CLADDING TECHNOLOGY SHANXI CO., LTDOverlay Repair of Construction Machinery Parts Practical Case Study
Literature Overview
This study note focuses on practical overlay welding repair cases of construction machinery components, drawing from field experience in equipment maintenance and surface hardening applications. Construction machinery such as excavators, bulldozers, loaders, and cranes operate under severe wear, impact, and corrosion conditions. Their critical components — including bucket teeth, blade edges, boom pins, hydraulic cylinder rods, and slewing ring bearings — are subject to accelerated degradation. Overlay welding repair offers an economical and efficient alternative to full component replacement, particularly when the base material retains sufficient structural integrity.
Core Technical Content
The literature presents several representative repair scenarios commonly encountered in construction equipment maintenance. The following table summarizes typical repair applications, selected filler materials, and process parameters.
| Component | Failure Mode | Recommended Filler | Process | Typical Hardness |
|---|---|---|---|---|
| Bucket teeth | Abrasive wear | Stellite 6 / D2737 | SAW / GTAW | 40–45 HRC |
| Blade edges | Galling wear | High-carbon steel D2736 | SAW | 45–50 HRC |
| Hydraulic rods | Corrosion + fretting | 308L / 316L | GTAW | 20–25 HRC |
| Boom pins | Fatigue + wear | D2737 | SAW multi-pass | 40–44 HRC |
| Slewing ring race | Rolling contact fatigue | Inconel 625 | PTA / GTAW | 28–32 HRC |
The repair workflow generally follows a structured approach: inspection and assessment, surface preparation, preheating, multi-pass overlay welding, post-weld heat treatment, and final dimensional verification. Surface preparation is critical — the worn surface must be machined to remove all affected material, with a minimum undercut of 1–2 mm to ensure sound metallurgical bonding. Oxide scale, rust, and contaminants must be completely removed through grinding or shot blasting to a minimum Sa 2.5 cleanliness level.
Process Analysis and Key Parameters
Preheating temperature is one of the most critical parameters in overlay repair of construction machinery parts. For low-alloy steel components such as those used in boom and arm structures (typically Q345B or 16Mn), preheating to 150–250°C is recommended to reduce residual stresses and minimize the risk of cold cracking. For high-alloy overlay deposits, interpass temperature control between 150–250°C ensures proper dilution management and avoids excessive grain coarsening.
Multi-pass welding strategies are essential for achieving the required overlay thickness. A typical approach for bucket tooth repair involves a transition pass using a low-hydrogen electrode (e.g., E7018) to ensure compatibility between the carbon steel base and the high-alloy overlay material, followed by 2–4 overlay passes with the selected hardfacing electrode. The transition pass should have a bead width of 10–15 mm with a penetration ratio of approximately 0.5–0.7 to ensure adequate bonding without excessive dilution of the overlay composition.
Post-weld heat treatment is often required for components subject to high residual stresses. Stress relief at 550–620°C for 2 hours per 25 mm of thickness (with furnace cooling) reduces residual stresses to below 50 MPa. However, for components requiring high hardness in the overlay, post-weld heat treatment must be carefully evaluated as it may soften the overlay deposit.
Common Defects and Countermeasures
The following table lists frequently encountered defects in overlay repair of construction machinery parts and their corresponding countermeasures.
| Defect | Root Cause | Countermeasure |
|---|---|---|
| Cracking in overlay | Excessive carbon content, high cooling rate | Preheat to 200–250°C, use low-carbon transition layer |
| Poor bonding | Inadequate surface preparation | Machine to bare metal, clean to Sa 2.5 |
| Excessive dilution | First pass too wide or too fast | Use narrow bead, reduce travel speed on first pass |
| Hardness below specification | Excessive dilution from base metal | Increase number of passes, use proper transition layer |
| Porosity | Contaminated surface or shielding gas | Improve surface cleanliness, check gas flow rate |
A particularly important insight from this literature is the concept of "repair zone assessment" — before any welding operation begins, the extent of material degradation must be accurately determined through ultrasonic testing (UT) or magnetic particle inspection (MT). If the damaged zone extends beyond 30% of the original component thickness, replacement rather than repair should be considered to avoid hidden structural failures.
Engineering Practice Integration
In actual field applications, the repair of construction machinery parts often occurs under challenging conditions — limited power supply, constrained workspace, and the need for rapid turnaround. Portable SAW equipment with flux-cored wire has proven particularly effective for on-site repairs of large components such as blade edges and bucket teeth. The flux provides self-shielding, eliminating the need for external shielding gas, and produces a wide, flat bead suitable for subsequent machining.
For hydraulic cylinder rods, GTAW overlay with ER308L or ER316L wire is preferred due to the precise bead control and low heat input. The overlay thickness is typically 1.0–2.0 mm, followed by precision grinding to restore the original diameter and surface finish (Ra ≤ 0.4 μm). Preheating to 100–150°C and using a back-gas shield (argon) on the root side prevents oxidation of the weld root.
Study Insights and Reflections
The practical value of this literature lies in its emphasis on the systematic approach to repair decision-making. Not every worn component should be repaired — a cost-benefit analysis considering repair cost, downtime, and residual service life must precede any repair operation. The concept of "repairability criteria" is crucial: components with fatigue cracks extending beyond the repair zone, components with more than 40% cross-sectional loss, or components with unknown material grade should generally be replaced rather than repaired.
From a metallurgical perspective, the transition layer strategy deserves particular attention. When overlaying high-alloy materials onto carbon steel, the dilution zone can develop martensitic structures prone to cracking. A two-layer transition system — first layer with a medium-alloy material (e.g., E8018), second layer with the high-alloy overlay — effectively manages the dilution gradient and prevents cracking. This approach has been validated through extensive field experience in mining and construction equipment repair.
The literature also highlights the importance of post-repair inspection. Visual inspection (VT) should be supplemented by magnetic particle inspection (MT) for ferromagnetic components and dye penetrant inspection (PT) for non-ferromagnetic overlays. Hardness testing at multiple locations across the overlay surface ensures uniformity, and dimensional verification confirms that the repaired geometry meets functional requirements. In my professional assessment, the integration of these systematic approaches with practical field experience represents the most reliable path to successful overlay repair of construction machinery components.