The influences of 0.008 to 0.074 mass % B and 0.21 to 0.79 mass % P on the structure and properties of cast iron brake shoe are examined with an image analyzer and an original braking test machine. The structure of cast iron consists of hard phases, viz. , eutectic cementite and steadite, distributed in a pearlitic matrix. The addition of high density P and B increases the hard phases, which raises the frictional wear resistance against the wheel steel. The wear proceeds by a series of phenomena ; intense deformation of matrix in the surface layer, crackings through the flaky graphite, after which galling occurs. The coarse eutectic cementite crystallizes in B added cast iron, which effectively improves wear resistance. The contact surface is heated above A₁ temperature and the. steadite is partially melted or softened, which enhances the braking ability of cast iron. The addition of high concentration P therfore significantly reduces braking distance.

View full abstract

  A series of semi-solid processing experiments were carried out under various conditions to clarify the effects of stirring condition and quenching temperature for hyper-eutectic cast iron. A characteristic cast structure was obtained when the slurry was cooled with stirring within the temperature region where the ternary phase coexists. Proper stirring of the semi-solid cast iron yielded microstructure, with uniformly distributed fine graphite and eutectic cell. Semi-solid processed hyper-eutectic cast iron gives reasonable mechanical strength and elongation values with good wear resistance, compared to hyper-eutectic cast iron obtained normally. In addition, functionally gradated cast iron was obtained by carburizing during the stirring of semi-solid hypo-eutictic cast iron. The microstructure, carbon content and mechanical properties are gradated from the inside to the outside of the specimen. Semi-solid processing cast iron has promising prospects for application in many industrial fields because of their attractive properties.

View full abstract

  The excellent toughness of austempered ductile irons is considered due to stress-induced martensitic transformation. Stress-induced martensites have however not directly been observed metallographically in austempered ductile irons. TEM and SEM observations were thus carried out on internal and surface microstructures of austempered ductile irons. Ductile iron just austempered consisted of bainitic-ferrite, retained massive austenite (RM-γ) and retained fine austenite (RF-γ). No carbides were observed in the ferrite and on boundaries between the ferrite and austenite phases. On the other hand, lenticular or plate-like martensites with mid-rib and internal twins were observed in the RM-γ of austempered ductile irons subjected to subzero-cooling or fatigue-fracture. It is thus concluded that the excellent toughness is attributed to the stress-induced martensitic transformation in RM-γ, because no martensites were observed in RF-γ.

View full abstract

  The evaluation method for 3-dimensional distribution of second phases in two-phase materials was investigated, regarding “local volume fraction” and “local particle density” as characteristics of a particle like the particle size and the shape factor. The relation between 2- and 3-dimensional spatial distribution parameters was obtained by modeling with computer. Using the proposed method, the 3-dimensional spatial distribution of graphites in spheroidal graphite cast irons was evaluated as “weak clustering”.

View full abstract

  Results of the wavelet analysis of noise generated during the shake-out of iron castings using self-hardening mold showed that the frequency spectrum right after the start of shake-out is close to that of the consolidated vibration of the shake-out machine and molding flask. On the other hand, after shakeout completes, the frequency spectrum closely resembles the characteristic frequency of the molding flask.
  Based on these analytical results, we developed a measurement system for determining the shake-out ending time. The measurement system consists of a filter, rectifier, differential, AND circuit and amplifier. We determined the ending time of the shake-out process using this system by applying noise as its input. The obtained results agreed well with that obtained by visual inspection.

View full abstract

  The solidification time of T-junctions in sand-cast iron castings was numerically calculated. The relative solidification time of a junction in respect to a plate of the same thickness showed a minimum of 0.77 at the thickness ratio (attached plate vs. main plate) of 0.15 (cooling fin effect). The relative solidification time was one at the thickness ratio of 0.45 (neutral) and 1.64 at the thickness ratio of one (hot spot effect). Compared with the numerical results, the conventional modulus method predicts a weaker fin effect and weaker hot spot. The inscribed circle method predicts no fin effect and a reasonably strong hot spot. Effects of the corner radius on solidification time can reasonably be estimated by the modulus method, while the inscribed circle method predicts an excessively long time and the modified method by Wlodawer predicts an excessively short time. Certain details of the cooling effects by fins and pins were also studied. It was found that the behavior of the T-junctions is strongly dependent on the thermophysical properties of the mold and metal materials. Therefore, the above results can be applied to iron and perhaps to steel, but should not be applied to aluminum castings, whose behavior can differ considerably from that of the iron studied here.

View full abstract