ＣＶ黒鉛鋳鉄の疲労強度，疲労き裂進展速度および破面の特徴について

Elevated temperature brittleness (ETB) of spheroidal graphite (s-g) cast iron has been referred to as reduced ductility within an elevated temperature range and has been related to grain boundary brittleness. The phenomenon of ETB has not been yet clearly understood. In this study, the factor affecting on ETB was studied in terms of strain rate and chemical composition. A study was carried out on the influence of phosphorus on ETB by using laboratory-made heats containing different phosphorus contents. ETB indicated the marked decrease in ductility at around 673K. S-g cast iron containing low phosphorus content manifested ETB at temperatures between 650K and 700K. There was a consistent correlation between the fractional increases in intergranular fracture appearance and the decrease in elongation. The increase of phosphorus suppressed ETB and s-g cast irons containing phosphorus exceeding 0.030 % were found to be immune to ETB. It was found that ETB could be suppressed by reducing the ratio of magnesium and phosphorus to less than 1.5.

Since ductile cast iron was invented, cast iron has been used for various purposes. However, because of its poor corrosion resistance, the use of cast iron in corrosive environments was restricted. As pre-viously reported, the authors succeeded in obtaining a prominent protective film on steel by silicon impregnation (so-called siliconizing).In the present work, 3 kinds of specimens, i.e. nodular cast irons having ferrite and pearlite matrix, respectively, and gray cast iron, were siliconized by means of a mixed gas of silicon tetrachloride and oxygen free argon in accordance with the silicon impregnation of steel. The results obtained were summarized as follows.(1) Microscopic examination showed that porous films were formed on nodular cast iron with ferrite matrix, and particularly, on gray cast iron. On the contrary, when nodular cast iron with pearlite matrix was siliconized at a relatively high temperature for a short time, the film obtained had comparatively less pores in number.(2) Immersion tests of the siliconized cast irons in dilute sulfuric acid showed that the siliconized film protected the underlying cast iron core from the attack of acid though it was porous. Above all, the film which had been formed on nodular cast iron with pearlite matrix by siliconizing at a high temperature for a short time showed the best corrosion resistance.

Cast irons are used extensively in the production of large diesel engines for power generation or oceangoing ships. One current trend is to replace grey iron with spheroidal graphite (SG) iron for fatigue critical components. In order to take advantage of the higher fatigue strength of SG iron and ensure the reliability of a design, better understanding of the typical defects for these large castings and the relationship between these defects and the endurance limit fatigue strength have been studied. Testing included uniaxial constant amplitude, constant amplitude torsion, and simple variable amplitude loading sequences in the long-life regime. Defects in several thick wall castings have been statistically evaluated. A fracture mechanics based model involving matrix hardness and √area successfully related the defect size to the experimentally observed fatigue limit. For ferritic-pearlitic SG iron, the hardness of the tougher pearlite phase was used in the model. The model also correlated the torsion and tension endurance limits. Endurance limit as a function of mean stress is presented in the form of Haigh diagrams.

Composite specimens with 3- and 5-layers composed of a mild steel and spheroidal graphite cast irons (steel/cast iron/steel, steel/cast iron/steel/cast iron/steel) were fabricated using diffusion bonding. The composite specimens were hot rolled and the final reduction was 88% and 92%. The main results obtained are as follows; (1) When the hot rollings of 92%-reduction were carried out for the composite specimens, cracks were not observed in the cast iron and on the bond interface between the mild steel and the cast iron. By the hot rolling, spheroidal graphites in the cast iron became the form of sheet. (2) The tensile strength of the rolled composite sheets with pearlitic structure was higher than that of the mild steel. In case of ferritic structure the strength of the sheet with 3-layers was a little lower than that of the mild steel, however, the strength of the sheet with 5-layers was higher than that of the mild steel. (3) The specific damping capacity of the rolled composite sheets was higher than that of the mild steel and increased with increasing the reduction and the number of the layer. (4) The damping effect of the sound pressure of the gear made of the rolled composite sheet with 9-layers was very high in comparison with that of the gear made of the mild steel.

