This detrimental impact of tramp oil on emulsion performance can be a consequence of a number of factors. Such conditions require increased strength and enhanced thermal fatigue resistance with the materials used for engine production. Gray cast iron is by far the oldest and most common form of cast iron. [2] The variation of the tensile modulus of elasticity of the various grades is a reflection of the percentage of graphite in the material as such material has neither strength nor stiffness and the space occupied by graphite acts like a void, thereby creating a spongy material. On the one hand, it has been suggested that O and S in graphite impede slip and prevent curved graphite growth that is considered an essential feature of spheroidal growth. The graphite becomes cathodic to iron and a galvanic corrosion cell is formed. |  Construction Machinery 0000002616 00000 n Roy Elliott BSc, PhD, in Cast Iron Technology, 1988. Schematic representation of the growth of eutectic cells of (a) flake graphite; (b) spheroidal graphite; (c) degenerate graphite and their associated mushy zone configurations; ◼ graphite; □ austenite; liquid. The increase, from 100 GPa for grey cast iron to 150 GPa for cgi, results in diminished cylinder bore distortion as reported in [2], thus reducing oil consumption and emissions., Yi, Peng; Xu, Pengyun; Fan, Changfeng; Yang, Guanghui; Liu, Dan; Shi, Yongjun. It is named after the gray color of the fracture it forms, which is due to the presence of graphite. Elevated cutting forces measured during machining a high strength gray cast iron (1 lb = 4.448 N; 1 lb-foot = 13.8 kg-cm). In contrast, the same emulsion contaminated with 1.5% tramp oil, is seen to contain a broad range of droplet sizes which probably gives rise to a more inconsistent and non-uniform flow and delivery of lubricant to the cutting area. Our goal is to offer our customers products and services with the best possible quality, Copyright © Brechmann-Guss 2020 | All Rights Reserved |. The flake-like shape of graphite in gray iron exerts a dominant influence on its mechanical properties. Graphitic irons exhibit a high damping capacity, since vibrational energy is dissipated at these internal interfaces. Brechmann-Guss Graphite corrosion does not occur in nodular and malleable cast iron. [5] Gray iron is generally considered easy to weld. All rights reserved. Gray iron above class 40 requires alloying to provide solid solution strengthening, and heat treating is used to modify the matrix. There are more pounds of grey iron castings produced every year throughout the world than any other type of casting. The role of impurities that bond strongly with the host lattice (ordering impurities such as O) can be distinguished from those that bond weakly (clustering impurities such as S). These thin veins act as internal notches, which weaken the matrix, and at the tips of which internal stresses peak. The fatigue limit for grey iron is in the range of 62 to 79 MPa, depending on the carbon content, while for cgi, the fatigue limit is 175 MPa. The microstructure specification therefore should be carefully selected, depending on the production requirements and performance conditions of the product. Flakes branch during growth by lateral division and rarely by splitting along the plane of the sheets. 0 Thus while the machinability of standard gray cast iron is relatively high, newer alloyed gray irons with higher strength and increased thermal resistance are increasingly more difficult to machine. As the nodularity increases, the strength and stiffness also increase, but there is a reduction in castability, machinability and thermal conductivity. CGI microstructure containing 10% nodularity (1). ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL:, URL:, URL:, URL:, URL:, URL:, URL:, URL:, URL:, URL:, Applied Welding Engineering (Second Edition), 2016, Selection and testing of metalworking fluids, Metalworking Fluids (MWFs) for Cutting and Grinding, Principles of Corrosion Engineering and Corrosion Control, Applied Welding Engineering (Second Edition), Materials for Engineering (Third Edition), Complete Casting Handbook (Second Edition), Advanced and conventional internal combustion engine materials, Alternative Fuels and Advanced Vehicle Technologies for Improved Environmental Performance, John Campbell OBE FREng DEng PhD MMet MA, in. Because of the attack, the iron or steel matrix is dissolved and an interlocking nobler graphite network is left. The graphite phase in compacted graphite iron is presented as individual vermicular particles (see Fig. In keeping with these predictions, it is suggested that several impurities, including O and S, adsorb on the growth interface. Gray iron, or grey cast iron, is a type of cast iron that has a graphitic microstructure. When added in amounts of 12 to 35%, chromium imparts resistance to corrosion and oxidation at elevated temperatures. 