JIS Plating Callouts (Ep-Fe/Zn8/CM2) and ASTM Equivalents
You open a Japanese part drawing and the surface treatment note (表面処理, hyomen shori) reads Ep-Fe/Zn8/CM2, 三価クロメート, 無電解ニッケルめっき 10μm, or simply 硬質クロムめっき. Each one is a plating callout, and each one points to a different coating with different strengths, risks, and costs. Your local plater, however, may quote to ASTM B633, ASTM B733, or AMS 2460, not to JIS.
This guide decodes the plating notes you will see on Japanese drawings: the JIS designation system behind codes like Ep-Fe/Zn8/CM2, the four plating types used most on machine and electronic parts (zinc, electrolytic nickel, chromium, and electroless nickel), and the closest ASTM and ISO references for each. It ends with a checklist and a sample inquiry you can send to the Japanese side before you quote or substitute a local specification.
Contents
- Japanese Plating Terms on Drawings: Quick Translation
- How to Read a JIS Plating Designation (Ep-Fe/Zn8/CM2)
- JIS Plating Standards and Their Closest ASTM/ISO Counterparts
- The Four Main Plating Types Compared
- Electroplating vs. Electroless Plating
- Zinc Plating: Low-Cost Rust Protection
- Nickel Plating: Appearance and Undercoat
- Chromium Plating: Decorative Chrome vs. Hard Chrome
- Electroless Nickel: Complex Shapes and Tight Tolerances
- Hexavalent Chromium Rules and What They Mean for the Callout
- How to Choose (or Check) a Plating Callout
- Checklist: What a Complete Plating Callout Should Tell You
- Limits of This Guide
- Key Takeaways
- FAQ
- Sources
Japanese Plating Terms on Drawings: Quick Translation
めっき (mekki) means plating: a thin layer of another metal deposited on the part surface to add what the base metal lacks, such as rust resistance, hardness, or appearance. The table lists the notes you are most likely to meet, the JIS standard behind each, and the specification a US plater would usually ask for.
| On the drawing | Romaji | What it means | JIS standard | Closest US / ISO reference |
|---|---|---|---|---|
| 電気亜鉛めっき / 亜鉛めっき | denki aen mekki / aen mekki | Zinc electroplating | JIS H 8610 | ASTM B633; ISO 2081 |
| 光沢クロメート (ユニクロ) | kotaku kuromeeto (yunikuro) | Bright (clear-blue) chromate on zinc | JIS H 8625 | ASTM B633 Type III (hexavalent) or Type V (trivalent) |
| 有色クロメート / 黒色クロメート | yushoku / kokushoku kuromeeto | Yellow (iridescent) or black chromate on zinc | JIS H 8625 | ASTM B633 Type II (hexavalent) or Type VI (trivalent) |
| 三価クロメート | sanka kuromeeto | Trivalent chromate (Cr(VI)-free passivate) | No JIS symbol (see below) | ASTM B633 Type V / VI; ISO 19598 |
| 溶融亜鉛めっき (ドブ漬け) | yoyu aen mekki (dobuzuke) | Hot-dip galvanizing | Separate JIS standard (not covered here) | Confirm with the supplier |
| ニッケルめっき (光沢 / 無光沢) | nikkeru mekki (kotaku / mukotaku) | Electrolytic nickel (bright / dull) | JIS H 8617 | ASTM B456 (decorative Ni-Cr); ASTM B689 (engineering Ni); ISO 1456 |
| クロムめっき (装飾) | kuromu mekki (soshoku) | Decorative chromium over nickel | JIS H 8617 | ASTM B456; ISO 1456 |
| 硬質クロムめっき / 工業用クロムめっき | koshitsu / kogyoyo kuromu mekki | Hard (engineering) chromium | JIS H 8615 | AMS 2460 (replaced QQ-C-320); ASTM B650; ISO 6158 |
| 無電解ニッケルめっき | mudenkai nikkeru mekki | Electroless nickel-phosphorus | JIS H 8645 | ASTM B733; ISO 4527 |
| ベーキング / 水素脆性除去 | beekingu / suiso zeisei jokyo | Hydrogen embrittlement relief bake | Within each plating standard | ASTM B850 |
Two cautions before you go further. First, a bare "クロムめっき" (chrome plating) note is ambiguous: it can mean a thin decorative layer or a thick hard-chrome layer, which are completely different jobs. Second, shop-floor nicknames are common: ユニクロ (yunikuro), for example, is the popular name for bright chromate on zinc. For how the surface treatment note fits into the rest of a Japanese drawing, see How to Read Japanese Engineering Drawings.
