Study Note on Wear-Resistant Cladding Electrode for Hot Rolled Rolls

Literature Overview

This paper published in Hot Working Technology (1997, Vol. 26, No. 1, pp. 53-54) by Ying Pengzhan, Ge Changlu, and Cai Yingjun from China University of Mining and Technology, presents research on a wear-resistant cladding electrode developed specifically for hot rolled mill rolls. The study characterizes the cladding layer microstructure through metallographic analysis and X-ray diffraction, evaluates hardness before and after aging treatment, and validates wear resistance through both laboratory testing and industrial trials. The results demonstrate excellent wear resistance, with the cladding alloy exhibiting 6.1 times the wear resistance of 45 steel.

Core Technical Content

Hot rolled mill rolls are subjected to severe abrasive wear from contact with hot steel workpieces, often at temperatures exceeding 800°C. The cladding layer must maintain high hardness and wear resistance under these extreme conditions. The developed electrode produces a cladding layer with the following microstructure:

Hardness Performance

The remarkable stability of hardness after prolonged aging at 580°C is a critical finding. Most martensitic alloys experience significant softening at these temperatures due to carbide coarsening and martensite decomposition. The maintained hardness suggests the presence of stable carbides (likely M₇C₃ or M₂₃C₆ type carbides with high thermal stability) and possibly retained austenite that transforms to martensite during aging, compensating for any softening of the original martensite.

Wear Resistance

The industrial trial results show that the cladding alloy exhibits 6.1 times the wear resistance of 45 steel under high-stress abrasive wear conditions. This represents a substantial improvement in roll life, which directly translates to reduced downtime and lower production costs.

Electrode Design Considerations

Alloy Composition

The electrode composition is likely designed to:

• Provide sufficient carbon for martensite formation and carbide precipitation
• Include alloying elements (Cr, Mo, V, W) for carbide stability and secondary hardening
• Maintain adequate nickel or manganese for retained austenite retention

Flux Design

The flux coating must:

• Provide adequate slag coverage for protection
• Control cooling rate for desired microstructure
• Minimize inclusion formation
• Provide deoxidation to reduce oxide inclusions

Weldability

For production application, the electrode must:

• Provide stable arc characteristics
• Allow good slag removal
• Minimize spatter
• Be compatible with standard SMAW equipment

Engineering Practice Integration

Application Parameters

For hot rolled roll cladding, typical parameters include:

• Preheating: 200-300°C to reduce residual stress
• Interpass temperature: Below 250°C to maintain martensitic structure
• Welding current: Adjusted for electrode diameter (typically 250-400 A for 4-5 mm electrodes)
• Welding speed: Controlled for consistent bead profile

Post-Weld Treatment

The aging treatment at 580°C for 1000 minutes (approximately 16.7 hours) is a critical step. This extended aging serves to:

• Stabilize the microstructure
• Transform retained austenite to martensite
• Refine carbide distribution
• Relieve residual stresses

Engineers should carefully control the aging process to avoid over-aging, which could lead to carbide coarsening and softening.

Quality Assurance

Post-cladding inspection should include:

• Visual inspection for surface quality
• Hardness testing across the cladding layer
• Metallographic examination for microstructure verification
• Wear testing on coupon samples
• Non-destructive testing for defect detection

Study Insights and Reflections

This paper demonstrates the successful development of a specialized cladding electrode for a demanding industrial application. The key innovation lies in achieving hardness stability after prolonged exposure to elevated temperatures, which is critical for hot rolling applications where rolls are repeatedly heated during operation.

The 6.1 times wear resistance improvement over 45 steel represents a significant engineering achievement. In practical terms, this translates to substantially longer roll life between regrinding or replacement, which has direct economic benefits for steel mills.

The study also highlights the importance of aging treatment in achieving optimal properties. Without the aging step, the as-cladded microstructure may contain excessive retained austenite, which could transform during service, causing dimensional changes and potential cracking. The aging treatment ensures microstructural stability before the roll enters service.

From a metallurgical perspective, the martensite + retained austenite + carbide microstructure is a classic design for high-temperature wear resistance. The retained austenite provides a reserve of toughness that can be activated during aging or service heating, while the carbides provide the primary wear resistance.

Reference Value and Outlook

The research provides a validated electrode design for hot rolled roll cladding, with demonstrated industrial performance. Future developments could include:

• Optimization of electrode composition for specific roll applications (roughing vs. finishing rolls)
• Development of flux-cored wire alternatives for faster cladding
• Investigation of alternative welding processes (such as submerged arc or plasma arc) for thicker cladding
• Long-term field performance data to validate laboratory results
• Cost-benefit analysis comparing cladding with alternative roll protection methods

Engineers implementing this technology should establish rigorous process qualification and quality control procedures to ensure consistent performance in production environments.