Machining leaves iron. Passivation removes it.
Every cutting tool, fixture and bench transfers trace iron onto a stainless part. Left in place, it rusts — staining the surface and seeding corrosion. Passivation dissolves that free iron and lets the chromium-rich passive oxide layer reform, uniform and complete.
We in either nitric or citric acid baths, with the bath selected to the alloy: austenitic grades like 304 and 316 run in standard nitric solutions, while free-machining, martensitic and precipitation-hardened grades — 303, 416, 420, 17-4 PH — run in citric chemistry that protects them from etching during treatment. No dichromates are used anywhere on the line.
Parts are cleaned to a water break-free surface before treatment, then rinsed and verified. The result adds nothing to the part — no coating, no dimensional change — just stainless steel behaving the way it was specified to.
20–45 v% HNO₃
AMBIENT · 70–90 °F
30 MIN MINIMUM
Austenitic & duplex grades — 304, 316, 321, 347, 2205 and related.
45–55 v% HNO₃
120–130 °F
30 MIN MINIMUM
High-strength martensitic, ferritic & PH grades.
4–10 w% CITRIC ACID
140–160 °F
4 MIN MINIMUM
Gentler chemistry for all grades — including free-machining and PH alloys sensitive to nitric etching.
Verified the way the spec demands.
TEST PRACTICE PER DRAWING CALLOUT OR PO · RECORDS RETAINED WITH FULL BATCH HISTORY
Where passivation is called out.
Alloy determines the bath.
Tell us the grade and condition — the bath, temperature and immersion time follow from the specification. Mixed-grade lots are processed separately. Free-machining grades are never copper-sulfate tested; an alternative practice is used.