Ferritic Spheroidal Graphite Cast Iron Research Articles

Experimental and FEM Studies of Continuous Drive Friction Welding of Ferritic Spheroidal Graphite Cast Iron

Experimental and FEM studies of the friction welding process of spheroidal graphite cast iron (SGCI) are presented. A coupled thermal and mechanical 2.5 D FEM model was used to simulate the continuous drive friction welding (CDFW) process. The FE model predicted the peak temperature of the joint, effective stress, axial shortening, and the weld flash size. Additionally, the friction force on the axial shortening of specimens was studied. The peak temperatures were measured both on the axis and at the surface of the specimen. The predicted maximum temperatures in the axis, ½ radius, and 2 mm from the surface of the sample amounted to 1162 °C, 1177 °C, and 1061 °C, respectively. The maximum temperature of the spheroidal graphite cast iron joint was below the melting temperature of the base material (~1350 °C). The predicted temperature curves, outbursts, and shortening of welded elements indicated a good match with real models.

Influence of Inoculation on the Mass Effect in Heavy Section Ferritic Spheroidal Graphite Cast Iron

Influence of Inoculation on the Mass Effect in Heavy Section Ferritic Spheroidal Graphite Cast Iron

The mechanism of intermediate temperature embrittlement of cast irons by magnesium

Metallic alloys such as steels and nickel-based alloys are potentially vulnerable to high-temperature brittleness in the range of 500 °C to 1000 °C that results in a loss of ductility. Ferritic spheroidal graphite cast irons show similar loss of ductility at temperatures between 350 °C and 500 °C, suggesting the term intermediate temperature brittleness. Previous works have shown that sulfur and magnesium are detrimental while phosphorus added at a reasonable level is beneficial in preventing loss of ductility in ferritic spheroidal graphite castings.In order to clarify the role of magnesium, a ferritic spheroidal graphite cast iron with high silicon content and low sulfur and phosphorus contents was subjected to tensile tests between room temperature and 650 °C. It was found to be susceptible to embrittlement at intermediate temperatures around 400 °C. MgO precipitates were observed on the fracture surface, which increased in size with test temperature, confirming the role of the environment that was reported by previous researchers. This finding is cross-checked with the results of the literature and allows us to propose a scheme for intermediate temperature embrittlement of ferritic spheroidal graphite iron.

ISO1083/JS/400-15

Abstract ISO1083/JS/400-15 is a ferritic spheroidal graphite cast iron that has a minimum tensile strength of 400 MPa (58 ksi) and a minimum elongation of 15%, when measured on test pieces machined from separately cast samples. It has a tensile strength exceeding that of the highest-tensile-strength grade of gray cast iron, together with much higher elongation and impact resistance. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and shear strength as well as fatigue. It also includes information on casting and heat treating. Filing Code: CI-105. Producer or source: International Organization for Standardization.

ISO1083/JS/400-18-LT

Abstract ISO1083/JS/400-18-LT is a ferritic spheroidal graphite cast iron that has a minimum tensile strength of 400 MPa (58 ksi) and a minimum elongation of 18%, when measured on test pieces machined from separately cast samples. It has a tensile strength exceeding that of the highest-tensile-strength grade of gray cast iron, together with much higher elongation and impact resistance. It is specifically designed to provide good impact properties at low temperature. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and shear strength as well as fatigue. It also includes information on casting and heat treating. Filing Code: CI-104. Producer or source: International Organization for Standardization.

ISO1083/JS/350-22-RT

Abstract ISO1083/JS/350-22-RT is a ferritic spheroidal graphite cast iron that has a minimum tensile strength of 350 MPa (51 ksi) and a minimum elongation of 22%, when measured on test pieces machined from separately cast samples. It is specifically designed for applications where tensile strength is less important than impact and elongation properties. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and shear strength as well as fatigue. It also includes information on casting and heat treating. Filing Code: CI-103. Producer or source: International Organization for Standardization.

ACO EUROBAR EN-GJS-350-22C (5.3122)

Abstract ACO Eurobar EN-GJS-350-22C is a ferritic spheroidal graphite cast iron that is produced by the continuous casting process. It has a minimum tensile strength of 350 MPa (51 ksi) and a minimum elongation of 22%. It is specifically designed for applications where tensile strength is less important than the impact and elongation properties. This datasheet provides information on composition, physical properties, microstructure, hardness, elasticity, and tensile properties. It also includes information on casting and heat treating. Filing Code: CI-102. Producer or source: ACO Eurobar GmbH.