Related: How to Read Japanese Engineering Drawings (JIS B 0001)
How to Read a JIS Plating Designation (Ep-Fe/Zn8/CM2)
The symbolic callouts on Japanese drawings follow JIS H 0404 (Graphical Symbol for Electroplated Coating, 1988 edition). The plating standards themselves (JIS H 8610, H 8617, H 8645 and others) say only that the symbols follow JIS H 0404. A designation reads left to right: process, base metal, coating layers with thickness and type, post-treatment, and, optionally, the service environment.
Process / base metal / coating and minimum thickness / post-treatment.
Symbols and examples from JIS H 0404:1988 and JIS H 8617:1999. Compiled by MONOSCOPE; check the edition your customer cites.
Here are worked examples taken from the standards themselves:
| Designation | Meaning |
|---|---|
| Ep-Fe/Zn 15/CM2 : B | Zinc electroplate on steel, 15 µm minimum, colored chromate, normal outdoor use |
| Ep-Fe/Zn [2]/CM2 : C | Zinc electroplate on steel, grade 2, colored chromate, humid indoor use |
| Ep-Fe/Cu 20, Ni 25b, Cr 0.1r/ : A | Copper 20 µm, bright nickel 25 µm, regular chromium 0.1 µm on steel, severe outdoor use |
| Ep-Fe/Ni 25d, Cr 0.1mp | Double-layer nickel 25 µm with microporous chromium 0.1 µm on steel (JIS H 8617 grade 6) |
| ICr 50 | Industrial (hard) chromium, 50 µm minimum |
A few practical notes on these codes:
- Thickness is a minimum, not a target. Zn8 means at least 8 µm at the measuring points, so actual coatings on edges and threads can be thicker. ASTM B633 works the same way (SC2 = Fe/Zn 8, minimum).
- Grades in brackets refer to a table. JIS H 8610 groups zinc coatings into grades 1 to 6 by minimum thickness; one Japanese plater lists grade 2 as 5 µm minimum. Check the table in the edition your customer cites rather than guessing the number.
- Older shorthand still circulates. Codes such as MFZn2-C or MFZn8 come from older Japanese notation or company standards. The same code can mean different things in different specifications, so ask the Japanese side which standard and edition apply.
- Trivalent chromate has no symbol of its own in these standards. JIS H 0404 (1988) and JIS H 8625 (1993) predate the shift away from hexavalent chromium. Drawings therefore spell it out (三価クロメート, 3価, or Cr3+ added to the callout) or use the company's own code. If a drawing still says CM1 or CM2 and also requires RoHS compliance, confirm whether a trivalent equivalent is intended.
JIS Plating Standards and Their Closest ASTM/ISO Counterparts
When the Japanese drawing cites a JIS number, these are the standards to put next to it in your review. Several JIS plating standards were written as translations of ISO standards from the 1980s, while the ISO and ASTM documents have since been revised, so details have drifted apart.
| JIS standard | Title (English) | ISO it was based on | Closest US specification |
|---|---|---|---|
| JIS H 0404:1988 | Graphical symbol for electroplated coating | — | — (ASTM specs use their own class/type codes) |
| JIS H 8610:1999 | Electroplated coatings of zinc on iron or steel | ISO 2081:1986 | ASTM B633 (SC1–SC4 = Fe/Zn 5, 8, 12, 25) |
| JIS H 8625:1993 | Chromate conversion coatings on electroplated zinc and cadmium coatings | ISO 4520:1981 | ASTM B633 Types II, III (chromate) and V, VI (trivalent passivate) |
| JIS H 8617:1999 | Electroplated coatings of nickel and chromium | ISO 1456:1988 | ASTM B456 (decorative); ASTM B689 (engineering nickel) |
| JIS H 8615 | Electroplated coatings of chromium for engineering purposes | ISO 6158:1984 | AMS 2460; ASTM B650 |
| JIS H 8645:1999 | Autocatalytic nickel-phosphorus coatings on metals | ISO 4527:1987 | ASTM B733 |
The Four Main Plating Types Compared
Zinc, electrolytic nickel, chromium, and electroless nickel cover most plating callouts on machine and electronic parts. Each one is good at different things, and choosing the wrong one tends to show up later as rust, out-of-tolerance dimensions, or cracking.
