Green residue on 410 stainless bolts

A. Silicon Oxide (sand) is not green unless it is mixed with a green nickel compound like nickel nitrate. I suspect the passivator is not rinsing well (especially threaded parts), leaving some nitric acid residue which combines with the nickel on the surface and leaves a green compound. The silicon is probably coming out of the steel but is probably not the source of the "green".

A. Seems like abysmal quality from an unqualified, low ball supplier.

If the parts were properly passivated, there is a problem with the baking. The oven may be contaminated with chlorides or fluorides (salt bath, pickling or brazing flux residue). These combine with moisture in the air to attack the passivation and cause green crystalline Cr2O3. Silica doesn't form on 410 SS unless drastically overheated, e.g., as slag on the liquid metal. Not much nickel in 410, either. Maybe silica from disintegrating oven insulation. Contaminants are prohibited under 'Workmanship and Finish' provisions, e.g., Para. 10 in ASTM F593, which also requires descaling and cleaning per ASTM A380 . And, why not hydrogen bake before passivation?

Oxidation from heat treating threaded parts in air depletes chromium and reduces the amount of metal in the threads, weakening them and reducing corrosion resistance. I advise heat treating in vacuum and using forced gas quenching (helium at 55 psia). Eliminates cleaning off quench oil and pickling of oxide scale; thus, no need for hydrogen bake-out. Tempered parts can be directly passivated Type II (or VIII) per QQ-P-35C (canceled) [link is to free spec at Defense Logistics Agency, dla.mil]C or the equivalent ASTM A967 Nitric 1 (or 4).

"passivation (probably nitric acid)" -- Making jokes or parts? What does the vendor's Shop Traveler show? Was rolling lubricant removed prior to heat treatment? Also check that the austenitization and tempering temperatures are correct for ASTM F593 P or R bolts, if applicable.

Unless the vendor comes up with definitive answers and verifiable Corrective Actions, blacklist them. If not feasible to vacuum heat treat, at least do the hydrogen bake-out after pickling but before passivation. Perhaps eliminate the hydrogen bake by minimizing hydrogen pick-up. E.g., anodic electrocleaning, pickling inhibitors and limited pickling time. Test for hydrogen in wire and bolts: load to 80% yield strength & wait 4 days for possible fracture. Torsion loading is better than simple tension.