Japan is prone to natural disasters such as earthquakes and torrential rains. Since those disasters have become more severe, extending the life of infrastructure is an urgent issue. Modern sewer ...system in Japan have been constructed since 1884, and regular inspection, cleaning, and repair are essential to prolonging the life of sewage pipes. Manholes, which are entrances to sewage systems, can be regarded to be one of the important structures that support our safe, secure, and comfortable lives.
In this paper, two main parts composed of a manhole, a cover and its bottom, are introduced. The cover made of spheroidal graphite cast iron (cast iron cover) and the manhole bottom made of resin concrete have been developed to extend the life and performance of manholes. The cast iron cover has been made lighter by optimizing the material and structure, does not rattle even when automobiles pass through it at high speed, and automatically releases pressure when the pressure in pipe rises. In addition, the introduction of resin concrete compensates for the shortcomings of cement concrete, such as low curing speed, salt damage, and freezethaw characteristics. Finally, examples of implementations and achievements with the developed materials and structures are presented and discussed.
Cast iron welding improves the performance of joints using welding rods for cast iron. However, such rods are more than twice as expensive as those for mild steel. The authors found that when ...spheroidal graphite cast iron is melted and rapidly solidified, graphite nodules aggregate and move to the surface. If the graphite nodules in the fusion zone move to the surface, the carbon concentration may reduce, thereby suppressing the generation of ledeburite. In this study, by irradiating with YAG laser, I-type butt-welded joints were fabricated using L materials (with an average nodule diameter of 52 μm) specimens without groove width. Ferrite and pearlite matrices joints were undermatch joints. Applying PWHT (Post Weld Heat Treatment) restored the joint strength to more than 90 % that of the base metal. The impact value for the as-welded joint dropped to less than 15 % of that for the base metal. However, it could be recovered up to about 40 % of that for the base metal by PWHT. Ferrite matrix joints after PWHT exhibited similar level impact values as the as-welded pearlite matrix joints. Moreover, the surface of spheroidal graphite cast iron with different numbers and size of graphite nodules was irradiated with YAG laser. As a result, at irradiation feed rates above 100 cm/min L, materials specimen exhibited a much lower hardness in the fusion zone than S materials (with an average nodule diameter of 27 μm) specimen. The graphite nodules in the fusion zone moved to the surface during rapid melting by laser irradiation. In the S materials specimen studied, more ledeburite, martensite and retained austenite formed near the fusion boundary than with the L materials specimen.
In this study, titanium carbide (TiC) coatings were grown on the surface of a spheroidal graphite cast iron (SGI) via thermo-reactive diffusion (TRD) using powder-pack processing at 800 °C, 850 °C ...and 900 °C for 4 h. The TiC coatings obtained on the SGI were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), surface profilometry, microhardness, VDI adhesion testing, wear testing, and electrochemical corrosion testing. Depending on the TRD temperature, continuous, crack-free, and smooth TiC coatings of 5–11 μm thickness and 27.96–32.45 GPa hardness were obtained on the surface. The high chemical stability, high hardness, and good adhesion strength of TiC coatings resulted in a reduced friction, high wear resistance, and superior corrosion resistance compared to the untreated sample. Delamination and oxidation assisted abrasive wear transformed into oxidation-assisted adhesive wear in the coated samples. Galvanic corrosion was dominant in untreated SGI, while homogeneous corrosion occurred in the coated samples. TiC coatings grown using TRD have the potential to be used in engineering components exposed to tribo-corrosive conditions.
•Titanium carbide coatings were grown on ductile iron by thermo-reactive diffusion for the first time.•TiC coatings with 5–11 μm thickness and 27.96–32.45 GPa hardness formed on the surface.•The TiC coatings could be obtained at lower process temperatures compared to steels.•The friction, wear and corrosion behavior of the TiC coating were investigated.•The coatings reduced coefficient of friction and improved the resistance to wear and corrosion.
