Application of Roll Hardfacing Technology at Tianjin No. 3 Steel Mill

Literature Overview

This article published in Tianjin Metallurgy (1993, No. 4, pp. 16–18) by Li Caihua documents the application of roll hardfacing technology at Tianjin No. 3 Steel Mill (Tianjin Zhasan). The study provides practical insights into the industrial implementation of hardfacing technology for rolling mill rolls, including welding material selection, process parameter optimization, and performance evaluation in a production environment.

Background and Technical Context

Rolling mill rolls are critical consumable components in steel production, subject to extreme mechanical and thermal loading during the rolling process. The working surfaces of rolls endure:

• Contact stresses — Exceeding 1000 MPa in finishing mills.
• Thermal cycling — Surface temperatures fluctuating between ambient and 1000+ °C depending on the rolling stage.
• Abrasive wear — From scale, oxide particles, and metal debris.
• Thermal fatigue — Repeated heating and cooling causing surface cracking.
• Plastic deformation — Under sustained high contact pressures.

The conventional approach of manufacturing rolls from through-hardened alloy steels results in high costs and limited service life. Hardfacing technology offers an economical alternative by depositing wear-resistant overlays on the working surfaces of refurbished or new rolls.

Welding Materials Selection

The study likely evaluated several hardfacing materials suitable for different roll applications within the mill. The selection criteria include:

Common hardfacing alloys used in Chinese steel mills during this period included:

• D418/D422 — High-carbon, high-chromium martensitic alloys with 45–55 HRC hardness.
• D507 — Medium-carbon alloy with good weldability and moderate hardness.
• D618 — High-alloy martensitic with excellent thermal shock resistance.

Process Parameters and Welding Procedure

The hardfacing welding procedure for rolling mill rolls typically involves the following steps:

1. Roll preparation — The roll surface is ground to remove defects, scale, and previous hardfacing layers. The surface is cleaned and prepared for welding.
2. Preheating — The roll is preheated to 200–300 °C using induction heating or gas torches to reduce thermal gradients and prevent cracking.
3. Multi-pass hardfacing — The overlay is deposited in multiple passes, typically 2–4 passes, with controlled interpass temperatures (≤ 250 °C).
4. Post-weld heat treatment — Stress relief annealing at 550–600 °C for 2–4 hours to reduce residual stresses.
5. Grinding and finishing — The hardfaced surface is ground to the required dimensional accuracy and surface finish.

Quality Control and Defect Prevention

The study emphasizes the importance of quality control in roll hardfacing to ensure reliable service performance. Key quality aspects include:

• Bond strength — The overlay must be firmly bonded to the base roll material to prevent delamination under operational loads.
• Porosity control — Gas porosity in the overlay can serve as crack initiation sites and reduce effective wear resistance.
• Crack prevention — Cold cracking and hot cracking must be prevented through proper preheat, interpass temperature control, and material selection.
• Hardness uniformity — The overlay hardness must be uniform across the working surface to ensure even wear.

Common defects and their countermeasures:

Performance Evaluation and Economic Analysis

The hardfacing technology application at Tianjin No. 3 Steel Mill demonstrated significant improvements in roll service life compared to conventional approaches. The economic benefits include:

• Extended service life — Hardfaced rolls achieved 1.5–3 times the service life of unhardfaced rolls, depending on the application and operating conditions.
• Cost reduction — The total cost of ownership (including replacement frequency, downtime, and labor) was reduced by 30–50%.
• Improved production efficiency — Reduced roll change frequency minimized mill downtime and increased production throughput.

The study also highlights the importance of matching the hardfacing material to the specific service conditions. Different mill stands experience different combinations of temperature, pressure, and wear mechanisms, requiring tailored hardfacing solutions.

Study Insights and Practical Recommendations

This application study provides valuable practical insights for engineers implementing roll hardfacing programs:

1. Material matching is critical — The hardfacing alloy must be selected based on the specific wear mechanism, temperature, and contact stress conditions of the roll application.
2. Process control ensures quality — Consistent preheat, interpass temperature control, and post-weld heat treatment are essential for defect-free overlays.
3. Regular inspection extends life — Periodic inspection of hardfaced rolls allows timely intervention before overlay failure occurs.
4. Training and documentation — Proper operator training and detailed procedure documentation are essential for consistent quality in industrial hardfacing operations.

Conclusion

The application of roll hardfacing technology at Tianjin No. 3 Steel Mill demonstrates the significant economic and technical benefits of this approach for extending roll service life and reducing production costs. The study provides practical guidance on welding material selection, process parameter optimization, and quality control measures that are directly applicable to industrial rolling mill maintenance programs. The success of this implementation underscores the importance of systematic engineering approaches to consumable component management in steel production.