Formation of Fine Protrusions by Sputter Etching of Martensitic Stainless Steels

Abstract

Argon ion sputter etching was applied to three kinds of martensitic stainless steels (SUS410, SUS420J2 and SUS440C) and a ferritic stainless steel (SUS430) at a radio frequency power of 250 W for 0.6 ks to 21.6 ks. When the sputter etching time is 0.6 or 0.9 ks, the pillar-shaped protrusions with diameters smaller than 1 μm are formed on the surface of the SUS420J2 steel. With increasing sputter etching time, the cone-shaped protrusions are formed around the base of the pillars, and the size of the conical protrusions increases to more than 10 μm with further increase in the sputter etching time. When the sputter etching time is 21.6 ks, the size of the protrusion becomes more than 20 μm and the surface of the protrusions is heavily damaged. According to an EDX analysis, the Cr content of the surface of a cone is larger than that of the inside and the matrix surrounding the cone. Other steels show a similar protrusion formation process to the SUS420J2 steel, but the formation speed and the density of the cones are smaller for the SUS410 or SUS430 steels with smaller carbon content than the SUS420J2 steel, whereas they are a little larger for the SUS440C steel with larger carbon content. For the martensitic stainless steels, the quenching increases the hardness of protrusions, which is convenient for a traction roll and a transcription roll to imprint many holes to sheets.