The crankshaft is one of the structural components of the engine that converts the linear motion of the piston into rotational motion. In this study, the failure analysis of spheroidal graphite cast ...iron (SGCI) crankshafts of compact pickup truck diesel engine was investigated that premature failure occurred in the web-crankpin fillet zone of all four crankpins. A series of experiments including chemical composition, mechanical properties, hardness, and tensile tests were performed. Optical microscope (OM) and scanning electron microscopes (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) were used to investigate the microstructure, defects, fracture surface, and failure cause. To estimate the crankshaft stress field under cyclic bending combined with steady torsion, a nonlinear three-dimensional stress analysis model was used. Fractography showed that the failure is a type of transient low cycle fatigue and includes three zones of crack initiation, fatigue crack propagation, and fast final fracture. Also, hardness and microstructure results revealed that there is no hardened surface layer on both the crankpin and the main journal (>600 HV0.1 proposed standard). In addition, the microstructural characteristics showed that the material nodularity used in the failed crankshafts is within the acceptable minimum range (>80% nodularity). Besides, numerical stress analysis showed that the highest stress is in the web-crankpin fillet zone, which is in good agreement with the experimental field measurements. Finally, recommendations have been provided to ensure long fatigue life and prevent premature failure.
This study aims to investigate the corrosion characteristics of spheroidal graphite cast iron in an atmospheric environment and compare them with those of carbon steel and weathering steel. The ...atmospheric exposure test results showed that the corrosion rate of spheroidal graphite cast iron is significantly lower than that of carbon steel and less than or equal to that of weathering steel. The main reason for the differences in the corrosion rate of the three materials should be due to the high protectiveness of the rust layer. Previous research suggests that Si and Cu contribute to the rust protection of spheroidal graphite cast iron, but the details are unclear. In this study, an atmospheric exposure test was conducted using specimens with minimal additions of Si and Cu to confirm their effects on the corrosion behavior of spheroidal graphite cast iron in an atmospheric environment. The results showed that the corrosion rate of the specimens with added Si was significantly lower than that of the specimens with minimal addition of Si. It was also revealed that Si was concentrated in the oxide state in the inner layer of the rust, especially around graphite. In addition, the corrosion mechanism of spheroidal graphite cast iron in an atmospheric environment was studied, considering the effects of Si and Cu.
The objective of this experiment is to increase the heat resistance of high Si spheroidal graphite cast iron (3.3%C-4%Si-0.6%Mo) which is used as turbine housing. It is known that when Al is added ...to the spheroidal graphite cast iron melt, nodularity and fluidity decreases, but heat resistance increases. This experiment thus aimed to demonstrate the effective utilization of Al. In samples added with a small amount of Al, microstructure was observed and mechanical properties and fluidity were measured. High temperature oxidation tests and high temperature tensile tests were also carried out. The high temperature oxidation results were used as measures of heat resistance. The results of the experiment showed that good heat resistant cast iron can be fabricated without decreasing the mechanical properties and fluidity. When the added Al was less than 0.3%, the nodularity was high and elongation of mechanical property did not decrease greatly. Al was distributed across the matrix structure. When the added Al was over 0.3%, the removal of sticking slag inside the ladle posed as a significant factor to resolve the difficulty of mass production. Therefore the optimum Al addition amount was considered as 0.2%. As operations such as melting, casting, sand molding etc. are carried out at the manufacturing site at our company, the experimental results are easy to apply to both the fabrication of the prototype and the practical products.
•Fatigue crack growth of spheroidal and compacted graphite cast irons are studied.•Graphite of cast irons are observed with the help of X-ray microtomography.•The crack propagation rate is larger in ...compacted graphite cast iron than in spheroidal graphite cast iron.•Graphite fracture is the main mode of fatigue crack propagation for the compacted graphite cast iron.
The present paper focuses on the fatigue life of a Compacted Graphite cast Iron (CGI) as compared to a Spheroidal Graphite cast Iron (SGI). Fatigue crack growth laws have been determined with digital image correlation. Main difference between the materials is that cracks propagate faster in the CGI than in the SGI. X-ray tomography was also used in order to assess graphite morphologies and crack shapes. A complex morphology was observed for the vermicular graphite with rounded edges that limit notch effects. The crack spreads easily in CGI via a quasi cleavage mechanism and by propagating through graphite mainly by breaking the vermicules.
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