FCAW Surfacing Process for Large Draw Roll Wear-Resistant Layer

Literature Overview

This paper, published in Welding (No. 12, 1996, pp. 16-18) by Huang Xiaoou, Xu Lin, Wang Ruijun, and Ma Xiaobin from the Chinese Academy of Agricultural Mechanization Sciences, presents the development and application of a Flux-Cored Arc Welding (FCAW) surfacing process for the draw roll of a copper tube drawing machine. The draw roll is a critical component in copper tube drawing operations, subjected to severe abrasive wear from the continuous contact with copper tubes. The authors developed a surfacing process using flux-cored wire PK-YD212 to deposit a wear-resistant layer with single-pass hardness exceeding HRC 50, achieving low dilution and a narrow fusion zone without preheating.

Core Technical Content

The draw roll in a copper tube drawing machine operates under extreme conditions: high contact pressure, continuous sliding contact with copper tubes, and significant heat generation from friction. These conditions demand a surfacing layer that combines high hardness for wear resistance with adequate toughness to resist spalling and cracking under cyclic loading.

Surfacing Process Parameters

Process Analysis and Metallurgical Considerations

The selection of FCAW for this application is well-justified from a metallurgical perspective. Flux-cored arc welding offers several advantages for surfacing applications:

1. High deposition rate — The flux core provides additional alloy addition and improves wetting, allowing faster surfacing build-up compared to solid wire processes.
2. Low dilution — The flux slag formed during FCAW provides a protective layer that reduces the interaction between the molten pool and the base metal, resulting in lower dilution.
3. Good crack resistance — The flux core acts as a deoxidizer and sulfur/phosphorus scavenger, reducing the susceptibility of the surfacing layer to cracking.
4. Single-pass hardness >HRC 50 — This level of hardness is sufficient for wear resistance in copper tube drawing applications while maintaining adequate toughness to prevent spalling.

Heat-Affected Zone Considerations

The fact that the process does not require preheating is significant. In surfacing applications, preheating is typically employed to reduce the cooling rate of the heat-affected zone (HAZ) and minimize the risk of cracking. The ability to eliminate preheating suggests that:

• The base material of the draw roll has low carbon equivalent (CE), reducing its susceptibility to HAZ cracking.
• The FCAW process provides sufficient heat input to maintain adequate cooling rates without external preheating.
• The narrow fusion zone minimizes the thermal disturbance to the base material.

However, this does not mean that HAZ concerns can be entirely dismissed. Even with low dilution and narrow fusion zones, repeated surfacing passes can create a cumulative thermal effect that may lead to grain coarsening and reduced toughness in the HAZ. Engineers should monitor the HAZ microstructure through metallographic examination, particularly after multi-pass surfacing builds.

Engineering Practice Integration

The application of FCAW surfacing to large draw rolls presents unique practical challenges:

• Roll geometry — Large diameter rolls require specialized equipment for uniform surfacing coverage, including rotary fixtures and programmable wire feeders.
• Multi-pass build-up — Achieving the required surfacing layer thickness typically requires multiple passes, each of which must be carefully controlled to maintain consistent hardness and avoid defects.
• Residual stress management — The thermal cycling from multi-pass surfacing can introduce significant residual stresses, which may lead to distortion or cracking during subsequent machining or in service.
• Post-weld machining — The surfacing layer must be machined to precise dimensional tolerances, which requires adequate overbuild allowance and careful control of the surfacing layer's machinability.

Defect Analysis and Countermeasures

Key Questions and Reflections

The paper does not extensively discuss the long-term wear performance of the PK-YD212 surfacing layer in actual copper tube drawing service. While the initial hardness of HRC 50 is adequate, the actual wear life depends on a complex interplay of factors including tribological conditions, contact pressure, sliding speed, and the presence of lubricants or contaminants. A comprehensive tribological evaluation would be essential for optimizing the surfacing layer composition for this specific application.

Another important consideration is the effect of the surfacing layer on the draw roll's dimensional stability during service. Thermal expansion mismatch between the surfacing layer and the base material can lead to delamination or spalling under thermal cycling. The FCAW process, with its relatively high heat input, may exacerbate this issue compared to low-dilution processes such as HVOF or cold spray.

Study Insights and Implications

This paper demonstrates the practical application of FCAW technology for heavy-duty surfacing in industrial equipment. The key insight is that the selection of surfacing process must be matched to the specific service conditions — in this case, the combination of abrasive wear, moderate impact loading, and thermal cycling in copper tube drawing operations. The use of PK-YD212 flux-cored wire represents a cost-effective solution that balances hardness, toughness, and weldability. For engineers working on similar surfacing applications, the paper provides a valuable reference for process development and consumable selection.