This paper gives a brief introduction to the four research methods for the study on thermal conductivity of cast irons, including experimental measurement, statistical analysis, effective medium ...theory and numerical simulation. Recent studies on the thermal conductivity of various cast irons are reviewed through the influence of alloying elements, structural constituents, and temperature. The addition of alloying elements is the main reason that restricts the thermal conductivity of cast irons, especially spheroidal graphite cast iron. The connectivity of graphite has a significant effect on the thermal conductivity of flake and compacted graphite cast irons, semiquantitative and quantitative analysis of this factor is a key and difficult point in the study of thermal conductivity of cast irons. The thermal conductivities of different types of cast irons show varying degrees of dependence on temperature. This phenomenon is the combination of graphite and matrix, rather than just depending on graphite morphology. The study of the relationship between individual phase and temperature is the focus of future research. These summaries and discussions may provide reference and guidance for the future research and development of high thermal conductivity cast irons.
A hypereutectic high chromium cast iron (HCCI) is featured with high abrasion resistance and hardness, making it one of the most widely used materials in mining, minerals and cementation industries. ...However, the alloy is also naturally brittle partially due to the coarse needle-shaped primary M.sub.7C.sub.3 carbides. The present work challenges one of the long-term issues associated with HCCIs to modify the primary carbide through addition of a newly discovered additive, TiB.sub.2. Addition of 300 ppm such particles led to a significant decrease in the fraction of needle-shaped primary carbides by 35% and reduction in average size of the carbide by 32% in length for the needle-shaped carbide and by 32% in diameter for the equiaxed carbide. As a result, the transverse rupture strength (TRS) of the alloy after heat treatment was increased by 37% together with no noticeable loss in wear or hardness. Although excess TiB.sub.2 addition up to 8000 ppm continued reducing the amount of needle-shaped carbide, the improvement in TRS was annulled by the embrittlement of TiB.sub.2. Detailed microstructural examination showed that upon addition, TiB.sub.2 decomposed in the melt, leading to the formation of TiN particles with fresh surfaces, which acted as M.sub.7C.sub.3 carbide refiner through promotion of the heterogenous nucleation of the carbide.
Cast iron is widely used in engineering production and in the surface alloying of workpieces, which is exploited to improve the properties of the material. Research on cast iron is still valid and ...needed for the manufacturing processes throughout the product life cycle. In this study, the gray, cast iron GJL 200 laser processing is described based on surface alloying with WC and SiC particulates. SEM analysis and XRD analysis, as well as microhardness testing and tribological behavior studies, were employed. It was revealed that laser alloying with carbide particulates affects structural, mechanical, and operational properties compared to cast iron in its initial state. Most importantly, the right choice of laser processing conditions can increase the wear resistance of the cast iron base. The wear resistance after WC alloying was 4–24 times higher compared to the initial material, while after SiC alloying, it was 2–18 times lower than that of the initial material.
In this article, the influence of plasma nitriding on the fatigue behavior and fracture mechanisms of the GJS700 nodular cast iron has been investigated. Factors contributing to this influence, which ...included the microstructure, the phase detection, the surface roughness, and the hardness of the plasma‐nitrided specimens were discussed. Moreover, rotating‐bending high‐cycle fatigue testing was also done on standard samples, and then the field‐emission scanning electron microscopy was also utilized to find the failure mechanism on fracture surfaces. Obtained results demonstrated that the average surface roughness and the Vickers micro‐hardness increased by plasma nitriding, compared to the base material. However, fatigue lifetimes decreased in plasma‐nitrided samples due to the increase in the surface roughness and the formation of a compound layer. On the fracture surface, micro‐cracks, cleavage planes, and fatigue striations were observed. Debonding of the graphite from the matrix in all specimens was a dominant cause of the failure.
In this study, the potential of Fesub.3Al coating material as an environmentally friendly alternative to coatings containing critical elements for brake discs was investigated. A buffer layer of ...Cr–Mo steel (Ferro 55) that was about 500 µm thick was applied on a gray cast iron disc to enhance the coating quality and prevent the formation of hot cracks during solidification. The microstructural analysis of the cross-section of the coating showed that the buffer layer diffused into the Fesub.3Al coating, forming a combination of Fesub.3Al, Fe, and Fesub.3AlCsub.0.5 phases. The tribological properties of the Fesub.3Al-coated disc were evaluated using pin-on-disc tests against two different copper-free friction materials extracted from commercial brake pads. The wear results show a coefficient of friction comparable to that of an uncoated disc (≈0.55), but with a reduction in particulate matter (PM) emissions, which decreased from 600 to 476 #/cmsup.3. The last issue is an interesting aspect that is gaining increasing importance in view of the upcoming international standards.
