1. Low corrosion environment at 500 deg.C :
(1) High strength/creep required: 9Cr-1Mo-V
(2) Medium strength/creep required: 9Cr-1Mo
(3) Low strength/creep required: 5Cr-1/2Mo
2. Medium corrosion environment at 500 deg.C :
(1) High strength/creep required: 347H SS
(2) Medium strength/creep required: 321H/ 304H SS
(3) Low strength/creep required: 316H SS
3. High corrosion environment at 500 deg.C :
(1) High strength/creep required: 310 SS
(2) Medium strength/creep required: 309 SS
(2) Low strength/creep required: 446 SS
* Anticipated Mass of Corrosion: V (V2O5), SO2 (Na2SO4), S, etc.
vessel(furnace) design is more than picking a material and if you have specific issues redarding the electrical and or magnetic behavior and its effect on you process then a considerable amount of engineering is required just to establish the basis for design.
500 c (max)and use of austenetic stainless are little enough to define your problem, but if in addition you have a requirement as to non-magnetic, then you need to be specific as to the size of the furnace, the actual field strengths involved and at what location within the chamber, the skin temperatures involved, etc.