GB/T 3098.26-2021: Fastener Properties – Plain Washers

This standard specifies the mechanical and physical properties of plain washers made from carbon steel or alloy steel, intended for use in bolted connections with bolts, screws, studs, and nuts conforming to performance classes defined in GB/T 3098.1 and GB/T 3098.2. These properties are tested under ambient temperatures ranging from 10°C to 35°C.

Note 1: These plain washers may also be utilized with other fasteners, such as self-tapping screws.

Plain washers meeting this standard’s requirements under the specified test conditions may not retain their mechanical and physical properties at high and/or low temperatures. Note 2: Plain washers compliant with this document are suitable for service temperatures from -50°C to +150°C. For temperatures exceeding -50°C to +150°C, up to +300°C, users are advised to consult relevant experts.

This document applies to plain washers and washers for assemblies made from carbon steel or alloy steel with thicknesses from 0.2 mm to 12 mm, including:

• Plain washers (with or without patterns, ribs, or chamfers).
• Square plain washers.
• Square hole plain washers.
• Special-shaped plain washers.

This standard does not specify requirements for:

• Corrosion resistance.
• Weldability.

The scope emphasizes the importance of material selection and testing conditions to ensure reliability in fastener assemblies. For instance, in applications involving extreme temperatures, additional considerations such as thermal expansion and material degradation must be evaluated. This standard integrates with other GB/T series documents to provide a holistic framework for fastener performance, ensuring compatibility and safety in mechanical engineering applications. By limiting the thickness range, it focuses on common industrial uses while allowing for extensions through agreements. Professionals should note that for specialized environments, like marine or aerospace, supplementary standards for corrosion may be necessary. Overall, this scope ensures that plain washers contribute effectively to the load distribution and vibration resistance in bolted joints, preventing failures such as loosening or material fatigue. The exclusion of corrosion and weldability highlights the need for integrated system design where these aspects are addressed separately. In practice, engineers often combine this with standards like GB/T 5267.3 for hot-dip galvanizing to enhance durability. This comprehensive approach aids in selecting washers that optimize assembly performance, reducing maintenance costs and improving structural integrity. Furthermore, the temperature guidelines prevent misuse in high-heat scenarios, where alternative materials like stainless steel might be preferred. The document’s focus on carbon and alloy steels balances cost-effectiveness with mechanical strength, making it suitable for automotive, construction, and machinery sectors. By adhering to these parameters, manufacturers can produce consistent products that meet international equivalents, facilitating global trade and standardization.

Symbols

The following symbols are used in this document:

• d₁: Inner diameter of the through-hole, in millimeters (mm).
• d₂: Outer diameter, in millimeters (mm).
• F: Load, in newtons (N).
• G: Total decarburization layer depth, in millimeters (mm).
• r: Contact radius between support and pressure parts, in millimeters (mm).
• t: Nominal thickness of the plain washer, in millimeters (mm).
• t_eff: Effective thickness of the plain washer, in millimeters (mm).
• α: Contact angle between support and pressure parts, in degrees (°).

These symbols standardize communication in technical documentation, ensuring precision in design and testing. For example, d₁ and d₂ are critical for dimensional compatibility with bolts, preventing misalignment that could lead to assembly failures. The load F is essential in performance testing, simulating real-world stresses. Decarburization depth G relates to surface integrity, as excessive decarburization can weaken the washer. The radius r and angle α are used in test setups to replicate contact conditions accurately. Thickness parameters t and t_eff account for manufacturing variations, influencing load-bearing capacity. In engineering practice, these symbols facilitate calculations for stress distribution, where washers help evenly spread forces across joint surfaces. Understanding these notations is vital for interpreting test results and ensuring compliance. They align with international standards, promoting interoperability. Professionals should use these consistently to avoid errors in specifications. For instance, in finite element analysis, these parameters input into models predict washer behavior under load. This symbolism enhances the document’s usability, allowing quick reference during quality control processes. By defining them early, the standard builds a foundation for subsequent sections on materials and tests.

Designation System

The performance class of plain washers consists of a number and a symbol:

• The number indicates the minimum Vickers hardness value (see Table 3).
• The letters HV denote Vickers hardness.

Example: A steel plain washer with a minimum Vickers hardness of 200, as per Table 3, is designated as 200 HV.

If compliant with Tables 2 and 3, this designation system may also apply to specifications beyond standard thicknesses. Although multiple performance classes are specified, not all are suitable for every bolt, nut, and washer assembly. Combinations of plain washer performance classes with bolts, screws, studs, and nuts are shown in Table 1.

RC: Recommended combination.
^seorang 200 HV and 300 HV classes are applied in product standards for bolt and washer assemblies, per GB/T 9074.1 and GB/T 97.4.
^b 380 HV is not in current product standards; use requires supplier-buyer agreement.
^c For 380 HV, bolt connection design should prevent bending and tensile stresses in washers, especially slotted or countersunk types.
^d Combinations with footnote d may be used if connection design and installation are verified.
^e Combinations above the stepped bold line are usable for bolted connections.
^f Combinations below the stepped bold line (gray areas) should not be used.

