Assessment of Pulsed Nd: YAG Laser Welding on Microstructural Evolution and Mechanical Performance of Ultra-high strength steels (UHSS)

AISI4340 high-strength alloys are heat-treatable, medium carbon and low alloy steels which has been used in number of high demanding applications, such as power transmission gears, shafts, aircraft landing gear and other structural parts. The current research study was undertaken to investigate the similar welding of AISI4340 steel by using Nd: YAG laser with moderate power of 90w. For this purpose the effects of laser welding variables on the geometry, and also solidification behavior of the weld samples were considered. Indeed, the microstructural evolution of fusion weld zone and heat affected zones (HAZs) were investigated. It was found that the sizes of the HAZs are dependent on the heat input. Tensile and hardness tests were performed for characterization of mechanical performance of Nd: YAG laser welds. The micro-hardness tests across the samples indicate that maximum hardness achieved from fusion zone of AISI4340 high-strength alloy steel and the obtained results agreed well with the tensile test results Microstructural characterization through optical and scanning electron microscopy (SEM) was realized that the dominant microstructure which formed in the fusion weld zone is martensitic structure. This phenomenon is the main reason for hardness improvement of fusion weld zone. The results also indicate that, the weld volume decreases with welding speed. It has been shown that convenient laser parameters for mm thick plate in constant pulse duration and pulse frequency are 20 mm/s welding speed and 500 pulse voltage.

کلیدواژه ها:

AISI4340 high-strength ، Nd: YAG ، heat input ، Microstructural characterization