•Fatigue crack growth of spheroidal and compacted graphite cast irons are studied.•Graphite of cast irons are observed with the help of X-ray microtomography.•The crack propagation rate is larger in ...compacted graphite cast iron than in spheroidal graphite cast iron.•Graphite fracture is the main mode of fatigue crack propagation for the compacted graphite cast iron.
The present paper focuses on the fatigue life of a Compacted Graphite cast Iron (CGI) as compared to a Spheroidal Graphite cast Iron (SGI). Fatigue crack growth laws have been determined with digital image correlation. Main difference between the materials is that cracks propagate faster in the CGI than in the SGI. X-ray tomography was also used in order to assess graphite morphologies and crack shapes. A complex morphology was observed for the vermicular graphite with rounded edges that limit notch effects. The crack spreads easily in CGI via a quasi cleavage mechanism and by propagating through graphite mainly by breaking the vermicules.
Effect of nanocrystalline surface obtained by severe plastic deformation on fatigue strength of nodular cast iron has been studied in the paper. Surface nanocrystallization has been applied by means ...of standard air blast shot peening equipment with particularly severe parameters compared to the usual ones used for similar classes of material. Microscopy observation, microhardness, surface roughness and X-ray diffraction measurements were carried out to characterize the treated surface of differently shot peened specimens. Rotating bending fatigue tests were performed to investigate the effects of process parameters on fatigue behaviour. The results indicate a sensible fatigue strength improvement obtained through application of severe shot peening with respect to conventional shot peening, notwithstanding the specimen’s very high surface roughness due to high energy impacts. The obtained results are critically discussed.
The paper reviews original data obtained by the authors, from recent separate publications, specifically concerning graphite formation in the solidification pattern of industrial cast irons, ...focussing on grey iron versus ductile iron. Additional unpublished data and selected data from literature are represented in the paper. Complex compounds act as nucleation sites in commercial cast irons, generally in a three-stage graphite formation, but with different sequences: (1) first micro-compound formation is oxide/silicate in grey iron and sulphide in ductile iron; (2) the second compound nucleates on the first one, as complex manganese sulphide in grey iron and complex silicates in ductile iron; (3) graphite nucleation on the sides of stage 2 compounds, which have low crystallographic misfit with graphite. Resulphurization (Mn/S control), preconditioning with strong oxide forming elements (Al, Zr), more potent inoculants and inoculation enhancement with S, O and oxy-sulphide forming elements were found to be beneficial treatments especially in critical solidification conditions
The ductile irons of EN-GJS-400–15 grade were alloyed with various amounts of Al from 0 to 4 wt% by induction furnace melting. After fabrication, the Al-alloyed cast irons were characterized by XRD, ...SEM, EDS, optical microscope equipped with image analysis software, mechanical tests including hardness, tensile and Charpy V-notch tests, and dry sliding ball-on-disc type wear tests against Al2O3 ball. It was determined that the amount of ferrite phase and nodule counts increased and nodularity decreased with increasing Al content until it reached 4 wt%, which caused a huge pearlite formation with an improved nodularity and reduced graphite size. An increase in the amount of Al provided the increase in the ultimate tensile strength, yield strength, and hardness while it caused the decrease in elongation and impact strength as expected. Worn surface examinations demonstrated that the samples were suffered from abrasive and adhesive wear during sliding tests. The best wear resistance was achieved by the 4 wt% Al-alloyed nodular cast iron, given microstructural and mechanical properties.
•Carbide-free ductile cast irons alloyed with 0-4 wt.% Al were manufactured by induction furnace melting.•Alloying with Al up to 3% acted as ferrite stabilizer while 4% Al increased pearlite ratio by preventing C diffusion.•Nodule counts increased and nodularity decreased with increasing Al because of its strong graphitization effect.•Worn surfaces suffer from abrasion, adhesion, and delamination during sliding tests. Al addition reduced the wear failures.•4% Al-alloyed cast iron achieved the best wear resistance due to higher pearlite ratio and Al2O3 formation around graphite.
•A successful laser cladding of Ni-based alloy on gray cast iron was achieved.•The impact of laser parameters and microstructure on crack formation was studied.•An empirical relation for dilution ...ratio versus energy density was proposed.
This study aimed to investigate the influence of process parameters on crack formation in laser alloying or cladding of grey cast iron. For this purpose, the effects of laser power and feeding rate of Ni-based alloying powders were examined. The microstructure and hardness of the coating and the interface of the coating with cast iron (bonding zone) were studied. The results showed that the dilution ratio is crucial in crack formation, explaining the challenges in achieving a defect-free laser alloying coating on cast iron. The higher dilution ratio of laser alloying resulted in higher dissolved carbon and bigger (Nb, Ti)C carbides formation than in laser cladding coatings. In this study, cracks appeared in the coating due to the combination of the high amount of carbide in the layer and a sharp hardness gradient at the interface with the cast iron substrate. An empirical relation was proposed for dilution ratio as a function of specific energy density, which combined the most critical process parameters on crack formation.
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