Bending overload and thermal fatigue fractures in a cast exhaust manifold

Güiza, G.M. Castro; Hormaza, W.; Moreno, Luis Miguel Méndez

doi:10.1016/j.engfailanal.2017.08.016

Cited by 18 publications

(8 citation statements)

References 9 publications

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“…Exhaust manifolds deliver hot and oxidative exhaust gases from the combustion chamber to the atmosphere [1,2]. Initial exhaust manifolds were manufactured using unalloyed high carbon grey cast irons that could be used at operating temperatures up to 540 °C [3].…”

Section: Introductionmentioning

confidence: 99%

Matrix design of a novel ductile cast iron modified by W and Al: A comparison between thermodynamic modeling and experimental data

et al. 2020

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In high-temperature applications of ferrous materials, as in the case of exhaust manifolds, high thermal and mechanical stability are required. Stainless steels and Ni-resist alloys having austenitic matrices are good candidates to meet these requirements at elevated temperatures; however, they are expensive materials and present difficulties in casting. Ferritic ductile cast irons, like the commercial SiMo alloy, are comparatively cheaper materials with better castability but they cannot be used above approximately 800 °C. Thus, to meet the requirements with low-cost materials having improved high-temperature properties, new alloys must be developed by ferrite forming elements having the potential to increase equilibrium temperature. In this study, initially, a novel ductile cast iron matrix was designed using 1 W and 0-4 Al wt.-% and their phases stable at room temperature, transformation temperatures, solidification sequences and thermal expansivity values were determined using thermodynamic calculations with Thermo-Calc software. Computational studies revealed that (i) designed alloy matrices had graphite and M6C type carbides embedded in a ferritic matrix at room temperature as expected, (ii) A1 temperature increased as aluminum content increased. The obtained values were all above that of commercial SiMo alloy, (iii) the detrimental effect of increased aluminum addition on graphite content, and thermal expansivity was observed. Secondly, microstructural and thermal characterizations of cast alloys were performed for validation – the obtained data were in good agreement with the thermodynamic calculations.

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Section: Introductionmentioning

confidence: 99%

Matrix design of a novel ductile cast iron modified by W and Al: A comparison between thermodynamic modeling and experimental data

et al. 2020

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“…Such segregation promotes embrittlement of the ferrite and crack initiation at graphite boundary during thermal cycling. 24,25 The thermodynamic simulation of ductile iron with 3% C and 4.5% Si (shown by solid black line in Figure 1) suggests that initially formed austenite around graphite nodules (low FCC fraction in Figure 1) had elevated Si levels when compared to the last fraction of solidified austenite at eutectic cell boundary. The calculated degree of the Si segregation depends on assumptions used in the applied thermodynamic models.…”

Section: Simulation and Experimental Procedures Alloy Simulation And ...mentioning

confidence: 99%

Control of High-Temperature Static and Transient Thermomechanical Behavior of SiMo Ductile Iron by Al Alloying

et al. 2022

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Silicon and molybdenum (SiMo) ductile iron is commonly used for exhaust manifolds because these components experience thermal cycling in oxidizing environment, which requires resistance to fatigue during transient thermomechanical loads. Previous studies have demonstrated that alloying elements, such as Al, to SiMo ductile iron reduces the amount of surface degradation during static high-temperature exposure. However, deterioration of sphericity of the graphite nodules and a decrease in ductility could affect the tendency of cracking during thermal cycling. In this article, the effect of Al alloying on static and transient thermomechanical behavior of SiMo ductile iron was investigated to optimize the amount of Al alloying. A thermodynamic approach was used to confirm the effect of the Al alloying on the phase transformations in two SiMo cast irons, alloyed by 1.8% Al and 3% Al. These two alloys were cast in a laboratory along with the baseline SiMo ductile iron. Several experimental methods were used to evaluate the dimensional stability, physical properties, static oxidation, and failure resistance during constrained thermal cycling testing to compare their high-temperature capability. Experimental results verified that Al alloying increases the temperature range and decreases volume change during eutectoid transformation, which together with enhancement of oxidation protection improved the dimensional stability. Thermocycling tests showed that the number of cycles to failure depends on the amount of Al alloying and the applied high-temperature exposure during each cycle. SEM/EDX, high-resolution TEM and µCT analysis were used to verify the mechanism resulting from the Al alloying protection. It was shown that an optimal level of Al alloying for balancing oxidation and thermal cracking resistance depends on thermomechanical conditions of application.

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“…The material shows hardening properties without an obvious elastic loading regime and is often classified based on the minimum guaranteed tensile strength (Figure 2) (ASTM, 2016, BSI, 2011. It is common for grey cast iron to be assessed in a linear elastic manner, possibly due to its limited capability in strain (Wang et al, 2000, Castro Güiza et al, 2017. There are a number of extensive assets (large in terms of size, inventory, or both) that are formed of grey cast iron components, and which are still in operation today.…”

Section: Grey Cast Iron As a Structural Materialsmentioning

confidence: 99%

Finite element analysis on grey cast iron assets: a case study on penstocks in the wastewater system

Khor

Farrow

Mulheron

et al. 2022

Infrastructure Asset Management

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Penstocks have been used in the water industry for flow control since the Victorian expansion and consolidation of clean and waste water networks. However, the Victorians were the first to use grey cast iron (GCI) castings to manufacture large scale penstocks. Most of these ageing assets are still in operation, however engineering assessments are necessary to determine a structure’s fitness-for-service. Even today, penstocks in the sewer system tend to be made from GCI, due to ease of manufacturing, resistance to corrosion and cost. One characteristic property of grey cast iron is the graphite flake structure in the material, contributing to its low toughness, inconsistency in material strength and brittle behaviour, despite exhibiting slight hardening properties. Finite element analysis (FEA), is a numerical method which allows the analysis of complex structures by splitting it into finite parts and solving them with a computer processor. Despite the versatility of FEA, appropriate considerations and assumptions are necessary due to the difficulty to obtain data from inspection and unique material behaviour of GCI. The article shows concerns for an analysis of GCI penstocks using FEA, which extends into the application of fracture mechanics approaches for defect assessments.

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Bending overload and thermal fatigue fractures in a cast exhaust manifold

Cited by 18 publications

References 9 publications

Matrix design of a novel ductile cast iron modified by W and Al: A comparison between thermodynamic modeling and experimental data

Matrix design of a novel ductile cast iron modified by W and Al: A comparison between thermodynamic modeling and experimental data

Control of High-Temperature Static and Transient Thermomechanical Behavior of SiMo Ductile Iron by Al Alloying

Finite element analysis on grey cast iron assets: a case study on penstocks in the wastewater system

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