Kiumars Ahmadpoor - MSc student of material science and engineering (welding) University of Tehran, Iran
Seyed Ali Asghar Akbari Mousavi - Associated professor at department of Metallurgy and Materials Engineering, University of Tehran, Iran
Mehdi Alizadeh - MSc student of material science and engineering (welding) University of Tehran, Iran

Similar welding of SA508 Gr.4N low alloy steel by pulsed Nd:YAG laser beam welding equipment was investigated. This steel has special application in energy industries and gas turbine components. Due to high capacity of laser welding compare to traditional methods in reducing defects and problems related to the heat-affected zone, in this study the effect of laser welding parameters on weld pool size, microstructure and optimum joint parameters based on the importance and impact of heat input on depth and width and welding defects were investigated. The results of welding microstructure observed by optical and scanning electron microscopy. The optimum heat input is specified. According to the results of metallographic images fusion zone and heat affected zone microstructure is fine martensitic and results of hardness in weld width show increasing in hardness of this area. Also, the fine M23C6 carbides in the martensitic area of fusion zone was observed. Due to high thermal focus of laser welding method, narrow HAZ was observed and hardness in this zone is as hard as weld metal. however, due to thermal gradients in temperature decrease some microstructural orientation can be seen near fusion zone of weld metal.

Low alloy steel, Laser beam welding, Mechanical properties, Microstructure