Kazuo Ichii

Sputtering, deposition, and diffusion in ion-nitriding of an austenitic stainless steel

Abstract The surface of a commercial austenitic 18-8 stainless steel ion nitrided at 400 °C, 450 °C, and 550 °C was examined by scanning electron microscopy, energy-dispersive X-ray analysis and electron probe microanalysis. Non-metallic inclusions in the steel, particularly oxides, were not much affected by sputtering so they remained on the surface of the specimens, and were covered with deposit. A surface layer, 5–10 μm thick, was sputtered by ion-nitriding at 400 °C for 40 h (5 cycles of 8 h) and 550 °C for 4 h in an N 2 H 2 atmosphere at a pressure of 6.67 × 10 2 Pa. A layer 0.2 μm thick was deposited at 400 °C for 4 h and a layer about 2 μm thick was deposited at 400 °C for 40 h (5 cycles of 8 h) and 550 °C for 4 h. Cracks were observed in the layers deposited onto non-metallic inclusions at 400 °C and 450 °C. The cracks lower the corrosion resistance of the nitrided layer.

SIMULTANEOUS CHROMIZING-SILICONIZING DIFFUSION COATING ON AUSTENITIC STAINLESS STEEL

The simultaneous deposition of chromium and silicon on austenitic stainless steel SUS310S using a halide-activated diffusion coating process was performed in order to improve oxidation and wear properties at high temperatures. The specimen was placed in an Al 2 O 3 crucible filled with a powder containing Cr-Si powder, a halide activator of NH 4 Cl, NaF, and AlF 3 , and an Al 2 O 3 filler powder. The diffusion-coating treatment was carried out at 1073–1323 K for 18 ks in argon atmosphere. Simultaneous diffusion-coating layers were mainly characterized chromium silicide and alpha ferrite. An oxidation characteristic after diffusion coating was also investigated for 1000 ks at 1073 K in air. The mass increase of diffusion-coated specimen was less than that of the untreated specimen. This result indicates that the simultaneous deposition of Cr and Si markedly improved the oxidation resistance of the austenitic stainless steel.