Are you talking about one of these?
http://www.alliedvalveinc.com/pdf/dresser19000.pdfLook at the materials section on page 7 ofr 29 in the .pdf file and it will show the material as an SA 216 WCC Carbon Steel (Phosphated)... And even though I didn't check any other sources, I believe it is a P-1 number. I remember when I was Boilermaker/Tube welder back in the day and I'm talking in the early 1980's, we used to weld these all the time... I hated that phosphated film crap, but then maybe it's not so bad these days since you didn't comment on it.
I used to wonder why they even welded them on since all you needed to do was to thread it on instead which also made it easier to replace in any event... That's ASME for you!!! :) :) :) I'll check in another list I have at home just to make sure it's a P-1 number grade of CS. ;) Btw, the "WCC" stands for W = fusion Weldable quality... The first letter C = Cast Steel... the last letter C = respective grades based on composition and properties. Just in case you were interested in what those abbreviations meant and of course the las two letters: CS = Carbon Steel.
Respectfully,
Henry