If you are seeing magnetic behavior in a 302 sample, you quite probably have a ferrite or martensite phase as a result of cold work.  What you need to do to remove the ferrite depends upon what it is there.  You could try doing an annealing heat treatment at 1850 to 2050 F followed by a quench.  This should remove the cold work and avoid the formation of chrome carbides that would result in sensitization and a reduction in corrosion resistance.  But be aware that this will also result in a reduction in strength and can cause deformation.  So, you need to be very careful if your material is already in a "finished" state for whatever application you intend for it.

Dear Professor; 

Thanks for your reply. I'm gonna try your advice and will put a comment as an update.

Thanks a lot for your reply, I will also try with this method and put a reply.

It's important to note that if your alloy has delta ferrite, the solution treatment should occur in longer times if compared to the case of strain induced martensite occurrence. 

If the material experienced cold work, strain induced martensite could be formed, and heating between 1000-1100°C for 15min followed by air cooling will be sufficient to a "full" austenitic structure (with chromium carbides formed during cooling). If delta ferrite (arriving from as-cast microstructure) is present, solution at those temperatures will need longer times (in some cases, up to 48 h), also followed by air cooling.

If sensitization (and intergranular corrosion) is a concern, water cooling is a better choice after solution temperature step.