GB/T 3098.1-2010 Fasteners Mechanical Properties: Bolts, Screws, Studs

Introduction to GB/T 3098.1-2010 Standard

مخطط المقال

This article provides a comprehensive overview of the GB/T 3098.1-2010 standard, focusing on mechanical properties for bolts, screws, and studs made from carbon and alloy steels. The structure is as follows:

Introduction to the Standard
Marking System and Materials
الخواص الميكانيكية والفيزيائية
Application Guidelines and Test Applicability
الأسئلة الشائعة (FAQ)

Introduction to the Standard

GB/T 3098.1-2010 specifies the mechanical and physical properties of bolts, screws, and studs made from carbon steel or alloy steel, tested at ambient temperatures between 10 °C and 35 °C. This standard applies to fasteners with nominal thread diameters from 1.6 mm to 39 mm, ensuring consistency in performance for structural, automotive, and machinery applications.

It defines property classes based on tensile strength, yield strength, elongation, hardness, and other metrics, promoting quality control and safety. Aligned with ISO 898-1:2009, it facilitates international compatibility while addressing specific requirements for Chinese manufacturing standards.

Scope: Covers carbon and alloy steel fasteners under standard conditions.
Key Updates: Enhanced specifications for high-strength classes and testing methods.
Importance: Ensures fasteners meet load-bearing and durability needs in engineering.

Marking System and Materials

The property class marking system uses two numbers separated by a dot, where the left indicates nominal tensile strength (R_م) in MPa divided by 100, and the right represents the yield ratio multiplied by 10. For example, “8.8” denotes 800 MPa tensile strength and a 0.8 yield ratio.

Materials must comply with chemical composition limits and heat treatment requirements to achieve desired properties. Carbon steels with added elements like boron, manganese, or chromium are common, with minimum tempering temperatures specified to ensure hardenability.

Table 1: Yield Strength Ratios
Digit After Decimal	.6	.8	.9
نسبة	0.6	0.8	0.9

For reduced load-bearing capacity fasteners with properties equivalent to 8.8, mark as “08.8”.

Table 2: Materials and Chemical Composition Limits
فئة العقار	Material and Heat Treatment	Chemical Composition Limits (% Ladle Analysis)					Tempering Temperature min (°C)
		ج		P max	S max	B max
		مين	الأعلى
4.6	Carbon steel or carbon steel with additives	—	0.55	0.05	0.06	Not specified	—
4.8		—	0.55	0.05	0.06
5.6		0.13	0.55	0.05	0.06
5.8		—	0.55	0.05	0.06
6.8		0.15	0.55	0.05	0.06
8.8	Carbon steel with additives (e.g., B, Mn, Cr) quenched and tempered	0.15	0.4	0.025	0.025	0.003	425
	Carbon steel quenched and tempered	0.25	0.55	0.025	0.025
	Alloy steel quenched and tempered	0.2	0.55	0.025	0.025
9.8	Carbon steel with additives quenched and tempered	0.15	0.4	0.025	0.025	0.003	425
	Carbon steel quenched and tempered	0.25	0.55	0.025	0.025
	Alloy steel quenched and tempered	0.2	0.55	0.025	0.025
10.9	Carbon steel with additives quenched and tempered	0.20	0.55	0.025	0.025	0.003	425
	Carbon steel quenched and tempered	0.25	0.55	0.025	0.025
	Alloy steel quenched and tempered	0.2	0.55	0.025	0.025
12.9	Alloy steel quenched and tempered	0.3	0.5	0.025	0.025	0.003	425
12.9	Carbon steel with additives quenched and tempered	0.28	0.5	0.025	0.025	0.003	380

Notes:

Product analysis applies in case of dispute.
Boron up to 0.005%, controlled by titanium and/or aluminum for non-effective boron.
For 4.6 and 5.6 classes, heat treatment may be needed for cold-headed fasteners to ensure ductility.
Free-cutting steels allowed for certain classes with max S 0.34%, P 0.11%, Pb 0.35%.
For boron steels with C < 0.25%, min Mn is 0.6% for 8.8, 0.7% for 9.8 and 10.9.
Materials must ensure 90% martensite in core before tempering for higher classes.
Alloy steels contain at least one of Cr 0.30%, Ni 0.30%, Mo 0.20%, V 0.10%.
No white phosphide layer on 12.9 class surfaces; remove before heat treatment.
Use 12.9 class cautiously due to risk of stress corrosion cracking.