All four are "plating," but their strengths and weak points differ sharply.
Hardness values are figures published by Japanese plating companies. Cost is a general tendency and changes a lot with part shape, quantity, and thickness.
Two rows in the table set the types apart: how they stop rust and how evenly they build up. Only zinc keeps protecting the steel when the coating is scratched, and only electroless nickel builds an even layer on complex shapes, so it is the choice when dimensions must hold.
Electroplating vs. Electroless Plating
Plating splits into two processes. Electroplating (電気めっき, denki mekki) passes current to deposit metal. Electroless plating (無電解めっき, mudenkai mekki) deposits metal by chemical reaction, with no current. Zinc, nickel, and chromium are normally electroplated; electroless nickel, as the name says, is not. The same metal, nickel, behaves quite differently depending on which process deposits it.
Whether current is used decides how evenly the coating builds up.
Electroplating is fast and builds thickness at relatively low cost, but thickness variation between edges and holes is unavoidable. On parts with tapped holes or fits, the drawing has to allow for the plated dimensions.
In electroless nickel plating, the reducing agent releases electrons as it oxidizes, and nickel ions take them up and deposit. Phosphorus is taken up at the same time, so the coating is a nickel-phosphorus alloy. Because it grows at the same rate everywhere the solution reaches, one plater in Japan quotes thickness within ±10% of the specified value over the whole surface of complex parts.
Zinc Plating: Low-Cost Rust Protection
Zinc is the most common plating for protecting steel parts such as bolts, nuts, brackets, and sheet-metal parts. Small parts tumble in a rotating barrel and plate in bulk, so unit cost stays low. That is its biggest strength.
Zinc also protects steel in a different way from the other platings. The Japan Galvanizers Association explains it as two actions:
Besides acting as a barrier, zinc keeps protecting steel where the coating is damaged.
Sacrificial protection works by slowly consuming the zinc, so a thicker coating lasts longer.
Nickel and chromium only cover the surface, so the steel starts to rust at any pinhole or scratch. Zinc corrodes first to protect the steel, so red rust is slow to appear even when the coating is somewhat damaged.
Chromate Conversion: The Part of the Callout That Sets Performance
Bare zinc forms white rust (white corrosion of the zinc itself) easily, so almost all zinc plating gets a chromate conversion coating on top. A conversion coating is a thin protective film formed by reacting the surface with a chemical solution.
Chromates come in bright (clear to bluish), colored (yellow to reddish iridescent), and black versions, and their corrosion resistance differs. Published data from one plating company in Japan show salt spray results of about 24–72 hours for bright chromate and about 96–150 hours for colored and black chromate. In other words, the same zinc plating can differ widely in rust resistance depending on the chromate.
Traditional colored chromate contains hexavalent chromium, and it is increasingly being replaced by trivalent chromate (三価クロメート, sanka kuromeeto), which contains no hexavalent chromium. ASTM B633 reflects the same shift: Types II and III are chromate finishes, while Types V (colorless passivate) and VI (colored passivate) were added to allow non-chromate treatments. A typical US callout looks like "Zinc plate per ASTM B633, Fe/Zn 8, Type V, SC 2." Note that with trivalent passivates, color no longer tells you the corrosion resistance; the salt spray requirement does.
Electroplated Zinc vs. Hot-Dip Galvanizing
Besides electroplated zinc, Japanese drawings may call for hot-dip galvanizing (溶融亜鉛めっき, yoyu aen mekki, nicknamed ドブ漬け dobuzuke), where steel is dipped into molten zinc at about 420°C (790°F) or higher. Hot-dip coatings are thick and suit structures used outdoors for a long time, such as guardrails, towers, and structural steel.
Hot-dip thickness is hard to control precisely, so threaded parts and machine parts with tight dimensions get electroplated zinc, which is thinner and easier to control. A simple rule for reading drawings: large outdoor structures are hot-dip; small machine parts are electroplated.
Hydrogen Embrittlement and Baking
The main risk with electroplated zinc is hydrogen embrittlement (水素脆性, suiso zeisei). Hydrogen generated during plating enters the steel and makes it brittle, and a bolt can then snap suddenly after tightening. The harder the steel, the more susceptible it is: hardened high-strength bolts and springs are the classic cases.
