Mechanical behaviour of graphite in fracture of austempered ductile iron

Dai, Pinqiang; He, Z. R.; Wu, Weikai; Mao, Zhengdong

doi:10.1179/026708302225004874

Cited by 8 publications

(4 citation statements)

References 11 publications

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“…(However, it should be noted that the COMSOL Multiphysics program does not simulate the mechanical damage in galvanic corrosion.) The crystal structure of graphite is covalent bonded with neighboring atoms in the same layer, although layers are van der Waals bonded together [24,25] and thus the bonding force of graphite is very weak. Therefore, it is considered that the matrix is corroded galvanically and that the graphite is protruded and then graphite is peeled off layer by layer because of the weak bonding force of graphite.…”

Section: Corrosion Inhibition Mechanism Of Carbon Steel Andmentioning

confidence: 99%

Corrosion Inhibiting Mechanism of Nitrite Ion on the Passivation of Carbon Steel and Ductile Cast Iron for Nuclear Power Plants

Kim

Chang

et al. 2015

Advances in Materials Science and Engineering

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While NaNO2addition can greatly inhibit the corrosion of carbon steel and ductile cast iron, in order to improve the similar corrosion resistance,ca.100 times more NaNO2addition is needed for ductile cast iron compared to carbon steel. A corrosion and inhibition mechanism is proposed wherebyNO2-ion is added to oxidize. TheNO2-ion can be reduced to nitrogen compounds and these compounds may be absorbed on the surface of graphite. Therefore, since nitrite ion needs to oxidize the surface of matrix and needs to passivate the galvanic corroded area and since it is absorbed on the surface of graphite, a greater amount of corrosion inhibitor needs to be added to ductile cast iron compared to carbon steel. The passive film of carbon steel and ductile cast iron, formed by NaNO2addition showed N-type semiconductive properties and its resistance, is increased; the passive current density is thus decreased and the corrosion rate is then lowered. In addition, the film is mainly composed of iron oxide due to the oxidation byNO2-ion; however, regardless of the alloys, nitrogen compounds (not nitrite) were detected at the outermost surface but were not incorporated in the inner oxide.

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Section: Corrosion Inhibition Mechanism Of Carbon Steel Andmentioning

confidence: 99%

Corrosion Inhibiting Mechanism of Nitrite Ion on the Passivation of Carbon Steel and Ductile Cast Iron for Nuclear Power Plants

Kim

Chang

et al. 2015

Advances in Materials Science and Engineering

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“…High density of microvoids near the fracture surface is generally associated with high true strain in this region. During tensile testing, failure of ADI has been attributed to void formation, which has been observed primarily within the necked region at high local strain ( Ref 4,24,[28][29][30][31][32][33][34][35].…”

Section: Matrix Deformation and Microvoid Formationmentioning

confidence: 99%

The Nature of the Tensile Fracture in Austempered Ductile Iron with Dual Matrix Microstructure

Kılıçlı

Erdoğan

2009

J. of Materi Eng and Perform

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The tensile fracture characteristics of austempered ductile irons with dual matrix structures and different ausferrite volume fractions have been studied for an unalloyed ductile cast iron containing (in wt.%) 3.50 C, 2.63 Si, 0.318 Mn, and 0.047 Mg. Specimens were intercritically austenitized (partially austenitized) in two phase region (a + c) at various temperatures for 20 min and then quenched into a salt bath held at austempering temperature of 365°C for various times and then air cooled to room temperature to obtain various ausferrite volume fractions. Conventionally austempered specimens with fully ausferritic matrix and unalloyed as-cast specimens having fully ferritic structures were also tested for comparison. In dual matrix structures, results showed that the volume fraction of proeutectoid ferrite, new (epitaxial) ferrite, and ausferrite [bainitic ferrite + high-carbon austenite (stabilized or transformed austenite)] can be controlled to influence the strength and ductility. Generally, microvoids nucleation is initiated at the interface between the graphite nodules and the surrounding ferritic structure and at the grain boundary junctions in the fully ferritic microstructure. Debonding of the graphite nodules from the surrounding matrix structure was evident. The continuity of the ausferritic structure along the intercellular boundaries plays an important role in determining the fracture behavior of austempered ductile iron with different ausferrite volume fractions. The different fracture mechanisms correspond to the different levels of ausferrite volume fractions. With increasing continuity of the ausferritic structure, fracture pattern changed from ductile to moderate ductile nature. On the other hand, in the conventionally austempered samples with a fully ausferritic structure, the fracture mode was a mixture of quasi-cleavage and a dimple pattern. Microvoid coalescence was the dominant form of fracture in all structures.

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“…This anisotropy is related to graphite's layered structure with strong covalent bonds within the basal planes and weak van der Waals bonds between them, which makes graphite a transversely isotropic material (Figure 1.c) [2,5,[45][46][47][48][49]. This anisotropy is related to graphite's layered structure with strong covalent bonds within the basal planes and weak van der Waals bonds between them, which makes graphite a transversely isotropic material (Figure 1.c) [2,5,[45][46][47][48][49].…”

Section: Graphitementioning

confidence: 99%

Microstructural model for the time‐dependent thermomechanical analysis of cast irons

et al. 2015

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In this paper, a multiscale modelling approach is followed for the modelling of time and temperature dependent behaviour of compacted graphite cast iron (CGI) material. Cast irons are often used in heavy duty machinery parts subjected to elevated temperatures for prolonged periods of time. This, in combination with its complex heterogeneous microstructure, plays the crucial role in determining the life time of the material. In this work a 2D microstructural model of CGI is developed. The geometry is based on the micrographs of the material. The pearlitic matrix is modelled with the temperature dependent elasto‐visco‐plastic model calibrated on the pearlitic steel experiments. The graphite particles are modelled as anisotropic elastic. The results of the simulations of tensile and stress relaxation tests at different temperatures between 20 °C and 500 °C show that the macroscopic mechanical behaviour of the ma‐terial deteriorates rapidly above 350 °C. At the microstructural scale, the anisotropic graphite particles act as stress concentrators promoting the formation of strain percolation paths, that become more critical at higher temperatures. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Mechanical behaviour of graphite in fracture of austempered ductile iron

Cited by 8 publications

References 11 publications

Corrosion Inhibiting Mechanism of Nitrite Ion on the Passivation of Carbon Steel and Ductile Cast Iron for Nuclear Power Plants

Corrosion Inhibiting Mechanism of Nitrite Ion on the Passivation of Carbon Steel and Ductile Cast Iron for Nuclear Power Plants

The Nature of the Tensile Fracture in Austempered Ductile Iron with Dual Matrix Microstructure

Microstructural model for the time‐dependent thermomechanical analysis of cast irons

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