These specifications guide material selection, ensuring fasteners achieve required strength and resistance to failure modes like hydrogen embrittlement.

الخواص الميكانيكية والفيزيائية

Fasteners must meet specified mechanical properties at ambient temperature, including tensile strength, yield strength, elongation, hardness, and impact energy. Testing methods are outlined to verify compliance.

Table 3: Mechanical and Physical Properties of Bolts, Screws, and Studs
No.	Mechanical or Physical Property		فئة العقار
			4.6	4.8	5.6	5.8	6.8	8.8		9.8 (d≤16 mm)	10.9	12.9
			4.6	4.8	5.6	5.8	6.8	d≤16 mm	d>16 mm	9.8 (d≤16 mm)	10.9	12.9
1	Tensile strength R_م (MPa)	nom	400	400	500	500	600	800	800	900	1000	1200
1	Tensile strength R_م (MPa)	مين	400	420	500	520	600	800	830	900	1040	1220
2	Lower yield strength R_eL (MPa)	nom	240	—	300	—	—	—	—	—	—	—
2	Lower yield strength R_eL (MPa)	مين	240	—	300	—	—	—	—	—	—	—
3	Stress at 0.2% non-proportional elongation R_p0.2 (MPa)	nom	—	—	—	—	—	640	640	720	900	1080
3	Stress at 0.2% non-proportional elongation R_p0.2 (MPa)	مين	—	—	—	—	—	640	660	720	940	1100
4	Stress at 0.0048d non-proportional elongation for full-size fastener R_pf (MPa)	nom	—	320	—	400	480	—	—	—	—	—
4		مين	—	340	—	420	480	—	—	—	—	—
5	Proof stress S_ص (MPa)	nom	225	310	280	380	440	580	600	650	830	970
5	Proof stress ratio	0.94	0.91	0.93	0.9	0.92	0.91	0.91	0.9	0.88	0.88
6	Elongation after fracture for machined test pieces A (%)	مين	22	—	20	—	—	12	12	10	9	8
7	Reduction in area after fracture for machined test pieces Z (%)	مين	—					52	52	48	48	44
18	Surface discontinuities		GB/T 5779.1									GB/T 5779.3

Notes:

Values not for structural bolting.
For structural bolting d ≥ M12.
Nominal values for designation purposes only.
R_p0.2 may be measured if R_eL cannot be determined.
R_pf min values for 4.8, 5.8, 6.8 are under investigation.
Proof loads in Tables 5 and 7.
Hardness at end may be lower for certain classes.
Surface hardness limits apply; no more than 30 HV above core for some.
Impact test at -20 °C for d ≥ 16 mm.
GB/T 5779.3 may substitute by agreement.

These properties ensure fasteners perform under specified loads, with tests like tensile and hardness verifying quality. For high-strength applications, consider size effects on load capacity.

Application Guidelines and Test Applicability

The standard provides test methods for verification, applicable to full-size fasteners or machined specimens. Consider environmental factors, installation torque, and surface treatments to avoid failures like decarburization or embrittlement.

Use appropriate classes for load requirements; e.g., 10.9 for high-stress environments.
Apply tests for tensile, proof load, hardness, and impact as per size and class.
For hot-dip galvanized fasteners, refer to GB/T 5267.3.
Ensure marking for traceability and compliance.
Caution with 12.9 class in corrosive conditions.

These guidelines aid in selecting and testing fasteners, enhancing reliability in mechanical assemblies.

الأسئلة الشائعة (FAQ)

What does the property class marking like “8.8” signify?

It indicates nominal tensile strength of 800 MPa and a yield strength ratio of 0.8, ensuring standardized performance identification for selection in engineering designs.

How do material compositions affect fastener performance?

Compositions with added elements like boron enhance hardenability, allowing higher strength classes while limiting P and S to prevent brittleness, as per Table 2 limits.

When should impact testing be conducted?

For d ≥ 16 mm and classes requiring min 27 J at -20 °C, to assess toughness in low-temperature applications and avoid brittle failure.

What are the implications of decarburization on threads?

It reduces strength; the standard specifies max complete decarburization depth of 0.015 mm and min non-decarburized height to maintain load-bearing capacity.

How does the standard align with ISO 898-1?

It is modified from ISO 898-1:2009, with similar property classes but adapted for Chinese contexts, ensuring global interoperability in fastener specifications.

What tests are applicable for full-size fasteners?

Tensile, proof load, and wedge tensile tests verify real-world performance, especially for sizes where machined specimens may not represent actual behavior.