The influence of nitriding on the fatigue resistance of grey and nodular (ductile) cast iron piston rings was studied for six chemical compositions. The selected materials include three grey cast irons: one with a mixed initial microstructure (martensite plus bainite), the second martensitic and another martensitic alloyed with niobium; and three nodular cast irons: one common nodular cast iron, the second alloyed with Nb and another alloyed with Al and V. These materials were gas nitrided for 3 and 6 h. The relationship between the mechanical behaviour and the treatment time (depth of nitrided layer) was established. Samples were tested under a cyclical bending load. The stresses were determined in the cross-section, where the biggest moment was experienced. Results were statistically treated by means of Weibull analysis. Nitriding showed that fatigue resistance of grey cast iron with a martensitic structure is higher than that of a mixed structure. Fatigue resistance of nodular cast irons is red...

Cast irons continue to be first choice materials for cast components in a wide range of engineering applications. They solidify by non-faceted/faceted eutectic reactions where, via a grey iron reaction, the non-faceted metal phase is normally austenite and the non-metal faceted phase is graphite, or via a white iron reaction to form austenite and faceted iron carbide fe3C. The eutectic reaction which occurs depends on several factors such as charge materials, melting and pouring conditions, composition, liquid metal treatments, casting design, mould materials, and cooling conditions. In some cases, the two reactions can occur within the same cast section. For most applications, production conditions are controlled to ensure that only the graphitic eutectic reaction occurs to provide a range of flake, compacted or spheroidal graphite irons. These are often referred to as the engineering cast irons. Eutectic carbide reactions are only required when producing malleable irons or when resistance to wear is needed as in the special cast irons such as Ni-Cr and high Cr white Irons. In all cast irons the final structures can be controlled by alloying and heat treatment to provide ferritic, pearlitic, austenitic, acicular, or mixed matrix structures. The faceted nature of graphite growth controls the as-cast microstructure such that in flake graphite irons the graphite forms a continuously branched network within eutectic cells, thus limiting mechanical properties. In flake irons properties can be moderately improved by inoculation treatment to reduce eutectic cell size. The faceted nature of graphite allows its growth behaviour during solidification to be modified by the addition of small amounts of elements such as Mg and Ce which can change the graphite morphology from flake to spheroidal significantly improving mechanical properties. However, the sensitivity of graphite morphology to quite small amounts of certain elements also means that the structure and properties of graphitic irons can be seriously deteriorated by the presence of impurities such as S, Pb, Sb, Ti, etc., and by the dissolved gases H, O, and N. This paper reviews how optical microscopy and scanning electron microscopy has proved to be invaluable in developing understanding and control of the microstructures and properties of engineering cast irons.

A note on the effect of nodularization characteristics on the workability of quenchp-hardened and tempered cast irons

Tribological Characterization of Centrifugally Cast Graphite Cast Iron under Dry and Wet conditions

Spheroidal Graphite Irons (SGIs) have graphite particle inclusions in an iron matrix. The matrix structure controls overall mechanical properties, and the graphite morphology plays a vital role in crack initiation and propagation behavior. High silicon Solution Strengthened Ferritic (SSF) SGIs are developed to provide higher strength with excellent ductility. In SSF SGIs, graphite nodules shape has a key role in damage micromechanisms. The graphite nodule growth morphology can go through transitions to form degenerated graphite particles other than spheroidal graphite nodules in SGI microstructure. Additional thermal and mechanical processes influence SGI microstructure affecting mechanical properties and damage micromechanisms. Most of the damage mechanism studies on SGI were focused on the role of spheroidal graphite nodules on the stable crack propagation region. In this work, microstructure and properties of different SGI grades were compared, and EN-GJS-500-14 SSF SGI was further deep cold rolled and thermal cycled to study the effect of these processes on the material microstructure. Tensile and fatigue damage mechanisms were studied in detail to understand the role of different forms of graphite particles in SGI microstructure. The microstructure characterization result and damage mechanisms were formulated in a Representative Volume Element (RVE) model, and then to multiscale SGI material microstructure model.

