Overlay Welding of Ordinary Roll Grooves and Economic Analysis

Literature Overview

This 2009 publication in Special Steel Technology, authored by Ren Dachun from the Equipment Management Department of Chengde Special Steel Group (Panzhihua Steel Group), addresses the overlay welding repair of ordinary roll grooves and provides a comprehensive economic analysis. The work bridges the gap between technical feasibility and economic viability, demonstrating how overlay welding can be justified as a cost-effective alternative to roll replacement in the special steel rolling mill environment.

Core Technical Points

Roll Groove Wear Mechanisms

Ordinary rolls in special steel mills experience groove wear through multiple mechanisms:

Abrasive wear: From scale and oxide particles trapped between roll and workpiece
Adhesive wear: From direct metal-to-metal contact at elevated temperatures
Thermal wear: From softening of roll surface at elevated temperatures
Thermal fatigue: From repeated thermal cycling during rolling
Chemical wear: From oxidation and decarburization at the roll surface

The groove geometry concentrates stresses and accelerates wear at the groove bottom and edges, where contact pressure is highest.

Overlay Welding Process Selection

For roll groove repair, the following processes are commonly considered:

Process	Deposition Rate	Cost	Quality	Suitability
SMAW (Stick welding)	Low	Low	Good	Small repairs; field conditions
SAW (Submerged arc welding)	High	Medium	Excellent	Large surfaces; workshop conditions
FCAW (Flux-cored arc welding)	High	Medium	Very good	Flexible; good bead shape
TIG (GTAW)	Low	Medium	Excellent	Precision; thin layers
Plasma arc welding	Medium	High	Excellent	Precision; thick layers

For ordinary roll grooves, FCAW or SAW is typically preferred due to the combination of high deposition rate and good bead quality.

Overlay Material Selection

The overlay material must be compatible with the roll base material and provide superior wear resistance under rolling conditions:

Overlay Material Type	Hardness (HRC)	Wear Resistance	Thermal Resistance	Typical Application
High-carbon martensitic	55–65	Good	Moderate	Cold and warm rolling
High-alloy austenitic	40–50	Excellent	Good	Hot rolling
Cr-Mo-V high-speed steel	60–65	Excellent	Good	Heavy-duty hot rolling
Hardfacing cast iron	50–60	Good	Moderate	General purpose
Nickel-based alloy	35–45	Moderate	Excellent	Extreme thermal environments

Economic Analysis Framework

The economic analysis compares the total cost of ownership for overlay welding repair versus roll replacement:

Cost Component	Overlay Repair	Roll Replacement
Material cost	¥X (overlay wire/electrode)	¥Y (new roll)
Labor cost	¥A (welding + machining)	¥B (installation)
Downtime cost	¥C (short outage)	¥D (long outage)
Machine cost	¥E (grinding, etc.)	¥F (machining new roll)
Quality risk	Moderate (interface concerns)	Low (new roll)
Total cost per repair cycle	Significantly lower	Significantly higher

The payback period for overlay welding is typically less than one production shift, making it economically attractive even when accounting for the additional machining and inspection requirements.

Process Details for Roll Groove Overlay

Surface Preparation

Remove the worn groove surface by grinding to expose sound base metal
Create a groove profile that matches the desired final groove geometry
Clean the surface to remove oil, coolant, and oxide
Preheat the roll to 200–300 °C to minimize thermal stress

Welding Sequence

The welding sequence for a roll groove is critical to minimize distortion:

Apply the first pass along the groove bottom with moderate penetration
Build up the groove profile layer by layer, alternating between the two sides of the groove
Maintain interpass temperature below 250 °C to preserve overlay hardness
Use a stringer bead technique for the final profile layer
Allow controlled cooling to minimize thermal stress

Post-Weld Treatment

Stress relief annealing at 550–650 °C for 2–4 hours
Final grinding to achieve the exact groove profile and surface finish
Hardness verification at multiple points on the overlay surface
Dimensional inspection of the groove profile

Defect Analysis and Countermeasures

Defect	Root Cause	Impact	Countermeasure
Cracking at interface	Thermal mismatch; high carbon content	Structural failure	Optimize preheat; use compatible overlay material; apply stress relief
Excessive dilution	High heat input; poor parameter control	Reduced overlay hardness	Reduce current; increase travel speed; use smaller electrode
Groove profile deviation	Welding distortion; poor technique	Roll performance degradation	Use backing plate; apply symmetric welding sequence; final grinding
Insufficient penetration	Low current; high travel speed	Poor bond strength	Increase current; reduce travel speed; ensure first-pass penetration
Hardness variation	Cooling rate variation; parameter inconsistency	Uneven wear performance	Standardize parameters; monitor interpass temperature; use consistent technique

Study Reflections

The economic analysis component of this publication is particularly valuable, as it provides the quantitative justification that equipment managers and production planners need to approve overlay welding repair programs. The key insight is that the economic viability of overlay welding depends not only on the direct material and labor costs but also on the indirect costs associated with downtime and production loss. For special steel mills, where roll replacement can require days of downtime and the loss of high-value production, the economic case for overlay welding is compelling.

The technical insight is that overlay welding of roll grooves requires careful attention to the welding sequence to minimize distortion. The asymmetric geometry of a roll groove makes it inherently prone to distortion during welding, and the final grinding step is essential to restore the precise groove profile. The selection of overlay material must balance hardness (for wear resistance) against toughness (to resist cracking during rolling) and thermal compatibility (to avoid cracking during thermal cycling).