The fix is a relief bake (ベーキング, beekingu) soon after plating. JIS H 8610 requires the bake, when specified, to start no later than 4 hours after plating, and leaves the conditions to agreement between buyer and plater; platers in Japan typically describe it as several hours at about 200°C (390°F). In the JIS symbol system the bake is written as HB. On the US side, ASTM B850 is the guide for post-plating baking, and ASTM B633 excludes steels with tensile strength above 1,700 MPa (247 ksi, 46 HRC) from its scope. Because the decision depends on the actual steel strength, make sure the drawing or purchase order states whether baking is required.
Nickel Plating: Appearance and Undercoat
Electrolytic nickel has a slightly yellowish white luster that resists tarnish, so it is widely used on visible parts and electronic parts. It also bonds well to steel and copper alloys, which is why it is very often used as the undercoat for other platings.
A familiar example is the "chrome" finish on faucets and car bumpers. It is actually a multilayer system: a very thin chromium layer on top of nickel.
The surface you see is chromium, but the nickel underneath does the rust protection.
The layer combination and thicknesses change with the base metal and the required corrosion resistance.
Bright vs. Dull Nickel
Electrolytic nickel is bright, semi-bright, or dull (matte), depending on the brighteners added to the bath. Hardness changes along with the look: published figures put bright nickel at about HV 550 and dull nickel at HV 150–250.
Because bright nickel is hard, it is more likely to crack or cause defects in secondary operations after plating, such as bending or spot welding. For parts that are formed or welded after plating, specify dull or semi-bright nickel, and think about the downstream processes when you write the callout.
Magnetism
An easy point to miss: nickel is strongly magnetic. Electrolytic nickel puts a magnetic layer on the surface even when the base metal is nonmagnetic stainless steel or a copper alloy. That can be a problem for parts near sensors or in electronics that must avoid magnetic effects, so consider it together with the base metal choice. For which stainless grades are magnetic, see SUS304, SUS316, SUS430: JIS Grades and AISI/ASTM Equivalents.
Chromium Plating: Decorative Chrome vs. Hard Chrome
"Chrome plating" covers two processes used for entirely different purposes: decorative chromium and hard (engineering) chromium, called 硬質クロムめっき (koshitsu kuromu mekki) or 工業用クロムめっき (kogyoyo kuromu mekki) in Japanese. If the drawing just says "クロムめっき," you may get a different process than the designer intended, so the callout has to name one or the other.
Same metal, completely different purpose and thickness.
Hardness is the figure published by a Japanese hard-chrome plater.
Hard Chrome for Sliding Parts
Hard chrome is very hard (HV 800–1,000) with a slippery, low-friction surface. It has long been used to extend the life of parts that slide against each other, such as hydraulic cylinder rods, pistons, and rolls for papermaking and printing. Some platers can build it beyond 500 µm. As an electroplated coating, though, it does not reach well into holes or intricate shapes. On high-carbon steel, a hydrogen relief bake is used, just as with zinc. A common US specification for hard chrome is AMS 2460, which superseded QQ-C-320.
Decorative Chrome Depends on the Undercoat
The chromium layer in decorative chrome is very thin, and nickel does the rust protection. To improve corrosion resistance, look at the nickel thickness and layer structure, not the chromium. JIS H 8617 grades reflect this: higher grades call for thicker or double-layer nickel with microporous or microcracked chromium.
Some platers are switching from hexavalent to trivalent chromium plating baths. Trivalent chrome has a slightly different color, so when a visible part switches over, compare samples side by side with existing parts.
Electroless Nickel: Complex Shapes and Tight Tolerances
Of the four types, electroless nickel is the one made for precision parts. It coats the inside of holes and grooves to the same thickness as the outside, so parts can hold their dimensions without finishing after plating. It is used on precision machine parts, electronic parts, and mold components, and is often chosen to replace electrolytic nickel where that cannot coat every surface. The phosphorus content of the coating drives most of its properties.
Less phosphorus means harder; more phosphorus means better corrosion resistance and a nonmagnetic deposit.
The ranges are those used by Japanese platers and vary slightly between companies. ASTM B733 type ranges are from a US plater's summary; check the standard. Heat treatment changes the properties.
