Uniformity Analysis of Temperature Field During Steel Tube Quenching

Literature Overview

This study by Liu Guoyong and colleagues from University of Science and Technology Beijing investigates the temperature field uniformity during the immersion quenching of seamless steel tubes. The authors used ANSYS finite element software to numerically simulate the quenching temperature field and analyzed the influence of various factors on cooling uniformity, including spray velocity, tube rotation speed, and immersion angle. The research was supported by the Ministry of Education Doctoral Fund.

Core Technical Findings

The study examines two quenching configurations: partial immersion and full immersion. For partial immersion quenching, the optimal conditions for uniform cooling are: no water spray on either surface with an immersion angle of 180° to 270°, or no external spray with internal axial spray at 3 m/s. The tube rotation speed should not be lower than 60 r/min for good radial cooling uniformity. For full immersion quenching, the optimal conditions are: internal spray velocity of 8 m/s with external spray velocity of 6 m/s, or internal spray velocity of 10 m/s with external spray velocity of 7 m/s. The tube rotation speed should be between 60 and 90 r/min to balance cooling uniformity with energy consumption and stability.

Optimal Quenching Parameters

Technical Analysis of Cooling Uniformity Factors

The cooling uniformity during steel tube quenching is critical for achieving consistent microstructure and mechanical properties throughout the tube cross-section. Non-uniform cooling can lead to variations in hardness, residual stress, and dimensional stability, which can affect the performance of the finished tube in service.

Influence of Spray Velocity

The spray velocity determines the heat transfer coefficient at the steel tube surface. Higher spray velocities generally increase the heat transfer coefficient, leading to faster cooling. However, excessive spray velocity can create non-uniform cooling patterns due to jet impingement effects and turbulence variations. The optimal spray velocity represents a balance between sufficient heat transfer and uniform coverage.

For partial immersion quenching, the internal spray velocity of 3 m/s provides sufficient cooling while maintaining uniformity. This relatively low velocity suggests that the internal surface area is small enough to be effectively cooled by moderate spray pressure. For full immersion quenching, higher velocities (8-10 m/s internally and 6-7 m/s externally) are required to overcome the greater surface area and ensure uniform cooling.

Influence of Tube Rotation Speed

The tube rotation speed is a critical factor in achieving radial cooling uniformity. At low rotation speeds, the bottom of the tube (closest to the quenching medium) cools faster than the top, creating a significant temperature gradient across the diameter. As the rotation speed increases, the average cooling rate becomes more uniform because each point on the tube surface spends equal time in different thermal environments.

The study finds that a minimum rotation speed of 60 r/min is required for acceptable radial cooling uniformity. This corresponds to a surface velocity of approximately 1-2 m/s for typical tube diameters, which is sufficient to average out the cooling variations due to gravity and spray direction. The upper limit of 90 r/min is imposed by practical considerations of energy consumption and mechanical stability.

Influence of Immersion Angle

For partial immersion quenching, the immersion angle determines the proportion of the tube surface that is in direct contact with the quenching medium. An immersion angle of 180° to 270° provides the best cooling uniformity because it covers the bottom and lower sides of the tube while allowing the upper portion to cool through convective heat transfer. This configuration avoids the extreme temperature gradients that occur when the tube is fully submerged or when only a small portion is immersed.

Engineering Practice Implications

For steel tube manufacturing plants, the findings of this study provide practical guidelines for quenching process optimization. The recommended parameters can be directly applied to existing quenching systems to improve cooling uniformity and product quality. The study also highlights the importance of process control parameters that are often overlooked in practice, such as immersion angle and spray velocity matching.

Process Optimization Recommendations

1. Partial immersion systems: Implement no-spray operation with 180°-270° immersion angle, or use internal-only spray at 3 m/s, with rotation speed maintained at or above 60 r/min.
2. Full immersion systems: Use matched internal and external spray velocities (8 m/s internal / 6 m/s external, or 10 m/s internal / 7 m/s external), with rotation speed controlled between 60 and 90 r/min.
3. Monitoring: Implement temperature monitoring at multiple points around the tube circumference to verify cooling uniformity in real-time.
4. Validation: Conduct periodic hardness and microstructure testing to confirm that the optimized parameters produce consistent results.

Study Insights and Reflections

The most valuable contribution of this research is the systematic numerical simulation of quenching temperature fields under various process conditions. The identification of optimal parameter combinations provides a quantitative basis for process optimization that can be directly applied in manufacturing practice. The study also demonstrates the power of numerical simulation in understanding complex thermal processes that are difficult to measure experimentally.

The finding that partial immersion quenching can achieve better cooling uniformity than full immersion quenching under certain conditions is somewhat counterintuitive and has significant practical implications. This suggests that the choice of quenching configuration should be based on the specific requirements of the product rather than following conventional practices.

The study also highlights the importance of process parameter matching. The optimal spray velocity ratio between internal and external surfaces is not arbitrary but is determined by the relative surface areas and heat transfer characteristics. This matching principle should be considered in the design and operation of quenching systems.

One limitation of the study is that it focuses on temperature field uniformity but does not address the resulting microstructure and mechanical property variations. Future research should correlate temperature field uniformity with final product quality metrics to establish direct relationships between process parameters and product performance.

Overall, this study provides valuable technical guidance for steel tube manufacturers seeking to improve quenching process uniformity and product quality through systematic process optimization.