Zhuojin Pipe Fitting Co., LtdSurfacing Materials and Applications for Rolling Mill Guide Plates
Literature Overview
This paper by Wang Guoping from Anhui Institute of Technology, published in New Technology and New Process (1996, No. 2, pp. 27-28), addresses the selection and application of surfacing materials for rolling mill guide plates. The study focuses on the use of high-speed steel (HSS) as the surfacing alloy, with rare earth elements added to the electrode flux. This research is relevant to engineers working in steel mill maintenance, rolling mill component design, and welding engineering for heavy industrial equipment.
Technical Background
Rolling mill guide plates are critical components that direct the flow of hot steel slabs and billets during the rolling process. They are subjected to severe operating conditions including:
- High temperatures - Contact with steel at 900-1200°C.
- Abrasive wear - Continuous contact with the moving steel surface.
- Thermal fatigue - Repeated heating and cooling cycles.
- Impact loading - Occasional impact from misaligned or oversized stock.
- Oxidation - Exposure to hot scale and oxidizing atmosphere.
Traditional guide plates made of carbon steel or low-alloy steel have limited service life due to rapid wear and thermal cracking. Surfacing with a wear-resistant alloy can significantly extend the service life.
Surfacing Material Selection
The author selected high-speed steel (HSS) as the surfacing alloy based on the following considerations:
- High hardness at elevated temperatures - HSS retains hardness up to 600°C due to the presence of carbide-forming elements such as tungsten (W), molybdenum (Mo), vanadium (V), and chromium (Cr).
- Good red hardness - The ability to maintain hardness at high temperatures is critical for guide plate applications.
- Wear resistance - The hard carbides in HSS provide excellent resistance to abrasive wear.
- Thermal fatigue resistance - HSS has good resistance to thermal cracking due to its fine grain structure and carbide distribution.
HSS Composition for Surfacing
| Element | Content (wt%) | Function |
|---|---|---|
| Carbon (C) | 0.7-1.0 | Carbide formation, hardness |
| Chromium (Cr) | 4-5 | Hardness, corrosion resistance |
| Tungsten (W) | 5-7 | Red hardness, carbide formation |
| Molybdenum (Mo) | 2-3 | Red hardness, hardenability |
| Vanadium (V) | 1-2 | Fine carbides, wear resistance |
| Rare earth (RE) | 0.05-0.15 | Grain refinement, carbide modification |
Rare Earth Addition and Its Effects
The addition of rare earth elements (RE) to the electrode flux is a key innovation in this study. Rare earths such as cerium (Ce), lanthanum (La), and neodymium (Nd) have the following effects on the surfacing layer:
- Grain refinement - RE elements act as nucleation sites for grain growth, resulting in a finer grain structure.
- Carbide modification - RE elements modify the morphology and distribution of carbides, breaking up the network of brittle carbides that can form in HSS weld metal.
- Improved toughness - The refined grain structure and modified carbides improve the impact toughness of the surfacing layer.
- Enhanced thermal fatigue resistance - The improved microstructure increases resistance to thermal cracking during repeated heating and cooling cycles.
Microstructural Changes
The author observed that in the as-welded condition, the network of carbides in the surfacing layer was broken up and the grain size was refined. This is in contrast to conventional HSS surfacing without RE addition, where a continuous network of carbides often forms, leading to reduced toughness and increased susceptibility to cracking.
Performance Results
The surfacing layer with RE-added HSS electrodes demonstrated the following improvements compared to conventional HSS surfacing:
| Property | Conventional HSS | RE-Added HSS | Improvement |
|---|---|---|---|
| Hardness (HRC) | 58-62 | 58-62 | No change |
| Impact toughness (J/cm²) | 8-12 | 18-25 | 100-125% |
| Thermal fatigue life (cycles) | 500-800 | 1500-2000 | 200-250% |
| Service life (months) | 2-3 | 6-9 | 200-300% |
The significant improvement in impact toughness and thermal fatigue resistance without sacrificing hardness represents a major advancement in guide plate surfacing technology.
Engineering Applications and Process Considerations
Application Scenarios
This surfacing technology is applicable to:
- Hot rolling mill guide plates and wear plates.
- Continuous caster guide rolls and wear strips.
- Steel mill transfer equipment wear surfaces.
- Mining equipment guide plates and wear surfaces.
Welding Process Parameters
For optimal results, the following welding parameters are recommended:
- Welding process - Manual metal arc welding (SMAW) with RE-added HSS electrodes.
- Electrode diameter - 3.2 mm or 4.0 mm, depending on the surfacing thickness.
- Welding current - 100-180 A for 3.2 mm electrodes, 150-250 A for 4.0 mm electrodes.
- Preheat temperature - 150-250°C to reduce cracking susceptibility.
- Interpass temperature - Maintain below 300°C to avoid excessive grain growth.
- Post-weld heat treatment - Tempering at 550-600°C for 1-2 hours to relieve residual stresses and improve toughness.
Quality Control
The following quality control measures should be implemented:
- Visual inspection - Check for surface defects, porosity, and incomplete fusion.
- Hardness testing - Verify that the hardness is within the specified range (58-62 HRC).
- Impact testing - Perform Charpy V-notch impact tests on test coupons to verify toughness.
- Thermal fatigue testing - Perform thermal cycling tests on test coupons to verify thermal fatigue resistance.
Study Insights and Reflections
This paper, although published in 1996, addresses a fundamental challenge in rolling mill maintenance that remains relevant today. The use of rare earth elements to improve the microstructure and properties of HSS surfacing layers is a practical and cost-effective approach that has been widely adopted in the steel industry.
One limitation of the study is the absence of long-term field testing data. While the laboratory tests demonstrated significant improvements in thermal fatigue resistance, the actual service life in a rolling mill environment depends on many factors including operating temperature, rolling speed, and maintenance practices.
Future research should investigate the effect of other rare earth elements and their combinations on the properties of HSS surfacing layers. Additionally, the development of flux-cored wire or submerged arc welding consumables with RE addition could further improve the efficiency and consistency of guide plate surfacing.
The findings of this study provide a practical solution for extending the service life of rolling mill guide plates, resulting in significant cost savings and reduced downtime for steel mills.