A salt-spray test tells you how one defined chrome-plated specimen behaved in a salt-fog chamber for a stated period: how much of the surface showed corrosion, and where. It does not tell you how long a rod will last in service, how another bar from another heat will behave, or what an unstated chrome thickness will do. It is a comparative check, not a life prediction.
What does a salt-spray test actually measure?
A salt-spray test measures the visible condition of a prepared chrome-plated specimen after a defined exposure in a salt-fog chamber, judged against criteria agreed before the test. The output is a record of observations, not a material property.
That record is only useful if it states the test conditions. The specimen definition matters first: a full bar section, a cut coupon, or a machined part; whether the sawn ends, threads, chamfers and any machined features are included or masked; how the surface was cleaned before exposure. Then the exposure itself: salt concentration, chamber temperature, specimen angle, and duration. Then the evaluation: what counts as a failure, whether spots are counted, whether affected area is estimated, and whether edge corrosion is judged separately from the flat surface.
Two reports on the same bar are not comparable if any of these differ. This is the most common sourcing problem with salt-spray documents: the hours are quoted, the conditions are not, and the buyer compares numbers that were never measured the same way.
The test is well suited to comparing one plating process against another, checking that a change in chrome thickness moved the result in the expected direction, and watching process consistency over time. It is not suited to releasing a design on its own.
Why can't a salt-spray result be converted into service life?
Because the chamber holds one constant condition while service cycles through many. A continuous fog exposure does not reproduce wetting and drying, chloride concentration as water evaporates, standing water at seals and wipers, temperature swings, or mechanical damage to the chrome surface from grit and clamps.
Without a correlation study built on your own service conditions, hours in a chamber cannot be converted into months in the field. No responsible supplier should offer such a conversion, and no buyer should accept one.
For Yixin products, salt-spray performance is not part of the standard specification. Where a rating is required, we specify a thicker chrome layer and can have the order tested by a third-party laboratory. The test result then describes the sample tested, not the delivery and not the service life.
The honest use of a salt-spray report is a ranking: specimen A against specimen B under one protocol, or one production period against another. If corrosion is a design driver for your rod, treat the test as one input alongside chrome thickness, surface finish, and how the rod is protected at the seals and at machined ends.
Which properties does salt spray not verify?
Salt spray verifies corrosion appearance only. Chrome thickness, chrome hardness, diameter, straightness and surface finish each have their own check, and each is fixed on the drawing and order.
| What you need to know | How it is normally verified | Does salt spray help? |
|---|---|---|
| Hard chrome thickness (10–50 μm per side, chosen per order) | Coating thickness measurement on an agreed specimen | No |
| Chrome hardness (can reach HV800+) | Hardness test | No |
| Diameter and tolerance (for example 0/−0.02 mm from Ø12 on the 45 Steel Chrome-Plated Linear Shaft) | Micrometer or comparable gauge at agreed positions | No |
| Straightness and cut length | Straightness measurement and length check | No |
| Chrome surface finish (Ra ≤ 0.4 μm on chrome surfaces) | Roughness measurement | No |
| Corrosion appearance of the plated surface | Salt-spray exposure of a defined specimen | This is the only item the test addresses |
A salt-spray report sitting alone in a document package therefore proves very little. It becomes meaningful when the dimensional and coating requirements are already specified and verified separately, and the corrosion test is added on top of them as a defined, comparable observation.
How should I specify a salt-spray requirement?
Fix four things in writing before the order: the specimen, the exposure, the evaluation criteria, and who does the testing.
Specimen: state whether the test uses a section of the finished bar with its sawn ends, or plated surface only, and whether threads, chamfers and centre holes are in scope or masked. Exposure: state the salt concentration, chamber temperature, specimen angle and duration you want, rather than a duration alone. Evaluation: state what counts as a failure and how it is recorded. Testing party: name the laboratory, or state that the supplier may select one and report the result.
Keep the requirement on a separate test line in the enquiry, not as a note on the drawing. A drawing note tends to be attached to the wrong process step, and it makes the plating specification and the test hard to quote together.
Yixin applies one rule here: salt-spray performance is not part of the standard specification. Where a rating is required, we specify a thicker chrome layer and can have the order tested by a third-party laboratory. Thicker chrome layers are chosen per order; their lead time is quoted per order.
Does one report cover every bar in the order?
No. A report describes the sample tested. It does not transfer automatically to bars made later, to another heat of steel, or to a different chrome thickness.
Per-order third-party inspection is arranged on request, and it should be written into the RFQ if you need it. Otherwise the standard export documents are the commercial invoice, packing list and the steel mill certificate for each heat, forwarded unaltered.
This is also why a rating should be treated as a specification item rather than a document request. If the rating matters to your design, it belongs in the enquiry, where the plating specification, the test and the schedule are quoted together. Asking for a report after the bars are made leaves no room to change the chrome layer or the specimen definition.
What to put in your RFQ
- State whether a salt-spray rating is required, on a separate test line, not as a drawing note.
- Give the exposure conditions you want, including salt concentration, chamber temperature, specimen angle and duration.
- Define the specimen: finished bar section or plated surface only; whether sawn ends, threads and chamfers are included or masked.
- State the evaluation criteria: what counts as a failure and how the result is recorded.
- Name the third-party laboratory, or confirm that the supplier may select one.
- Say whether the test applies to a qualification sample or to each order, and whether per-order third-party inspection is required.
- If corrosion is a design driver, state the hard chrome thickness you want within the 10–50 μm per side range, chosen per order.
- Keep diameter, tolerance, straightness and surface finish on the drawing as separate requirements, so the corrosion test is not asked to carry them.
Summary
A salt-spray test is a controlled observation: one specimen, one set of chamber conditions, one agreed evaluation. It is useful for comparing plating processes and chrome thicknesses, and for checking consistency, but it cannot be converted into service life, and it says nothing about thickness, hardness, tolerance, straightness or finish. Specify it as a test line with the specimen, exposure, criteria and laboratory defined, and keep the dimensional and coating requirements on the drawing as separate, verifiable items.
References
- GB/T 699-2015 Quality carbon structure steels — the product standard covering Grade 45 steel.