National Standards for Solid Hardness Testing: GB Standards, Methods, and Applications

Solid hardness testing is a cornerstone of materials quality control, and China's national standards (GB) provide a rigorous, internationally harmonized framework for determining the hardness of metals, polymers, ceramics, coatings, and other solid materials. This article explains the principal GB/T standards for hardness determination, including Brinell, Rockwell, Vickers, Shore, and Leeb methods, together with applicable sample types, testing procedures, verification requirements, and typical industrial applications.

Technical Overview

Hardness describes a solid material's resistance to localized plastic deformation, indentation, or scratching, and it is one of the most frequently measured mechanical properties in manufacturing, construction, and research. In China, hardness determination methods are governed by the national standards system (GB, "Guobiao"), in which the suffix "/T" denotes a recommended technical standard. Most GB/T hardness standards are technically aligned with, or directly adopted from, corresponding ISO standards, and they are broadly comparable to ASTM and JIS methods, which facilitates international trade and mutual recognition of test data.

The national standards framework covers not only the test methods themselves, but also the verification of hardness testing machines, the certification of reference blocks, and the conversion of hardness values between scales. Key documents in this system include:

• GB/T 231.1 — Metallic materials, Brinell hardness test, Part 1: Test method (aligned with ISO 6506-1), supplemented by GB/T 231.2 and GB/T 231.3 for machine verification and reference blocks
• GB/T 230.1 — Metallic materials, Rockwell hardness test, Part 1: Test method (aligned with ISO 6508-1), supplemented by GB/T 230.2 and GB/T 230.3
• GB/T 4340.1 — Metallic materials, Vickers hardness test, Part 1: Test method (aligned with ISO 6507-1), supplemented by GB/T 4340.2 and GB/T 4340.3
• GB/T 4341 — Metallic materials, Shore hardness test (dynamic rebound method)
• GB/T 17394.1 — Metallic materials, portable hardness testing by the Leeb method
• GB/T 3398.1 — Plastics, determination of hardness by the ball indentation method (aligned with ISO 2039-1)
• GB/T 2411 — Plastics and ebonite, determination of indentation hardness by durometers (Shore hardness, aligned with ISO 868)
• GB/T 531.1 — Vulcanized or thermoplastic rubber, durometer (Shore) hardness (aligned with ISO 7619-1)
• GB/T 6031 — Rubber, determination of hardness in international rubber hardness degrees (IRHD, aligned with ISO 48)
• GB/T 1172 — Conversion of hardness and strength values for ferrous metals

Testing performed by accredited third-party laboratories against these GB/T standards ensures that hardness data are traceable to national metrology institutes and are legally and commercially defensible.

Testing Samples

Metallic Materials

Metals are the largest category of samples covered by national hardness standards. Typical specimens include carbon and alloy steels, stainless steels, cast irons, aluminum, copper, and titanium alloys, as well as finished or semi-finished components such as forgings, castings, plates, tubes, fasteners, gears, bearings, and welded joints. Case-hardened, carburized, nitrided, or quenched-and-tempered surfaces are frequently tested to verify heat treatment quality, with case depth determination carried out according to GB/T 9450 for carburized cases and GB/T 11354 for nitrided layers.

Plastics and Rubber

Polymeric solids, including thermoplastics, thermosets, engineering plastics, ebonite, and vulcanized or thermoplastic elastomers, are tested under GB/T 2411, GB/T 3398.1, GB/T 531.1, and GB/T 6031. Specimens range from molded plaques and O-rings to seals, hoses, tires, and soft-touch components.

Ceramics, Glass, and Hard Metals

Engineering (fine) ceramics, cemented carbides, sintered hard metals, and glasses are extremely hard and brittle, and are typically evaluated by low-load Vickers or Knoop indentation. National practice for fine ceramics is consistent with ISO 14705, while cemented carbide products are commonly verified using Vickers or Rockwell A procedures referenced in their product standards.

Coatings, Films, and Surface Layers

Paint films are assessed by pencil hardness under GB/T 6739 and by Buchholz indentation under GB/T 9275. Electroplated, electroless, anodized, PVD, and CVD coatings on substrates are measured by micro-Vickers or instrumented indentation, taking care that the indentation depth remains below approximately one tenth of the coating thickness.

Natural and Construction Materials

Wood hardness is determined under GB/T 1941, while natural stone and concrete products are evaluated using hardness and rebound-based procedures specified in their respective national and industry standards. These methods provide rapid indicators of surface durability and consistency.

