A new concept, in which free magnesium might be a key indicator of the state of graphite spheroidization in spheroidal graphite irons, is proposed and verified in this study. Chilled samples containing different amounts of total magnesium were prepared. The total, inclusive and free state magnesium contents were analysed by a special procedure. Free magnesium increased in steps as total magnesium increased. On the other hand, inclusive magnesium was nearly equal among the chilled samples. The nodularity and the mechanical properties in 50 mm Y-blocks showed good correlation to the value of the free magnesium, but no relation to that of the inclusive magnesium. The quality of spheroidal graphite cast iron should be controlled by the content of free magnesium in practice. The experimental results well supported the site theory.

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  The coating on iron castings was prepared using mechanically ground (MG) composite powder consisting of Ni powder and low melting point Ni-P powder as the coating powder with no segregation of the compositions on the mold. Several properties of the coated iron castings obtained were tested. The main results are as follows :
(1) Only when the MG time exceeds 36ks, the composite powder becomes even, and use of this powder produces a coating with no segregation of Ni and P.
(2) Compared with mixed powder, the composite powder dissolves the castings less. This enable the formation of a Ni rich coating layer with smaller amounts of powder in 10 mm thin castings. This coating showed good performance in salt spray corrosion test.

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  The coating on thich iron castings (50 mm in thickness) was prepared using a mixture of Ni powder and low melting point Ni-P powder as the coating powder on the mold. Several properties of the coated iron castings were tested. The main conclusions are :
(1) When each Ni/(Ni-P) = 90/10, 75/25, 50/50 powder coated in single phase, no sound coated layer was obtained in spite of coating mass, much or less.
(2) When coating with Ni/(Ni-P) = 75/25 powder first and then Ni/(Ni-P) = 90/10 powder at 120 mg/cm² respectively, a soft surface layer (100∼200 HV1) containing 10∼20 % Ni was obtained. This layer showed good corrosion resistance to spraying NaCl solution. When Ni/(Ni-P) = 50/50 powder was costed followed by Ni/ (Ni-P) = 90/10 powder, a hard surface layer (∼400 HV1) containing 4∼8 % Ni was obtained. This showed good resistance to wet abrasion.
(3) The choice of the ratio of Ni/(Ni-P) and double coating powder layers makes it possible to control excessive dissolution and assist surface sintering. The functional phase can be formed on the necessary parts even of the complex castings.

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  The influences of alloy elements on the friction wear properties were examined on Fe-2.2 % C-6 % V-5 % Cr-5 % Mo-0/5 % W-0/5 % Co alloys by a Nishihara type wear test machine and a lathe in dry conditions. The cast alloy specimens were heated at 1273K for 3.6ks and then tempered twice at 823K for 3.6ks. As the mating materials, stainless steel SUS304, SUS430 and carbon steel S55C were used. For all the mating materials, the wear resistance of W free Fe-2.2 % C-6 % V-5 % Cr-5 % Mo-5 % Co alloy took the highest value, indicating that plate-like M₂C type carbides decreased wear resistant value and Co increased wear resistant value. The wear resistant values of these alloys were higher than that of hypereutectic high Cr-V cast iron (Fe-3.7 % C-9 % V-15 % Cr-2 % Mo) with coarse eutectic M₇C₃. The addition of 6 % Ni and 3.4 % Si to this high speed steel type alloy resulted in the precipitation of small amount of graphite flakes and the lower hardness. The wear resistant value was the lowest. The experimental results obtained by using lathe are similar to those by Nishihara type wear test machine, indicating that the former can be utilized as a simple rolling and sliding wear test method.

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