How to Choose Quenching Methods and Quenchants for Galvanized Square Tubes

Selecting the right quenching process for galvanized square tubes requires balancing two key factors:

1. Achieving the desired cooling rate to obtain the target microstructure

2. Ensuring uniform cooling to minimize deformation for subsequent processing

1. Optimal Quenching Methods for Galvanized Square Tubes

Currently, water is the most common quenchant for steel tube heat treatment due to its cost-effectiveness, safety, and environmental friendliness. However, its rapid cooling rate often causes excessive deformation in galvanized square tubes, sometimes leading to rejection in later production stages.

Recommended Approach:

· Rotary Quenching: Ideal for galvanized square tubes, combining internal and external cooling:

o Internal Cooling: High-speed water jets (≥10 m/s) through nozzles

o External Cooling: Spray or immersion in a stirred quenching tank

· Goal: Maximize cooling uniformity while meeting hardness requirements

2. Selecting the Right Quenchant

An ideal quenchant should:

· Cool rapidly in high-temperature zones (to prevent austenite decomposition)

· Slow down in low-temperature zones (to reduce martensitic stress and cracking)

Quenchant Options for Galvanized Square Tubes

3. Practical Considerations

· For High-Strength Tubes (e.g., API pipes): Water quenching is suitable due to lower carbon content and uniform wall thickness, reducing crack risks.

· For High-Carbon/Alloy Tubes: Fast oil or polymer quenchants minimize deformation.

· Post-Quenching: Tempering (180–400°C) enhances toughness, while re-galvanizing may be needed if the zinc layer is damaged.

Conclusion

For galvanized square tubes, rotary quenching with controlled water flow or polymer-based fluids offers the best balance of hardness and minimal distortion. Always test quenching parameters to optimize performance while protecting the zinc coating.