Hi
nottoobright,
Please search for & read some info on the heat treatment of stainless, solution annealing stainless, sensitization...
'Solution' means refers to the microstructure of the stainless steel. The SS is heated hot enough (usually in air, but a protective atmosphere or vacuum can be used if you are willing to pay more) to dissolve carbides such as Cr
23C
6 into the (solid) austenitic (fancy way of saying that the metal atoms have a face-centered cubic microstructure) alloy, and then cooled fast enough that the carbon does not have time to precipitate and grow into carbide phase. Thus, the carbon is said to remain in solution (within the solid alloy).
A solution annealing procedure is given in this thread:
Need for solution annealing
thread330-76941
Re your procedure:
"The product we produce is a stainless steel well screen used in the water well industry. After dipping the 6 meter screen in a Nitric and Hydroflouric mixture for about 30 minutes, we then wash the screens using soap. Finally the screens are mechanically pollished with brushes."
1) It is necessary to know the fabrication details -- are you welding, bending, cutting, grinding...?
2) It is pointless to use soap
after pickling in nitric + HF (pickling solution). If oil or dirt is presnt, clean prior to pickling.
3) 304, 304L, 316 & 316L can be passivated in 25-45 vol.% nitric acid for 20-30 minutes,
after any brushing. Is this brushing for appearance or for removing weld scale? Weld scale removal should be done prior to pickling; it may reduce the necessary pickling time.
Passivation (+ rinsing & drying) is normally a final process.
Please read QQ-P-35C 'PASSIVATION TREATMENTS FOR CORROSION-RESISTANT STEEL' (free download):