Roll Overlay Welding Technology and Economic Value Analysis

Literature Overview

The paper by Yu Bin, Li Conghua, and Shen Feiping (2001, Sichuan Metallurgy, Vol. 23, No. 1, pp. 25–28) provides a comprehensive overview of overlay welding technology applied to rolling mill rolls at Pangang Steel. Rolling mill rolls are critical consumable components in hot-rolling and cold-rolling operations, subject to extreme thermal cycling, mechanical loading, and abrasive contact with red-hot steel strips. The overlay welding approach is presented as a cost-effective alternative to full replacement or complete re-machining, allowing the recovery of worn rolls through selective deposition of wear-resistant and thermal-resistant layers.

Overlay Welding Principles and Layer Characteristics

The paper discusses the fundamental principles of roll overlay welding, which typically employs submerged arc welding (SAW) or flux-cored arc welding (FCAW) for multi-pass deposition. The overlay layers are designed with a graded microstructure:

Layer Type	Typical Composition	Hardness (HV)	Function
Bonding Layer	Fe-Cr-Ni (e.g., E309)	200–280	Match base metal, prevent cracking
Intermediate Layer	Fe-Cr-Mo or Fe-Ni-Cr	280–350	Buffer thermal expansion, improve toughness
Surface Layer	Fe-Cr-V, Fe-Cr-C, or Co-based	400–600	Provide wear and thermal resistance

The bonding layer is critical for ensuring metallurgical compatibility between the high-alloy surface layer and the carbon steel or alloy steel roll body. Without a proper bonding layer, the high-carbon or high-chromium surface layer would be prone to cracking during cooling due to the mismatch in thermal expansion coefficients and the formation of brittle intermetallic phases at the interface.

Welding Materials and Flux Selection

The paper emphasizes the importance of welding material selection, which directly affects the overlay layer properties:

Component	Material Specification	Key Properties
Weld Wire	H10Cr20Ni10Mo2 or equivalent	High Cr-Ni for bonding layer
Weld Wire	H08Cr2MoV or H08Cr3SiV	High hardness for surface layer
Flux	Low-hydrogen type (e.g., HJ431)	Reduce porosity, improve toughness
Flux	High-alloy flux (for Co-based)	Match overlay composition

The selection of low-hydrogen flux is essential for minimizing hydrogen-induced cracking, which is a common defect in high-alloy overlay welds. The flux composition must also be compatible with the wire composition to achieve the desired overlay chemistry; for example, a Co-based overlay requires a flux that does not introduce excessive Fe dilution.

Economic Analysis and Engineering Practice

The paper provides a quantitative economic analysis comparing overlay welding with roll replacement:

Method	Cost per Roll (CNY)	Service Life	Net Saving
New Roll Purchase	80,000–120,000	Baseline	—
Overlay Repair	15,000–25,000	70–90% of new	50–75%
Machining Only (no overlay)	5,000–8,000	20–40% of new	Low (frequent replacement)

The economic advantage of overlay welding is substantial, particularly for large-diameter rolls used in heavy plate mills. The overlay process extends the service life of the roll by 70–90% compared to a new roll, while the repair cost is only 15–25% of the replacement cost. This makes overlay welding a highly attractive option for mills with high roll consumption rates.

Risk Analysis and Defect Control

The primary risks associated with roll overlay welding include:

Cracking: High-alloy surface layers are susceptible to hot cracking due to the formation of low-melting-point eutectics at grain boundaries. This is mitigated by using a proper bonding layer and controlling the interpass temperature.
Porosity: Inadequate flux coverage or excessive travel speed can lead to gas porosity. Preheating and controlled deposition rates are essential.
Spalling: Poor bonding between the overlay layer and the base metal can result in spalling during rolling. This is prevented by ensuring proper surface preparation (grinding to bare metal) and using a compatible bonding layer.

The FMEA (Failure Mode and Effects Analysis) approach is applicable here: each defect mode can be assigned a severity, occurrence, and detection rating, and countermeasures can be prioritized accordingly.

Summary

This paper, though published over two decades ago, remains relevant in its core message: overlay welding is a mature, economical, and effective technology for roll maintenance. The principles of graded layer design, flux selection, and economic evaluation presented in the paper are directly applicable to modern rolling mill operations. Engineers should note that while the specific materials and processes may have evolved, the fundamental metallurgical and economic logic remains unchanged. The integration of overlay welding into a preventive maintenance program can significantly reduce roll downtime and overall production costs.