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Corrosion Resistant Alloys
Description of material
MarinoxEG2 is a Nickel–Copper alloy with very high corrosion resistance and whose strength is increased by the precipitation of particles of Ni3 (Ti, Al) obtained by an exact aging heat treatment.
Many marine applications and boat propeller shafting. Boat shafts of Marinox EG2 offer a high performance in terms of corrosion resistance and high strength in sea water.
MarinoxEG2 is not as susceptible to pitting and crevice corrosion in stagnant sea water as other grades in the martensitic and austenitic Marinox series but the effect of fouling should be always considered. In any case, for this grade, this kind of corrosion is not so rapid in the propagation of deep pits. However, if the propeller shaft stays motionless for a lengthy interval of time and doesn’t operate continuously, a periodical rotation of the shaft would be a good prudential measure. In any case, cathodic protection is always recommended in order to avoid certain kinds of localized corrosion. The choice of sacrificial anodes, such as zinc, magnesium and aluminum, depends on the kind and nature of the water where the propeller shaft works.
MarinoxEG2 is classified as difficult when machining but has approximately the typical machinability of the austenitic structure strengthened by Nitrogen, and some difficulties could happen in turning, threading and milling processes. Operators should know that MarinoxEG2 requires more rigid and powerful machines in addition to the correct choice of tools, coating carbides and cutting fluids. Particular care is recommended to obtain a shaft with very low surface roughness and a good geometry of its keyway, avoiding sharp corners and poor interior roughness. Top and interior corners must have a suitable filleting and sled-runner type keyway end should be used to increase the service life. Machining parameters must avoid operations able to cause stresses in the shaft. A precision straightening after machining operations is also very much important to increase the service life, improving the fatigue resistance of the boat shaft propeller.
MarinoxEG2 is supplied in precision straightened cold finished bars ready for fabricating boat propeller shafts. In the case of limited welding repairs, no preheating is required but it is important to point out that any localized heating may cause a certain amount of bending of the shaft and this amount depends on the width/ thickness of the heated zone. A matching filler with a chemical composition close to that of the base metal (shaft) should be used in order to obtain approximately the same corrosion resistance. Its useful underline that this filler doesn’t age harden and the weld metal will have a lower strength.
Surfaces of products must free of any contaminants and very clean before heat treatment. Structural hardening of EG2 is generated by a precipitate of submicroscopic particles of Ni3 (Ti, Al) in the matrix. This means a special care should be adopted to allow to these particles to achieve the expected mechanical properties during the age-hardening. Therefore, EG2 must be solution annealed before the aging treatment, paying attention that both heating and soaking have to be kept to a minimum followed by a fast water quenching. It’s important to underline that a long time soaking or at an excessive temperature, results in both coarse grains and the formation of detrimental Ti–Carbides, jeopardizing the required structural hardening after age treatment. Moreover, it’s important to point out that EG2 should be supplied in the hot or cold working conditions followed by a suitable choice of aging heat treatment parameters if higher mechanical properties were required.
|Commercial name||Alloy K-500|