I always use Google for my searches. Here is one of the pages it came up with. It appears to be a 420F grade stainless, now that is not the ASTM just the grade.
http://www.westyorkssteel.com/Steel_Specifications/ssintstd.htm
I don't think you have given enough information for anyone to give you a adequate response. The preheat is given by the code of record and the P91 will govern here. For ASME B31.1, P91 requires a 400 degree preheat(ref. 131.4.5). You then need to concern yourself about interpass for the...
nerd4life has a valid point to pursue, but if you need these joints to be slip critical, then you have a resolve your problem. There are reasons to place the washer under the bolt head and for using the harden washer if under the item being rotated. I don't know which year of the...
