Mumetal is normally supplied in the”mechanically annealed” condition to allow for forming operations such as bending, and in this state it will mechanically react in a similar fashion to 316 grade stainless steel. This is quite different from a magnetic anneal which is a much higher temperature process (1100+degrees C instead of 900 for a mechanical anneal.)

Any mechanical deformation of mu metal after this final magnetic anneal will significantly reduce its properties, the exact amount is difficult to define as it depends on several factors:- the amount of deformation, the thickness of the mumetal, and the actual shape and direction of the field for which the shield is required, it is not unusual to find properties have been reduced to 30% of their original value by forming operations after the magnetic annealing process. In most shielding applications the rule is for optimum shielding and the magnetic anneal should be the last production process.

Regarding your second point , yes – as explained above, shield properties are fully recoverable by a further specialised magnetic annealing process (refer to my article on mumetal specifications for further information on this heat treatment process)