Noun
work hardening (uncountable)
(metallurgy) The repeated plastic deformation of a material, causing a permanent distortion of its crystal structure, and an increase in its strength
Work hardening can make austenitic stainless steels slightly magnetic. Source: Internet
Some refer to this as a 'fitted' neck, however it is a function of both the carefully cut precision neck and the case adjusted to fit with very little clearance. citation Work hardening happens to all cases, even low-pressure handgun cases. Source: Internet
Work hardening creates microscopic defects in the metal, which resist further changes of shape. Source: Internet