News - Further Review On Round Link Chain Heat-Treatment, Breaking Force and Elongation

The balance between strength and ductility in high-grade lifting chains like G80 and G100 is fundamentally governed by their heat treatment. Achieving a higher tensile strength (moving from G80 to G100) inherently involves metallurgical trade-offs that directly impact elongation and toughness.

The Core Principle: The Strength-Ductility Trade-off

At the heart of the difference between G80 and G100 round link chain is a fundamental metallurgical rule: increasing strength (hardness) typically reduces ductility (elongation). This is controlled almost entirely by heat treatment, which manipulates the steel's microstructure.

- Objective: Transform the soft, ductile "pearlite-ferrite" microstructure of low-carbon steel into a much stronger "tempered martensite."

- Process: The round link chain is first austenitized (heated to a high temperature), then quenched (rapidly cooled) to form a very hard but brittle microstructure called martensite. Finally, it is tempered (reheated to a moderate temperature) to restore some ductility and toughness.

- The Trade-off: Higher tempering temperatures increase ductility but decrease strength. Lower tempering temperatures preserve higher strength but result in lower ductility. This is the primary lever used to differentiate G80 from G100 chains.

Chain Heat Treatment in Practice: G80 vs. G100

With different base materials used (20Mn2 for G80 chains as typical and SAE8620 for G100 chains), the heat treatment parameters are meticulously adjusted.

Performance Implications & Selection Guidance

This engineered difference dictates their optimal applications:

- G80 chains (The "Tough" Performer): Its excellent elongation makes it the preferred choice for dynamic, high-impact, or unpredictable lifting scenarios (e.g., construction, shipyards, waste handling). Its ability to absorb energy and deform before breaking provides a critical visual and physical safety warning.

- G100 chains (The "Strong" Specialist): Its higher strength-to-weight ratio is ideal for applications where load capacity is paramount and motions are more controlled (e.g., precision overhead cranes in factories, hoists where minimizing chain weight is beneficial). The user must be aware that its lower elongation means it operates closer to its ultimate limit after yielding.

To choose the right grade, you can follow this logic:

A Critical Safety Note on "Over-Tempering"

A dangerous, non-compliant practice sometimes occurs in the market: selling a lower-grade chain as a higher grade by under-tempering it (or skipping tempering). For example, a chain quenched but not properly tempered might achieve G100's breaking force. However, its elongation would be catastrophically low (perhaps 5-8%), and it would be extremely brittle. This is why testing both breaking force and elongation is non-negotiable for chains safety certification—one number alone does not guarantee a chain's true quality or safe behavior.

The journey from G80 to G100 is one of precise, calculated compromise. By lowering the tempering temperature, manufacturers "trade" some of the ductility and safety margin for higher load capacity. The optimal choice depends entirely on whether the application demands maximum toughness (G80) or maximum strength (G100).

Still, someone may consider quenching only for round link chains to achieve good hardness whle accepting less strength for some conveyor chains applications.

Achieving a target hardness of around 50 HRC through quenching-only heat treatment is technically possible. However, for chains that will experience any dynamic load, skipping the tempering step introduces significant risks of brittle failure and unpredictable performance.

The table below compares the properties of steel in an as-quenched state versus after proper tempering:

Key Risks of a Quenching-Only Process

The high hardness comes at the cost of other critical properties:

- Catastrophic Brittleness: As-quenched martensite, especially from medium-carbon steels, has very low ductility. A chain link could snap without warning or plastic deformation.

- Unstable Dimensions: The high internal stresses can lead to distortion or cracking, either immediately after quenching or later in service.

- Sensitivity to Defects: The brittle material is highly sensitive to notches, scratches, or minor manufacturing flaws, which can act as crack initiation points.

Recommended Approaches to Meet Your Target

Instead of omitting tempering, consider these safer, controlled methods:

1. Select Leaner Alloy Steels: For chains strength between Grade 30 (≈ 300 MPa) and Grade 50 (≈ 500 MPa) with 50 HRC hardness, low-carbon or low-carbon alloy steels (like 20CrNiMo or 20Mn2) are better suited. When quenched, they form low-carbon martensite, which naturally offers a better combination of high strength (up to ~1300 MPa yield) and good toughness at hardness levels of 45-50 HRC.

2. Apply a Low-Temperature Temper: If using a medium-carbon steel, a brief, low-temperature temper (e.g., 150-250°C) can relieve the most dangerous internal stresses and slightly improve toughness with minimal reduction to your 50 HRC target.

3. Consider Advanced Processes: For the best balance, explore the Quenching and Partitioning (Q&P) process. It is designed to achieve very high strength while retaining significantly higher toughness by stabilizing retained austenite.

While quenching alone can hit your hardness number, it produces a chain that is metallurgically unsound for real-world use.

Post time: Jan-19-2026