Zhuojin Pipe Fitting Co., LtdSurfacing Materials and Applications for Rolling Mill Guide Plates
Literature Overview
The paper by Wang Guoping from Anhui Institute of Technology, published in New Technology and New Process in 1996 (Issue 2, pp. 27-28), addresses a practical and economically significant problem in rolling mill operations: the selection and optimization of surfacing materials for guide plates. Guide plates in rolling mills are subjected to severe conditions including high temperatures, mechanical impact, and thermal cycling, leading to rapid wear and frequent replacement. The author selected high-speed steel as the surfacing alloy composition and introduced composite rare earth elements into the electrode coating, achieving significant improvements in impact toughness, crack resistance, and thermal fatigue resistance of the surfacing deposit.
Technical Approach and Innovation
The core innovation of this work lies in the combination of high-speed steel chemistry with rare earth modification in the electrode flux. High-speed steels are renowned for their excellent red hardness, wear resistance, and toughness, making them ideal candidates for guide plate surfacing. However, conventional high-speed steel surfacing deposits often suffer from coarse network carbides that degrade toughness and promote cracking. The introduction of composite rare earth elements into the electrode coating addresses this limitation through two primary mechanisms: carbide modification and grain refinement.
Carbide Modification Mechanism
Rare earth elements, particularly cerium and lanthanum, have a strong affinity for sulfur and oxygen impurities in the molten weld metal. By scavenging these impurities, rare earths reduce the formation of brittle intergranular phases and modify the morphology of carbides from continuous network structures to dispersed particles. The original continuous network carbides in the high-speed steel surfacing deposit are broken into fragmented particles, which dramatically improves the ductility and fracture toughness of the deposit.
| Property | Conventional High-Speed Steel Surfacing | Rare Earth Modified Surfacing | Improvement Factor |
|---|---|---|---|
| Carbide morphology | Continuous network | Fragmented/dispersed particles | Qualitative improvement |
| Grain size | Coarse | Refined | Significant refinement |
| Impact toughness | Low | Substantially improved | Major increase |
| Crack resistance | Poor | Significantly enhanced | Major improvement |
| Thermal fatigue resistance | Limited | Substantially improved | Major increase |
| Service life | Baseline | Greatly extended | Economic benefit |
Rare Earth Effects on Weld Metal
The rare earth elements added to the electrode coating exert several beneficial effects on the surfacing deposit:
- Grain refinement: Rare earths act as heterogeneous nucleation sites during solidification, promoting finer grain structures that improve both strength and toughness.
- Carbide shape modification: The interaction between rare earths and carbide-forming elements (W, Mo, V) alters the morphology and distribution of carbides, converting detrimental network structures into beneficial dispersed particles.
- Inclusion modification: Rare earths modify non-metallic inclusions, converting harmful stringer inclusions into compact, less detrimental shapes.
- Solidification improvement: The addition of rare earths improves the fluidity of the molten weld pool and reduces hot cracking susceptibility.
Application Context and Operating Conditions
Rolling mill guide plates operate under extreme conditions that demand carefully selected surfacing materials. The operating environment includes:
- Thermal cycling: Guide plates experience repeated heating from hot rolled slabs and cooling from ambient conditions, creating thermal fatigue stresses.
- Mechanical impact: Moving slabs strike the guide plates with significant force, requiring the surfacing to have adequate toughness to resist impact damage.
- Abrasive wear: Scale and oxide debris on the slab surface create abrasive wear conditions against the guide plate surface.
- Sliding friction: Continuous sliding contact between the slab and guide plate generates frictional wear.
The high-speed steel surfacing with rare earth modification addresses all these conditions simultaneously. The red hardness of high-speed steel maintains surface hardness at elevated temperatures, while the rare earth-modified microstructure provides the toughness necessary to withstand impact loading without cracking.
Process Implementation and Quality Control
The implementation of this surfacing technology requires attention to several process parameters and quality control measures:
| Process Parameter | Recommended Range | Purpose |
|---|---|---|
| Preheat temperature | 200-300°C | Reduce cracking risk |
| Interpass temperature | ≤300°C | Maintain microstructure quality |
| Welding current | Per electrode manufacturer | Ensure adequate penetration |
| Travel speed | Moderate to slow | Optimize dilution and cooling rate |
| Post-weld treatment | Stress relief at 600-650°C | Reduce residual stresses |
Quality control should include visual inspection for surface defects, hardness testing to verify the achieved hardness level, and metallographic examination of cross-sections to confirm the expected microstructure with dispersed carbides and refined grains. Non-destructive testing such as magnetic particle inspection should be performed to detect any surface cracks that might compromise the service life of the surfacing.
Economic Impact and Practical Significance
The economic benefits of this technology are substantial. By extending the service life of guide plates through effective surfacing, rolling mills can reduce the frequency of guide plate replacement, decrease downtime for maintenance, and lower overall production costs. The author specifically notes that the technology significantly reduces production costs while extending guide plate life, demonstrating clear cost-effectiveness.
For engineers managing rolling mill operations, this technology represents a practical solution to a recurring maintenance challenge. The key advantage is that it allows existing guide plate components to be refurbished through surfacing rather than requiring complete replacement, which is both economical and environmentally beneficial.
Study Insights and Implications
This relatively concise paper from 1996 addresses a highly practical industrial problem with an elegant solution. The use of rare earth modification in electrode coatings is a technique that has since been widely adopted in various welding applications, and this early application to rolling mill guide plate surfacing demonstrates its effectiveness in demanding industrial environments.
The study highlights an important principle in surfacing technology: microstructural control through flux modification can achieve performance improvements that are difficult to obtain through base metal selection alone. The rare earth elements act as microstructure modifiers without significantly altering the bulk composition, providing a cost-effective route to enhanced performance.
For contemporary engineers, this research serves as a reminder that sometimes the most impactful improvements come from subtle process modifications rather than wholesale changes to materials or processes. The combination of high-speed steel chemistry with rare earth flux modification remains a viable approach for guide plate refurbishment, and the fundamental principles described in this paper continue to inform modern surfacing technology development.