Surfacing Repair of φ650 Rolling Mill Rolls Using Sintered Flux

Literature Overview and Background

The paper by Zhu Yan, published in Machinery Design and Manufacture in 1997 (Issue 3, pp. 37-38), describes the practical application of sintered flux submerged arc surfacing for the repair of φ650 rolling mill rolls at Dalian Second Steel Plant. The study documents the industrial practice of recycling worn rolling mill rolls through surfacing repair, providing a cost-effective solution for maintaining rolling mill productivity while reducing the consumption of new roll inventory.

Core Technical Content and Process Description

Rolling mill rolls are critical consumable components in steel rolling operations, subject to severe wear, thermal fatigue, and mechanical loading during the rolling process. The φ650 designation refers to the roll diameter, indicating a medium-sized work roll used in finishing or intermediate rolling mills. Over time, the roll surface develops wear grooves, surface cracks, and dimensional deviations that necessitate either replacement or repair.

The surfacing repair process described in this paper involves the following sequential steps:

1. Roll removal and inspection: After each rolling campaign, worn rolls are removed and inspected for surface defects including wear depth, cracks, and dimensional accuracy.
2. Surface preparation: The worn roll surface is cleaned by grinding or machining to remove scale, oxidation, and severely worn material, creating a sound substrate for surfacing.
3. Sintered flux submerged arc surfacing: Multiple layers of alloy surfacing material are deposited using automatic submerged arc welding with sintered flux. The sintered flux provides shielding, alloying, and slag protection during the welding process.
4. Annealing heat treatment: The surfaced roll undergoes annealing to relieve residual stresses and refine the microstructure of the surfacing layer.
5. Machining and reprofiling: The rolled surface is machined to restore the original roll profile and dimensional accuracy.
6. Reinstallation and return to service: The repaired roll is reinstalled in the rolling mill for continued production.

Sintered Flux Characteristics and Advantages

Sintered flux, as opposed to fused flux, offers several advantages for rolling mill roll surfacing applications:

The sintered flux used in this application likely contains iron oxide, manganese oxide, silicon dioxide, and calcium fluoride, with additional alloying elements tailored to the desired surfacing composition. The flux serves multiple functions: it shields the molten weld pool from atmospheric contamination, provides alloying elements to the weld metal, forms a protective slag layer during solidification, and improves the fluidity and workability of the weld pool.

Engineering Practice and Quality Control

The success of rolling mill roll surfacing repair depends on several critical quality factors:

• Base metal preparation: The surface must be free of cracks, scale, and contamination. Any surface cracks must be repaired by grinding or welding before surfacing to prevent crack propagation through the surfacing layer.
• Preheating: Preheating the roll to 200-300 °C reduces thermal stress and prevents cold cracking, particularly important for high-carbon or high-alloy roll materials.
• Layer thickness control: The total surfacing layer thickness must be sufficient to cover the wear area but not excessive, as thick layers increase residual stress and may require more extensive post-weld machining.
• Annealing parameters: The annealing temperature and holding time must be optimized to achieve complete stress relief without softening the surfacing material excessively. Typical annealing temperatures range from 650-750 °C with holding times of 1-2 hours per 25 mm of roll diameter.
• Dimensional accuracy: Post-machining must restore the roll profile to within tight tolerance limits (typically ±0.05 mm) to ensure proper rolling performance and product quality.

Study Insights and Economic Implications

This paper documents a practical, cost-effective approach to extending the service life of rolling mill rolls, which is of significant economic importance in the steel industry. The cost of a new φ650 roll can be substantial, and the ability to repair and reuse rolls through surfacing can reduce roll consumption costs by 30-50% compared to a replace-only strategy. The use of sintered flux, which is less expensive than fused flux, further reduces the repair cost.

From a metallurgical perspective, the key challenge in rolling mill roll surfacing is achieving a surfacing layer with sufficient hardness and wear resistance while maintaining adequate toughness to resist thermal fatigue cracking. The alloy composition of the surfacing material must be carefully selected based on the specific rolling conditions, including rolling temperature, reduction ratio, and steel grade being rolled. For hot rolling applications, surfacing materials based on high-speed steel compositions (such as those containing chromium, tungsten, and molybdenum) or medium-alloy steel compositions (containing chromium, manganese, and molybdenum) are commonly used.

The practical experience documented in this paper highlights the importance of systematic quality control throughout the repair process. Each stage—from surface preparation through post-weld heat treatment and final machining—must be carefully controlled to ensure the repaired roll meets the required performance standards. Engineers responsible for roll maintenance programs should establish standardized procedures and quality checkpoints at each stage of the repair process to ensure consistent results and maximize the number of repair cycles achievable per roll.