Zhuojin Pipe Fitting Co., LtdMicrostructure and Properties of Wear-Resistant Electrode Overlay Layer for Water Gate Additive Repair
Literature Overview
Published in Materials in Mechanical Engineering (2025, Vol. 49, No. 11, pp. 106–112), this study addresses the challenge of underwater repair welding for hydraulic gate structures, a critical maintenance activity for hydropower infrastructure. The research was conducted by China Yangtze Power Co., Ltd. and the National Engineering Research Center for Efficient Utilization of Water Resources and Engineering Safety, with additional input from Hohai University. The work is particularly relevant to engineers responsible for the maintenance and rehabilitation of large-scale hydraulic structures.
Electrode Design and Welding Procedure
The study designed a specialized wear-resistant electrode with a carefully formulated flux composition. The electrode core is 0Cr13 stainless steel wire, while the flux coating comprises a complex mixture of ingredients designed to optimize both metallurgical quality and wear resistance.
| Component | Function |
|---|---|
| Reduced iron powder | Carbon source, dilution control |
| Sepiolite mineral | Stabilizer, slag former |
| Potassium feldspar | Flux, slag viscosity control |
| Water glass | Binder, gas shielding |
| Rutile | Slag stabilizer, arc stability |
| Fluorite | Deoxidizer, arc penetration |
| Manganese powder | Alloying, hardening |
| Cellulose | Gas shielding, arc stability |
| Al-Si alloy | Deoxidizer |
| Silicon iron alloy | Deoxidizer, alloying |
| Rare earth silicon iron | Refining, grain refinement |
The welding procedure involved SMAW (Shielded Metal Arc Welding) underwater multi-layer multi-pass overlay on Q235 steel substrate. The underwater welding environment introduces unique challenges including arc instability, hydrogen absorption, and difficulty in achieving proper slag-metal separation.
Microstructural Analysis
The overlay layer produced with the wear-resistant electrode exhibited a microstructure consisting primarily of lenticular martensite with a small volume fraction of δ-ferrite. The martensite grew along the temperature gradient direction, forming columnar crystals. No cracks or other welding defects were observed in the overlay layer, which is a significant achievement for underwater welding where hydrogen-induced cracking is a persistent concern.
| Microstructural Feature | Wear-Resistant Electrode | Conventional Electrode |
|---|---|---|
| Martensite grain size | Smaller | Larger |
| Martensite volume fraction | Higher | Lower |
| δ-ferrite content | Lower | Higher |
| Microhardness | Higher | Lower |
| Defect presence | No cracks | Not specified |
The smaller martensite grain size and higher martensite volume fraction in the wear-resistant electrode overlay are attributed to the synergistic effects of the flux composition. The rare earth silicon iron component likely promoted nucleation and grain refinement, while the balanced deoxidizer package ensured clean melt composition and reduced inclusion content.
Wear Performance Evaluation
The tribological testing demonstrated that the wear-resistant electrode overlay layer exhibited lower friction coefficient and lower wear rate compared to the conventional electrode overlay. The wear surface morphology analysis revealed shallow and uniformly distributed ploughing grooves, with localized minor spalling, debris, and microcracks. The primary wear mechanism was identified as mild abrasive wear.
This wear mechanism classification is important for practical applications. Abrasive wear dominance indicates that the overlay layer is performing as intended in the hydraulic gate environment, where solid particle impact and sliding contact are the primary damage modes. The absence of severe adhesive or oxidative wear mechanisms suggests adequate thermal stability and surface integrity under operating conditions.
Engineering Practice Integration
The application of this technology to hydraulic gate repair carries significant practical implications. Hydraulic gates in hydropower stations are subjected to continuous water flow, sediment abrasion, and cyclic loading. The ability to perform effective repair welding underwater, without requiring complete dewatering of the structure, represents a major operational advantage in terms of maintenance scheduling and cost reduction.
The use of 0Cr13 stainless steel as the electrode core provides inherent resistance to water-induced corrosion in the repair zone. The lenticular martensite microstructure offers a favorable combination of hardness and toughness, which is essential for withstanding the impact loading from sediment particles carried in the water flow.
From a quality assurance perspective, the absence of cracks in the underwater overlay weld is a critical finding. In the FMEA (Failure Mode and Effects Analysis) framework, cracking in underwater welds is a high-severity failure mode that can lead to rapid structural degradation. The electrode design and welding procedure demonstrated in this study effectively mitigate this risk.
Study Insights and Conclusions
This literature demonstrates that through careful electrode composition design, it is possible to achieve high-quality wear-resistant overlay welds even in the challenging underwater environment. The key technical insight is that the flux composition serves a dual purpose: providing arc stability and gas shielding in the submerged condition, while simultaneously controlling the metallurgical evolution of the weld metal to produce a fine martensitic microstructure with low δ-ferrite content. The wear performance results confirm that mild abrasive wear is the dominant mechanism, and the overlay layer effectively resists this damage mode. For engineers planning hydraulic structure maintenance programs, this technology offers a viable and cost-effective solution for extending the service life of hydraulic gates without requiring complete structural removal or dewatering.