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Maximum Diameter for hardening low-alloy steels (AISI 4130, 4140, 4340)

Maximum Diameter for hardening low-alloy steels (AISI 4130, 4140, 4340)

Maximum Diameter for hardening low-alloy steels (AISI 4130, 4140, 4340)

(OP)
Good day,

This has been bothering me for a while:
The table attached is from the MIL-HDBK-5H.

We often specify heat treatment on these steels in the range of 125-145 KSI (usually purchased in the heat-treated condition) or 145-160 KSI (requires additional heat treating). Both these ranges are below the minimum tensile strength in the table.

Now looking at this table, it appears that for everything below 180 KSI, 4140 can only be used up to 1'' diameter, and 4340 should be used above 1'' up to 3.5'' for 90% martensite at center.

Is this really the case? I ask because I found other threads on Eng-Tips where users specify much larger limiting ruling sections for these steels (with no reference, however).

So my question is, what reliable references are available for the limiting ruling sections for these 3 materials?

Thanks.



RE: Maximum Diameter for hardening low-alloy steels (AISI 4130, 4140, 4340)

Look at Jominy curves for these alloys.
You will see that for 1040 there is a distinct hardness drop (at center) for oil quenched material beyond 1/2" diam, with 4140 the drop is at about 2" diam, and with 4340 there isn't really a limit (you loose less than 5Rc clear out at 15"diam).
Look in the Timken heat treat guide.
It also depends on what strength you are aiming for and how much safety margin you need.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Maximum Diameter for hardening low-alloy steels (AISI 4130, 4140, 4340)

(OP)
EdStainless,
thanks for the reply.

Quote (EdStainless)

You will see that for 1040 there is a distinct hardness drop (at center) for oil quenched material beyond 1/2" diam, with 4140 the drop is at about 2" diam, and with 4340 there isn't really a limit (you loose less than 5Rc clear out at 15"diam).

This is exactly the kind of information I am trying to learn to retrieve myself.

Essentially, I now have a component made of 4340 at 140-160 KSI with an equivalent round diameter of 1.5''. I am trying to evaluate what the effects would be of replacing the material to 4140 at the same strength.
According to the MIL-HDBK-5H, at 1.5'' 4340 should be used, but for the application, maybe 4140 would be ok.

What reference would you use to get this info? I would definitely be interested in acquiring it and adding it to my library.

Thanks.

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