CLADDING TECHNOLOGY SHANXI CO., LTDOverlay Welding Repair Technology and Performance Research on 45 Steel
Literature Overview
This study focuses on the overlay welding repair of 45 steel (a medium-carbon steel equivalent to AISI 1045) components, investigating the process parameters, microstructural characteristics, and mechanical performance of the overlay layer. 45 steel is one of the most widely used structural steels in Chinese manufacturing, employed in shafts, gears, bolts, and mechanical components. When these components suffer from surface wear, corrosion, or dimensional loss, overlay welding provides an economical and effective repair solution.
Core Technical Points
The research systematically examines the overlay welding repair of 45 steel using various welding processes and filler materials:
- Welding processes evaluated: Submerged arc welding (SAW), shielded metal arc welding (SMAW), and gas metal arc welding (GMAW) are compared for their suitability in repairing 45 steel components.
- Filler material selection: Multiple filler materials are tested, including high-carbon steel wires, medium alloy steel wires, and specialized repair electrodes designed for medium-carbon steels.
- Microstructural analysis: The overlay layer and the dilution zone at the interface between the overlay and base metal are examined for grain structure, phase composition, and hardness distribution.
Typical Overlay Welding Parameters for 45 Steel Repair
| Parameter | SAW | GMAW | SMAW |
|---|---|---|---|
| Current (A) | 300–500 | 150–250 | 100–180 |
| Voltage (V) | 30–38 | 22–30 | 20–28 |
| Travel speed (mm/min) | 150–300 | 100–200 | 50–150 |
| Heat input (kJ/mm) | 1.0–2.5 | 0.5–1.5 | 0.3–1.0 |
| Interpass temp (°C) | <200 | <200 | <150 |
| Preheat temp (°C) | 150–250 | 100–200 | 100–200 |
Process Analysis and Engineering Implications
The primary challenge in overlay welding repair of 45 steel is controlling the carbon content and hardness in the dilution zone. Due to the relatively high carbon content of 45 steel (0.42–0.50% C), the HAZ is susceptible to hardening and cracking during welding. Preheating to 150–250 °C and controlling the heat input are essential to prevent cold cracking in the HAZ.
The study reveals that the dilution rate between the overlay layer and base metal significantly affects the mechanical properties of the repaired zone. For SAW, the dilution rate is typically 30–50%, while for GMAW it is lower at 15–30%. Higher dilution results in a harder but more brittle dilution zone, which may be prone to cracking under service loading. The optimal approach involves using multiple thin layers with controlled dilution to build up the required thickness while maintaining acceptable mechanical properties at the interface.
Post-weld stress relief treatment at 550–650 °C for 1–2 hours per 25 mm of thickness is recommended to reduce residual stresses and improve the toughness of the repair zone. The hardness profile across the overlay typically shows a gradient from the base metal (180–220 HB) through the dilution zone (250–350 HB) to the overlay surface (300–400 HB), depending on the filler material used.
Key Questions and Reflections
A practical concern raised by this study is the long-term reliability of overlay-welded repairs on 45 steel components subjected to dynamic loading. The overlay layer, while providing dimensional restoration, introduces a zone of metallurgical discontinuity that can act as a stress concentration point. For components such as shafts and gears that experience cyclic bending or torsional loads, the fatigue life of the repaired zone may be significantly lower than the original material.
Additionally, the study highlights the importance of matching the thermal expansion coefficient of the overlay layer with the base metal. If a dissimilar material is used for the overlay, thermal cycling during service can lead to delamination or cracking at the interface. For 45 steel repair, using a filler material with similar thermal expansion characteristics is strongly recommended.
Study Insights and Implications
This research provides a comprehensive framework for the overlay welding repair of 45 steel components, covering process selection, parameter optimization, and performance verification. The key insight is that successful repair requires not only achieving the required dimensional tolerance but also ensuring metallurgical compatibility and mechanical integrity of the entire repair zone. Engineers should adopt a systematic approach that includes pre-weld preparation, in-process monitoring, and post-weld inspection and testing to guarantee the long-term reliability of overlay-welded repairs. The study also emphasizes that for critical components subjected to high cyclic loads, overlay welding repair should be considered as a temporary measure, with component replacement planned within a defined service interval.