bobdz;
I would say that you need to have a quenched and tempered heat treatment as a minimum, with fine grain practice, to safely meet your requirement of 20 ft-lbs at -22 deg F.
SA 216 Grade WCC has a specified carbon content of 0.25% Max. In looking at a graph of CVN versus carbon content for wrought, plain carbon steels, 20 ft-lbs correlates to roughly -25 deg F (very rough approximation). This is too close to call, and in dealing with an as-cast material (no heat treatment) versus a wrought material, I would put your chances for the as-cast Grade WCC meeting 20 ft-lbs at -22 deg F at or below 50-50.
A216 specifies that "castings shall be furnished in the annealed, or normalized, or normalized and tempered conditions unless supplementary requirement S15 is specified." So if you are supplying A216 Gr. WCC, then as-cast is not an option anyway. Supplement S15 specifies Q&T heat treatment, so that could be an option. You might be able to meet the impacts with N&T and a low CE, but again, to agree with Metengr, it might be iffy.
I agree with GRoberts. You may go for a double temper treatment in case your carbon is high. Normally aim for a lower carbon and silicon. Addition of small percentage of Moly and Ni preferred if costs permit.