Heat Treatment Raises Hardness
As plated, electroless nickel is about HV 400–500, harder than electrolytic nickel. Heat treatment after plating at roughly 300–400°C (570–750°F) changes the coating structure and raises hardness to about HV 700–800 (one plater specifies 320°C). Some data show it reaching about HV 1,000 under certain conditions, and a reference annex of JIS H 8645 gives heat treatment conditions for HV 600–1,000. Heat-treated electroless nickel approaches hard chrome in wear resistance, which is why it is considered for complex parts that hard chrome cannot coat well. Since heat treatment changes the coating, the drawing or purchase order should state whether it is required and at what temperature.
Cost and Bath Control
The drawback of electroless nickel is cost. The bath's chemical concentrations, temperature, and pH must be held in range at all times, which takes skill and equipment, and materials and processing time add up, so it usually costs more than electrolytic nickel. For a simple steel part where rust protection is the only goal, zinc is almost always enough. Choose electroless nickel when you need dimensional accuracy, coverage of complex shapes, or a nonmagnetic coating (high phosphorus); otherwise you are paying for quality the part does not need.
Hexavalent Chromium Rules and What They Mean for the Callout
Hexavalent chromium (Cr(VI)) is highly toxic and is a restricted substance under the EU RoHS Directive, with a maximum concentration of 0.1 wt% in homogeneous materials. The EU ELV Directive (end-of-life vehicles) also restricts it, together with lead, mercury, and cadmium. The confusing part is that several processes have "chromium" in their names. The restriction targets hexavalent chromium compounds, not chromium metal.
Chrome plating (a metal coating) and chromate (a conversion coating) are different things.
For products, the real issue is hexavalent chromate on zinc. Chrome plating reduces the chromium compound to metal as it deposits, so the coating itself contains no hexavalent chromium compounds and is generally regarded as RoHS compliant. However, some customers' green procurement standards (グリーン調達基準, guriin chotatsu kijun) ban hexavalent chromium in the process as well. Check legal compliance and the customer's own requirements separately.
Rules at the plating plant are changing too. Under Japan's Water Pollution Control Act, the national effluent standard for hexavalent chromium compounds dropped from 0.5 mg/L to 0.2 mg/L on April 1, 2024, with a provisional 0.5 mg/L limit for electroplating plants for three years. For buyers, the cost of compliance may show up in plating prices or in which processes a Japanese plater still offers.
How to Choose (or Check) a Plating Callout
Whether you are choosing a plating yourself or checking whether a Japanese designer's choice makes sense, start by fixing one purpose for the plating. A vague "nickel, just in case" wastes money or falls short on performance.
Purpose, then shape and tolerances, then base metal and downstream steps, then regulations.
Settle the final spec with the plater, including thickness, pretreatment, and masking areas.
Most of the conditions in the second half are decided at the design stage and written onto the drawing during detailed design. Fixing the surface treatment at the same time as the material and tolerances cuts rework after prototyping.
State Whether Dimensions Apply Before or After Plating
Plating adds material, so fits and threads change by the coating thickness. If the drawing does not say whether a dimension applies before or after plating, parts may not assemble or threads may not engage. For machined or ground precision parts, decide whether you will grind to size after plating or machine undersize to allow for the coating, and plan it together with the machining steps. For how general tolerances apply on Japanese drawings, see JIS Tolerance Chart: JIS B 0405 General Tolerances vs. ASME.
Common Mistakes
- Electroplated zinc on high-strength bolts with no baking instruction; bolts fractured after tightening
- A callout of just "クロムめっき" when wear resistance was the goal; parts came back with decorative chrome
- Bright nickel on sheet metal that was bent after plating; the coating cracked at the bends
- Nickel plating on a nonmagnetic stainless part; a nearby sensor malfunctioned
- Electroless nickel specified "just to be safe" on a part that only needed rust protection; unit cost rose sharply
None of these is a problem with the plating type itself. They come from how the purpose and conditions were communicated. When you talk to a plater, describe how the part is used and what performance you need, and you will get better proposals.
