CLADDING TECHNOLOGY SHANXI CO., LTDResearch on Manufacturing Wind Turbine Blades Using Weld-Overlay Clad Steel Plates
Overview and Motivation
Wind turbine blades are increasingly being designed with metallic leading-edge and spar-cap components to resist erosion from sand, hail, and rain in harsh operating environments. Traditional approaches rely on polymer coatings or sacrificial leading-edge strips that require frequent replacement. The concept of using weld-overlay clad steel plates as structural blade components represents a paradigm shift, combining the structural integrity of steel with the surface durability of a hard-facing overlay layer. This literature review explores the feasibility, process parameters, and performance evaluation of such an approach.
Core Technical Approach
The study proposes manufacturing blade segments from base carbon steel plates with a hard-facing overlay applied on the leading-edge surface. The overlay is applied using submerged arc welding (SAW) or gas metal arc welding (GMAW) processes, depending on the geometry and thickness requirements. The base material is typically Q345R or equivalent low-carbon structural steel, while the overlay material is selected from martensitic or austenitic hard-facing alloys such as D2 tool steel equivalents or high-chromium cast iron compositions.
Key Process Parameters
| Parameter | Typical Range | Rationale |
|---|---|---|
| Base material | Q345R / Q420R | Structural strength and weldability |
| Overlay material | Martensitic / Austenitic hard-facing | Erosion resistance and hardness |
| Welding process | SAW or GMAW | Deposition rate and geometry control |
| Interpass temperature | 150–250 °C | Prevent cracking and control dilution |
| Overlay thickness | 3–8 mm | Balance between protection and weight |
| Number of passes | 2–4 | Achieve uniform composition and reduce dilution |
| Post-weld treatment | Stress relief at 550–600 °C | Reduce residual stresses |
Performance Evaluation and Defect Analysis
The critical challenge in this application is ensuring sufficient bond strength between the overlay and the base plate while maintaining the desired hardness profile. Dilution from the base metal is a primary concern; excessive dilution softens the overlay and reduces erosion resistance. Multi-pass welding with back-step technique is recommended to minimize dilution in the first pass.
Common defects identified include:
- Porosity caused by inadequate flux coverage or moisture contamination
- Cracking at the overlay-base interface due to high carbon content and rapid cooling
- Uneven overlay thickness leading to aerodynamic performance degradation
- Hardness variation across the overlay surface
Non-destructive testing protocols include magnetic particle testing (MT) for surface defects, ultrasonic testing (UT) for subsurface porosity and lack of fusion, and hardness profiling across the overlay cross-section.
Engineering Practice Integration
From a fabrication standpoint, the blade geometry introduces significant challenges. The curved surface of the blade spar-cap requires either pre-formed clad plates or post-forming of flat clad plates. Post-forming is more economical but introduces risk of overlay cracking during bending. A minimum bend radius of 3 times the total plate thickness is recommended, with pre-heating to 200 °C during forming operations.
The literature highlights that the overlay thickness must be optimized against blade weight constraints. For large-diameter blades (60–80 m), even a small increase in leading-edge mass affects fatigue life and thrust loading on the hub. A thickness of 3–5 mm is generally sufficient for erosion protection in moderate environments, while 6–8 mm may be warranted for desert or offshore locations.
Key Reflections and Study Insights
The most valuable insight from this study is the systematic approach to dilution control. By using a multi-pass strategy where the first pass is intentionally thin (1–2 mm) to establish a transition zone, and subsequent passes deposit the full overlay composition, the effective dilution in the final surface layer can be reduced below 15 percent. This is critical because hardness in martensitic overlays is highly sensitive to carbon content.
Another important observation is the correlation between residual stress and blade fatigue performance. The welding-induced residual stresses in the overlay layer, if not properly relieved, can act as stress concentrators at the overlay edge under cyclic aerodynamic loading. Stress relief annealing is therefore not merely a quality assurance step but a structural necessity.
This research provides a solid foundation for developing metallic blade components that combine structural efficiency with surface durability. The key to successful implementation lies in rigorous process qualification, thorough non-destructive inspection, and careful management of the dilution-hardness relationship throughout the fabrication sequence.