CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of SUS301L Stainless Steel CO2 Laser-MIG Composite Welding Joints
Literature Overview
This study, published in the journal Chinese Journal of Lasers in 2014 by Chen Yang, Wu Shikai, and Xiao Rongshi from the Beijing University of Technology, investigates the microstructural evolution and mechanical properties of SUS301L austenitic stainless steel welded joints produced by CO2 laser-MIG composite welding. The research was supported by the National Natural Science Foundation of China (Grant No. 51275013) and the National Science and Technology Major Project (2013ZX04001-131), indicating its significance in advancing high-efficiency welding technologies for austenitic stainless steels.
Core Technical Content
SUS301L is a low-carbon austenitic stainless steel with a nominal composition of approximately 18% Cr, 8% Ni, and a carbon content limited to 0.03% maximum. This material is widely used in applications requiring good formability and resistance to sensitization during welding. The composite welding process combines the deep penetration capability of CO2 laser welding with the high deposition rate of MIG (GMAW) welding, achieving a synergistic effect where the laser keyhole acts as a guide for the MIG arc, enhancing both penetration and deposition efficiency.
The study examines the microstructure across the weld zone, including the fusion zone, heat-affected zone (HAZ), and base metal. Key observations include:
- The fusion zone exhibits a columnar dendritic structure with possible equiaxed grain formation near the centerline due to the high thermal cycling from the composite process.
- The HAZ shows a gradient of microstructural features, transitioning from fully austenitic to partially transformed regions depending on peak temperature.
- Mechanical properties including tensile strength, hardness distribution, and impact toughness are evaluated across the weld cross-section.
Typical Process Parameters
| Parameter | Range |
|---|---|
| Laser power (CO2) | 2.0 - 4.0 kW |
| MIG wire diameter | 1.0 - 1.2 mm |
| MIG current | 150 - 250 A |
| MIG voltage | 22 - 30 V |
| Travel speed | 0.5 - 1.5 m/min |
| Shielding gas (MIG) | CO2 or Ar + CO2 mix |
| Laser-arc spacing | 1 - 5 mm |
Engineering Practice Integration
From the perspective of cladding and bimetal product manufacturing, this research has direct relevance to the fabrication of stainless steel clad plates and pressure vessels. The SUS301L steel is often used as a cladding layer or as a structural material in environments where cold work hardening is beneficial. The composite welding process offers several advantages for cladding applications:
- Higher deposition rate compared to laser welding alone, making it suitable for thick cladding layers.
- Better dilution control when the laser-arc spacing is optimized, which is critical for maintaining the corrosion resistance of the overlay layer.
- Reduced residual stress compared to conventional arc welding due to the rapid heating and cooling cycle of the laser component.
However, engineers must be aware of potential issues such as hot cracking susceptibility in the austenitic weld metal, particularly when the carbon equivalent is elevated due to dilution from the base metal. The low carbon content of 301L (0.03% max) provides some resistance to sensitization, but proper heat input control remains essential.
Key Reflections and Insights
The fundamental insight from this work is that the synergy between laser and arc in composite welding is not merely additive but rather creates a fundamentally different thermal field and fluid flow pattern within the weld pool. The laser-generated keyhole provides a stable gas flow that enhances the MIG arc stability and promotes a more uniform heat distribution. This has implications for the solidification mode and grain structure, which directly influence the mechanical and corrosion properties of the weld.
For pressure vessel fabrication, the ability to produce high-quality welds in austenitic stainless steels with controlled dilution is paramount. The composite welding approach offers a pathway to achieve both the required penetration depth and the metallurgical quality necessary for compliance with standards such as ASME VIII Div.1 and GB/T 150.
This research contributes meaningfully to the understanding of composite welding metallurgy and provides a solid foundation for process development in industrial applications involving austenitic stainless steels.