SmCo Magnet Grade Equivalents: Translating Chinese (GB/T) Specs for Global Procurement

One of the most common friction points in global magnet procurement occurs the moment an engineering drawing crosses a buyer's desk and is sent to a supplier. The drawing, drafted by an engineer in North America or Europe, specifies a Samarium Cobalt grade based on an older US standard (like MMPA) or an international standard (like IEC). However, the buyer sends this RFQ to a manufacturer in China—the epicenter of rare earth processing—and receives a quote back for a grade starting with "YXG".

This mismatch immediately stalls the procurement cycle. The buyer must ask engineering: "Is YXG-28H the exact same as SmCo 28?" The engineer looks at the data sheet, sees slight differences in testing conditions or intrinsic coercivity margins, and hesitates.

Without a clear framework for translating magnet grades across regional standards, procurement teams face two severe risks: either they over-specify the material (driving up costs unnecessarily), or they accept a "close enough" equivalent that eventually fails in high-temperature validation.

This guide provides a definitive cross-reference methodology for mapping Chinese (GB/T) Samarium Cobalt standards to MMPA and IEC standards, ensuring your RFQs are quoted accurately and your application boundaries are protected.

Scope and limits (reviewed July 22, 2026): This article is for global OEM procurement and engineering teams translating sintered SmCo grade names for RFQ screening. It is not a substitute for purchased standards, supplier datasheets, or lot-specific B-H curve validation. Use the mapping below as a controlled RFQ starting point, then confirm guaranteed minimum Br, Hcj, BHmax, operating temperature, and geometry-specific flux acceptance before production release. For product-family context, compare SmCo5 magnets and Sm2Co17 magnets.

The Global Landscape of Magnet Standards

To understand why grade mismatches occur, you must first understand the origins of the three primary naming systems used in the permanent magnet industry today.

1. MMPA (Standard Specifications for Permanent Magnet Materials)

The Magnetic Materials Producers Association (MMPA) was historically the standard-bearer for magnet specifications in the United States. Although the MMPA was absorbed by the International Magnetics Association (IMA) and the standards haven't been heavily updated in recent years (Standard 0100-00), MMPA nomenclature remains deeply embedded in legacy engineering drawings, particularly in the aerospace and defense sectors. MMPA grades are typically straightforward, indicating the material family and the nominal Maximum Energy Product (BHmax). For example, SmCo 18 implies a Samarium Cobalt magnet with a typical BHmax of 18 MGOe.

2. IEC (International Electrotechnical Commission)

The IEC 60404 series (specifically IEC 60404-8-1) is the globally recognized European standard for magnetically hard materials. IEC standards use an alphanumeric coding system that is highly precise but notoriously difficult to read at a glance. A grade might be designated as R5-1-140/60, where the numbers indicate material class, coercivity, and energy density. While technically superior for strict compliance, it is rarely used in daily commercial dialogue.

3. GB/T (Chinese National Standards)

Because over 80% of global rare earth extraction and physical magnet sintering occurs in China, the Chinese National Standard (Guobiao, or GB/T 17951-2022 for magnetically hard materials) is the defacto language of the manufacturing floor. Chinese manufacturers formulate, test, and stock raw materials based on GB/T criteria. If you do not translate your MMPA or IEC requirement into the equivalent GB/T standard, the factory must do it for you—often making assumptions about your thermal requirements in the process.

Decoding the Chinese GB/T Naming Convention (YXG)

When you receive a quote from a Chinese supplier, the SmCo grade will almost always start with the letters YXG. Understanding this prefix is the first step to validating the quote.

• Y (Yongci): This stands for "Permanent Magnet" in Chinese pinyin.
• X (Xitu): This stands for "Rare Earth".
• G (Gu): This stands for "Cobalt" (the chemical element Co).

Therefore, YXG simply means "Rare Earth Cobalt Permanent Magnet".

Following the prefix, you will see a number. This number represents the typical Maximum Energy Product (BHmax) in MGOe. For example, in YXG-28, the material has a BHmax of around 28 MGOe.

Finally, for Sm2Co17 (2:17 series) magnets, the grade is often followed by a suffix letter that designates the Intrinsic Coercivity (Hcj) level, which dictates its resistance to demagnetization at high temperatures:

• No suffix or M (Medium): Standard coercivity, suitable for normal motor applications up to 250°C.
• H (High): High coercivity, pushing the temperature threshold to 300°C.
• SH / UH / EH: Ultra-high coercivity variations for extreme environments (350°C+), heavily used in downhole drilling and aerospace sensors.

