Guide
Nickel plating vs chrome: which one should a machined part get?
Nickel plating vs chrome is really a choice between three finishes: nickel alone for general corrosion protection, decorative chrome (a thin chromium layer over nickel) for a hard, bright, tarnish-free face, and hard chrome (thick chromium, usually ground) for wear surfaces. Pick by the job the surface does, then name the specification and class on the drawing, because “chrome plated” on its own can mean any of the three.
By Saola Manufacturing engineering team · Published · Updated
Most confusion on RFQs comes from the word “chrome.” A bright faucet handle and a hydraulic rod are both called chrome plated, yet one carries a chromium layer far thinner than the nickel under it and the other carries thousandths of an inch of chromium ground to size. This guide sorts the three finishes by what a machined part needs, then shows how to write the callout and how to accept the plated parts. For replacing hard chrome on cylinder rods specifically, see what can replace hard chrome on piston rods; for choosing between nickel processes, see electrolytic vs electroless nickel.
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What is the actual difference between nickel, decorative chrome and hard chrome?
Nickel is the corrosion barrier, decorative chrome is a thin hard skin on top of that nickel, and hard chrome is a thick functional chromium layer plated straight onto the steel for wear.
Decorative chrome is a system, not a single layer. The current ASTM specification for it, ASTM B456, covers copper plus nickel plus chromium and nickel plus chromium coatings, and grades them by service condition from mild up to extended very severe. The nickel does most of the corrosion work; the chromium on top resists tarnish and scuffing and gives the blue-white color. Remove the nickel from the specification and the chromium alone will not protect steel.
Hard chrome, also called engineering or functional chromium, is described in the ASTM guide B177 as usually applied directly to the base metal and usually thicker than decorative coatings. Its job is wear, abrasion and fretting resistance, and it is often plated oversize and ground back. Nickel alone, finally, is a softer, ductile coating used where corrosion protection or a solderable or reworkable layer matters more than hardness.
| Property | Nickel only | Decorative chrome (Ni + Cr) | Hard chrome |
|---|---|---|---|
| Main job | Corrosion protection, engineering build-up | Appearance plus corrosion, tarnish and scuff resistance | Wear, abrasion, rebuild of worn parts |
| Chromium layer | None | Thin top coat over the nickel (Class 1 chromium is over 0.00001 in) | Over 0.002 in (Class 2); commonly 0.0020–0.0050 in after grinding |
| Nickel layer | QQ-N-290A Class 1 corrosion-protective grades, set by thickness | Carries the corrosion protection; thickness set by the B456 service condition | Usually none; chromium goes directly on the steel |
| Thickness tolerance on the drawing | Per the specification grade | Minimum thickness on significant surfaces | Commonly 0.0010 in as plated under 0.0020 in; 0.0005 in when ground |
| Post-plate machining | Rare | None; polish is done before plating | Grinding is common on Class 2 |
| Relative cost driver | Plating time for the grade | Prepolish and the multi-layer system | Long plating time, bake, peening and grinding |
Which finish fits which machined part?
Choose by the surface’s job: sliding or rubbing contact points to hard chrome, a visible face that must stay bright points to decorative nickel-chromium, and a hidden part that only needs corrosion protection points to nickel or to a cheaper finish altogether.
A rule of thumb that holds up on most drawings:
- Shafts, plungers, rods and guide pins that slide in seals or bushings: hard chrome, plated oversize and ground. The wear life comes from the chromium thickness, so specify the final ground thickness, not just “chrome.”
- Handles, knobs, trim and visible fittings on steel, brass or zinc: decorative nickel-chromium, specified by service condition. Indoor dry use and outdoor or marine use are very different classifications in ASTM B456, and the nickel thickness rises with severity.
- Brackets, internal fittings and parts later soldered or reworked: nickel alone, or a different finish entirely if appearance and wear do not matter. Zinc plating with a chromate is often the lower-cost answer for hidden steel parts.
- Precision bores and close-fit diameters: neither decorative chrome nor heavy nickel unless the machining allowance accounts for the coating. Mask the bore or size it for the coating.
Cost follows the process steps more than the metal. Decorative chrome needs a well-polished substrate, because the bright nickel and chromium reproduce every scratch. Hard chrome on high-strength steel adds shot peening, a hydrogen bake and grinding. Plain nickel to a specified grade is usually the simplest of the three.
Is hard chrome more corrosion resistant than nickel?
Not by default: hard chrome is chosen for wear, and its crack network means it gives only incidental corrosion protection unless the thickness, an underlayer or a seal is specified for it.
NASA’s chromium process specification states the split plainly: Class 1 chromium protects steel against corrosion and may be used for appearance, while Class 2 engineering chromium is used primarily for wear and abrasion resistance with incidental corrosion protection (NASA JSC PRC-5003, 2020). The same document notes that chromium plate often has cracks running from the surface to the substrate, and that the crack frequency rises with thickness. That is why hard chrome rods exposed to weather or salt water still rust in service when the coating or the sealing is inadequate.
