MARINOX17- Indurenti per precipitazione

Valbruna Grade

MARINOX17

Description of material

Marinox17 is a precipitation hardening stainless steel that is able to combine high strength with a good general corrosion resistance and good stress-corrosion cracking resistance in marine atmospheres and environments. Bars of this grade are hardened at a higher temperature of aging condition, in order to obtain a matrix of tempered martensite structure with a certain amount of stable austenite. This condition warrants the best stress- corrosion cracking resistance. See grades V174 and similar to know the properties and metallurgical behavior of Marinox17. Mechanical properties of boat shafts of this grade are according to ASTM 564 / (EN 10088) condition H1150 / (P930).

Applications

Many marine applications and boat propeller shafting, where Marinox17 offers a combination of high strength – toughness- corrosion resistance, allowing the use of a smaller shaft diameter and, consequently, a reduction of its weight.

Melting practices

Argon Oxygen Decarburization, AOD + ESR

Corrosion resistance

Generally, Marinox17 has a same corrosion resistance of type 304 series but offers a better resistance to stress corrosion cracking. This grade is susceptible to pitting and crevice corrosion in stagnant sea water if the propeller shaft stays motionless for lengthy intervals of time and doesn’t operate continuously. In this case, a periodical rotation of shafts should be done because this movement of sea water (flow) avoids a stagnant situation able to prime pitting and crevice corrosion. Cathodic protection is highly suggested and recommended in order to avoid these kinds of corrosion. The choice of sacrificial anodes such as zinc, magnesium and aluminum depends on the kind and nature of water where the propeller shaft works.

Machinability

Marinox17 has a very good machinability in turning, threading and milling processes. Particular care is recommended to obtain a shaft with very low surface roughness and a good geometry of its keyways 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 that cause stresses in the shaft. A precision straightening after machining operations is also very important to increase the service life, improving the fatigue resistance of the boat shaft propeller.

Weldability

Marinox17 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 untempered martensite results in FZ and HAZ, reducing ductility in this zone. Matching fillers should be used for this operation but austenitic fillers may be an alternative. In this case a reduction of strength in repaired zones should be well considered. In addition, it is useful to underline 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.

Designations