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Ferritic Stainless Steel
Description of material
X17L is the most popular stainless ferritic grade. It is extensively used where a combination of good formability and corrosion resistance is required.
Typical applications of X17L are fresh water pump shafts, washing machines, kitchen household items, screws, and bolts manufacturing. In addition, it finds applications in electromagnetic devices, fuel injection components, sensors in automotive applications, electromagnetic switches and relays, sensors and fuel pumps where free machining ferritic grades cannot be used.
X17L has a good resistance to mildly corrosive environments such as fresh water, crude oil, gasoline, alcohol, some beverages and atmospheres. It should be noted that this grade, as for every kind of stainless steel, surfaces should be free of contaminant and scale, heat tint, and passivated for optimum resistance to corrosion. It’s useful to remember that X17L, as with all the ferritic grades, offers a better stress corrosion cracking resistance than Austenitic grades.
This grade is suitable for cold heading and up-setting and has been specifically designed for cold forming.
X17L has a machinability typical of all Ferritic machined grades not micro – resulphured. Productivity gain depends on the type of machines used, the kind of tools used and their geometry, cutting fluids and the kind of machine operations on the pieces produced. Its structure influences the surface finish (roughness) and the chip morphology. Within certain limits, a little bit harder structure typical of annealing + cold finishing operations (such as cold drawing) offers advantages in some machine operations and better surface roughness.
It should be noted that this grade, as for every kind of ferritic steel, produces large grain structures in FZ and HAZ caused by high temperatures of welding with some risk of embrittlement at room temperature. Austenitic fillers, in order to increase the ductility of weld, don’t solve the problems in HAZ unless a PWHT is applied. A PWHT restores the ductility in the improbable case of Martensite formation and also diffuses back the Chromium into the depleted zones close to grain boundaries restoring its corrosion resistance.
X17L has a very good hot plasticity thanks to a wide range of possible forging temperatures. Avoid overheating and long soaking since this could cause grain growth. The last final steps of forging must be carried out at a lower temperature range with a suitable reduction in order to obtain a structure with fine and uniform grains. Blooms and ingots may require a suitable preheating to avoid cracks and an air cooling after forging. Overheating must always be avoided in order to reduce the risk of internal bursts and a structure with large coarse grains. An annealing after forging should always be performed in order to restore both corrosion resistance and enhance the ductility.