ASTM G65 and ASTM G75 are both useful abrasion tests, but they answer different engineering questions. G65 evaluates dry sand abrasion with a rubber wheel and reports material volume loss, making it useful for ranking materials under controlled scratching abrasion. G75 evaluates slurry abrasivity and the abrasion response of materials in a liquid-solid slurry, using Miller Number and SAR Number concepts. Choosing between them should therefore be based on the actual wear medium and mechanism rather than simply selecting the test with the more familiar name. :contentReference[oaicite:0]{index=0}

ASTM G65 vs ASTM G75: The Core Difference

The simplest distinction is dry abrasive contact versus slurry abrasion. ASTM G65 uses a dry sand/rubber wheel arrangement to evaluate resistance to scratching abrasion. ASTM G75 is designed for slurries and can characterize either the abrasivity of the slurry or the abrasion response of a material in a particular slurry. :contentReference[oaicite:1]{index=1}

What ASTM G65 Actually Measures

ASTM G65 is intended to produce reproducible rankings of metallic materials under specified dry scratching-abrasion conditions. The test result is reported as volume loss in cubic millimetres. A lower volume loss indicates higher abrasion resistance within the specified test conditions. :contentReference[oaicite:2]{index=2}

The method includes several procedures for different material conditions. Procedure A is relatively severe and is suitable for ranking materials across a broad range of abrasion resistance. Procedure B is a shorter variation and is particularly useful for medium- and low-abrasion-resistant materials. Procedures C, D and E are intended for other material thicknesses or resistance ranges. :contentReference[oaicite:3]{index=3}

How to Read a G65 Result

The basic interpretation is straightforward:

• Lower volume loss: better resistance under the specified test conditions.
• Higher volume loss: greater material removal during the test.
• Small difference: check test repeatability before declaring a meaningful performance advantage.
• Different procedures: do not compare values directly without confirming that the test conditions are equivalent.

G65 should primarily be used for relative ranking. ASTM specifically notes that the test does not reproduce every real operating condition, including actual abrasive particle size, shape, pressure, impact and corrosive effects. Therefore, a G65 result should not be interpreted as an exact prediction of component service life. :contentReference[oaicite:4]{index=4}

What ASTM G75 Measures

ASTM G75 addresses a different problem: abrasion caused by a slurry. The method can generate a Miller Number for the relative abrasivity of a slurry or a SAR Number for the abrasion response of a material in a specified slurry. :contentReference[oaicite:5]{index=5}

The distinction is important. Miller Number focuses on the slurry, while SAR Number focuses on the material's response to a particular slurry. This makes the method useful when the operating system contains water or another liquid together with abrasive solid particles.

ASTM G75 also notes that Miller Number, D2 Number and SAR Number values around 50 or lower have historically been associated with minor abrasive damage during pumping, while values above about 50 require greater precautions. This should be treated as practical guidance rather than a universal service-life limit because actual equipment conditions vary. :contentReference[oaicite:6]{index=6}

Dry Sand or Slurry? Choose the Test from the Application

The correct test should begin with the wear mechanism in the actual equipment, not with the material grade.

Why G65 and G75 Results Should Not Be Compared Directly

A common mistake is to assume that a lower G65 volume loss automatically means better performance in a slurry application. That conclusion is not justified. G65 and G75 use different wear environments, test mechanisms and reporting systems.

For example, a hardfacing layer may perform very well against dry mineral particles but behave differently when liquid is introduced. The liquid can change particle movement, contact conditions, material removal mechanisms and the way debris leaves the contact zone. Consequently, test environment can change the relative ranking of materials.

How Carbide Hardfacing Layers Affect the Results

For chromium-rich and other carbide-containing hardfacing layers, the test result should be evaluated together with the microstructure. Carbide type, size, morphology, volume fraction and distribution can affect abrasive wear behavior.

A very high carbide fraction does not automatically produce the lowest wear loss. If coarse carbides are poorly supported by the matrix, they can fracture or detach. Conversely, a refined carbide structure with an appropriate matrix can provide more stable resistance against abrasive particles.

This is especially important when comparing hardfacing materials. A complete evaluation should combine hardness, chemical composition, carbide morphology, carbide distribution and abrasion-test results rather than relying on hardness alone.

Hardfacing Cladded Plate

Overlay Plate

Hardfaced Plate Hardcarb

Overlay Wear Plate

A Practical Test Selection Workflow

1. Identify the wear medium. Determine whether the abrasive is dry or suspended in a liquid.
2. Identify the dominant mechanism. Separate scratching abrasion from slurry-induced material removal.
3. Select the standard. Use G65 for standardized dry sand/rubber wheel abrasion and G75 for slurry abrasivity or material response.
4. Define the test procedure. For G65, specify the applicable procedure rather than reporting only the standard number.
5. Record the complete test conditions. Include specimen condition, test procedure and relevant slurry or abrasive information.
6. Compare like with like. Do not compare results generated by fundamentally different test conditions.
7. Link the result to microstructure. Examine carbide morphology and matrix structure when evaluating hardfacing materials.

What Should Be Included in a Professional Abrasion Test Report?

A useful report should contain more than one abrasion number. For material qualification or supplier comparison, the following information should be recorded:

• Material grade and overlay composition
• Test standard and revision
• G65 procedure, where applicable
• Test specimen dimensions and surface condition
• Abrasive or slurry description
• Test result and measurement unit
• Number of repeated specimens
• Average and individual results
• Hardness data
• Metallographic observations
• Any deviations from the standard procedure

This format makes the result much more useful for procurement and engineering decisions because the number can be traced back to the actual test conditions.

Teda Ganghua Support for Wear-Resistant Material Selection

For industrial applications where abrasive wear is a major design concern, Teda Ganghua can support material sourcing and specification matching for wear-resistant steel products. Test requirements can be considered together with hardness, chemical composition, dimensions, application conditions and inspection requirements.

When the application involves mining, conveying, crushing, material handling or other abrasive service, buyers should define whether the dominant environment is dry particle abrasion or slurry abrasion before selecting a laboratory test. For suitable wear-resistant steel options, material selection can then be matched with the required service conditions and inspection criteria.

FAQ

Is ASTM G65 better than ASTM G75?

Neither test is universally better. G65 is more appropriate for standardized dry scratching abrasion, while G75 is intended for slurry abrasivity and material response in a slurry. The correct method depends on the actual wear environment.

What does a lower G65 volume loss mean?

A lower volume loss generally indicates better abrasion resistance under the specified G65 test conditions. It should primarily be used to rank materials tested under comparable conditions.

What is the difference between Miller Number and SAR Number?

Miller Number characterizes the relative abrasivity of a slurry using a specified reference material. SAR Number characterizes the abrasion response of a material when tested in a particular slurry. :contentReference[oaicite:7]{index=7}

Can G65 results predict the exact service life of a wear plate?

No. G65 is designed primarily for reproducible material ranking under specified conditions. Actual service life also depends on particle size, particle shape, impact, load, sliding conditions, corrosion and other field variables. :contentReference[oaicite:8]{index=8}

Should a hardfacing layer be tested by both methods?

It can be useful when the component operates under both dry and wet abrasive conditions, or when the actual field mechanism is uncertain. Testing should be selected based on the intended service environment rather than performed simply to obtain more numbers.