アンモニア合成雰囲気におけるステンレンス鋼および低合金鋼の侵食挙動について
1971 年 20 巻 4 号 p. 158-164
詳細
1971 年 20 巻 4 号 p. 158-164
A study was made on the corrosion behavior of various stainless steels and low alloy steels in three types of ammonia converters. Test periods were 230, 1, 200 and 1, 986 days for austenitic stainless steels.
(1) Corrosion rate of stainless steels was ranged from 0.06 to 0.15mm/yr, and de-carburization occurred in nitriding layer of stainless steels. When stabilizing elements such as titanium and niobium were sufficiently added to steel, the de-carburization in nitriding layer was prevented. The thickness of nitriding layer was decreased with increasing nickel content. The metallographic structures were determined by X-ray diffraction method. These results showed that the layer consisted of ferrite, austenite and chromium nitride, whereas the core was austenite only.
(2) The nitriding layer was formed in the low alloy steels, i.e. 21/4 Cr-Mo steel, 5 Cr-Mo steel, 9 Cr-Mo steel and Cr-Mo steels stabilized with titanium, niobium and vanadium. The Cr-Mo steel, 31/2 Ni steel and Ni-Cr-Cu steel were nitrided from surface to centre, and also microcracks were observed. Carbon was scarecely detected in nitriding layer of 5 Cr-Mo steel and 9 Cr-Mo steel, and cracks were not observed. On the contrary, both the decarburization and microcracks were not observed in the nitriding layer of titanium and niobium-bearing Cr-Mo steels.
