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Austenitic Stainless Steel
Description of material
Marinox22/22HS is a Chromium –Nickel –Manganese austenitic stainless steel strengthened by an addition of Nitrogen. This grade provides a very good corrosion resistance together with high strength in marine environments.
Many marine applications and boat propeller shafting. Boat shafts in Marinox22/22HS is the best choice in terms of corrosion resistance in sea water.
Argon Oxygen Decarburization
Marinox22/22HS is not so susceptible to pitting and crevice corrosion in stagnant sea water as other grades in the martensitic and austenitic Marinox series. 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. It’s important to point out that Marinox22/22HS could not be immune from stress corrosion cracking above certain levels of stress and sea water temperature. Strain hardened structures increase the risk of this form of corrosion. This situation should be evaluated.
Marinox22/22HS has the typical machinability of austenitic structures strengthened by Nitrogen and some difficulties could happen in turning, threading and milling processes due to their capacity to cold work harden. Machining parameters should consider that this grade work hardens more than other austenitic Marinox grades and operators should know that Marinox22/22HS 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.
Marinox22/22HS is supplied in precision straightened cold finished bars ready for fabricating into 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. Matching fillers should be used if the same corrosion resistance as the base metal is required for this operation, but other austenitic fillers may be an alternative.