Today we want to deal with a very complex subject: magnetism in austenitic steel.
Austenitic steel. Why do they become magnetic?
Austenitic steels contains Cr (16 – 20%), Ni (7 – 18%) and only some kinds Mo (2 – 6%) with a carbon content of typically less than 0.08%. The presence of stabilizing elements (such as Ti) improves the corrosion resistance, particularly intergranular, and at the same time it provides increased resistance to high temperatures.
This type of steel is characterized by a stable austenitic structure at any temperature. After a heat treatment, it does not show any increase of mechanical strength. But how is it possible to increase mechanical resistance? With added nitrogen, or by cold deformation processes (rolling, drawing, molding, extrusion etc., which are able to “work-hardening” the material, thereby increasing its hardness and introducing some magnetism, more or less pronunced.
AISI 303 – X8CrNiS18-9, steel number 1.4305 303
A high content of sulfur in the stainless steel austenitic ensures a better workability and a non-optimal corrosion resistance; in the latter case, it works only in the atmposhere, to food substances and organic type of chemicals.
The mechanical strength, however, can be increased by means of cold deformation. This type of steel is also not weldable, so it is mainly used for machined on high-speed automatic machines (e.g. pins, bushings, screws, nuts, bolts, turnbuckles).
Magnetism. How is it transmitted?
The processes mentioned above such as rolling, drawing, molding or extrusion are fundamental for the production of screws and bolts stainless. In particular, during the molding of the washers a strong magnetism is transmitted.
To make the process possible some articles with small dimensions ( like plugs) are manufactured specifically for A1 steel.
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