<div>This article investigates the deformation mechanics of cast iron and its implications for notch analysis, particularly in the automotive industry. Cast iron’s extensive use stems from its cost-effectiveness, durability, and adaptability to various mechanical demands. Gray, nodular, and compacted graphite cast irons are the primary types, each offering unique advantages in different applications. The presence of graphite, microcracks, and internal porosity significantly influences cast iron’s stress–strain behavior. Gray and compacted cast iron display an asymmetrical curve, emphasizing low tensile strength and superior compression performance due to graphite flakes and crack closures. Nodular cast iron exhibits a symmetrical curve, indicating balanced mechanical properties under tension and compression. The proposed simplified macrostructural approach, based on monotonic stress–strain, aims to efficiently capture graphite and crack closure effects, enhancing compressive strength and stiffness. By employing the Neuber and Molski–Glinka methods for notch analysis, we assume nominally elastic behavior of notched components. This represents a novel application for gray and compacted cast iron, aiding in predicting material fatigue life, as demonstrated in other materials with asymmetrical behavior.</div>

The nitriding process can be effectively applied to steel with alloying elements. The higher the alloying element in the steel maximizes the mechanical properties, including hardness. However, the raw material can be costly, therefore using cheap materials (without alloys) is a challenge in increasing surface hardness through iron nitride formation. Furthermore Grey and nodular cast iron have different properties and characteristics in the structure. This research focuses on the ability of the cast-iron structure to affect the nitride layer formation. Gas nitriding was conducted in a fluidized bed reactor with a 550°C in 20 % N2 and 80 % NH3 atmosphere at a flow rate gasses of 0.7 m3/hr process temperature and holding for 2, 4, and 6 hours. Tests are conducted by observing the depth of hardening, SEM, and EDAX. According to the results, the nitriding process increases the surface hardness of cast iron. The highest hardness value is nodular cast iron with a holding time of 6 hours (345 HV) and a hardening depth of up to 20-micron meters. The compounds formed in the nitride layer include FeN, Fe2-3N, Fe4N, and Fe2N. The compound formed is strongly influenced by the treatment time. Furthermore, the comparison of nitriding treatment on gray and nodular cast iron was influenced by the flake and nodule structure. In general, the nodule structure is responsible for maximum hardness. The longer treatment time allows the nitrogen atoms to diffuse more to the surface, while the flake structure limits the absorption of nitrogen atoms into the surface of the cast iron. Characterization of Nodular Cast Iron shows that The hardening depth distribution trend due to the nitriding process in nodular cast iron was not much different from gray cast iron.

In ductile cast irons with copper, cementite stability was investigated against an annealing heat treatment used to obtain a fully ferritic matrix. Copper controls cast-iron mechanical properties, but its role in the matrix microstructure formation remains unclear. Some reports suggest the copper layer around graphite or cementite. They can be barrier to carbon diffusion at eutectoid reaction, however it is difficult to understand the mechanism of pearlite stability by copper. To confirm the existence of the barrier and effect of copper addtion, ten 9-mm-thick spheroidal graphite cast iron castings were prepared with different copper contents of 0.16 wt% – 0.69 wt%. The samples’ as-cast microstructures included spheroidal graphite, ledeburite, and pearlite. The pearlite fraction degreases to about 10% by heat treatment for ordinary ductile irons without intentional copper addition. The samples’ copper content and the pearlite fraction after heat treatment are not linearly related. The retained pearlite increased suddenly with increased copper content greater than 0.4 wt%. However, even the sample with the highest copper content showed no precipitation of a copper solid solution around graphite nodule or cementite.

