Bellm, if your 312 or 316 is cold worked, to say a half hard to fully hard condition, it will show some ferromagnetism. 300C will not be high enough to anneal it, so it will still be able to retain a magnetic field- i.e., it will show some remanent induction, Br. If your material is annealed, then no- it won't retain a magnetic field.
Hope this helps!
Lee Gearhart