For thread-forming screws and screws connecting soft materials (e.g., plastic, wood), combinations with plain washer performance classes should be determined based on intended use.

This designation system ensures traceability and compatibility in assemblies, critical for safety. By linking hardness to performance classes, it allows engineers to select washers that match bolt strengths, avoiding under- or over-specification. Table 1’s recommendations prevent mismatches that could cause failures like stripping or cracking. In high-load applications, such as bridges, higher classes like 380 HV provide superior resistance but require careful design to mitigate hydrogen embrittlement risks (see GB/Z 41117). The system’s flexibility for non-standard thicknesses supports custom applications. Overall, it promotes standardization, reducing errors in procurement and assembly.

Materials

Table 2 specifies the chemical composition limits for carbon steel and alloy steel used in plain washers of different performance classes. These compositions must comply with relevant national standards.

Nota: Alloy steel includes spring steel and alloy spring steel suitable for plain washers.

For washers requiring hot-dip galvanizing, materials must meet GB/T 5267.3 requirements. If assemblies are quenched and tempered as a whole, untreated washers may be supplied; in such cases, chemical composition per GB/T 9074.1 is by agreement.

For self-tapping screw assemblies surface-hardened per GB/T 97.5, washer carbon content should not exceed 0.12%. Each manufacturing batch must use material from the same heat.

NA: Not applicable.
^seorang In disputes, perform product analysis.
^b For assembly washers, see GB/T 9074.1 or GB/T 97.4; composition and tempering temperature by agreement.
^c For special applications (e.g., hot-dip galvanized), composition and tempering temperature by agreement.
^d Maximum boron 0.003%, up to 0.005% if non-effective boron controlled by titanium/aluminum.
^e 200 HV washers may use suitable raw materials or be quenched and tempered post-manufacture; process by manufacturer if Table 3 met.
^f Materials must have sufficient hardenability for ~90% martensite in core before tempering.
^g Carbon steel may include chromium, manganese, nickel, etc.
^h Alloy steels contain at least one element: Cr 0.30%, Mn 0.20%, Ni 0.30%, V 0.10%, Mo 0.08%, B 0.0008%. For combinations, total at least 70% of individual minima.
ⁱ For hydrogen embrittlement, see GB/Z 41117.

Material specifications ensure washers achieve required hardness and durability. Carbon limits control strength, while low P and S minimize brittleness. Alloying elements enhance hardenability for higher classes. Tempering temperatures prevent over-hardening, reducing crack risks. This section guides manufacturers in selecting steels for consistent performance, vital in industries like automotive where vibration resistance is key. Compliance with related standards ensures galvanizing compatibility, avoiding issues like coating adhesion failure.

Mechanical and Physical Properties

Plain washers of specified performance classes must meet the mechanical and physical properties in Table 3 under ambient temperature, whether tested during manufacturing or final inspection.

Chapter 6 provides applicable test methods and arbitration procedures to verify compliance with Table 3. For 380 HV class washers, ductility testing per Annex A is required when specified.

^seorang 380 HV not in current product standards; use by agreement.
^b Exceeding max to 250 HV not grounds for rejection.
^c For knurled or ribbed washers, limits as for 380 HV.
^d Measured per 6.2.3 on cross-section; hardness at 0.1 mm from support surface ≥ center hardness – 30 HV.
^e Whichever is smaller.
^f Measured per 6.3 on cross-section; hardness at 0.1 mm from support surface ≤ center hardness + 30 HV.

These properties ensure washers withstand compressive loads without deformation or failure. Hardness ranges balance strength and ductility, preventing cracking. Decarburization and carburization controls maintain surface integrity, crucial for corrosion resistance in coated washers. Retempering limits verify heat treatment adequacy. In applications, these specs support reliable joints, e.g., in machinery where vibration could loosen connections. Compliance testing per Chapter 6 guarantees quality.

Test Methods

Hardness Test

General

The hardness test aims to verify compliance with Table 3 min/max values and material requirements for quenched and tempered washers. Applicable to all classes, tested in as-received state except for post-assembly treated ones.

Perform on suitable surfaces or cross-sections per Table 4.

^seorang For 200 HV quenched and tempered per request, cross-section test is arbitration if dispute.

Vickers Hardness on Surface

Select test load based on class and thickness per Figure 1. Use Rockwell if no suitable Vickers load.

Example: For 0.3 mm thick 300 HV washer, use HV5.

 Rockwell Hardness on Surface

Select load per Figure 2 based on class and thickness. Use Vickers if no suitable Rockwell load.

Example: For 0.5 mm thick 380 HV washer, use 294 N (HR30N).

Test Procedure

Remove coatings/oxides, test at half-radius on support surface. For galvanized, remove transition layer. Average three readings at 120° if size allows.

Requirements for 100 HV, 140 HV, 200 HV

Routine: Per 6.1.2, meet Table 3. Arbitration: Vickers per Figure 1; for t_eff > 0.5 mm, lower load ≥ HV1.

Requirements for 300 HV, 380 HV

Routine: Per 6.1.2, meet Table 3. Arbitration: Cross-section per 6.1.3.

