Bimetallic Runner Upper Crown Manufactured by Stainless Steel Strip Electrode Surfacing Technology

Technical Background and Application Context

The research by Du Bing, Li Yan, Xia Weimin from the Harbin Welding Research Institute, in collaboration with Wang Aimin and Li Lin from Harbin Electric Machinery Factory, presents a successful application of stainless steel strip electrode surfacing technology for manufacturing the upper crown of a bimetallic mixed-flow runner. The runner is a critical component in hydroelectric generators, where it must withstand the combined effects of water flow erosion, cavitation, and mechanical loading. The bimetallic design, with a stainless steel overlay on a carbon steel base, addresses the need for corrosion and cavitation resistance while maintaining the structural strength and economic feasibility of the carbon steel substrate.

Strip Electrode Surfacing Technology

The strip electrode surfacing process uses a continuous strip of stainless steel as the filler metal, which is fed into the arc along with a consumable electrode. This process offers several advantages over conventional wire-fed surfacing methods, including higher deposition rates, better control of overlay thickness, and the ability to produce uniform, continuous layers on large curved surfaces. The Harbin Welding Research Institute developed proprietary stainless steel strip electrode materials specifically for this application, optimizing the chemical composition and mechanical properties for the runner service environment.

The development of the strip electrode material involved careful consideration of the alloy composition to ensure adequate hardness, toughness, and corrosion resistance. The strip must also exhibit good weldability and resistance to cracking during the surfacing process. The proprietary materials developed by the institute likely incorporated specific alloying additions to enhance cavitation resistance, such as molybdenum and nitrogen, while maintaining the austenitic structure necessary for corrosion resistance.

Process Development and Performance Validation

The research methodology followed a systematic approach, beginning with process trials and mechanical property testing on simulation specimens before proceeding to the manufacture of the actual runner upper crown. This staged approach is essential in nuclear and hydroelectric component manufacturing, where the cost of failure is extremely high and the consequences of defects can be catastrophic.

The mechanical property testing of the surfacing metal included hardness, tensile strength, impact toughness, and corrosion resistance evaluations. The results demonstrated that the strip electrode surfacing process could produce overlay layers with properties meeting the design requirements for the runner application. The successful manufacture of the bimetallic runner upper crown validated the process and demonstrated the feasibility of strip electrode surfacing for large, complex components.

Engineering Significance and Practical Considerations

The successful application of strip electrode surfacing to runner manufacturing represents a significant advancement in hydroelectric component technology. The process offers economic advantages over solid stainless steel runners by allowing the use of a less expensive carbon steel base material while achieving the required surface properties through overlay. This approach is particularly valuable for large runners where the volume of stainless steel required for a solid construction would be prohibitively expensive.

The work also demonstrates the importance of specialized welding consumable development for critical applications. The proprietary strip electrode materials developed by the Harbin Welding Research Institute represent a significant technical achievement, combining metallurgical expertise with practical manufacturing knowledge. For engineers involved in similar bimetallic component manufacturing, this paper highlights the value of investing in consumable development and process optimization as a means of achieving performance targets that cannot be met with standard welding materials.

The integration of research and manufacturing capabilities, as demonstrated by the collaboration between the Harbin Welding Research Institute and Harbin Electric Machinery Factory, is a model for successful technology transfer in heavy industry. The close partnership between the research organization and the manufacturing facility ensured that the process development was guided by practical requirements and that the final process was robust enough for production use.