鉄銹の発生機構とその防止

Abstract

We investigated the mechanism of rust formation on the surface of C-steel and low Cr-steel in atmosphere and researched its prevention. The results are as follows: (1) Rust particles formed on the polished surface of steel are classified as dotted, granular, thread-like and lumpy rust in their appearance. (2) The lumpy rusts are produced by a limited number among many dew drops condensed on the steel surface and grow rapidly. This is the principal source of rusting. (3) About the action of dust adhered to the steel surface, soluble chloride and sulphate particles (NaCl, NH4Cl, MgCl2 and Na2SO4 etc.) have strong accelerating action and lumpy rusts start at every particle of them; Fe2O3 particles have nearly the same action; contrary to this, SiO2, Al2O3, CaO particles show no action. (4) Lumpy rust generally starts in the pearlite area of steel surface, therefore, high carbon steels rust more rapidly than low carbon steels. (5) 0.6%C-steel is quenched from 800° and tempered at various temperatures; the one which is tempered at 450° is most resistive to rust. (6) If the steel surface initially bears complete oxide film (invisible) it can resist rust; finished steels held in dry air for long period or immersed in 0.5%K2Cr2O7, 1%Na2HPO4 solution show good resistivity. (7) Waselin and animal oils have generally greater rust prevention effect than vegetable oils.