Heat treatment drawing specification

[Pimech]

Hi.
Could anyone suggest me a standard or a correct way to specify heat treatment on a drawing?

Which international standard could I refer?

For example, I am specifying a steel "SAE 4340" per AMS6409. According to this standard, this steel should be supplied +NT "normalized and tempered". Should I add this suffix in the drawing material specification?

Thanks

 

[redpicker]

As with any drawing callout, you want to be clear and unambiguous so that somebody you've never met knows exactly what you want.

I'm thinking "Material: SAE 4340 per AMS6409 in the normalized and tempered condition".

The last thing you want is someone reading your callout and getting it wrong.

 

[Pimech]

Hi redpicker,
thanks for your suggestion.

 

[tbuelna]

You should think of an engineering drawing as a set of inspection requirements for the product defined on the drawing.

In the example you gave, the raw material is defined as "SAE 4340 per AMS6409". The AMS6409 spec covers aircraft quality SAE 4340 alloy steel bar/tubing/forgings in a normalized & tempered condition, so your description is fairly complete. The only thing you might add is a more explicit description of the material form and size, such as "2.5 to 3.0 inch diameter round bar".

If this is a raw material requirement listed on your engineering drawing/BOM, it becomes something that must be verified by your QA process. Usually this involves receiving inspection checking the paperwork/certs delivered with the material. If no other heat treatment is specified for the component on the drawing, then it is assumed whatever heat treat condition the component has when finished is acceptable.

On the other hand, you could add a note stating something like "Rough machine all surfaces to within .XX" of final profile and heat treat Rc38-42 in accordance with AMS2759/1". That would require additional QA verification for things like dimensions of the rough machined part and documentation/certs for the heat treat processing.

 

[Pimech]

Hi tbuelna,

thanks for your reply. It is exactly what I needed.

""SAE 4340 per AMS6409". The AMS6409 spec covers aircraft quality SAE 4340 alloy steel bar/tubing/forgings in a normalized & tempered condition, so your description is fairly complete."

Ok, it's clear. So the material SAE 4340 is supplied already heat-treated (normalized & tempered).


"On the other hand, you could add a note stating something like "Rough machine all surfaces to within .XX" of final profile and heat treat Rc38-42 in accordance with AMS2759/1"."

Ok. I have some doubt at this point. I can specify "heat treat Rc38-42 in accordance with AMS2759/1", even if these values are not listed in the TABLE 4A of AMS2759/1 (SUGGESTED APPROXIMATE TEMPERING TEMPERATURES
BASED ON AS-QUENCHED HARDNESS), since they are only "suggested values". Is there no need to specify Class of Atmospehere? Is it determined by heat treating processor?

Thanks

 

[tbuelna]

Pimech-

Sorry for the confusion regarding my heat treat note above. It was just meant as an example, and you are correct about AMS 2759/1 table 4A recommendations for tempering 4340.

One reason there is an AMS spec for this aircraft quality 4340 wrought raw material in a N&T condition is because that is the condition often preferred for rough machining. While a N&T condition provides good machining characteristics, it likely won't provide the mechanical properties you require in the finished product. So you'll need to perform some additional heat treatment to obtain the mechanical properties required. If you add a note to your drawing that simply says "Heat treat Rc XX-YY per AMS 2759/1", that does not define at what point in the manufacturing process the heat treatment should be performed, and this might have an effect on your finished product. If you read thru AMS 2759/1 sec 3.3.1, there are four types described for how the part will be processed. You can specify one of these types in your note to provide more control over the heat treat processing.