ACO EUROBAR EN-GJS-350-22C-LT (5.3120)

Abstract ACO Eurobar EN-GJS-350-22C-LT is a ferritic spheroidal graphite cast iron that is produced by the continuous casting process. It has a minimum tensile strength of 350 MPa (51 ksi) and a minimum elongation of 22%, and it is specifically designed to provide good impact properties at low temperature. This datasheet provides information on composition, physical properties, microstructure, hardness, and tensile properties. It also includes information on heat treating. Filing Code: CI-101. Producer or source: ACO Eurobar GmbH.

Relation between microstructural heterogeneities and damage mechanisms of a ferritic spheroidal graphite cast iron during tensile loading

AbstractIn this work, the influence of the metallic matrix heterogeneities and the spheroidal graphite nodules distribution on both crack initiation and propagation and damage evolution during tensile loading of ferritic spheroidal graphite cast iron is examined. The experimental methodology involves specialized metallographic techniques, step by step tensile loading, microscopic observation by using optical and scanning electron microscopy and three‐dimensional (3D) reconstruction of the graphite nodules distribution.The results show that the graphite nodules are the major heterogeneities responsible for inducing the development of cracks in the metallic matrix. Crack initiation is preferentially located at the irregular contour of graphite nodule cavities, ferritic grain boundaries and internodular areas highly strained. The final fracture involves cracks mainly propagating through the internodular ligaments of matrix‐nodule debonded areas belonging to the first‐to‐freeze zones resulting from the solidification process.

Impact Characteristics and Fracture Toughness of Ferritic Spheroidal Graphite Cast Iron

Impact Characteristics and Fracture Toughness of Ferritic Spheroidal Graphite Cast Iron

Coarsening and dendritic instability of spheroidal graphite in high silicon cast iron under thermal cycling in the ferritic domain

High silicon ferritic spheroidal graphite cast irons have been developed for high temperature service, in particular under thermal cycling conditions. The theoretical maximum service temperature is defined as the upper limit of the two-phase ferrite+graphite domain, which increases with the alloy silicon content. While isothermal heat treatment close to this temperature showed little evolution of the graphite distribution, thermal cycling led to a significant coarsening of the graphite particles associated with dendritic overgrowth of the large graphite particles. This unexpected behaviour is here observed and described for the first time.

Chunky Graphite in Ferritic Spheroidal Graphite Cast Iron: Formation, Prevention, Characterization, Impact on Properties: An Overview

Ferritic spheroidal graphite cast iron (SGI) materials have a remarkable technical potential and economic impact in modern industry. These features are closely related to the question of how the cast materials can be produced without structural defects and graphite degenerations such as, for example, chunky graphite. Although the chunky graphite degeneration superficially seems to be well known, its metallurgical background is still controversially discussed, appropriate field-tested nondestructive tools for its quantification in castings are lacking, and the knowledge on its impact on material properties is fairly limited. Addressing this status, the article is providing a current overview on the subject. Existing theories on formation and growth mechanisms of chunky graphite are briefly reviewed. Furthermore, from a metallurgical point of view, causes for the appearance of chunky graphite as well as preventive measures are concisely summarized. Particular attention is paid to the morphology of chunky graphite and how it can be characterized by destructive and nondestructive techniques. Special emphasis was laid on providing a comprehensive overview on the impact of chunky graphite on strength, ductility, fatigue limit, fatigue crack growth rate as well as fracture toughness of ferritic SGI materials based on experimental data. Moreover, conclusions for the assessment of castings affected by chunky graphite are drawn.

