Assigning SA-516 plates to Curve C or Curve D of Fig UCS-66

[Some Curious Guy]

I do not know if its only me noticing this but I have some confusion regarding assigning SA-516 plates to Curve C or Curve D of fig UCS-66,Sec VIII Div 1.
Let us assume we have a SA-516 Gr 65 plate.
If the plate is not normalized it will fall under Curve B. This is clear.
If the plate is normalized it will fall under Curve D. This is also clear but I need confirmation from you all
If the plate is Quenched and tempered it will fall under Curve D. This is also clear but I need confirmation from you all

Confusion is with Curve C. If I am reading it correctly the following plates are assigned to Curve C
1) Fine Grain Practice + Normalized
2) Normalized and Tempered
3) Liquid Quenched and Tempered.

If you notice both Curve C and Curve D can lay claim to 1) Fine Grain Practice + Normalized and 2) Liquid quenched and Tempered plates.

I am not a metallurgist so please excuse me if I draw the below conclusion for SA-516 plates assuming I read Curve C and Curve D requirements correctly.

1) Fine Grain Practice ( FGP ) and Normalized plates have less toughness as compared to just normalized plates. Since Curve C is assigned to FGP + Normalized plates and curve D is assigned to Normalized plates.
2) Tempering reduces the toughness of Normalized plates since Tempered and Normalized plates is assigned to Curve C and Curve D is assigned to just Normalized plates
3) Liquid Quenched and tempered plates have less toughness as compared to Quenched ( I assume Air / inert gas Quenching ) and tempered plates.

I request you to highlight where I am reading the code incorrectly. Apologies if my queries appear stupid. As I said I am not a metallurgist and I graduated from university a very long time ago.

 

[SnTMan]

Some Curious Guy, though I am no metallurgist either and have also been out of uni for a long time myself, I will attempt to at least partially some of your questions.

As a preface, Fig UCS-66 is intended to apply to the wide range of materials permitted under Table UCS-23. As such, the proper assignment of a particular material to a particular curve must be based on knowledge of the material specification. This is illustrated by such as the Note 3)(b) reference to "as permitted in the material specification".

To your examples, SA-516-70 is, by specification, made to fine grain practice. Heat treatments permitted are either none or normalized. In my experience at least, it is never furnished in any tempered condition. Therefore as per Note 3)(b) SA-516-65 will never be assigned Curve C, only either B or D, depending on the heat treat.

I am sure others more knowledgeable than myself can expand

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Some Curious Guy]

Yes this makes sense. Proper understanding of material specification is essential before reading the curves. I also missed " not listed for curve D below " in note 3(b). Careful reading is required.
Thanks @SnTMan for your reply and guidance.