Micro-CT Quantitative Evaluation of Graphite Nodules in SGI

Lekakh, Semen Naumovich; Zhang, Xueliang; Tucker, W.A.; Lee, Hyoung-Koo; Selly, Tara; Schiffbauer, James D.

doi:10.1007/s40962-019-00354-9

Cited by 8 publications

(7 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These two variables are responsible for delineating the final microstructure and controlling the quality of the produced SG irons. 5,[9][10][11][12] Gue et al 4 demonstrated that the graphite morphology as well as microstructure constituents influence the mechanical properties such as hardness, strength and elongation of the SG irons. Pedersen et al 13 and Sosa et al 14 established that high nodule count in the matrix is required at high cooling rate conditions to prevent carbides formation in the final microstructure.…”

Section: Introductionmentioning

confidence: 99%

Ultrafine Ductile and Austempered Ductile Irons by Solidification in Ultrasonic Field

Ahmed

Riedel

Kovalko³

et al. 2021

Inter Metalcast

View full text Add to dashboard Cite

In this research, ultrasonic melt treatment (UST) was used to produce a new ultrafine grade of spheroidal graphite cast iron (SG iron) and austempered ductile iron (ADI) alloys. Ultrasonic treatment was numerically simulated and evaluated based on acoustic wave streaming. The simulation results revealed that the streaming of the acoustic waves propagated as a stream jet in the molten SG iron along the centerline of the ultrasonic source (sonotrode) with a maximum speed of 0.7 m/s and gradually decreased to zero at the bottom of the mold. The metallographic analysis of the newly developed SG iron alloy showed an extremely ultrafine graphite structure. The graphite nodules’ diameter ranging between 6 and 9 µm with total nodule count ranging between 900 to more than 2000 nodules per mm2, this nodule count has never been mentioned in the literature for castings of the same diameter, i.e., 40 mm. In addition, fully ferritic matrix was observed in all UST SG irons. Further austempering heat treatments were performed to produce different austempered ductile iron (ADI) grades with different ausferrite morphologies. The dilatometry studies for the developed ADI alloys showed that the time required for the completion of the ausferrite formation in UST alloys was four times shorter than that required for statically solidified SG irons. SEM micrographs for the ADI alloys showed an extremely fine and short ausferrite structure together with small austenite blocks in the matrix. A dual-phase intercritically austempered ductile iron (IADI) alloy was also produced by applying partial austenitization heat treatment in the intercritical temperature range, where austenite + ferrite + graphite phases coexist. In dual-phase IADI alloy, it was established that introducing free ferrite in the matrix would provide additional refinement for the ausferrite.

show abstract

Section: Introductionmentioning

confidence: 99%

Ultrafine Ductile and Austempered Ductile Irons by Solidification in Ultrasonic Field

Ahmed

Riedel

Kovalko³

et al. 2021

Inter Metalcast

View full text Add to dashboard Cite

show abstract

“…The 1000 projections using 1004 × 1024 pixels were collected for each µCT scan (140 kV, 0.4× objective) using 1 µm pixel size. After µCT scan data were acquired, a quantitative analysis of particle dispersity and shape was done accordingly to a method described by the authors [26,27].…”

Section: Methodsmentioning

confidence: 99%

Effect of Micro-Structural Dispersity of SiMo Ductile Iron on High Temperature Performance during Static Oxidation

Lekakh

Bofah

Godlewski

et al. 2022

Metals

Self Cite

View full text Add to dashboard Cite

High silicon and molybdenum (SiMo) ductile iron is commonly used for car exhaust systems, and its micro-structural dispersity depends on intrinsic parameters, which include alloy composition and inoculation efficiency, as well as extrinsic factors, such as casting wall thickness and molding material, which define cooling rate during solidification. Micro-structural dispersity is referred to as the degree of heterogeneity of sizes of structural constituencies within the microstructure. A variation in the micro-structural dispersity could impact the high temperature performance of SiMo ductile iron during static oxidation and transient thermo-mechanical loading conditions. In this study, static high temperature tests were performed on SiMo ductile iron solidified in a casting with varying wall thicknesses from 5 mm to 100 mm. The faster solidified specimens (taken from near chilled casting surfaces) had extremely high micro-structural dispersity as compared to the thicker section samples. After thermal exposure, each of the samples were characterized using 2D sections and 3D µCT images, and the results indicated an order of magnitude difference in graphite phase dispersity. The surface degradation was quantified after static oxidation experiments were implemented at temperature intervals between 650 °C and 800 °C. Non-destructive µCT 3D analysis and SEM/EDS were performed on cross sections and used to quantify the scale topology and structure. Carbon analysis was used to decouple the scale formation and decarburization phenomena that occurred within the samples. These methods enabled the quantification of the oxidation of the SiMo cast iron with different micro-structural dispersity levels after being exposed to high temperature static oxidation. Additionally, the complex material behavior during oxidation-assisted transient thermo-mechanical loading will be presented in a separate article.

show abstract

“…In addition to the detection of cracks, X‐ray CT has proved to be an excellent tool for the fast and accurate reconstruction of the graphite morphology, 56 which is known to be strongly linked to the material mechanical properties 57 . In this context, X‐ray CT represents a fast alternative to serial sectioning combined with optical microscopy and it is particularly useful in presence of irregular particles, since a statistical analysis of the graphite shape based on 2D images is not accurate in such a case 58 . Compared with optical microscopy, a limitation of X‐ray CT is the difficulty of separating the small GPs from the porosities, due to the lack of sufficient contrast 59 .…”

Section: Mechanical Loadingmentioning

confidence: 99%

Recent trends in X‐ray‐based characterization of nodular cast iron

Andriollo

Zhang

et al. 2020

Mat Design & Process Comms

View full text Add to dashboard Cite

Through various examples, this short review presents the main X‐ray‐based techniques that are available to characterize nodular cast iron at the microstructural level. Emphasis is placed on the enormous potential offered by the recent developments in X‐ray tomography, X‐ray diffraction, and digital volume correlation, which allow collecting microstructural and micromechanical information in 4D (3D plus time) during both casting and subsequent mechanical loading. The goal is to demonstrate that for nodular cast iron, which has an inherently three‐dimensional, composite microstructure, X‐ray‐based techniques provide some significant advantages over conventional microscopy. For this reason, these techniques can be instrumental in unveiling the mechanisms controlling both the formation of the microstructure as well as its micromechanical behavior during in‐service loading, thus paving the way to the development of improved process–structure–property relations.

show abstract

Micro-CT Quantitative Evaluation of Graphite Nodules in SGI

Cited by 8 publications

References 16 publications

Ultrafine Ductile and Austempered Ductile Irons by Solidification in Ultrasonic Field

Ultrafine Ductile and Austempered Ductile Irons by Solidification in Ultrasonic Field

Effect of Micro-Structural Dispersity of SiMo Ductile Iron on High Temperature Performance during Static Oxidation

Recent trends in X‐ray‐based characterization of nodular cast iron

Contact Info

Product

Resources

About