Checklist: What a Complete Plating Callout Should Tell You
Before you quote, release, or substitute a local specification, confirm each of these with the drawing or the Japanese side:
- Standard and edition: JIS H 8610 / H 8617 / H 8615 / H 8645, or a company standard, and which edition
- Plating type: for chromium, decorative or hard; for nickel, electrolytic or electroless
- Thickness: minimum or nominal, and where it is measured (significant surfaces)
- Post-treatment: chromate type (bright, colored, black) and whether it must be trivalent or Cr(VI)-free; meaning of any CM1/CM2 code
- Corrosion requirement: salt spray hours to white rust and red rust, if any
- Nickel type: bright, semi-bright, or dull; layer structure for decorative chrome
- Electroless nickel: phosphorus range, and heat treatment (yes/no, temperature)
- Hydrogen embrittlement: steel hardness or strength, baking required (HB), and conditions
- Dimensions: before or after plating; masking areas; threads and fits
- Compliance: RoHS, ELV, and the customer's green procurement standard
- Local spec: if you plan to plate to ASTM B633, B733, AMS 2460, or similar, written approval from the Japanese customer
Sample Inquiry to the Japanese Side
Edit the bracketed parts and send it before you quote:
Subject: Plating requirements for drawing [drawing number]
We are reviewing drawing [drawing number], rev. [x]. The surface treatment note reads "[note as written, e.g., Ep-Fe/Zn8/CM2]." Before we quote, please confirm the following:
1. Applicable standard and edition (e.g., JIS H 8610:1999, or your company standard)
2. Minimum coating thickness and the surfaces where it applies
3. Chromate type, and whether a trivalent (Cr(VI)-free) chromate is required
4. Salt spray requirement (hours to white rust / red rust), if any
5. Whether hydrogen embrittlement relief baking is required, and the conditions
6. Whether the dimensions shown apply before or after plating, and any masking areas
7. RoHS / ELV or green procurement requirements that apply to this part
8. Whether plating to [ASTM B633 Fe/Zn 8, Type V, SC 2, or other local specification] is acceptable as an alternativeThank you.
Limits of This Guide
- The JIS symbol system here is from JIS H 0404:1988, and the plating standards are cited in the editions available to us (mostly 1999). Your customer may cite a different edition or a company standard; that takes precedence.
- JIS-to-ASTM correspondences are process-level comparisons. Thickness classes, test methods, and acceptance criteria differ, so a JIS callout cannot be replaced with an ASTM callout without the customer's agreement.
- Hardness, salt spray hours, and thickness accuracy are figures published by individual Japanese platers, not limits from the standards. Actual results depend on the plater, part shape, and process conditions.
- Hydrogen embrittlement relief depends on the steel's actual strength and the plating process. Whether and how to bake is a decision for the designer and plater, not something to settle from this article.
- Regulatory points (RoHS, ELV, Japanese effluent standards) are summarized for context. Check the current legal text for your product and market.
Plating is one of several surface treatments that show up on Japanese drawings. For aluminum parts, see Alumite (Anodizing) on Japanese Drawings: Types and Callouts; for painted parts, see E-Coat vs Powder Coat: Coating Callouts on Japanese Drawings.
Key Takeaways
- JIS plating callouts like Ep-Fe/Zn8/CM2 follow JIS H 0404: process / base metal / coating and minimum thickness / post-treatment
- Electroplating and electroless plating build thickness very differently; only electroless nickel is uniform on complex shapes
- Zinc protects steel sacrificially at low cost; watch the chromate type (trivalent, ASTM B633 Type V/VI) and hydrogen embrittlement
- Nickel is the go-to undercoat and decorative finish; watch magnetism and cracking in post-plating forming
- Decorative and hard chrome are different jobs; a callout must name one. Electroless nickel suits precision parts but costs more
FAQ
What does Ep-Fe/Zn8/CM2 mean?
It is a JIS H 0404 plating designation: electroplated (Ep) zinc on iron or steel (Fe/Zn), 8 µm minimum thickness, with a colored chromate post-treatment (CM2). CM1 would be bright chromate. Ask whether a trivalent chromate is required, since the 1988 symbol system has no separate code for it.
What is the ASTM equivalent of JIS H 8610?
The closest US specification is ASTM B633 (electrodeposited zinc on iron and steel), whose SC1–SC4 classes correspond to Fe/Zn 5, 8, 12, and 25. JIS H 8610 was based on ISO 2081. The two are comparable, not interchangeable, so get approval before substituting.
Is trivalent chromate the same as ASTM B633 Type V or VI?