Testing Items

Depending on the material, geometry, and purpose of the evaluation, the following hardness parameters are routinely reported under the national standards:

• Brinell hardness (HBW), measured with a tungsten carbide ball, suitable for coarse-grained and inhomogeneous materials such as castings and forgings
• Rockwell hardness (HRA, HRB, HRC, and superficial HRN/HRT scales), providing fast, direct-readout results without optical measurement
• Vickers hardness (HV) across macro, low-force, and micro ranges, applicable from bulk sections down to thin foils and individual microstructural constituents
• Shore hardness for metals (HS), a dynamic rebound method for large, heavy components such as mill rolls and large forgings
• Leeb hardness (HL) for portable, on-site testing of installed equipment, with conversion to HBW, HV, or HRC
• Shore A, Shore C, and Shore D durometer hardness, and international rubber hardness degrees (IRHD) for elastomers and plastics
• Ball indentation hardness (H) for plastics requiring a fundamental, load-dependent measurement
• Martens hardness (HM) and instrumented indentation parameters, including elastic modulus, determined by depth-sensing indentation consistent with ISO 14577 and the national nanoindentation general rules GB/T 22458
• Pencil hardness (scratch resistance grades) and Buchholz indentation resistance for coatings

Testing Methods

Brinell Hardness Testing (GB/T 231.1)

A polished tungsten carbide ball of 1 mm to 10 mm diameter is pressed into the prepared surface under a controlled test force. After the dwell period, typically 10 to 15 seconds for standard conditions, the indentation diameter is measured in two perpendicular directions, and the hardness value HBW is calculated as the test force divided by the curved surface area of the indentation. The force-to-ball-diameter ratio (0.102 F/D²) is selected as 30 for steels and cast irons, 5 or 10 for light alloys such as aluminum, and 1 for very soft metals such as lead and tin. The relatively large indentation averages over local heterogeneities, making Brinell testing the preferred method for cast structures and welded joints.

Rockwell Hardness Testing (GB/T 230.1)

Rockwell testing measures the permanent increase in penetration depth between application of a preliminary force and the total force. A spheroconical diamond indenter is used for the A, C, D, and N scales, while tungsten carbide balls of 1.5875 mm or 3.175 mm diameter are used for the B, E, F, G, H, K, and T scales. Common combinations include HRC at 150 kgf total force for hardened steels, HRB at 100 kgf for medium-strength steels and copper alloys, and HRA at 60 kgf for cemented carbides and thin hard layers. Because the result is read directly from the machine dial or display, the method is fast and well suited to production-line quality control.

Vickers and Microhardness Testing (GB/T 4340.1)

A diamond pyramid with a 136-degree included angle is pressed into the specimen under test forces ranging from approximately 0.01 kgf in the micro range up to 100 kgf in the macro range, designated HV0.01 through HV100. After force removal, both diagonals of the square indentation are measured with a calibrated microscope or automatic image system, and the HV value is calculated from the mean diagonal. The geometry of the indenter is scale-independent, allowing a single continuous hardness scale to be applied from soft annealed metals to hard ceramics. Microhardness traverses are used to characterize case depth, decarburization, weld heat-affected zones, and individual phases in the microstructure.

Shore and Leeb Dynamic Methods (GB/T 4341 and GB/T 17394.1)

For components too large or heavy to bring to a bench machine, national standards provide dynamic methods. In the Shore (rebound) test, a diamond-tipped hammer drops onto the surface and the rebound height indicates hardness (HS). In the Leeb test, an impact body with a tungsten carbide ball is propelled against the surface by spring force, and the ratio of impact to rebound velocities yields the Leeb value (HL), which is converted to conventional scales using standardized tables. These methods require adequate specimen mass, thickness, and surface preparation, and bench methods remain preferable for arbitration-grade measurements.

Polymer and Elastomer Hardness Testing

For plastics and rubber, durometer tests per GB/T 2411 and GB/T 531.1 press a calibrated truncated cone (Shore A) or a rounded needle (Shore D) into the specimen under a spring force, reporting the depth-sensing value. Ball indentation hardness under GB/T 3398.1 applies a 5 mm ball at a fixed load to plastics, giving a more fundamental measure suited to specification work, while IRHD testing under GB/T 6031 uses dead-load indentation with specified preload and total load for elastomeric products.

