Abstract
The surfaces of steels (Cr-Mo-carburized steel) quenched into several kinds of oil in argon gas atmosphere were studied by electron diffraction method. In many cases, oxide in the form of Fe3O4 or FeO⋅Cr2O3 is found on the surface of steel specimens quenched into oil. FeS is, however, found in case of 90-turbine oil containing 1%-dibenzyl-disulfide. On the other hand, the diffraction pattern could not be taken on account of adhesion or scorching of organic matters in oil to steel specimen. After all, the causes of tarnish or discoloration of steel surface may be scorching of organic matters or formation of oxide or sulfide. Oxide is produced owing to the existence of oxygen dissolved or combined in oil. If sulfur is present in oil, oxidation is so much accelerated that steel surface is tarnished even if oxygen is too little to act as the cause of tarnish. The effect of sulfur changes according to the chemical activity of sulfur compounds. Thus, sulfide is produced under the existence of the active compounds like dibenzyl-disulfide.