Problems and Improvements on the Production of Large Casting with Hi–Si Ductile Iron

We have studied the problems and improvement on producing large casting with solid solution strengthened ferritic spheroidal graphite cast irons (hereafter Hi–Si). As the matrix of Hi–Si material becomes hardened with silico-ferrite, hardness, tensile strength and yield strength increase. But elongation and impact value decrease conversely. If silicon content increases or if the cooling rate decreases due to heavy section, as silicon segregation progresses, the elongation and impact value are remarkably reduced. When increasing the graphite nodule count with optimum inoculation and setting chiller, the segregation of silicon decreases and then the mechanical properties are recovered. In addition, when Hi–Si reaches around 400 °C, its elongation decreases largely, which is called 400 °C embrittlement. This high-temperature embrittlement can be prevented with setting the ratio of Mg/P less than 1.5 and reducing the free Mg, because the grain boundary fracture occurs due to the free Mg not fixed as Mg3P2 at the grain boundary.

Study of the fracture of ferritic ductile cast iron under different loading conditions

AbstractThis work is a continuation of the studies presented in a recent paper by the authors, where the fracture surfaces of pearlitic ductile cast iron under different loading conditions were exhaustively analysed. In this study, fracture surfaces of ferritic ductile cast iron (or ferritic spheroidal graphite cast iron) generated under impact, bending and fatigue loading conditions were characterised and compared. The fracture surfaces were characterised qualitatively and quantitatively from the observation under a scanning electron microscope. The fracture mechanisms in each case were identified. For impact tests, as test temperature increases, the dominant fracture mechanism changes from brittle to ductile. For bending tests, a fully ductile fracture micromechanism dominates the surface. In fatigue tests, the surface shows a mix of flat facets that appear to be cleavage facets and ductile striations, but the typical fatigue striations are not easily found on the fracture surface. Methodologies for the determination of the macroscopic direction of main crack propagation in both ductile and brittle failure modes are proposed. These allow identifying main crack propagation direction with good approximation.The results are potentially useful to identify the nature of loading conditions in a fractured specimen of ferritic spheroidal graphite cast iron. The authors believe that it is necessary to extend the methodologies proposed in samples with different geometry and size, before they can be used to provide additional information to the classical fractographic analysis.

Influence of silicon and addition elements on the mechanical behavior of ferritic ductile cast iron

An experimental study of mechanical properties and microstructural analysis was carried out on different compositions of ferritic spheroidal graphite cast iron. The influence of silicon on the ductility and strength of the material was noticed. The observation of microstructure and failure modes allowed us to explain the important role of chemical composition on the initiation and propagation of cracks. The high silicon segregation between the graphite nodules and the joints of eutectic cells decreases the mechanical material resistance. A metallurgical development was indispensable and necessary to ensure characteristics conformed to the industrial requirements.

Effect of Mean Stress on Fatigue Strength of Spheroidal Graphite Cast Iron

Mechanical properties, especially fatigue strength, of ferritic spheroidal graphite cast iron might depend not only on the graphite size but also on the ferrite grain size, little systematic research has been made on these factors. To clarify the influences of these structural factors as well as loading condition, fatigue tests have been carried out on ferritic spheroidal graphite cast iron with different sizes of graphite nodules and ferrite grains, under the axial loading with mean stress from -70MPa to 240MPa. The results obtained in this study are summarized as follows: (1) The fatigue limits are decreased with increasing graphite nodule and matrix grain sizes. (2) The fatigue limit decreases with increasing tensile mean stress. The fatigue limit at an arbitrary mean stress has been estimated by the modified Goodman diagram as well. (3) The parameter α is evaluated from the experimental results relating to the stress ratio R, for the mean stress acting on the tensile side and on the compressive side separately. For the case of R0, the value of α is 0.324. The result has been applied to the fatigue limit evaluation equation of Y.Murakami et al, the fatigue limit ratio falls within the range of about ±10%.

Effect of Ferrite Grain and Graphite Nodule Size on Fatigue Strength of Ferritic Spheroidal Graphite Cast Iron

To clarify the effect of graphite nodule size and ferritic gain size on fatigue strength of ferritic spheroidal graphite cast iron, tensile tests and fatigue tests were carried out. Six types of test specimens were constructed with different gain sizes from the speroidal graphite cast iron blocks. Two block sizes were considered as 32mm and 80mm in thickness. The ferritic spheroidal graphite cast iron was constructed by three types of ferritization heat treatment of the speroidal graphite cast iron. The ferrite grain refinement improved both tensile and proof strengths. The initiation-site of fatigue fracture was different based on the graphite nodule size. The fatigue cracks of large graphite nodule iron initiated from abnormal graphite, that is, closely adjoining graphite nodules or coarse graphite. On the other hand, the fatigue cracks of small graphite nodule iron initiated from small shrinkage cavity. The fatigue strength with large graphite nodules was improved, while the fatigue strength of small graphite nodule was unchanged by the ferrite gain refinement. It was also noted that the fatigue strength of spheroidal graphite cast iron with different ferritic grain size was determined by the maximum length of the non-propagating micro-crack.

