The making of free cutting steels with additions of lead, bismuth, tellurium, selenium and tin

摘要

Steels with additions of lead, bismuth and tellurium comprise the high sulphur free cutting steels but also Al-killed grades such as carbon steels, cold heading and alloyed steels. With an annual output of 500000 t, Saarstahl is a major producer of these steels.Equipment for slag retention, for lead, bismuth and tellurium injection into the ladle and for EMF-oxygen measurements are important tools for the production of these steels. Collection of all lead, bismuth, tellurium and selenium emissions is an essential prerequisite.The effect of the metallurgy on machinability is discussed. The roles of lead, bismuth, tellurium, selenium and tin are explained.The EU-Directive on End of Life Vehicles (ELV) prohibits the recycling of vehicle components containing heavy metals including lead. Although leaded steels are exempt, the need of lead will be periodically reviewed.As a lead substitute a SAE 1215 type free cutting steel containing 0.04-0.08 percent tin has been developed at the University of Pittsburgh. Further investigation - including tool design - is needed, to bring out the potential of this steel.In addition, an ECSC-funded project has been granted to study the role of tin also in engineering steels and quenched and tempered grades.