News - Introduction to Lifting Chain of Grades: G80, G100 & G120

Lifting chains and slings are critical components in all construction, manufacturing, mining, and offshore industries. Their performance hinges on material science and precise engineering. The chain grades of G80, G100, and G120 represent progressively higher strength categories, defined by their minimum tensile strength (in MPa) multiplied by 10:

- G80: 800 MPa minimum tensile strength

- G100: 1,000 MPa minimum tensile strength

- G120: 1,200 MPa minimum tensile strength

These grades adhere to international standards (e.g., ASME B30.9, ISO 1834, DIN EN818-2) and undergo strict inspection and testing to ensure reliability under dynamic loads, extreme temperatures, and corrosive environments .

1. Materials and Metallurgy: The Science Behind the Lifting Chains Grades

The mechanical properties of these lifting chains arise from precise alloy selection and heat treatment.

Grade	Base material	Heat-treatment	Key Alloying Elements	Microstructural Features
G80	Medium-carbon steel	Quenching & Tempering	C (0.25-0.35%), Mn	Tempered martensite
G100	High-strength low-alloy (HSLA) steel	Controlled quenching	Cr, Mo, V	Fine-grained bainite/martensite
G120	Advanced HSLA steel	Precision tempering	Cr, Ni, Mo, micro-alloyed Nb/V	Ultra-fine carbide dispersion

Why and how these materials matter:

- Strength Enhancement: Alloying elements (Cr, Mo, V) form carbides that impede dislocation movement, increasing yield strength without sacrificing ductility .

- Fatigue Resistance: Fine-grained microstructures in G100/G120 hinder crack initiation. G120’s tempered martensite offers superior fatigue life (>100,000 cycles at 30% WLL).

- Wear Resistance: Surface hardening (e.g., induction hardening) in G120 reduces abrasion in high-friction applications like mining draglines.

Welding Protocols for Chain Integrity

• Pre-Weld Prep:

o Clean joint surfaces to remove oxides/contaminants.

o Pre-heat to 200°C (G100/G120) to prevent hydrogen cracking.

• Welding Methods:

o Laser Welding: For G120 chains (e.g., Al-Mg-Si alloys), double-sided welding creates fusion zones with H-shaped HAZ for uniform stress distribution.

o Hot Wire TIG: For boiler steel chains (e.g., 10Cr9Mo1VNb), multi-pass welding minimizes distortion.

• Critical Tip: Avoid geometric defects in HAZ – major crack initiation sites below 150°C.

Post-Weld Heat Treatment (PWHT) Parameters

Grade	PWHT Temperature	Hold Time	Microstructural Change	Property Improvement
G80	550-600°C	2-3 hours	Tempered martensite	Stress relief, +10% impact toughness
G100	740-760°C	2-4 hours	Fine carbide dispersion	15%↑ fatigue strength, uniform HAZ
G120	760-780°C	1-2 hours	Inhibits M₂₃C₆ coarsening	Prevents strength loss at high temp

Caution: Exceeding 790°C causes carbide coarsening → strength/ductility loss.

2. Lifting Chains Performance in Extreme Conditions

Different environments demand tailored material solutions.

Temperature Tolerance:

- G80: Stable performance up to 200°C; with rapid strength loss above 400°C due to tempering reversal.

- G100/G120: Chains Retain 80% strength at 300°C; special grades (e.g., with added Si/Mo) resist embrittlement down to -40°C for arctic use.

Corrosion Resistance:

- G80: Prone to rust; requires frequent oiling in humid environments.

- G100/G120: Options include galvanization (zinc plated) or stainless-steel variants (e.g., 316L for marine/chemical plants). Galvanized G100 withstands 500+ hours in salt spray tests.

Fatigue and Impact Toughness:

- G80: Adequate for static loads; impact toughness ≈25 J at -20°C.

- G120: Exceptional toughness (>40 J) due to Ni/Cr additions; ideal for dynamic lifting (e.g., shipyard cranes).

3. Application-Specific Selection Guide

Selecting the right grade optimizes safety and cost-efficiency.

Applications	Recommended Grade	Rationale
General Construction	G80	Cost-effective for moderate loads/dry environments; e.g., scaffolding.
Offshore/Marine Lifting	G100 (Galvanized)	High strength + corrosion resistance; resists seawater pitting.
Mining/Quarrying	G120	Maximizes wear resistance in abrasive rock handling; survives impact loads.
High-Temperature (e.g., Steel Mills)	G100 (Heat-treated variant)	Retains strength near furnaces (up to 300°C).
Critical Dynamic Lifts	G120	Fatigue-resistant for helicopter lifts or rotating equipment installation.

4. Failure Prevention and Maintenance Insights

- Fatigue Failure: Most common in cyclic loading. G120’s superior crack propagation resistance reduces this risk.

- Corrosion Pitting: Compromises strength; galvanized G100 slings last 3× longer in coastal sites vs. uncoated G80.

- Inspection: ASME mandates monthly checks for cracks, wear >10% diameter, or elongation. Use magnetic particle testing for G100/G120 links.

5. Encouraging Innovations and Future Trends

- Smart Chains: G120 chains with embedded strain sensors for real-time load monitoring.

- Coatings: Nano-ceramic coatings on G120 to extend service life in acidic environments.

- Material Science: Research into austenitic steel variants for cryogenic lifting (-196°C LNG applications) .

Conclusion: Matching Chains Grade to Your Needs

- Choose G80 for cost-sensitive, non-corrosive static lifts.

- Specify G100 for corrosive/dynamic environments requiring balanced strength and durability.

- Opt for G120 in extreme conditions: high fatigue, abrasion, or precision critical lifts.

Final Note: Always prioritize certified chains with traceable heat treatments. Proper selection prevents catastrophic failures—material science is the backbone of lifting safety.

Post time: Jun-17-2025

SHANGHAI CHIGONG INDUSTRIAL CO., LTD

Introduction to Lifting Chain of Grades: G80, G100 & G120