Chromium diffusion coating is an effective method for improving the oxidation and corrosion resistance of steels. However, in the case of applying this method to the production of automotive parts, there are many problems to be solved such as operating cost and quality control. The key points in solving our problems are, first, a novel coating method by using a special granular diffusion agent and, secondly, the establishment of a new operating process and its control for massproduction. Our chromium diffusion coating system has been adopted successfully to substitute chromium coated steel for stainless steel with material cost in the production of automotive emission control device parts.

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A structural study of Co₇₅W₂₅ (atomic %) and Ni_100-xP_x (x=16-25) alloys both prepared from aqueous solutions has been made to see whether they have nonequilibrium structures. Their structural models were constructed and examined by the correlation method. The model for the Co-W alloy consists of close packed tetrahedra, each composed of four hard spheres of equal size. The tetrahedron contains three Co atoms and one W atom of 2.55A in diameter. In modeling the Ni-P alloys, however, Ni and P atoms were treated as non-hard spheres of different mean diameters; 2.61Å and 1.88Å, respectively. Furthermore, Ni-P alloys, irrespective of their alloy compositions, were treated as the mixture of structural units Ni₂P and isolated Ni atoms. These units and atoms were randomly deposited on a plane surface of (100) in the bcc structure. Interference functions calculated from the above models agree quite well with x-ray diffraction data of these alloys. The atomic arrangement in these models forms distorted icosahedra which forbid crystallinity in the alloys, indicating that they indeed have nonequilibrium structures. It should be noticed that the present result violates the thermodynamical depolarization theory, which does not allow the deposition from aqueous solutions of nonequilibrium tungsten or phosphorus alloys.

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A theory has been developed to account for the formation of binary A-B alloys from electrolyte solutions. The alloy formation process involves the catalytic deposition of a B atom on an n-atom cluster of deposited A atoms. Among a number of parameters affecting the alloy composition and structure, the clustering tendency of A atoms and the net gain in interaction energy between the B atom and the cluster of A atoms are found very important, as well as the previously suggested material balance of A and B ions at the electrode surface. The above theory accounts for the experimental results quite well in Fe-W alloy electrodeposition. It was also found that the theory can interpret qualitatively the deposition conditions reported empirically for the induced- and other types of alloy electrodeposition, eg. for Ag₃Sn, Cu₂As, and NiSn deposition.

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The effect of hot dip galvanizing on the mechanical properties of high strength bolt steel with tensile strength in the range 80 to 120kg/mm² tempered at high temperatures was investigated. Elongation and contraction of the galvanized steel decreased with increasing roughness of steel surface. Configuration of Fe-Zn alloy layers affected considerably the elongation and contraction of the gaivanized steel with rough steel surfaces, thick palisade δ₁ layers and ζ layers grown disorderly. The roughness and configuration, however, did not affect the yield point and tensile strength of the galvanized steel. Sensitivities to delayed fracture of the galvanized steel in solutions saturated with H₂S were lower than those for steel specimens with no treatment, since zinc coatings had a protective action. Charpy impact values of the galvanized steel at room temperature were lower than those for steel specimens without treatment. The values decreased with the increase in the compactness of compact δ₁ layer when it was harder than steel and also the values decreased with the increase in the thickness of compact δ₁ layer when it was softer than steel. Fatigue limit in rotating bending tests was affected by configuration of Fe-Zn alloy layers; the limit was low for the ζ layer grown vertically to the surface of steel and for a thin palisade δ₁ layer.

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Methods for precipitating copper ions in industrial waste water were investigated to obtain a precipitate of low water content with high filtration rate. Such a precipitate is favorable for electrolytical metal recovery in which the sludge is supplied to the anode compartment of a diaphragm cell. With addition of alkali carbonate or alkali hydrogen carbonate to a copper sulfate solution, a bluish white precipitate was formed initially. This precipitate changed gradually (but in a short time on warming) to green crystalline Malachite Cu(OH) (CO_3)0.5, characterized by outstanding filtration rate and low water content (20% or less, as filtrated). The electrolytic recovery of copper from Malachite is then technically easy and economical.

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Pure iron and steels ion-nitrided in N₂-H₂ gas mixtures under 1.8-10 Torr pressures at 450-600°C were examined by photomicroscopy, X-ray analysis etc. Hard surface layers were formed neither on ion-nitrided iron nor on S15C steel though ε-Fe_2-3-N and γ′-Fe₄N were present. On the other hand, hard surface layers were formed on ion-nitrified SCM21, SACM 1 and SUS 304 steels. In these layers, ε-Fe_2-3-N and γ′-Fe₄N were present but only the ε-Fe_2-3N was precipitated in the inner part of the hard layer of SACM 1. In SUS304, CrN was also precipitated in the layer. Relationship between the increase in hardness and the amounts of precipitates is discussed.

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