SmCo5 (1:5 Series) Grade Equivalency

The SmCo5 family was the first commercially viable Samarium Cobalt magnet. Because the metallurgy of 1:5 magnets is relatively straightforward compared to the 2:17 series, grade matching across standards is generally highly reliable. These grades are typically chosen when moderate magnetic strength is acceptable, but excellent temperature stability (up to 250°C) and ease of magnetization are required.

Below is a robust equivalency matrix for the most common SmCo5 grades.

Note: The SmCo5 family rarely uses suffix letters because the intrinsic coercivity is naturally high relative to its remanence. YXG-24 is often the upper limit of mass-produced 1:5 technology.

Sm2Co17 (2:17 Series) Grade Equivalency

Translating Sm2Co17 grades is significantly more complex. The 2:17 alloy matrix contains Iron (Fe), Copper (Cu), and Zirconium (Zr) alongside Samarium and Cobalt. By tweaking the ratios of these transition metals and altering the heat-treatment cycle, manufacturers can dramatically shift the balance between Remanence (Br) and Intrinsic Coercivity (Hcj).

Because MMPA standards often group these variations under broad umbrellas, relying on a 1:1 name match is dangerous. A buyer asking for "SmCo 26" might receive a standard coercivity part (which fails at 300°C) when their engineer actually intended for a high-coercivity part.

Notice the critical divergence in the YXG-28/30/32 families. If your application pushes past 250°C, or faces strong external reverse magnetic fields (like in a high-speed traction motor), you must explicitly specify the "H" (High Coercivity) variant, even if the legacy drawing just says "SmCo 28".

Grade Translation Workflow

To prevent miscommunication during the quoting process, engineering and procurement teams should follow a standardized translation logic before finalizing the RFQ package.

The "Typical" vs "Minimum" Value Trap

When transitioning from Western drawings to Chinese manufacturing floors, buyers often stumble into the tolerance trap.

MMPA and IEC standards often emphasize minimum acceptable values for critical properties like Remanence (Br) and Intrinsic Coercivity (Hcj). If a drawing strictly calls out MMPA standards, the engineer expects every single part in the lot to exceed those baseline numbers.

Conversely, some Chinese factories quote GB/T standard grades based on typical batch averages. If you order YXG-28, the factory aims for an average BHmax of 28 MGOe. However, within a standard distribution curve, a small percentage of that batch might actually test closer to 26.5 MGOe.

If your application is hyper-sensitive to magnetic flux variations (such as a tightly calibrated Hall-effect sensor array), a typical batch average is not good enough.

The Solution: When asking a supplier to cross-reference an MMPA grade to a GB/T grade, you must explicitly state in the RFQ: "All magnetic properties for the proposed GB/T equivalent must be guaranteed minimums per lot, not typicals."

Procurement & Engineering Checklist for Grade Specification

Before releasing a Samarium Cobalt RFQ to a global supplier base, ensure your documentation bridges the standards gap. Use this checklist to verify your RFQ package:

• Dual Nomenclature: Does the drawing list both the legacy standard (e.g., MMPA SmCo 26) AND the acceptable GB/T equivalent (e.g., YXG-26H)?
• Explicit Hcj Minimums: Are the minimum Intrinsic Coercivity (Hcj) values explicitly written on the drawing, regardless of the grade name?
• Operating Temperature Callout: Is the continuous and peak operating temperature clearly stated, so the supplier can catch obvious grade mismatches?
• B-H Curve Requirement: Does the RFQ require the supplier to provide demagnetization (B-H) curves at room temperature (20°C) AND your maximum operating temperature?
• Traceability: Does the quality clause require material origin tracing to ensure the rare earth elements comply with your specific geographic sourcing policies?

By checking these five boxes, you remove the guesswork from the supplier's quote, forcing them to commit to a specific metallurgical baseline rather than hiding behind ambiguous naming conventions.

Magnetic Testing & Validation: Proving the Grade Matches

Even if you successfully translate an MMPA standard to a GB/T standard on paper, the physical validation of the delivered magnets is where many global procurement programs fail. A factory may accept your PO for "YXG-28H (Equivalent to SmCo 28 High Coercivity)", but how do you verify the incoming batch actually meets those thermal and magnetic baselines?

1. The Room Temperature B-H Curve (Demagnetization Curve)

The most fundamental proof of material grade is the B-H curve. Every reputable Chinese supplier has a hysteresisgraph (often NIM-2000 or similar system) used to plot the second quadrant of the hysteresis loop.

• What to look for: The curve will show Remanence (Br) on the Y-axis and Coercivity (Hcb/Hcj) on the X-axis.
• The Pitfall: Many suppliers only provide a theoretical curve from their catalog. Your RFQ must explicitly demand a batch-specific B-H curve tested from the actual sintered block that your parts are cut from.

2. High-Temperature Testing

Because the primary reason for choosing SmCo over NdFeB is high-temperature stability, room temperature testing is insufficient.

