Yoshinari Komatsu

Slurry erosion of Fe-15 mass%/25 mass% Cr–C–B eutectic alloys

Abstract The following slurry erosion experiment is carried out for the purpose of clarifying the behavior of Fe-15 mass%/25 mass% Cr–C–B eutectic alloys. This is done in comparison with the slurry erosion behaviors of both austenitic and ferritic stainless steels. Three kinds of impact velocity and four kinds of sand content are selected in this experiment. In examining the relationship of the slurry erosion rate ( R s ) with both impact velocity ( v ) and sand content ( V ) on a three-dimensional graph, it may be seen that erosion mainly dominates R s at the high-impact velocity/high sand content rate corner of the graph. On the other hand, corrosion highly dominates R s at the low impact velocity/low sand content corner of the graph. The 25Cr–0C–2.2B and 25Cr–0.6C–2B alloys show higher slurry erosion resistance compared with the others in both corners of the graph. The R s and impact velocity ( v ) follow the relationship, R s =K v n . The n -value is approximately 5 in the low-corrosive slurry erosion test using tap water. In the seawater slurry, however, the low corrosion resistant alloy shows either decreasing of the n -value or losing of the linear relationship between ln R s and ln v .

Wear characteristics of Fe–25Cr–C–B eutectic cast alloys

Abstract To clarify the characteristics of Fe–25Cr–C–B cast alloys, a pin on disc friction and wear test was conducted on Fe–25Cr–0C–2.2B, Fe–25Cr–2.2C–1.0B and Fe–25Cr–3.5C–0B eutectic alloys, at various sliding velocities ranging from 0.125 to 1.99 m s-1. The effects of sliding velocity on the wear resistance of these alloys were studied by the pin on disc friction and wear test, SEM and an X-ray diffraction method. The results show that the effects of sliding velocity on the increase in wear loss were different due to the differences in structure among the alloys. The X-ray diffraction method shows the presence of Fe2 O3 and Fe3 O4 in the alloys after conducting wear tests for almost all of the wear conditions. From the sliding velocity dependence of wear loss, worn surface observation after the wear tests and X-ray diffraction results, the relationships between the type of oxide and wear loss for Fe–25Cr– 0C–2.2B and Fe–25Cr–2.2C–0B alloys are not clear. However, the wear loss of Fe–25Cr–3.5C–0B alloy decreases at a sliding velocity of 0.5 m s-1 or lower, due to the presence of red Fe2 O3 oxide on the worn surface. The wear loss peaks at a sliding velocity of 0.95 m s-1, and decreases again at a sliding velocity of 1.99 m -1 due to the presence of black Fe3 O4 oxide.

Composite reinforcement of the surface of cast iron by WC powder inserts

Inserts represent a convenient means of improving the properties of cast materials by the use of other materials, such as steel, iron, and ceramics. These reinforcement materials are generally used in the form of blocks or plates. The use of hard powders as reinforcement materials for inserts is also the topic of much research. The purpose of the present research is to investigate the reinforcement of gray cast iron locally by inserting tungsten carbide (WC) powders. Three WC powders were used for the inserts, having average grain diameters of 1 μm, 6 μm and 60 μm, respectively. The experiment on the inserts was carried out by firstly inserting WC powders only and then by mixing some alloy powders into the WC powders separately, such as electrolytic chromium, Fe-Mo alloy, and Fe-P alloy. The mold for the insert, which makes five cylindrical specimens, is made by the carbon dioxide process, and each of the specimens measures 30 mm diameter by 50 mm long. WC powders were mixed with a sodium silicate of 0.7 mass% as a binder and then filled into a bottom-mold about 5 mm thick. Gray cast iron (FC150) was used as a parent material for the insert. It was melted with a high frequency induction furnace and poured into the mold at 1623 K. The results confirmed that an approximately uniform inserted layer formed at the bottom of specimens regardless of the particle size of the WC. In the inserted layer, the dispersion form of the WC particles depended on particle size. Here, the matrix structure of the inserted layer remains the same as gray cast iron when only WC powders were inserted. In contrast, when adding chromium powders or Fe-Mo alloy powders to the WC powders, the matrix structure transformed to white cast iron. The hardness of the gray cast iron increases from about 200HV0.3 to about 400HV0.3 with the insert. When adding further alloying elements, the hardness increased further than when inserting WC powders only. Specifically, addition of chromium into WC powders under 6 μm in size increased the hardness to 700HV0.3 or above.

Evolution of dislocation structure and fatigue crack behavior in Fe-Si alloys during cyclic bending test

The evolution of dislocation structures was investigated by means of TEM in Fe-Si alloys with 0, 0.5 and 1.0 mass% Si during a cyclic bending test in conjunction with fatigue crack behavior. The addition of Si increased the fatigue strength. In steel without Si the cell structure develops, whereas in steel with 1%Si the vein structure evolves, which is considered to lead to the increased fatigue strength. The cell structure in 0%Si steel is postulated to be caused by the easy cross slip of dislocations, whereas the vein structure in the steels with Si is inferred to be caused by the difficulty in cross slip presumably due to the decrease in stacking fault energy. Furthermore, the steel containing Si shows a dislocation free zone (DFZ) along grain boundaries. A transgranular fracture takes place in 0%Si steel, while in 1%Si steel many intergranular cracks were observed just beneath the top surface, which was thought to be caused by the fact that a) strains are dispersed within grains owing to the vein structure and b) micro cracks are initiated and propagated along a DFZ.

Observation of pearlite-ring and graphite particles in decarburized spheroidal graphite cast iron

Spheroidal graphite cast irons, which are referred to as FCD materials in the Japanese Industrial Standard (JIS), are often used for automotive parts. This is due in part to their net shape castability and relatively low cost. When welded, however, they show serious drawbacks, particularly brittle fracture due to chilling of excess carbon in the matrix. This study looks at decarburized spheroidal graphite cast iron (FCD-D material), which is more suitable for welding. In this study, heat treatment for decarburization was conducted by a solid decarburizing method for 86.4 ~ 345.6ks at 973 ~ 1373K to produce a decarburized layer on the surface of the FCD cast iron parts. In the decarburized layer of the cast iron parts, a ring-like pearlite layer, voids and decarburized spheroidal graphite particles were observed. In this study, we have investigated the evolution behaviour of the decarburized layer, the pearlite-ring and the decarburized spheroidal graphite particles during the decarburization.