Sample Preparation and Test Conditions

Regardless of the method, valid results require that the test surface be clean, free of scale, oxide, and lubricant, and smooth enough that indentation edges can be measured accurately. Surfaces should be flat and parallel to the support face, specimen thickness should be at least ten times the indentation depth with no visible deformation on the underside, and adjacent indentations must be spaced according to the limits in each standard to avoid work-hardening interaction. Tests are normally conducted at ambient temperatures between 10 °C and 35 °C, with tighter control required during calibration and reference-block certification.

Metrological Traceability and Verification

Hardness testing machines must be verified periodically, both directly (force, indenter geometry, measuring device) and indirectly (using certified reference blocks) in accordance with the Part 2 and Part 3 documents of the GB/T 230, GB/T 231, and GB/T 4340 series, together with the applicable metrological verification regulations (JJG series). Reference blocks must be traceable to national metrology institutes, ensuring that results from different laboratories and countries remain comparable.

Applications

Hardness determination under national standards supports a wide spectrum of industrial and scientific activities:

• Heat treatment verification, confirming that quenching, tempering, carburizing, and nitriding operations achieve specified hardness and effective case depth
• Fastener and component acceptance testing, including hardness requirements for bolts, screws, and studs in product standards such as the GB/T 3098 series
• Weld procedure qualification and weldment inspection, with hardness surveys across the weld cross-section per GB/T 2654 to detect hard or soft zones
• Tooling and die manufacturing, where HRC and HV values validate cutting tools, molds, dies, and wear parts
• Automotive, aerospace, energy, and rail industries, for incoming material inspection, supplier qualification, and root-cause failure analysis of fractured or worn components
• Polymer and rubber product control, including seals, gaskets, tires, footwear, and soft-touch parts, using Shore and IRHD scales
• Coating and paint qualification in construction, appliances, and general industrial finishing
• Research and development, including instrumented indentation for thin films, coatings, welds, additively manufactured parts, and advanced ceramics

Accredited third-party laboratories performing these tests according to ISO/IEC 17025 management system requirements provide manufacturers, buyers, and regulators with hardness data suitable for product certification, customs clearance, dispute resolution, and design substantiation.

FAQ

What does the designation HBW mean, and is HBS still used?

HBW indicates a Brinell hardness value obtained with a tungsten carbide ball indenter. The older HBS designation, which referred to steel ball indenters, was withdrawn when GB/T 231.1 (consistent with ISO 6506-1) mandated tungsten carbide balls for all Brinell testing, because steel balls flatten at high hardness and cause systematic error.

Can Rockwell, Brinell, and Vickers values be converted into one another?

Approximate conversions are possible, and GB/T 1172 provides standardized hardness-to-strength and hardness-to-hardness conversion tables for ferrous metals. However, conversions depend on material class, processing history, and work-hardening behavior, so contractual and arbitration acceptance should always be based on testing in the specified native scale.

How thick must a specimen be for a valid hardness test?

As a general rule, the specimen must be at least ten times the indentation depth, and no bulge or marking may appear on the side opposite the indentation. For very thin sheet, foils, coatings, or surface layers, low-force Vickers or superficial Rockwell scales should be selected, and the indentation depth should not exceed one tenth of the layer or section thickness.

Which standard applies to on-site hardness testing of installed equipment?

Portable Leeb hardness testing under GB/T 17394.1 is the standard approach for large, installed, or heavy components that cannot be moved to a bench machine. The method requires sufficient mass, rigidity, and surface preparation, and coupling or support measures may be needed for thin-walled parts.

How is hardness testing equipment qualified under the national standards?

Bench and portable hardness testers are verified directly and indirectly at scheduled intervals in accordance with the machine verification and reference-block standards, such as GB/T 230.2, GB/T 230.3, GB/T 231.2, GB/T 231.3, GB/T 4340.2, and GB/T 4340.3, together with the applicable JJG metrological verification regulations. Certified reference blocks traceable to national metrology institutes guarantee the accuracy and comparability of reported values.

Which hardness standards govern plastics and rubber products?

Shore durometer hardness for plastics and ebonite is determined under GB/T 2411, ball indentation hardness for plastics under GB/T 3398.1, Shore durometer hardness for vulcanized and thermoplastic rubber under GB/T 531.1, and IRHD hardness for rubber under GB/T 6031. The choice depends on product specification, hardness range, and whether a rapid comparative or a fundamental measurement is required.