Is it possible/safe to mount a grinding disc on a circular saw?

Doesn't sound like a good idea to me. Circular saws are not meant for side loads, AFAIK, but beyond that, is the cost of a grinder so prohibitive? It will be more efficient for the job anyway. Revolving abrasive wheels can do some damage if they come apart- why take chances?

There are quite a number of metal-cutting blades available for circular saws.

One thing to consider, however, is the saw case material: if it's a plastic you'd be sorry if the blade guard and/or housing melted from the sparks thrown and, on the other hand, if it's metal it'll be either an AL or MG housing...

HF has a 4 1/2" grinder on sale for under $20 that'd do a better job.

BTW, you may be radically overestimating the rotational speed of that saw: the ones that I have all seem to run around 3600 RPM.

EXcellent point

I'll look

I picked a representative speed of circular saw shown at HD - Mike