Water main failures are very expensive for municipalities because they typically result in expenses associated with repair costs, flood damage, and loss of revenue to affected businesses. Water main failures also interrupt the operation of vital services, such as medical care and fire-fighting operations. Currently, millions of dollars are spent annually by the water utility industry and by municipalities on the repair of failed components of the water distribution infrastructure, such as components that are made from gray cast iron or "gray iron” pipe and ductile cast iron or "ductile iron” pipe. The rate of municipal water main failures is expected to increase as the existing cast iron infrastructure continues to age. The cost of repairing damages caused by broken water mains (and subsequent flooding damage) may become an important item in many municipal budgets. It is important to develop a corrosion program to prevent catastrophic failures of water mains. This paper presents a plan consisting of several phases including preassessment, indirect assessment, direct assessment, and integrity assessment of failed water mains. We will elaborate on the failure mechanisms, failure analysis protocols, and corrosion mitigation strategies for water mains that experience breaks. Water main breaks are mainly due to corrosive soil, pipe material, galvanic action, stray current corrosion, or microbiological induced corrosion (MIC). This paper provides an overview of corrosion issues commonly experienced by water main pipes, presents specific case histories involving graphitic corrosion, galvanic corrosion, stray current corrosion, and MIC. In this paper, we will introduce a graphitization sensor for condition assessment of water mains. This sensor can identify the location and extent of graphitization on water main.

Objectives: This paper reports an investigation that was carried out for modelling and structural analysis of cam shaft. Methods/Statistical Analysis: The modelling of cam shaft is carried out using the software solid works and the structural analysis of the model is carried out by using Ansys software. Initially, the model is designed with Solid works software and then it is converted into Initial Graphics Exchange Specification (IGES) file. Then it is systematically analyzed using the IGES model of cam shaft. Experimental results under static load containing the stresses and deflection are predicted cast iron material. Findings: Testing was carried out for unidirectional different materials like ductile cast iron, nodular iron and carbon epoxy. By considering these materials, it is noted that the ductile cast iron is a good material compared to the nodular iron because the breakage of nodular cast iron is higher than the ductile cast iron. Application Improvements: Ductile cast iron is considered for making the cam shaft in vehicles because the cost of material slightly higher than nodular iron. In the development of modelling and also analyse by software helps to better result in design.

Fusion weldings of cast irons are very difficult to cause the cold cracking in the weld metal and heat affected zone. So, solid state bonding of ductile cast irons having the strength of 360, 390, 490 and 690 MPa and the ductile cast irons to a mild steel have been investigated using the diffusion welding technique at 730 to 980°C under restraint of test pieces or constant bonding pressures. The results obtained are as follows; (1) When the bonding of the cast irons were performed without a insert metal under the bonding temperature of higher than 820°C and for the bonding time of 1.8 ks, both graphites and ferrites precipitated at the bonding interface according to the transformation of γ→α+Gr on the cooling process. However, the fracture in the tensile test of the joints occurred in the base metal, and also in case of the bondings of the ductile cast irons using a insert metal of Ni foil of 10μm thickness, Cu foil of 10μm thickness or Fe foil of 100μm thickness the fracture in the base metal. Welding deformation of the joints was less than 1% in the diameter of the test piece. (2) The tensile fracture of the ductile cast irons bonded with the Ni foil at 820°C and for the bonding time of more than 0.24 ks under constraint of the test pieces or the bonding pressure of more than 0.8 MPa for 1.8 ks occurred in the base metal. (3) When the ductile cast irons and a mild steel were bonded by the diffusion welding using the Ni foil as the insert metal, the tensile fracture of the joint occurred in the base metal of the mild steel. However, in the bondings of the ductile cast irons and the mild steel with the Cu or Fe foil as the insert metal and without insert metal, the tensile fracture occurred at the bonding interface between the ductile cast iron and the insert metal. The tensile sterngths were about 400 MPa in all joints. (4) The phenomenon of the fracture at the bonding interface in the joints of the cast iron and the mild steel is considered that radial strain abruptly increases on the tensile axis because the hardness became discontinuity and the ductility of the cast irons is much smaller than that of the mild steel.