18Ni350 Maraging steel samples were martensite aged (maraged) at 480 oC for 180 min in a vacuum furnace under pure argon (99.99%) and commercially pure nitrogen gas atmospheres. Samples were also maraged in an air furnace under commercially pure nitrogen atmosphere for comparison. In all these samples increase in the weight% of the samples and different surface colors i.e. bright, golden or brown were observed. The chemical elements as a function of depth after maraging were analyzed by Auger Electron Spectroscopy (AES) to investigate the reasons for the coloration of the surfaces of the samples. The AES revealed that oxygen, nitrogen and carbon elements are present at the top of the sample surface. It is concluded that the surface films formed were homogeneous due to the binding of N2 with the Ti, Fe and Co; binding of O2 with the Fe and binding of the C with the Mo. The nature of film appears to be chemisorbed reaction between the alloying elements and the O2, N2 and C, probably present as impurity in the gases used.

Anwar ul Haq, M. Afzal Khan and Abdul Qadeer Khan