• If your application runs at 250°C, a room temperature curve cannot guarantee performance.
• You must require a B-H curve tested at your maximum operating temperature. The supplier will heat the sample in the hysteresisgraph and generate a high-temperature curve.
• What to look for: Check the "knee" of the curve (the point where the curve drops off sharply). If the knee occurs before your operating permeance coefficient (Pc) line, the magnet will suffer irreversible demagnetization in the field, proving the supplied grade (e.g., YXG-26) was inadequate or improperly heat-treated, regardless of what the paperwork says.

3. Helmholtz Coil Flux Testing for Mass Production

While a B-H curve is required for lot qualification, it is a destructive test (requires a specific sample cylinder or cube). For mass production incoming inspection, you cannot rely on B-H curves.

• Instead, translate your chosen GB/T grade into a Total Magnetic Flux (Maxwell or Weber) value for your specific geometry.
• Use a Helmholtz coil connected to a Fluxmeter. Establish a minimum flux value (e.g., Min 2.45 mWb) based on the agreed GB/T grade's minimum Remanence.
• This allows 100% non-destructive testing of incoming parts, bridging the gap between Chinese material standards and your local receiving inspection.

Frequently Asked Questions (FAQ)

Can we just use the supplier's proprietary grade instead of a standard GB/T grade? Yes, many top-tier manufacturers have proprietary grades (often indicated by an "S" or custom suffix, like YXG-28S). These are often highly optimized for specific applications like low reversible temperature coefficients or enhanced machinability. However, using a proprietary grade locks you into a single source. It is safer for long-term procurement to specify the closest standard GB/T grade as the baseline, and accept proprietary grades only if they offer a distinct, validated performance advantage.

Why do two suppliers quote different GB/T grades for the exact same MMPA spec? This happens when your drawing lacks continuous operating temperature data. Supplier A might quote YXG-26 (standard Hcj) assuming a room-temperature application to win on price. Supplier B might quote YXG-26H (high Hcj) assuming an aerospace application to guarantee safety. Always define the thermal environment to force suppliers to quote on a level playing field.

Is the GB/T 17951 standard strictly enforced by all Chinese manufacturers? The GB/T standard provides the baseline framework for the industry, but actual lot-to-lot consistency depends entirely on the manufacturer's internal ISO 9001 or IATF 16949 quality controls. The standard defines the naming convention and test methods, but the factory's process control dictates whether they actually hit those numbers consistently.

Does a higher GB/T number (e.g., YXG-32 vs YXG-26) mean the magnet is physically harder or more brittle? Not necessarily. The number represents magnetic energy (BHmax), not mechanical hardness. All Sm2Co17 magnets are extremely brittle (Vickers hardness ~500-600). However, ultra-high coercivity variations (the "H" or "SH" suffixes) often require slightly different heat treatments that can induce micro-stresses, making them marginally more prone to chipping during machining compared to standard grades. Therefore, higher magnetic performance often demands wider mechanical tolerances.

What happens if a Chinese supplier quotes a NdFeB grade (like N45SH) instead of a SmCo YXG grade? This is a red flag indicating a severe miscommunication. Suppliers sometimes substitute NdFeB if they see a 150°C requirement because NdFeB is cheaper and easier to machine. However, NdFeB has a completely different temperature coefficient and corrosion profile. If your design specifies SmCo (MMPA or IEC), you must explicitly reject any Neodymium substitutions unless your engineering team has fully re-qualified the magnetic circuit for NdFeB's higher flux drop-off at elevated temperatures.

Next Steps for Your RFQ

Stop letting ambiguous grade translations delay your project schedules or inject hidden thermal risks into your assemblies. By mapping your legacy MMPA and IEC requirements directly to the GB/T YXG-series, you take control of the sourcing narrative.

Need help translating a legacy drawing, verifying a supplier's proposed equivalent, or locking down your RFQ validation criteria? We can map your exact flux and temperature requirements to the optimal global standard. Send the drawing through the contact page, contact our engineering support at [email protected], or reach out via WhatsApp.

Sources & References

To delve deeper into the exact testing methodologies and full metallurgical spectrums, consult the primary standards:

1. GB/T 17951-2022 - SAMR/SAC public standards record for GB/T 17951-2022, the Chinese national standard record for magnetically hard materials.
2. MMPA Standard 0100-00 - Standard Specifications for Permanent Magnet Materials PDF, the legacy US permanent-magnet material classification reference still used on many drawings.
3. IEC 60404-8-1:2023 - IEC Webstore publication record, the current IEC entry for specifications of permanent magnet (magnetically hard) materials.
4. IEC 60404-8-1:2015 - IEC Webstore legacy publication record, useful when validating older drawings that cite the previous edition.