Welding technology encompasses the methods and equipment used to join metals or thermoplastics through coalescence. This process typically involves melting the material to be joined, often with the addition of a filler material, to form a strong joint upon cooling. One interesting material is 316L stainless steel which is a low-carbon variant of 316 stainless steel. It’s known for its excellent corrosion resistance, particularly against chlorides and other industrial solvents. 316L is highly resistant to corrosion, making it ideal for marine environments and applications involving exposure to harsh chemicals. The ‘L’ in 316L stands for ‘low carbon’, which minimizes carbide precipitation during welding. This is important because carbide precipitation can lead to corrosion problems in some environments. Common methods for welding 316L include TIG, MIG, and stick welding. The choice depends on the specifics of the project, including thickness and location. The filler materials and electrodes must be compatible with 316L’s chemical composition to maintain corrosion resistance and mechanical properties. Overall, welding technology and the specifics of welding 316L stainless steel are critical in industries where strong, durable, and corrosion-resistant joints are essential.
In a new study published in the peer-reviewed Journal Optics and Laser Technology by Postgraduate student Zhenmu Xu, Associate Professor Jianfeng Wang, Cancan Yan, Jingxin Ren, Yuqi Zhou, Yue Li, and Professor Xiaohong Zhan from the Nanjing University of Aeronautics and Astronautics, the researchers focused on exploring the microstructural evolution in the interlayer regions of multi-layer welded joints using Narrow Gap Laser Wire Filling Welding (NGLWFW) on 316L stainless steel. They employed both experimental and computational techniques. They conducted temperature field simulation to model the thermal cycles during welding. Microstructural analysis involved examining the welded sections through advanced microscopy, revealing the granular details of the weld’s internal structure. Mechanical property evaluation, including tensile and hardness tests, provided insight into how these microstructural changes translate into real-world performance.
The authors uncovered significant inhomogeneities in the microstructure of welded joints, such as variations in grain size, orientation, and phase content. These inhomogeneities were attributed to differences in thermal cycles experienced by each weld layer.
The authors performed temperature field simulation and found that the peak temperature during the welding process increased from 1985 °C to 2183 °C with the addition of layers, affecting the molten pool’s size and shape. When they conducted microstructural analysis they observed the microstructure of the weld seam consisted mainly of γ-austenite phases and some δ-ferrite phases. The δ-ferrite content decreased with the addition of layers, and the average grain sizes varied across different layers. The growth directions of columnar grains also changed, showing an increase from the bottom layer to the upper layer. According to the authors, the hardness of the weld center showed a general downward trend from the bottom layer to the upper layer, with variability due to grain refining and thermal effects. The tensile strength and elongation rate of the welded joint were high, indicating good strength and plasticity at both room and high temperatures. These findings demonstrate the complex interplay of temperature, microstructure, and mechanical properties in welded joints, highlighting the importance of understanding these factors in welding processes. Moreover, the findings emphasized how the unique thermal history of each layer during the welding process influences the microstructure, impacting the mechanical strength and fatigue resistance of the weld. The authors provided crucial insights for industries where welding quality is critical, such as aerospace and nuclear sectors. The detailed understanding of microstructural variations aids in predicting welding quality and identifying potential weaknesses in welded structures.
The thermal cycles inherent in the welding process emerged as a crucial factor in microstructural evolution. Each layer of the weld experienced a unique thermal history, leading to layer-specific microstructural characteristics. In conclusion, the new study demonstrated successfully the microstructural inhomogeneity in 316L stainless steel welds using NGLWFW and provided the complex nature of welding processes.
Zhenmu Xu, Jianfeng Wang, Cancan Yan, Jingxin Ren, Yuqi Zhou, Yue Li, Xiaohong Zhan, Inhomogeneity of microstructure and mechanical properties in the interlayer regions for narrow gap laser wire filling welding of 316L stainless steel, Optics & Laser Technology, Volume 169, 2024, 110050,