Most "rust converters" contain some sort of acid (phosphoric?) that attacks the chemical makeup of the rust (iron oxide) and turns it into something that theoretically doesn't continue to deteriorate the metal. Sometimes the cure is worse than the disease, when the acid that's trapped in crevices leaks out and lifts primer or paint. I'd suggest using a high pressure washer to blow any residue out after using any kind of chemical to kill the rust.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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