Thermocracks®, a Specific Testing Machine for Evaluation of the Thermal Fatigue Resistance of Materials

Cracking by thermal fatigue is one of the major problems encountered during the operation of numerous parts such as exhaust manifolds or brake discs. One way to improve their lifespan is to develop new materials solutions. Estimating thermo-mechanical fatigue resistance of new materials can be performed with a specific test machine developed by CTIF, associating a multi-position wheel, an induction heating and a cooling by air blowing. Test consists in measuring the number of thermal cycles corresponding to the first crack appearance and to the complete failure of a specific versatile sample.Two examples of studies performed with this machine are shown hereafter.First tests were performed to compare the thermo-mechanical fatigue resistance of different grades of ferritic spheroidal graphite cast iron. These materials are an interesting alternative to alloyed steels or nickel-alloyed cast irons, for the constitution of exhaust manifolds and turbine housings working in the upper-middle temperatures (up to 950°C). The compared materials are SG irons alloyed with silicon (with or without molybdenum), and aluminium.Truck brakes dissipate several megajoules of energy every few seconds, which leads to high thermal stresses in the rubbing discs. Therefore, truck brake discs are mainly damaged by thermal fatigue cracking. One improvement way is to evolve disc material with the aim of increasing their thermal fatigue resistance while keeping the braking performance. For the thermal fatigue tests being as close as possible to real brake conditions, a specific geometry of sample and inductor was developed, to reproduce the thermal gradients observed during tests on real brake discs. The test parameters were then chosen after a coupled numerical-experimental study on full-scale braking. Behaviour of different materials under cycling loading (microstructural changes and cracking) is compared with regard to the results obtained during braking tests.

Surface Hardening of Ferritic Spheroidal Graphite Cast Iron by Friction Stir Processing

A ferrite-based spheroidal graphite cast iron (FCD450) is difficult to harden using a conventional surface hardening method, because the carbon content in the matrix is very low. In order to solve this problem, the friction stir processing (FSP) was used in this study as a new hardening method for cast irons. The authors have clarified in a previous study that the pearlite-based cast iron, such as FC300 and FCD700, can be hardened using the friction stir processing and that there are several advantages, such as a higher hardness and no required post surface machining. In this study, it was clarified that a Vickers hardness of about 700HV is obtained due to the formation of fine martensite even in the ferrite-based spheroidal graphite cast irons, although the optimal process range is much narrower than that of the pearlite-based cast iron due to the requirement of both the heat input for diffusion of the carbon into the matrix and the high cooling rate for the martensitic transformation.

Microstructural Features and Erosion Wear Resistance of Friction Stir Surface Hardened Spheroidal Graphite Cast Iron

A ferritic spheroidal graphite cast iron (also named as SG cast iron, ductile cast iron, ductile iron) was treated with friction stir process (FSP) to harden the surface layer owing to a unique microstructure into which the ferritic structure transforms after high temperature deformation and subsequent direct cooling. When the friction stirred surface experiences thermomechanical cycle during FSP (here named friction stir surface hardening, FSSH), a non-traditional bainite structure can be obtained through subsequent cooling process. The bainite structure primarily consists of iron carbide (Fe3C), acicular ferrite and martensite with retained austenite aggregates. It is evident that the FSSH structure caused by deformation at austenite temperature has resulted in a significant increase in the microhardness of about 1000HVyielding a primarily martensitic accompanying bainitic phase transformation. The experimental results also show that the process has resulted in significant improvement in erosion resistance at low angle impingement than that of ferritic specimens. In addition, the maximum erosion rate of ferritic specimens occurs at 20­25°of impact while the peak of the FSSH specimen shifts to higher angle resulting from the formation of continuously cooled martensitic and bainitic structure. [doi:10.2320/matertrans.M2011224]