Nickel, by contrast, is a continuous barrier when it is thick enough and free of pores. If a part needs both wear resistance and serious corrosion resistance, the usual answers are a nickel underlayer beneath the chromium, a thicker chromium layer, or one of the alternative coatings covered in the piston-rod guide linked above. Write the environment into the RFQ so the plater can propose the system rather than guess.
How do you call out nickel or chrome plating on the drawing?
Name the specification, the class or service condition, the thickness and where it is measured, plus any masking, bake and post-plate grinding.
NASA’s chromium specification gives two model notes that work for any shop: one for Class 1 chromium to an as-plated thickness range of 0.0005–0.0015 inch, and one for Class 2 chromium to a final thickness after grinding of 0.0020–0.0050 inch (PRC-5003). The useful pattern is “specification, class, type, thickness, and whether the thickness is before or after grinding.” For commercial work, SAE AMS 2460 is the chromium plating specification that PRC-5003 now points to.
For nickel, the old federal specification QQ-N-290A defined Class 1 corrosion-protective plating in thickness grades and Class 2 engineering plating (QQ-N-290A, 1971). SAE now publishes it as AMS-QQ-N-290D, listed as stabilized, so check whether your program calls for the general-purpose AMS 2403 instead; either way, the grade or thickness goes in the note. For decorative work, cite ASTM B456 with its classification code, which carries the substrate, the nickel type and thickness, and the chromium type.
Then add what the specification cannot know about your part: which surfaces are significant (where thickness is measured), which threads and bores are masked, and whether the dimensions on the drawing apply before or after plating. A note such as “dimensions apply after plating” on a ground hard chrome diameter tells the machinist to leave grinding stock and the plater to plate oversize.
What should you watch for when plating hardened or high-strength steel?
Hydrogen embrittlement and fatigue loss: hardened steel parts need a bake after plating, and hard chrome on fatigue-loaded parts usually needs shot peening first.
PRC-5003 requires a hydrogen bakeout within four hours of plating for carbon, low-alloy and martensitic stainless parts other than fasteners at 40 HRC or above, using 375 °F for 23 hours, and lowers the threshold to 36 HRC for fasteners (NASA JSC PRC-5003). Case-hardened parts are referred to the bake tables in SAE AMS 2759/9.
On the drawing, state the base material hardness and say “bake per” the specification you cite. Ask for the bake record (time and temperature) with the lot. Also remove pits and scratches before plating: the NASA document notes that most anomalies present before plating are amplified after it, which matters most on bright decorative work.
What should the RFQ say, and how does Saola handle plated parts?
Send the finish callout with the drawing, plus the service environment and which surfaces are functional, so the coating can be confirmed at drawing review before quoting.
Machining is done at our lead CNC plant in Vietnam, on CNC turning for shafts and pins and CNC milling for second operations on castings. Electroplating is one of the eight finishes on our managed surface finishing menu, applied at partner plants; which coating and specification a partner can meet is confirmed at drawing review. Decorative chrome-look plating is not on the current menu, and hard chrome is not listed either, so raise either one before quoting rather than after. Every new part gets a first-article inspection report, and each lot gets a dimensional inspection record.
For the RFQ, include: the specification and class or service condition; the minimum thickness on significant surfaces; masking; whether dimensions apply before or after plating; base material and hardness; and any bake or salt-spray requirement. Then send the drawing for a quote.
Frequently asked
Is chrome plating just nickel with a coat of chromium?
Decorative chrome is, in effect: ASTM B456 classifies it as nickel plus chromium, or copper plus nickel plus chromium, and the nickel carries most of the corrosion protection. Hard chrome is different, a thick chromium coating usually plated directly on the steel.
Which is harder, nickel or chrome?
Chromium is the harder coating, which is why hard chrome is used for wear surfaces. Electrolytic nickel is softer and more ductile. If wear life matters, specify hard chrome thickness and a hardness check; do not rely on the thin chromium of a decorative finish.
Can you plate chrome over a part that was already nickel plated?
That is how decorative chrome is built, but it is done as one controlled sequence. Adding chromium to a part plated and shipped earlier is a rework decision for the plater, who will need to strip or activate the old nickel.
Does plating change the part dimensions?
Yes. Every coating adds thickness on each surface, so a diameter grows by about twice the coating. State whether drawing dimensions apply before or after plating, and leave grinding stock on hard chrome diameters that are ground to size.
Is chrome plating being phased out?
Hexavalent chromium processes are under regulatory pressure in several markets, which is why trivalent decorative processes and hard chrome alternatives exist. If your end market restricts hexavalent chromium, say so in the RFQ so the process can be checked against it.
Sources
- PRC-5003 Rev. D, Process Specification for Electrodeposited Chromium Plating, NASA Johnson Space Center, June 2020
- QQ-N-290A, Federal Specification: Nickel Plating (Electrodeposited), General Services Administration, November 1971 (cancelled; via EverySpec)
- AMS-QQ-N-290D, Nickel Plating (Electrodeposited), SAE International, October 2021
- ASTM B456, Standard Specification for Electrodeposited Coatings of Copper Plus Nickel Plus Chromium and Nickel Plus Chromium, ASTM International, 2017 edition (catalog page updated 2022)
- ASTM B177/B177M, Standard Guide for Engineering Chromium Electroplating, ASTM International, reapproved 2017