GB/T 3098.1-2010 specifies the mechanical properties of bolts, screws, and studs made of carbon steel and alloy steel. This standard defines property classes, materials, and performance requirements to ensure reliability in various applications. It applies to fasteners with nominal thread diameters from M1.6 to M39, operating at temperatures between -50°C and +300°C, with core provisions for room temperature performance.
Table of Contents
- Marking System for Property Classes and Materials
- Propiedades mecánicas y físicas
- Preguntas frecuentes (FAQ)
Marking System for Property Classes and Materials
5. Marking System for Property Classes
The property class designation for bolts, screws, and studs consists of two numbers separated by a dot :
- The number(s) to the left of the dot represent 1/100 of the nominal tensile strength (Rm, nom) in MPa.
- The number to the right of the dot is 10 times the ratio of the nominal yield strength (lower yield strength ReL, nom), or the nominal stress at 0.2% non-proportional extension (Rp0.2, nom), or the nominal stress at 0.0048d non-proportional extension for fasteners (Rpf, nom) to the nominal tensile strength (Rm, nom) .
Example: A fastener with nominal tensile strength Rm, nom = 800 MPa and yield ratio 0.8 has property class “8.8”. For products with similar material properties but reduced loadability, mark as “08.8” (see 10.4).
The product of nominal tensile strength and yield ratio gives the nominal yield strength in MPa. Appendix A provides data on the relationship between nominal tensile strength and elongation after fracture for each property class.
Marking and labeling of property classes shall follow 10.3, and for reduced loadability, 10.4. This marking system may apply to sizes beyond the standard range (d > 39 mm) if Tables 1 and 2 are met.
6. Materials
Table 1 specifies the chemical composition limits and minimum tempering temperatures for steels used in each property class. Chemical compositions shall comply with relevant national standards.
Note: Certain chemical elements may be restricted or prohibited by regulations in some countries. Attention should be paid when applicable.
GB/T 5267.3 Chapter 4 requirements for fastener materials apply to hot-dip galvanized fasteners.
Table 1: Materials
| Clase de propiedad | Material y tratamiento térmico | Chemical Composition Limits (Cast Analysis, %)a | Tempering Temperature (°C min) | ||||
|---|---|---|---|---|---|---|---|
| do | PAG | S | Bb | ||||
| mín. | máximo | máximo | máximo | máximo | |||
| 4.6c,d | Carbon steel or carbon steel with additives | — | 0.55 | 0.05 | 0.06 | Not specified | — |
| 4.8d | |||||||
| 5.6e | 0.13 | 0.55 | 0.05 | 0.06 | |||
| 5.8d | — | 0.55 | 0.05 | 0.06 | |||
| 6.8d | 0.15 | 0.55 | 0.05 | 0.06 | |||
| 8.8f | Carbon steel with additives (e.g., B, Mn, Cr) quenched and tempered or | 0.15e | 0.4 | 0.025 | 0.025 | 0.003 | 425 |
| Carbon steel quenched and tempered or | 0.25 | 0.55 | 0.025 | 0.025 | |||
| Acero aleado templado y revenidogramo | 0.2 | 0.55 | 0.025 | 0.025 | |||
| (Table continues with similar structure for property classes 9.8, 10.9, and 12.9. Refer to standard for full details.) | |||||||
a En caso de disputa se aplica el análisis del producto.
b Boron content up to 0.005%, non-effective boron controlled by titanium and/or aluminum.
c For 4.6 and 5.6 cold-headed fasteners, heat treatment may be needed for plasticity and toughness.
d Free-cutting steel allowed with max S 0.34%, P 0.11%, Pb 0.35%.
e For boron-added carbon steel <0.25% C, min Mn 0.6% for 8.8, 0.7% for 9.8 and 10.9.
f Materials must have sufficient hardenability for ~90% martensite in core before tempering.
gramo Alloy steel with at least one of Cr 0.30%, Ni 0.30%, Mo 0.20%, V 0.10%; for multiples, total not less than 70% of sum.
h No white phosphide layer on 12.9 surface; remove before heat treatment.
i Use 12.9 cautiously, considering manufacturer capability, service conditions, and tightening methods; risk of stress corrosion cracking.
Propiedades mecánicas y físicas
Fasteners of specified property classes shall meet the mechanical and physical properties in Tables 2 to 7 at ambient temperature1. Chapter 8 provides test methods to verify compliance.
Note 1: Even if material meets Tables 2, some fastener types may have reduced loadability due to size (see 8.2, 9.4, 9.5).
Note 2: Not all classes apply to all fasteners; product standards specify classes, which may reference non-standard fasteners.
Table 2: Mechanical and Physical Properties of Bolts, Screws, and Studs
| No. | Mechanical or Physical Property | Clase de propiedad | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 4.6 | 4.8 | 5.6 | 5.8 | 6.8 | 8.8 | 9.8 (d ≤ 16 mm) | 10.9 | 12.9 | |||||
| d ≤ 16 mma | d > 16 mmb | ||||||||||||
| 1 | Tensile strength Rmetro / MPa | nomc | 400 | 400 | 500 | 500 | 600 | 800 | 800 | 900 | 1000 | 1200 | |
| mín. | 400 | 420 | 500 | 520 | 600 | 800 | 830 | 900 | 1040 | 1220 | |||
| (Table continues with properties like yield strength, hardness, etc. Refer to standard for full data.) | |||||||||||||
a Values not for structural bolting.
b For structural bolting d ≥ M12.
c Nominal values for designation only (Chapter 5).
1 Impact energy test at -20°C (see 9.14).
Preguntas frecuentes (FAQ)
- 1. What is the significance of the property class marking like “8.8”?
- It indicates nominal tensile strength (800 MPa) and yield ratio (0.8), ensuring standardized performance for selection in engineering applications.
- 2. Why might a fastener have reduced loadability despite meeting material requirements?
- Due to geometry or size effects, as noted in 8.2 and 9.4; mark as “08.8” for such cases.
- 3. What precautions are needed for 12.9 class fasteners?
- Consider manufacturing capability, service conditions, and tightening methods to avoid stress corrosion cracking; no white phosphide layer allowed.
- 4. How are chemical compositions verified?
- By cast analysis, with product analysis in disputes; comply with national standards and regional restrictions on elements like P and S.
- 5. What tests confirm mechanical properties?
- Tensile tests for Rmetro y ReL, hardness tests (HV, HB, HR), impact energy at -20°C for d ≥ 16 mm, and surface defect inspections per GB/T 5779.1 or 5779.3.
- 6. Are these standards applicable to fine thread fasteners?
- Yes, Tables 6 and 7 provide minimum tensile and proof loads for fine threads, calculated similarly to coarse threads.
