Wear-Resistant Surfacing Repair Process for Cold-Rolling Rolls

Literature Overview

This paper by Yu Chengkui (Wuhan University of Technology) and Yang Zhenlin (Tianjin Quality and Technical Supervision Bureau), published in Welding Technology in 2006, presents a practical approach to the local surfacing repair of Cr3-type cold-rolling work rolls. The study addresses the critical challenge of restoring worn cold-rolling rolls through wear-resistant surfacing, incorporating both process parameter optimization and metallurgical evaluation of the surfacing layer.

Background and Problem Statement

Cold-rolling work rolls are subjected to extreme conditions during steel strip production: high contact pressure, severe sliding friction, and continuous contact with lubricating oils. The working surface of a Cr3-type cold-rolling roll typically experiences abrasive wear from the steel strip being processed, as well as adhesive wear from the high-pressure contact. When the roll surface wears beyond acceptable limits, the strip surface quality deteriorates, dimensional accuracy is compromised, and the roll must be either reground (with material loss) or replaced entirely.

Local surfacing repair offers an economical alternative: selectively rebuilding worn areas with a hard, wear-resistant alloy layer that matches or exceeds the original surface hardness, while preserving the remaining roll material.

Surfacing Process Parameters

Parameter	Value	Justification
Surfacing material	Cr3-type hardfacing electrode	High Cr content promotes Cr7C3 carbide formation
Electrode diameter	3.2 mm	Suitable for localized repair areas
Welding current	90-110 A	Controls penetration and dilution
Arc voltage	22-26 V	Maintains stable arc for consistent bead profile
Travel speed	150-250 mm/min	Balances deposition rate and bead overlap
Number of passes	2-4	Achieves required repair thickness (1.5-3.0 mm)
Interpass temperature	<150°C	Prevents excessive grain growth in HAZ
Preheating temperature	100-150°C	Reduces hydrogen-induced cracking risk
Post-weld treatment	Controlled cooling in air	Promotes fine carbide distribution

Metallurgical Analysis of Surfacing Layer

The microstructure of the Cr3-type surfacing layer is dominated by primary chromium carbides (primarily Cr7C3 and Cr23C6) dispersed in a martensitic or austenitic matrix. The wear resistance mechanism operates on multiple levels:

Carbide hard phase mechanism: Cr7C3 carbides with hardness exceeding 1800 HV provide primary resistance to abrasive wear from the cold-rolled strip.
Matrix support mechanism: The surrounding matrix provides toughness and prevents carbide fracture under impact loading.
Work hardening contribution: The martensitic matrix undergoes work hardening during service, maintaining surface hardness under sliding contact.

The dilution rate between the surfacing layer and the roll base metal (typically 40CrNiMo or similar alloy steel) is a critical factor. Excessive dilution reduces the carbide volume fraction and lowers surface hardness below the required threshold of 60-65 HRC.

Comparison of Surfacing Methods

Method	Hardness (HRC)	Dilution Rate (%)	Surface Quality	Productivity
SMAW (manual arc)	58-63	25-35	Acceptable with dressing	Low
GTAW (TIG)	62-67	15-25	Excellent surface finish	Medium
Submerged arc	55-60	30-40	Requires grinding	High
Laser cladding	65-70	5-15	Excellent	Medium-high

Wear Testing Results

The study conducted pin-on-disc and dry sliding wear tests on the surfacing layer. Key findings include:

The Cr3 surfacing layer exhibited 3-5 times the wear resistance of the base metal under dry sliding conditions.
The specific wear rate was approximately 0.002-0.005 mm³/N·m, compared to 0.01-0.02 mm³/N·m for the base steel.
Wear mechanism transitioned from abrasive (dominant at low loads) to mixed abrasive-adhesive (at higher loads) as the test progressed.
The presence of fine, evenly distributed carbides in the microstructure correlated directly with lower wear rates.

Engineering Practice Considerations

For cold-rolling roll repair in industrial settings, several practical considerations must be addressed:

Roll geometry constraints: The cylindrical surface and proximity of the roll neck require careful electrode positioning and travel control to avoid undercutting or excessive reinforcement.
Thermal distortion control: Localized heating can cause dimensional changes in the roll journal, affecting bearing fit. Preheating and controlled cooling are essential.
Surface finish requirements: After surfacing, the layer must be ground to achieve a surface roughness of Ra ≤ 0.4 μm for cold-rolling applications.
Heat treatment compatibility: The surfacing layer must withstand subsequent tempering or stress-relief treatments without significant hardness loss.

Study Insights and Implications

This work demonstrates that careful selection of surfacing material, process parameters, and post-weld treatment can effectively restore worn cold-rolling rolls to service condition. The emphasis on metallurgical analysis—particularly the relationship between microstructure and wear performance—provides a scientific foundation for process optimization. For rolling mill maintenance engineers, this approach offers a cost-effective repair strategy that extends roll service life while maintaining strip quality standards.