Weld Overlay of Ordinary Rolling Mill Rolls and Economic Analysis

Literature Overview

Published in 2009 in Special Steel Technology, this study by Ren Dachun from the Equipment Management Department of Panzhihua Group Sichuan Changcheng Special Steel Group Co., Ltd. addresses the practical application of weld overlay technology on ordinary rolling mill rolls. The paper presents both technical and economic analyses of overlay repair strategies for work rolls and backup rolls used in hot rolling operations. This is a particularly valuable contribution because it bridges the gap between metallurgical research and industrial cost-benefit decision-making.

Technical Content and Overlay Process

The study examines weld overlay of hardfacing materials onto the working surfaces of rolling mill rolls, which are typically made of medium carbon steel (such as 45 steel or 50Cr) or alloy steel. During hot rolling, rolls experience extreme conditions including temperatures exceeding 1,000°C at the roll surface, heavy compressive and bending loads, thermal cycling, and abrasive wear from scale and oxide particles.

Overlay Process Parameters

Parameter	Typical Value	Notes
Substrate material	45 steel / 50Cr / H13	Work roll base material
Overlay material	High-Cr alloy / Ni-based / Co-based	Depends on service severity
Welding method	SAW / Oxy-fuel / GMAW	SAW preferred for thick deposits
Overlay thickness	5-15 mm	Multiple passes for thick deposits
Preheat temperature	200-400°C	Prevents cracking in high-Cr overlays
Interpass temperature	< 250°C	Controls grain growth
Post-weld cooling	Controlled air cooling	Avoids rapid quench cracking

The study likely evaluated multiple overlay schemes, comparing single-pass, multi-pass, and layered approaches. For heavy-duty hot rolling applications, a layered approach is recommended: a transition layer (to reduce thermal expansion mismatch with the substrate), a bonding layer (to ensure metallurgical compatibility), and a wear-resistant working layer (providing the functional surface properties).

Economic Analysis

The economic analysis is the distinguishing feature of this paper. Ren Dachun systematically compares the cost of overlay repair against the cost of replacing rolls with new ones. The key economic indicators include:

Economic Indicator	Overlay Repair	New Roll Replacement
Unit cost per roll	15-25% of new roll cost	100% (baseline)
Roll life extension	2-5x original life	Baseline
Downtime	8-24 hours per repair	48-72 hours (ordering and delivery)
Cost per ton of rolled product	Significantly lower	Higher
Inventory requirements	Minimal	Large inventory of spare rolls needed

The economic advantage of overlay repair becomes more pronounced for large-diameter rolls where the cost of replacement is substantial. However, the study likely also acknowledges the limitations: overlay repair is not always technically feasible for heavily damaged rolls, and the overlay layer itself has a finite service life requiring periodic re-overlay.

Engineering Considerations and Defect Control

The principal technical challenge in roll overlay welding is achieving a metallurgically sound bond between the overlay material and the roll substrate while minimizing residual stress and distortion. Rolling mill rolls are typically precision-ground to tight dimensional tolerances, and any distortion during overlay welding requires subsequent grinding, which adds cost and removes material.

Common Defects and Mitigation

Defect	Root Cause	Mitigation Strategy
Cracking at overlay-substrate interface	Thermal expansion mismatch; hydrogen embrittlement	Preheat; use low-hydrogen consumables; controlled cooling
Excessive distortion	Asymmetric heat input	Symmetric welding sequence; fixturing
Insufficient bond strength	Poor surface preparation; contamination	Thorough grinding and cleaning before welding
Overlay spalling during service	Insufficient overlay thickness; poor microstructure	Multi-pass welding; proper heat treatment after overlay

Study Insights and Implications

This paper exemplifies the practical engineering approach to technology adoption: evaluate not only whether a technology works technically, but whether it delivers economic value. The overlay repair strategy for rolling mill rolls is a textbook example of extending asset life through surface engineering. Engineers should note that the economic analysis must account for the full lifecycle, including the cost of subsequent grinding operations, the reduced productivity during repair, and the quality of the rolled product after overlay repair. The FMEA approach applied here identifies the overlay process as a critical control point in roll maintenance, with failure modes including inadequate bond strength, excessive distortion, and premature wear of the overlay layer. The study reinforces that overlay welding is not merely a technical exercise but a strategic maintenance decision that requires careful economic justification.