They describe the same kind of finish: a Cr(VI)-free passivate on zinc, colorless (Type V) or colored (Type VI). Japanese drawings usually write it out as 三価クロメート rather than a standard symbol, so confirm the color and any salt spray requirement with the customer.
Electroless nickel vs. hard chrome: which should I use?
Hard chrome is harder as plated (about HV 800–1,000) and suits simple sliding parts such as cylinder rods. Electroless nickel coats complex shapes and holes evenly, and after heat treatment it reaches about HV 700–800, so it is the alternative where hard chrome cannot reach.
Does chrome plating violate RoHS?
Generally no. The deposited chromium is metal, not a hexavalent compound. The RoHS issue is hexavalent chromate on zinc. Some customers, however, ban hexavalent chromium in the process as well, so check their green procurement standard.
Sources
- JIS H 0404:1988 (graphical symbol for electroplated coating): kikakurui.com, text of the standard (Japanese)
- JIS H 8610:1999 (electroplated coatings of zinc on iron or steel): kikakurui.com (Japanese)
- JIS H 8625:1993 (chromate conversion coatings on electroplated zinc and cadmium): kikakurui.com (Japanese)
- JIS H 8617:1999 (electroplated coatings of nickel and chromium): kikakurui.com (Japanese)
- JIS H 8645:1999 (autocatalytic nickel-phosphorus coatings): kikakurui.com (Japanese)
- JIS H 8615 (chromium for engineering purposes) and ISO 6158 correspondence: AFNOR standards catalog
- ASTM B633 scope, Types V and VI, high-strength steel limit: ASTM International, B633-23
- ASTM B633 classes and types, typical callout: Gleco Plating, "Zinc Plating Specifications (ASTM B633)"
- ASTM B733 phosphorus types: Gleco Plating, specification reference
- ASTM B456 scope: ASTM International, B456-17; ASTM B689: ASTM International
- AMS 2460 superseding QQ-C-320: US Chrome
- ASTM B850 (post-coating treatment for hydrogen embrittlement): Nimonik standards listing
- ISO 19598:2016 (zinc and zinc alloy coatings with Cr(VI)-free treatment): Standards Council of Canada listing
- Codes such as MFZn8 depend on the governing specification: finishing.com Q&A
- RoHS substances and maximum concentration: JETRO, "Overview of the EU RoHS Directive" (Japanese)
- ELV Directive substances: EnviX, "EU ELV Directive" (Japanese)
- Japan's hexavalent chromium effluent standard revision: Ministry of the Environment, Japan (Japanese); Osaka Prefecture (Japanese)
- Chrome plating vs. chromate and RoHS: mekkikakou.com, "Trivalent and Hexavalent Chromium" (Japanese)
- How zinc protects steel: Japan Galvanizers Association (Japanese)
- Zinc chromate types, salt spray hours, baking, designation examples: Sanwa Mekki Kogyo, "Zinc Plating" (Japanese)
- Bright chromate nicknamed "yunikuro": Negurosu Denko technical note (Japanese)
- Hot-dip vs. electroplated zinc: Nissin Kogyo (Japanese)
- Nickel hardness, magnetism, secondary operations: Sanwa Mekki Kogyo, "Nickel Plating" (Japanese)
- Nickel plating types and phosphorus content: Kiyokawa Mekki Kogyo (Japanese)
- Electroless nickel principle and phosphorus types: Suzuki Hi-Tech (Japanese); electrolytic vs. electroless: Suzuki Hi-Tech (Japanese)
- Electroless nickel hardness and thickness accuracy: Kinki Boshoku (Japanese); hard chrome hardness and uses: Kinki Boshoku (Japanese)
Original article in JapaneseThis guide is adapted from a MONOSCOPE article written for readers in Japan: めっきの種類と違い｜亜鉛・ニッケル・クロム・無電解の選び方
About the editor
MONOSCOPE EditorFOUNDER & EDITORSpent about ten years at a plant equipment maker and a plant engineering company, proposing, designing, and commissioning equipment, then moved into web marketing. Now a web consultant for B2B manufacturers, helping them explain their products and technology. Licensed in Japan as an Energy Manager and a Third-Class Chief Electrical Engineer.
Has run an engineering blog since 2017 (500+ articles) and a Japanese YouTube channel with about 20,000 subscribers. Each English guide is written from the Japanese shop-floor point of view and checked against the cited standards.
