Abstract
Welds made by high power laser beam have deep and narrow geometry. Addition of filler wire by the arc source, forming the laser-arc hybrid welding (LAHW) process, is very important to obtain required mechanical properties. Distribution of molten wire throughout the entire weld depth is of concern since it tends to have low transportation ability to the root. Accurate identification of filler metal distribution is very challenging. Metal-cored wires can provide high density of non-metallic inclusions (NMIs) which are important for acicular ferrite nucleation. Accurate filler distribution can be recognized based on statistical characterization of NMIs in the weld. In the present study, it was found that the amount of filler metal decreased linearly towards the root. The filler metal tends to accumulate in the upper part of the weld and has a steep decrease at 45–55 % depth which also has wavy pattern based on longitudinal cuts. Substantial hardness variation in longitudinal direction was observed, where in the root values can reach > 300 HV. Excessive porosity was generated at 75 % depth due to unstable and turbulent melt flow based on morphology of prior austenite grains. The delicate balance of process parameters is important factor for both process stability and filler metal distribution.
Highlights
Welding is a very sophisticated manufacturing process where all four states of matter are involved with rapid spatial thermal gradients resulting in weld metal with several microstructural constituents having different mechanical properties [1]
One of the main reasons is that the filler wire/metal is used as additional material to fill large grooves. This is essential for thick sections joining and to influence the weld metal (WM) microstructure
The samples were etched with 2% Nital for 30 s to identify the various microstructure constituents and physical filler metal distribution along the weld centerline
Summary
Welding is a very sophisticated manufacturing process where all four states of matter are involved with rapid spatial thermal gradients resulting in weld metal with several microstructural constituents having different mechanical properties [1]. In the more advanced processes such as LAHW, there is high penetration depth with narrow geometry of welds. They can be termed as highdepth-to-width ratio welds. The filler wire from the arc source is delivered, or transported, to the weld pool and its distribution throughout the depth in narrow welds is of high concern. This commonly appears in welding of highly alloyed materials, e.g. stainless steel [3]. With application of automated optical microscope/SEM system and pattern recognition (based on algorithms for image analysis), the method can be extensively used in the future for the research and quality assessment in production of thick metallic sections
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