Is a reciprocating saw the right tool to saw 2cm/0.8" hardened steel?
For cutting locks, nothing beats an angle grinder.  Good locks are all made with hardened steel that should be as hard as any metal cutting blade for a saw.  The reciprocating saw will be able to make a little progress into the shackle, but its speed will dull the blade quickly, and once it's even a little dull, it will stop cutting and melt/grind the teeth completely off.

A grinder on the other hand works by heating the metal, softening it and scraping away particles.  The grinding disk is meant to be consumable, so rather than getting dull, it just wears away as it does the job.

Of course, you should also consider that a lot of locks are very easy to pick open.  While you are trying to get access to a grinder, spend a few minutes to research picking and determine the type of lock you have.  It's unfortunate, but many locks claiming to be "high security" can be picked in minutes or seconds using improvised tools.