Radial Cross-Section Hardness Test

General

Per GB/T 4340.1, Vickers for quenched and tempered washers.

Procedure

Take radial section through hole center, embed/mount, grind/polish for metallography. Test at mid-section per Figure 3; average at least three points if possible.

1: Test area (radius 0.25 t_eff).

Requirements

Meet Table 3. If difference > 30 HV in 0.25 t_eff radius, verify ~90% martensite per Table 2.

Decarburization Test

General

Detects surface decarburization for 300 HV knurled/ribbed and all 380 HV washers. Areas per Figure 4.

1: Support surface; 2: Total decarb layer; 3: Partial decarb layer; 4: Base metal; x: No test area.

Metallographic Method

Sample Preparation

Remove coatings, take radial section, embed/mount, grind/polish. Note: Etch with 3% nital to reveal changes.

Procedure

Examine at 100x magnification; measure with scale or eyepiece.

Requirements

Max G per Table 3.

Hardness Method

Sample Preparation

For t ≥ 0.4 mm; prepare per 6.2.2.1 without etching.

Procedure

Measure points 1 and 2 per Figure 5 with HV0.3 (2.942 N).

No decarb: HV(2) > HV(1) – 30 HV; No carb: HV(2) ≤ HV(1) + 30 HV. 1: Center; 2: 0.1 mm from surface.

Requirements

HV(2) ≥ HV(1) – 30 HV. Note: Not for max G per Table 3.

Carburization Test

General

Detects surface carburization during heat treatment for 300 HV knurled/ribbed and all 380 HV washers, t ≥ 0.4 mm. Measured on radial cross-section hardness.

Procedure

Prepare per 6.2.2.1 without etching; measure per Figure 5 with HV0.3.

Requirements

HV(2) ≤ HV(1) + 30 HV. Exceeding indicates carburization. Additionally, support surface ≤ 370 HV0.3 for 300 HV, ≤ 450 HV0.3 for 380 HV per Table 3.

Retempering Test

General

Verifies minimum tempering temperature in heat treatment for 300 HV and 380 HV washers.

Procedure

Measure Vickers in Figure 3 area (three points). Retemper at 10°C below Table 2 min, hold 30 min; re-measure in same area.

Requirements

Average hardness reduction < 20 HV after retempering.

Test methods ensure washer quality through standardized procedures, critical for reliability. Hardness tests confirm material strength, while decarburization/carburization checks prevent surface weaknesses. Retempering validates heat treatment, avoiding brittleness. These methods align with international practices, enabling consistent manufacturing.

Marking

General

Washers manufactured per this document may be marked per Chapter 3 only if fully compliant.

Washer Marking

By manufacturer decision or agreement; if agreed, include manufacturer ID and performance class. Distributors using own ID are considered manufacturers. No raised markings; recessed not recommended due to torque-clamping effects or stress concentrations. Use durable methods like laser. Mark class per Table 5 code or clock-face symbols.

Package Marking

All packages must be labeled with manufacturer/seller ID, performance class per Chapter 3, and lot number per GB/T 3099.4.

Marking ensures traceability, essential for quality control and liability. It prevents counterfeit products and aids in recalls. In supply chains, proper marking facilitates inventory management and compliance verification.

Annex A: Ductility Test for 380 HV Performance Class Washers

A.1 General

Determines if washers became brittle during manufacture. Applicable upon customer request, to finished washers including coatings.

A.2 Test Procedure

Use support and indenter with angle α based on thickness; min 60 HRC hardness, ground surfaces. For concentric round washers, use conical contacts per Figure A.1. For others, V-shaped per Figure A.2. Place washer in device; disassemble assemblies first. Align axes. Apply axial load steadily until full contact; hold 2 min, remove load.

A.3 Requirements

No fracture. If damaged, cut opposite fracture; separation into two parts indicates failure.

This annex verifies ductility for high-hardness washers, preventing brittle failures in service. It’s crucial for safety-critical applications, ensuring washers deform without breaking under load.

Soalan Lazim

1. What temperature range is suitable for plain washers per this standard? The recommended service temperature is -50°C to +150°C. For extremes up to +300°C, consult experts to assess property retention.
2. How do I select the appropriate performance class for my bolt assembly? Refer to Table 1 for recommended combinations (RC). Avoid gray areas to prevent mismatches that could lead to joint failure; verify design if using footnote d combinations.
3. What if my washers need hot-dip galvanizing? Materials must comply with GB/T 5267.3. Chemical composition and tempering may require supplier-buyer agreement for special applications.
4. Why is decarburization testing important for higher performance classes? Excessive decarburization weakens the surface, increasing failure risk under load. Tests ensure limits per Table 3, maintaining integrity especially for 380 HV washers.
5. Can I use 380 HV washers without agreement? No, as they are not in current product standards. Use requires protocol, with design considerations to avoid bending or tensile stresses.
6. How does the retempering test confirm heat treatment quality? It checks if hardness reduction after additional tempering is ≤20 HV, verifying the original process met minimum temperatures per Table 2, preventing brittleness.