Effect of Ultrasonic Vibration on Microstructure and Mechanical Properties of High Nitrogen Steel Laser-arc Hybrid Welding Joints

doi:10.3901/JME.2018.16.118

Abstract

Abstract: To solve poor mechanical properties of the welding joints caused by the porosity and nitrogen loss, high nitrogen steel plates with a thickness of 6.5 mm are welded by laser-arc hybrid heat source with ultrasonic vibration. By analysis of microstructure and properties of welding joints obtained under different ultrasonic power, it is indicated that the ultrasonic vibration is capable of changing the flow velocity in the melting pool and fusion ratio of welding seam. However, excessive ultrasonic power deteriorates the quality of the weld surface. Ultrasonic cavitation causes porosity defects to decrease first and then increase with the increase of ultrasonic power. However, the effect of ultrasonic vibration on the nitrogen content of the weld bead is not significant. Moreover, ultrasonic vibration inhibits the growth of coarse dendrite and transforms the growth orientation of grains. It also leads to grain refinement which significantly improves the hardness of the columnar zone. With the increase of ultrasonic power, the tensile and impact properties of the joints increase first and then decrease. Both the blowhole defect and microstructure of the welding joint impact on the tensile strength together. It is concluded that grain refinement is helpful to the fracture mode of welded joints, and then improves its toughness. Compared without the ultrasonic vibration, when the ultrasonic power is 160 W, the pores in the welding joints are significantly reduced and the crystallites are refined, which increase the tensile strength by 3.97% and the impact toughness by 10.8%.

Key words: high nitrogen steels, hybrid welding, mechanical property, microstructure, ultrasonic vibration

CLC Number:

TG456

LIU Jia, BAI Chenming, CUI Bo, SHI Yan, LI Zhong, ZHANG Hong. Effect of Ultrasonic Vibration on Microstructure and Mechanical Properties of High Nitrogen Steel Laser-arc Hybrid Welding Joints[J]. Journal of Mechanical Engineering, 2018, 54(16): 118-126.

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