SA105N, is a Carbon Steel forgings for piping appications.
chemical:
Carb=0.35 max
Mang=0.6 to 1.05
phosp=0.035 max
sulfur=0.040 max
silicon=0.10 to 0.35
copper= 0.4 max
nickel=0.4 max
chrom=0.3 max
Molyb=0.12 max
Vanad=0.05
columb=0.02
TENSILE STRENGTH 70000 PSI
YIELD STRENGTH 36000 PSI
HARDNESS 187 HB MAX.

I understand that both A105 and A105N have the same chemical composition. The designation "N" is normalization. In the present, most manufacturers make A105N without special request from the purchaser. It is not a good practice to order A105 without normalization. You can specify SA105N as material for pressure vessel service in plant.

Heat treatment is almost mandatory for A-105 used for pressure parts; only flanges with rating 300 and below may be exempted.
The heat treated forging has a finer grain, hence more uniformity, and, generally speaking, better properties (minimum tensile properties do not change though).
Heat treatment may be annealing or normalizing, and there is not much difference between them, except that the former requires cooling in the furnace and is therefore more costly, I presume.
As the type of treatment is at supplier's choice if not specified, I guess that the suffix N implies a choice on the type of treatment.

prex
motori@xcalcsREMOVE.com
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