Assumed/implied material heat treat

I am in a discussion with an engineer about the heat treat on a part. The drawing calls out a few parts as '4340 H/T 45-50 RC' and one part called out as '4340'. I was going to toss this part in to get heat treated with the others on the basis that it machines much nicer and pretties up a bit better in this condition. And it would increase the service life of this part as one end has a morse taper on it.

His argument is that the '4340' callout implies annealed. My argument is the '4340' callout simply specifies material.

Is there a standard anywhere saying that unless specified assume the material to be annealed?

I have had drawings call out for 'steel' annealed.

Ultimately the customer wins, I am just wondering if there is a standard out there.

Thanks for your input.

I'd agree that "4340" only specifies material. I don't think that gives you license to do arbitrary HT to it, especially since there's another different callout for the same material. On the other hand, any actual part obviously must have some heat treat condition, or range of conditions.

I honestly don't know if there is a standard for heat treat condition, if not explicitly specified. Even if one exists, it's so poorly known that I wouldn't lean on it too heavily, nor would I expect customer or shop drawing standards to universally have adopted it. In fact, I'd expect to run into customer-specific rules much more often than a national (much less world) standard for this.

Unless there's some design reason for the exceptional part to be soft, I think you've got a very reasonable argument. But as you said, it's up to the customer to make that call at the end of the day.

If it was annealed I'm not sure why they would even spec 4340, 1045 is much cheaper and probably not much different in strength in the annealed state but who knows what they were thinking, or, more likely they may have forgotten the H/T spec on the print. I would have skipped the discussion with the engineer and called the customer, personally.

I can't fathom why a drawing would not be explicit in the notes.

Example:
"Make from 4140-annealed (or 4140-ht acceptable), Heat treat to Rc 48-50 after machining"

It's very easy to type out a few words to completely eliminate all cornfusion.....

No callout implies use material as supplied.

Not a great idea as what you have could be almost anybodys guess. Especially if the buyer is shopping around in the specified by properties / specified by composition. Possibly OK if its customer supplied material from a customer who buys to their own specific requirements.

Clive

Are you working with an aircraft spec? Some of the aircraft specs (AMSnnnn) do have the heat treatment and mechanical properties specified.

If the guy you're talking to is an engineer, he should know if the part needs HT. Talk to the customer.

The 4340 at 45-50Rc is tempered between 600-800°F, that’s not a good area if you need toughness or good impact numbers.

Good luck,
Matt