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Formation of Conical Carbides on the Surface of SUS304 Stainless Steel by Sputter-Etching

The surface of SUS304 austenitic stainless steel was sputter-etched by Argon ions in a R.F. magnetron sputtering apparatus. The shape and chemical composition of precipitated carbides on the surface were examined by SEM, SIM, FIB and EPMA. Conical chromium carbides with an aspect ratio of about 2.8 between height and radius (radius: 0.1∼0.8 μm) protrudes from surface especially along grain boundaries. The precipitation and growth of such conical carbides is considered to be dependent on the surface temperature, gradient of temperature, numbers of introduced vacancies and diffusion coefficient of carbon. The aspect ratio of a conical carbide seems to be related to the growth rate of the carbide normal to sputter direction and the difference in sputtering rate between matrix and carbide.