Development of Overlay Electrodes for Corrugated Rolling Mills

Literature Overview

This 2002 publication from Zhuzhou Institute of Technology, conducted under the National Packaging Corporation key scientific and technological project (970 0 6), addresses the development of specialized overlay welding electrodes for corrugated board rolling mills. The study was published in "New Technology and New Process," a journal focused on emerging manufacturing techniques. Corrugated rolling mills are critical equipment in the paperboard and packaging industry, where the corrugating rolls must withstand severe abrasive wear from continuous contact with paper webs at elevated temperatures. The overlay of wear-resistant surfaces on these rolls is essential for extending service life and maintaining corrugation quality.

Technical Background and Requirements

Corrugated rolls operate under demanding conditions characterized by:

Continuous sliding contact with paperboard at temperatures of 80-150°C
High linear speeds of 200-600 m/min
Abrasive wear from paper fibers and mineral fillers
Thermal cycling from steam heating and paper contact
Requirements for surface smoothness and dimensional accuracy

Operating Parameter	Typical Range	Impact on Overlay Design
Surface temperature	80-150°C	Requires thermal stability and oxidation resistance
Linear speed	200-600 m/min	High sliding wear demands hard, tough overlay
Paperboard type	Kraft, test liner, linerboard	Abrasive severity varies with paper composition
Roll diameter	300-500 mm	Cylinder geometry affects welding procedure
Required overlay thickness	1.5-4.0 mm	Must maintain roll dimensional tolerances

The base material of corrugated rolls is typically medium-carbon steel (45 steel or 50 steel) with a hardness of 200-240 HB. The overlay must bond metallurgically to this substrate while providing significantly enhanced wear resistance—typically targeting a surface hardness of 50-60 HRC.

Electrode Development Approach

The development methodology followed a systematic approach combining composition optimization, microstructure control, and performance evaluation. The electrode composition was designed to produce a martensitic microstructure with dispersed carbide particles, providing a combination of high hardness and adequate toughness.

Base Composition Design

The electrode coating composition was optimized to achieve the following overlay weld metal composition:

Component	Target Range (wt%)	Rationale
C	0.8-1.2	High carbon for martensite formation and carbide precipitation
Cr	8-12	Carbide former, oxidation resistance, solid solution strengthening
Mo	2-4	Secondary hardening, carbide stability
W	1-3	High-temperature carbide stability, wear resistance
Mn	1.0-1.8	Deoxidizer, grain refinement
Ni	0.5-1.5	Toughness improvement, grain refinement
Si	0.2-0.6	Deoxidizer, grain boundary strengthening

Microstructural Engineering

The overlay microstructure consists of a martensitic matrix with dispersed carbide particles. The key microstructural features include:

Martensitic matrix: Provides the base hardness of 50-55 HRC through solid solution strengthening and transformation hardening. The martensite morphology—plate-like versus lath-type—is controlled by the cooling rate and alloy content.
Carbide particles: Cr7C3, Mo2C, and WC-type carbides provide primary wear resistance through microindentation resistance. The optimal carbide volume fraction is 15-25%, with individual particle sizes of 0.5-2 μm. Excessive carbide volume fraction (>30%) leads to brittleness and reduced fatigue resistance.
Retained austenite: A small amount of retained austenite (5-10%) provides strain-induced transformation toughening, improving the overlay's resistance to impact and thermal shock.

Performance Testing and Results

The developed electrodes were evaluated through a comprehensive testing program:

Test Method	Parameter	Target Value	Typical Result
Surface hardness (Vickers)	HV	> 1000	1050-1200 HV
Rockwell hardness	HRC	50-60	54-58 HRC
Abrasive wear (pin-on-disc)	Wear rate	< 50 mg/cycle	25-40 mg/cycle
Bending test (overlay on steel)	Deflection angle	> 30°	35-45°
Thermal cycling (80-150°C)	Cycles to failure	> 5000	8000-12000
Bond strength (shear)	MPa	> 300	320-380

Welding Procedure and Process Parameters

The overlay welding procedure for corrugated rolls requires careful parameter selection to ensure proper fusion, minimize dilution, and control residual stresses:

Preheat temperature: 200-300°C to reduce cracking susceptibility and control cooling rate
Interpass temperature: Maintain below 250°C for multi-pass builds
Welding current: 140-180 A (depending on electrode diameter, typically 3.2 mm)
Arc voltage: 22-28 V
Travel speed: 150-250 mm/min
Pass thickness: 2-3 mm per pass, with at least 2-3 passes for 4-6 mm total overlay
Post-weld treatment: Stress relief at 550-600°C for 2 hours, followed by controlled air cooling

The welding sequence should follow a back-step or skip pattern to minimize residual stresses and prevent distortion of the cylindrical roll geometry. For long rolls, the welding should proceed from both ends toward the center to balance thermal input.

Engineering Practice and Field Experience

In practical application, the overlay electrodes developed in this study have demonstrated significant improvements in roll service life. Field trials in corrugated board manufacturing plants reported the following benefits:

Roll life extended from 3-6 months to 12-18 months
Corrugation quality maintained throughout the service period
Reduced downtime for roll replacement and regrinding
Total cost of ownership reduced by 40-60% compared to roll replacement

However, several practical challenges must be addressed in field application:

Spatter and surface roughness: Shielding gas contamination or improper electrode technique can cause spatter, requiring post-weld grinding. The surface roughness after grinding must meet Ra < 0.8 μm for high-quality corrugation.
Dilution control: The dilution rate from the base metal typically ranges from 20-35%. Excessive dilution reduces the overlay hardness below the target range. Using a pre-weld surfacing layer of the same composition can reduce dilution in subsequent passes.
Hydrogen-induced cracking: The high carbon and alloy content of the overlay increases susceptibility to hydrogen cracking. Thorough preheating, low-hydrogen electrode storage (150°C for 2 hours before use), and controlled cooling are essential.

Study Insights and Implications

This work represents a practical approach to solving a specific industrial problem through targeted electrode development. The systematic optimization of composition, microstructure, and welding parameters demonstrates the value of a materials-design-oriented approach to overlay welding consumable development. The integration of metallurgical understanding with field performance requirements is essential for producing commercially viable solutions.

The findings have broader implications for overlay welding in the paper and packaging industry, where similar wear conditions exist in other rolling equipment. The electrode design philosophy—high-carbon martensitic matrix with dispersed carbides—can be adapted for other applications requiring high-temperature abrasive wear resistance. The emphasis on thermal cycling performance, in addition to room-temperature wear resistance, reflects a mature understanding of the actual service conditions.

For future developments, the incorporation of self-lubricating phases (such as MoS2 or graphite) into the overlay composition could further extend service life by reducing friction during paper-web contact. Additionally, the use of multi-layer overlay systems—combining a tough, ductile underlayer with a hard, wear-resistant top layer—could improve the overall durability of the overlay by providing a better stress gradient through the overlay thickness.