Multi-pass Laser Welding of 50 mm-thick Steel Plates Using Cut Wire Particles

01 Introduction
In the development of laser welding technology, achieving high-quality connections in thick steel plates has always been a technical challenge. While traditional filler-wire methods can improve gap adaptability and weld chemistry, their application is limited by complex edge preparation, wire-feed control, and high cost. To address these issues, this study proposes an innovative method: using cut steel-wire particles as filler material to simplify multi-pass laser welding and simultaneously enhance weld quality. The research focuses on 50 mm-thick SM490A steel plates, optimizing process parameters for the root pass, fill passes, and final pass. Comprehensive testing and analysis of mechanical properties and microstructure aim to provide new strategies and practical guidance for thick-plate laser welding.

02 Laser Wavelength
The paper investigates a multi-pass laser welding process using cut steel-wire particles as filler material. For 50 mm-thick SM490A plates, process parameters (laser power, welding speed, particle fill height) were optimized to achieve full penetration. Results show that:

• The root pass produced uniform, defect-free welds.

• The fill passes effectively filled side grooves and reduced hot cracking.

• The final pass, using laser–arc hybrid welding, significantly improved surface quality.
  Mechanical testing revealed that the weld’s tensile strength exceeded that of the base metal, and its impact toughness met standards. Microstructural analysis indicated the formation of multiphase structures—ferrite, bainite, and martensite—with hardness increasing with depth. Overall performance was excellent. This study offers an efficient and feasible technical route for thick-plate laser welding.

03 Figures & Analysis

• Figure 1: Schematic of the multi-pass laser welding setup, showing filler-particle placement, laser-head angle, and welding-parameter configuration.

  

  
  

• Figure 2: Effect of fill heights (20 mm, 22 mm, 25 mm) on root-pass pool shape and weld quality; 22 mm was optimal.

  

• Figure 3: Macrostructure of the fusion zone after eight passes on a 50 mm plate; welds are uniform and defect-free.

  

• Figure 4: Microhardness distribution; root-pass exhibits highest hardness (310 HV), followed by fill (247 HV) and final (220 HV), showing increasing hardness with depth.

  

• Figure 5: Charpy impact results; final and fill passes show 100 J toughness, while the root pass is 45 J (bainite/martensite), above the minimum 27 J.

  

• Figure 6: Microstructures: (b) final pass—acicular and boundary ferrite; (c) fill—refined acicular ferrite; (d) root—bainite and martensite, fastest cooling rate.

  

04 Conclusion

1. Eight passes are sufficient to complete full-penetration butt joints in 50 mm SM490A plates; joint strength surpasses base metal strength.

2. Eliminating solid wire feed reduces process complexity, though final pass requires additional filler to fill particle gaps and ensure adequate reinforcement.

3. A heat-affected zone hardness of over 350 HV was recorded. All fusion zones exceeded the minimum Charpy toughness of 27 J at –20 °C, with the root area at a minimum of 45 J.

4. Microstructure in fill and final passes consists of acicular and boundary ferrite, while the root pass shows bainite/martensite.

5. Further study is needed to ensure elimination of welding defects, particularly addressing incomplete fusion between root and fill passes.

**--Cite the article published by 高能束加工技术 on December 30, 2024, in the WeChat public account "High-Energy Beam Processing Technology and Applications."