Hi, You can always add new materials to the library If you have the required properties of the material.
In this case, if you have magnetic properties (and loss data) of the material (steel AISI 316 L),
Go to Tools > Edit Libraries > Materials
Select Add material at the bottom of the window.
Select relative permeability as non-linear to add the BH-Curve
Refer to the Add new Material section in ANSYS Maxwell Help.
Help > Maxwell Pdfs > Maxwell help
Regards
Navya