Junichi Asami

In Situ Observation of Sintered Iron and Carbon Steel Compacts Using a Low-Temperature Acoustic Microscope

Sintered iron compacts and carbon steel compacts (0.3 mass% carbon) were observed in situ using a low-temperature acoustic microscope (LTSAM). The effects of structure, pore distribution, tensile load and testing temperature were evaluated by using the acoustic images. Before the tensile test was conducted, initial inner defects, such as pores and cracks, existed in the specimens and the conditions of the defect distribution were different for each specimen. As the tensile load increased, the newly generated defect area was extended where expansion, deformation and connection of pores occurred. As the testing temperature was lowered, the area became more localized. In different structures, for example, in ferrite and in ferrite-pearlite, the trend of the acoustic images also differed, and the defect area of the latter was sharper than that of the former. These results are consistent with elongation data obtained by tensile tests and observations using an optical microscope. Therefore, the LTSAM is useful for understanding the low-temperature brittleness of sintered iron and carbon steel compacts.

Study of Elastic Moduli of Sintered Low Alloy Steels by Acoustic Pulse Method

The influence of porosity (P) on Young’s modulus (E) and Poisson’s ratio (υ) of sintered steels produced from four types of steel powders were investigated. The values of E and υ depends mainly on the value of P, and those were a little affected by alloying elements. The relationship between compacting pressure (CP) and P and the relationships between E, υ, and P were described as following equations: P = P1 + P2 exp(- CP / P3), E = E0 (1 - kEP)2, and υ = (υ0 - υsub)(1 - kυP)2 + υsub, where subscript 0 means P = 0, and P1 - 3, kE, kυ and υsub were empirical constants. It was clarified that if powder and sintering temperature is defined, the elastic moduli of sintered steel can be calculated as a function of compacting pressure.

Application of the Plated Powder to Fe-50%Cu Sintered Compacts

Cu-plated Fe powder by the use of the etching waste solution is produced. Since the amount of plated Cu can be regulated, the composition of plated powder in this study is controlled Fe-50wt%Cu. As the result, there is the excellent compactibity of plated powder and it is possible to sinter at low temperature. For instance, the rattler value of 0.25% was obtained by the compacting pressure of 294MPa and the radial crushing strength was 171MPa at the sintering temperature of 973K for 3.6ks. The sintered compacts of the plated powder in comparison with mixedpowder have the low dimensional change, the uniform in the pore distribution and reasonable mechanical strength. Conseqently this Cu-plated Fe powder appears to be very suitable oil-impregnated bearing. Furthermore, this sintered compact is very superior in roundness and cylindricity which are important from the standpoint of the precision of bearing.