Composition structure and magnetisation of rf plasma nitrided 304 stainless steel

Nitriding of an austenitic 304 stainless steel has been carried out using inductively coupled radio frequency (rf) nitrogen plasma. The composition structure and magnetisation of samples of as-nitrided and nitrided/annealed steel have been investigated using X-ray diffraction and vibrating sample magnetometery (VSM). Unnitrided 304 stainless steel and standard iron powder nitrided under the same heat conditions have also been studied for the purpose of comparison with nitrided 304. It is shown that nitrided AISI 304 has a high saturation magnetisation (Ms) relative to the original material and behaves as a ferromagnetic material. With annealing temperatures up to 900°C, under vacuum, the Ms values increase up to about 200 emu/g. These increments in the Ms values have been ascribed to Fe–N compositional variation and mainly due to formation of α-Fe.