In reply to Piers Harley:
I'm no chemist but I think the high alkaline content of chalk that hastens rusting if gear is not cleaned after every outing. The sea air is probably less of an issue.
Incidentally, both myself and Rob Marson's crampons sporadically cracked in an identical place last year (in the middle of the front portion of crampon), which was no doubt due to the chalk.