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1. Overview

The 12Cr rotor is widely used in ultra-supercritical steam turbine units both domestically and internationally due to its excellent toughness, high-temperature durability, and minimal creep deformation after long-term operation. However, the rotor body and bearing alloys exhibit poor wear resistance and a tendency for adhesion, which can lead to premature failure. As a result, applying a wear-resistant surfacing layer has become a critical task for turbine welding professionals. This paper discusses the current methods of surfacing the 12Cr rotor, based on the development status of domestic technologies.

2. Challenges in Rotor Surfacing

The ultra-supercritical 12Cr rotor is made from martensitic stainless steel forging, which has poor weldability and a high risk of cracking. The operating conditions of the rotor are complex, making the surfacing process particularly challenging. The main difficulties include:

(1) Surfacing Material Requirements: The material must withstand thermal stress during start-up and shutdown cycles, as well as centrifugal forces from high-speed rotation. Therefore, it needs to have high creep rupture strength at elevated temperatures and pressures.

(2) Multi-layer Multi-pass Welding: The surfacing process involves repeated thermal cycles, and improper temperature control or welding parameters can lead to uneven microstructure, coarse grains, and element segregation, resulting in low hardness and reduced performance.

(3) Fusion Zone Properties: Since the surfacing is a dissimilar metal weld, there is a fusion zone with different composition and structure compared to the heat-affected zone and base metal. This can create a brittle layer that may crack or delaminate under high-temperature conditions due to differences in thermal expansion coefficients.

3. Surfacing Methods

Currently, three main surfacing techniques are commonly used in China for 12Cr rotor wear layers:

(1) Submerged Arc Surfacing: This method offers stable weld quality, easy mechanization and automation, and high efficiency. It is ideal for rough surfacing. Preheating before welding is essential, and interlayer temperature must be strictly controlled to prevent low hardness. Post-weld dehydrogenation and heat treatment are also necessary. Careful slag removal and attention to pore formation are important. The first few layers should use smaller parameters to reduce dilution and ensure good fusion.

(2) TIG Welding: Tungsten Inert Gas (TIG) welding provides excellent visibility, stable arc, and minimal spatter, resulting in high-quality surfacing. It is often used for rework of defects such as undercut, incomplete fusion, and porosity from submerged arc welding. With optimized parameters, a high-quality, low-dilution surfacing layer can be achieved, though the process is slower. It is also suitable for localized repair in finished components.

(3) Micro-Arc Plasma Welding: This technique uses an ion arc as a high-temperature heat source and can employ powder or wire as filler material. It offers concentrated heat input, is easy to automate, and produces minimal distortion and low dilution. It is mainly used for rework on large-area surfacing during finishing. After welding, rotor deformation can be kept within 0.05mm. Preheating is not always required, but local post-weld heat treatment is needed. This method demands high precision in welding equipment.

4. Conclusion

With the continuous advancement of 12Cr rotor surfacing technology, many large domestic steam turbine manufacturers have gradually mastered these techniques and achieved successful operational results. However, as international thermal power units evolve toward higher parameters and larger capacities, steam temperature and pressure continue to rise, presenting new challenges for welding professionals. Only through continuous research, independent innovation, and in-depth study of welding mechanisms can we meet global standards and help domestic power equipment manufacturers reach world-class levels.

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