Magnetic Characterization of Powder Metallurgy Austenitic Stainless Steels Sintered in Nitrogen Atmosphere

摘要

The magnetic behaviour of AISI 304L and AISI 316L obtained through powder metallurgy and sintered in nitrogen was studied. AISI 304L sintered in nitrogen showed an abnormal ferromagnetic behaviour in as-sintered state while AISI 316L showed the typical paramagnetic behaviour. After solution annealing both steels were paramagnetic. After post-sintered aged treatment the abnormal magnetic response appeared again but only for AISI 304L. Magnetic behaviour was analysed by using a vibrating sample magnetometer, a magnetic ferritoscope and magnetic etching. AISI 304L and AISI 316L sintered in vacuum showed the typical paramagnetic behaviour in as-sintered, solution annealing and aged conditions. The abnormal magnetic response was explained based on some specific microstructural features related to the influence of nitrogen in these stainless steels. The cellular precipitation of chromium nitrides and subsequent chromium depletion with α/α'-phase formation could consistently cause the magnetic response of AISI 304L sintered in nitrogen.