0000008986 00000 n It is named after the gray color of the fracture it forms, which is due to the presence of graphite. Figure 3.15. Optical micrograph of grey cast iron (unetched) × 500. By continuing you agree to the use of cookies. The requirements for a CGI cylinder block or head are as follows: 0–20% nodularity, for optimal castability, machinability and heat transfer; no free flake graphite or flake type graphite (as in grey cast iron) which causes localised weakness; 90% pearlite, to provide high strength and consistent properties; < 0.02% titanium, for optimal machinability. The particles, as in grey iron, are elongated and randomly oriented but are shorter and thicker with rounded edges. The graphite flakes, which are rosettes in three dimensions, have a low density and hence compensate for the freezing contraction, thus giving good castings that are free from porosity. Gray cast iron is a broad term used for a number of cast irons whose microstructures are characterized by the presence of flake graphite in the ferrous matrix. Different explanations have been given for the role of impurities, such as O and S, in promoting the flake morphology. The comparatively low strength of cast iron with flake graphite can be explained by its heterogeneous microstructure. The structural strength of gray iron components under dynamic loading is therefore barely affected by the form of the part. class 20 gray iron has a minimum tensile strength of 20,000 psi (140 MPa). 0000001678 00000 n The increase in spacing is attributed to S adsorption, which lowers the kinetic undercooling and hence, the interface undercooling and the frequency of branching. 0000006910 00000 n [1][4] Rapid cooling partly or completely suppresses graphitization and leads to the formation of cementite, which is called white iron.[5]. [2], It is used for housings where the stiffness of the component is more important than its tensile strength, such as internal combustion engine cylinder blocks, pump housings, valve bodies, electrical boxes, and decorative castings. [3] Grey iron cannot be worked (forged, extruded, rolled etc.) The combination of these effects produces a marked decrease in strength compared to SG cast iron. Casting   Automatic Molding The calcium treatment is necessary before the addition of magnesium because the latter also has an affinity for both sulphur and oxygen, but its spheroidizing ability depends on its presence in solution in the liquid iron. It appears gray … Gray cast iron has an interconnected flake graphite shape. CGI also shows a higher elastic modulus when compared with grey cast iron. One common mistake in the books is to use the term ‘graphitization' rather than graphitic corrosion. This reduces the demand and level of lubrication required from the metalworking fluid used. 1987). Grey cast irons are softer with a microstructure of graphite in a transformed-austenite and cementite matrix. Casting returns in such foundries are known to contaminate the new melts, although the contamination would be expected not to be nitrogen in solution, but nitride bifilms in suspension. These irons are so-called because the presence of graphite in the microstructure leads to a grey-coloured fracture surface. Silicon is important to making grey iron as opposed to white cast iron, because silicon is a graphite stabilizing element in cast iron, which means it helps the alloy produce graphite instead of iron carbides; at 3% silicon almost no carbon is held in chemical combination with the iron. The recommended applied tensile stress is therefore only a quarter of its actual ultimate tensile strength. When CGI is used instead of grey cast iron in the manufacture of cylinder blocks, the weight reduction is in the 10–30% range. 3.21, with C (graphite) replacing Fe3C and it may still be used to account for the microstructures that develop. In comparison with aluminium, the mechanical properties of CGi have the potential for: reduced cylinder bore distortion and improved oil consumption; no cylinder liners or surface etchant/coating; The mechanical properties of CGI are pre-defined by its structure. Home Page  |  (b) Microphotograph at 400x obtained after cast iron machining of 12% fluid containing 1.5% tramp oils (1.0% Way Lube + 0.5% hydraulic fluid). Proof of the keenly trained nose of a Master Caster, who can smell the difference after so many years! 11842 0 obj<>stream Figure 3.17. It is clear that gray cast irons alloyed to give higher strength present increased difficulty and challenges in machining and require the use of higher lubricating metalworkingfluids. Cu, etc. Table 11.2. The Ford PSA Jaguar V6 is the first high volume engine with a CGI cylinder block, production having started in October 2003 (see Fig. In assessing the performance of a metalworking fluid tested both as a freshly made emulsion and also following extended use in a gray cast iron machining operation, it is seen that reduced cutting forces and tool wear are obtained with the aged fluid, relative to that measured with a freshly prepared water-based fluid. Although the flake structure is often described as characteristic, it only forms in the presence of impurities.

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