Zhuojin Pipe Fitting Co., LtdStrip Electrode Overlay Welding Repair of Continuous Casting Guide Rolls
Literature Overview
This paper by Zhang Xiangfu from Jinan Iron and Steel Group, published in Welding Technology (2007, Vol. 36, No. 2, pp. 71–72), documents the application of strip electrode overlay welding technology for the repair of continuous casting guide rolls. The study analyzes the working environment and failure mechanisms of guide rolls in continuous casting machines, then demonstrates that the combination of strip electrode longitudinal welding, edge overlap welding technique, carbon-nitrogen strengthening, and 0Cr13NiMoN overlay material yields high-quality overlay welds with satisfactory service performance. This case study is directly relevant to engineers involved in the maintenance and refurbishment of heavy industrial equipment.
Analysis of Guide Roll Working Conditions and Failure Mechanisms
Continuous casting guide rolls operate under extremely demanding conditions:
| Parameter | Typical Condition |
|---|---|
| Operating temperature | 500–1200°C (depending on steel grade) |
| Contact pressure | 5–15 MPa |
| Sliding speed | 0.5–2.0 m/min |
| Molten steel splashing | Intermittent, high thermal shock |
| Scale adhesion | Continuous, abrasive |
| Service life (before repair) | 500–3000 hours |
The primary failure mechanisms include:
- Thermal fatigue cracking: Repeated thermal cycling from molten steel contact and water cooling creates thermal stresses that exceed the fatigue limit of the roll surface.
- Abrasive wear: Solidified scale and oxide particles abrade the roll surface during sliding contact.
- Adhesive wear (galling): At high temperatures and pressures, material transfer occurs between the roll surface and the solidifying steel shell.
- Cavitation erosion: In the meniscus region, the interaction between molten steel and the roll surface causes localized material removal.
Technical Details of the Strip Electrode Overlay Process
The paper describes a sophisticated overlay welding approach that combines multiple techniques:
Process Parameters:
| Parameter | Value |
|---|---|
| Overlay material | 0Cr13NiMoN (high Cr stainless steel with Ni, Mo, N) |
| Welding method | Strip electrode submerged arc welding (SAW) |
| Strip electrode width | 25–35 mm |
| Current | 400–600 A |
| Voltage | 28–34 V |
| Travel speed | 150–300 mm/min |
| Flux | Low-hydrogen rutile type |
| Preheating | 200–300°C |
| Interpass temperature | ≤350°C |
| Overlay thickness | 6–12 mm |
Key Process Innovations:
- Longitudinal strip welding: The strip electrode is deposited in longitudinal passes along the roll axis, ensuring uniform heat input and consistent microstructure across the overlay width.
- Edge overlap welding technique: Adjacent passes are overlapped by 30–50% of the strip width, ensuring complete fusion and eliminating potential interpass defects. This technique also provides a self-peening effect that introduces compressive residual stresses at the surface.
- Carbon-nitrogen strengthening: The addition of nitrogen to the 0Cr13NiMoN composition enhances solid solution strengthening and promotes the formation of fine nitride precipitates. Nitrogen also improves high-temperature strength and thermal stability of the austenitic structure.
- Multi-pass build-up: The overlay is deposited in 3–5 passes, with each pass providing progressive strengthening through thermal cycling and solidification refinement.
Quality Control and Acceptance Criteria
The paper implicitly addresses quality control through the emphasis on "high-quality welds." For engineers implementing this technology, the following quality criteria should be established:
| QC Parameter | Acceptance Criteria |
|---|---|
| Surface hardness | ≥45 HRC (after aging) |
| Dilution rate | ≤10% (measured by XRF) |
| Surface roughness | Ra ≤ 6.3 μm |
| Penetrant testing | No linear indications > 1 mm |
| UT inspection | No lack of fusion, porosity > 2 mm |
| Macrostructure | No segregation, uniform microstructure |
| Residual stress | Compressive (preferred) or <150 MPa tensile |
Engineering Practice Integration
This case study demonstrates the practical application of overlay welding technology for the economic refurbishment of expensive rotating components. The key engineering lessons include:
- Economic justification: Repair by overlay welding typically costs 30–50% of new component replacement, with equivalent or superior performance when properly executed.
- Process design: The combination of longitudinal welding with edge overlap is superior to circumferential welding for cylindrical components, as it minimizes circumferential shrinkage stresses and reduces the risk of circumferential cracking.
- Material selection: The 0Cr13NiMoN composition provides an excellent balance of high-temperature strength, oxidation resistance, and thermal fatigue resistance, making it suitable for guide roll applications where temperatures exceed 800°C.
- Post-weld treatment: While not explicitly detailed in the paper, aging treatment (600–700°C for 2–4 hours) is typically required to stabilize the microstructure, relieve residual stresses, and optimize hardness.
Study Insights and Implications
This paper represents a practical bridge between overlay welding research and industrial application. The systematic approach to process development — analyzing failure mechanisms, selecting appropriate materials, optimizing process parameters, and validating through service performance — provides a model for overlay welding engineering in other applications. For engineers working on pipe fitting repair and equipment refurbishment, the key takeaway is that overlay welding technology, when properly designed and executed, can restore or enhance the service life of worn components at a fraction of replacement cost. The carbon-nitrogen strengthening approach, in particular, offers a novel material design strategy that extends the capabilities of conventional overlay compositions.