A pair of ring-like same species of chromium cast iron specimens with 3 × 10^-2 m of diameter was set on Nishihara type wear testing machine. They were previously heated at 1173 to 1273 K for 7.2 ks and then they were quenched into oil bath and tempered at 773 K and 973 K for 7.2 ks. Rolling contact fatigue test of these irons was carried out under the condition of 800 to 2700 MPa of applied stress and 1.2 × 10^-1 m/s of slip rate and with lubricant. High chromium cast irons with rod-like carbides (M₇C₃) has superior rolling fatigue characteristic than low chromium irons with coarse and brittle plate-like cementite (M₃C) when they have almost same hardness. The rolling contact fatigue endurance limit of these irons increases with increase in hardness of irons. Cracks propagate along the interface between crystallized carbides and matrix, they pass through M₃C or M₇C₃ of crystallized carbides and they go through precipitated fine carbides.

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  SG irons containing 0.3 % Mo were austempered after preheating at 973 K. The machinability of these irons were improved more than twice of ordinary ADI and were more than the irons austempered after quenching, tensile strength and hardness of these irons were also a little higher than that of the irons austempered after quenching. As the result of examination on the austenitizing process, it was supposed to the improvement of machinability that the delay of transformation was due to ferritization from pearlite by preheating, and that the fine distribution of γ-pool was due to suppression of austenite grain growth by the cementite precipitated near eutectic cell boundary.

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  From the growth test, it was suggested that cyclic normalization modified cast iron. Therefore in this paper, to make sure of the result the iron of the class of FC 250 was normalized repeatedly between 1223 K and room temperature up to 15 cycles and some properties were investigated in details. The main results obtained were as follows. With cyclic normalization, irreversible expansion increased and density decreased, but by only one normalization, it was found that tensile strength increased by about 20 %, damping capacity increased by about 10 % and moreover thermal conductivity was almost equal to that of as cast. Therefore the heat treatment by only one normalization was considered to raise the additional value of cast iron easily. This fact might prove to be a new and effective knowledge to manufacture brake materials with low squeak noise for cars, damping materials and so on.

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  The mode of vibration applied to the Expendable Pattern Casting process consists of various cases. On the other hand, from the viewpoint of vibro transportation, rotary motion is very useful for the sand filling in E. P. C. process. For the purpose of ascertaining the usefulness, this experiment made clear trajectories of different vibration at various parts of flask and also investigated relationship between vibration character of PS pattern inserted in sand during vibration and the flow rate (the flow amount) of sand to horizontal hole. From the result, it would be suggested that rotary motion was found to be more useful for filling of sand than vertical motion. And in the case of rotary motion the sand particle bed was effectively given vibration to some extent of vibration intensity and then the flow amount was maximum.

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  In order to clarify the effectiveness of austempering from (α+γ) phase region, tensile tests and fatigue crack propagation tests were carried out, and then the fracture surface and the cross section of fatigue cracks were examined. When the matrix is changed into the dual-phases of ferrite and bainite by the austempering, the tensile strength is improved and also the fatigue crack propagation resistance is more improved than those of as cast materials. The effect of stress ratio on the fatigue crack propagation in the case of the material austempered from (α+γ) phase region is smaller than that austempered from (γ) phase region. The improvement of the fatigue crack propagation resistance may be due to increase the roughness-induced and oxide-induced crack closure, because of the dual-phases of ferrite and bainite in the matrix. Consequently, it is concluded that the austempering from (α+γ) phase region is an effective heat treatment to improve both the tensile strength and fatigue crack propagation registance.

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  Investigations were made on the fatigue crack propagation behaviors of ferritized cast irons subjected to zero-tension cyclic loading, especially to clarify the influence of graphite shape. Repeated zero-tension fatigue tests were conducted under the constant stress amplitude with the test frequency 10 Hz by a hydraulic fatigue testing machine. According as the graphite shape turned to flaky from spheroidal, the fatigue crack propagation rate on the second region was gradually increasing. The fatigue crack in the compacted vermicular graphite cast iron was propagated by a zig-zag path between graphites compared with that in the spheroidal cast iron. It was observed that the fracture patterns at the crack propagation regions consisted of quasi-striation, graphite fracture, intergranular fracture, dimple and cleavage fracture in the case of both spheroidal graphite cast iron and compacted vermicular graphite cast iron. And, the percentages of graphite fracture area on both materials were increasing as the stress intensity factor range was enlarging.

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  In order to clarify the effects of graphite nodule size and austempering conditions on tensile properties and fatigue strength of ADI, tensile tests and fatigue tests under completely reversed plane bending condition were carried out. It is observed that the austempering at 648 K for 3.6 ks is the best treatment condition for elongation and strength of the iron. Tensile strength decreases somewhat and elongation decreases a lot with the increase of graphite nodule diameter. The fatigue limit of ADI is strongly dependent on graphite nodule diameter, it linearly increases with the decrease of diameter on the logarithmic scales. The fatigue limit can be more accurately predicted by the equation : σ_w=1348/d_max^0.29 (γ=0.97). Therefore, it is most effective to reduce the graphite nodule diameter as much as possible in order to improve tensile properties and fatigue strength of ADI.

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