Santosh,
WELCOME TO THE AWS WELDING FORUM!!
So, for my non- metric mind, we are dealing with yields between 45k - 55k and tensile of 65k - 75k, very approximate. Thus, it is not because of the limitations on strength of steel that they are not pre-qualified to D1.1.
As Scott asked, could you give us the actual ASTM designations? And, you may be able to determine your groupings for the PQR from B2.1. Have you checked into that yet?
He Is In Control, Have a Great Day, Brent