Paper knife for the perforation cut for paper-processing machines are disposable knives and are made of tempered and hardened steel in the wear-prone part of the cutting edge or the teeth are hardened using electron or laser radiation so that a much greater hardness is available in this region. There is also a more finely distributed martensite in this region. The process according to the invention is executed in such a way that the wear-prone part of the paper knife is treated by applying an electron or laser beam in a short-term hardening process with self-quenching.