Treatment will be performed, resulting in a loss of hardness.

Is the PWHT going to be performed in accordance with the qualified weld procedure (that demonstrates sufficient hardness after the PWHT) and sufficiently below the tempering temperature? If so, this should help to alleviate these concerns.

 

[redpicker]

You don't mention what the original heat treatment was nor what your proposed heat treatment would be. For the original heat treatment, you need to find out the tempering temperature (if there was one).

For the original heat treatment, the product shape (OD, ID, an length) are all important. Was there any mechanical testing (other than hardness) done after original heat treatment and was it done on a QTC or was it done on a prolongation of the original piece?

If it was originally heat treated as a solid bar and what you have is just a 20" section of said bar, you might consider getting a hardness test performed on both end faces, approximately 1/4 inch from the ID. If they both are acceptable, you should be good, provided the PWHT temperature is at or below the original tempering temperature. If either is out of spec now, it will be out of spec later.