"As a metallurgist I can add that steel changes lattice structure from ferrite (ferromagnetic) to austenite (para- or nonmagnetic) in that region. By adding nickel this temperature is lowered to room temp, thats why stainless steels with nickel is not magnetic."
That suggests you can create steel with any Curie temperature you want just by controlling the amount of nickel. And that could also lead to steel with a known remanent magnetism decay time at room temperature.
Yeah but the ferromagnetic martensite or ferrite lattices do not form spontaneously in these steels upon cooling. They form when the steels are cold-worked i.e.: hammering, cold-rolling, bending. The Curie temperature for destruction of these ferromagnetic phases is quite high in the 600ºC - 800ºC range, but once destroyed they do not recreate themselves upon cooling, thus the transition is one-way only. Nickel acts as a stabilizer of the austenite phase thus the higher-nickel grade stainless steels (e.g. the 310) resist this transition altogether.
Below is a list of some Ni containing steels and their properties:
AISI 304: A_C1 ~727–850°C, A_C3 ~900–950°C, T_N ~35–48 K. Paramagnetic at room temperature unless cold-worked to form martensite (T_C ~600–770°C).
AISI 316/316L: A_C1 ~800–900°C, A_C3 ~950–1000°C, T_N ~30–40 K. Paramagnetic unless martensite forms.
AISI 301: A_C1 ~700–800°C, A_C3 ~850–900°C, T_N ~50–60 K. More prone to martensite formation.
AISI 310: A_C1 ~900–950°C, A_C3 ~1000–1050°C, T_N ~20–30 K. Highly stable austenite, consistently paramagnetic.
AISI 321: A_C1 ~800–900°C, A_C3 ~950–1000°C, T_N ~35–45 K. Paramagnetic unless heavily deformed.
Ferrite to Austenite Transformation (A_C1 and A_C3):
This is a structural transition where the body-centered cubic (BCC) ferrite (ferromagnetic) transforms to face-centered cubic (FCC) austenite (paramagnetic). Nickel stabilizes the austenite phase, lowering the temperature at which this transformation occurs.
Néel Temperature (T_N):
Some austenitic steels like the 304 exhibit antiferromagnetic behavior at very low temperatures.
Nickel’s Role:
Nickel is an austenite stabilizer, promoting the FCC structure over BCC, which makes austenitic stainless steels (e.g., 304, 316) paramagnetic at room temperature. The exact transition temperatures depend on the alloy’s composition, including nickel, chromium, carbon, and other elements.
If the goal is to achieve transition temperatures near the room temperature, then it is the easiest to just use Gadolinium.
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Topic: SEMP AI Smart Electromagnetic Generator (AISEG) (Read 57780 times)
