Analysis of Microstructure and Hardness of Weld Spots during Laser-Acoustic Heating of Stainless Steel

Abstract—Laser-acoustic method of spot heating of stainless steel AISI 316L is under consideration. Equipment for carrying out experiments with and without the application of ultrasonic vibrations with a frequency of 40 kHz and a power of 100 W is developed. The microstructure of weld spots is analyzed based on the obtained optical images. A globular form of dendrites during processing with ultrasonic exposure is revealed in contrast to the columnar form of dendrites obtained during processing in the traditional way. An algorithm is developed for determining the percentage content of phase components of the obtained microstructure—austenite and the conventionally introduced “X” phase, which takes into account ferrite and other possible new formations in the structure of the weld spot. Comparative analysis shows that the content of the X-phase on the fusion line is almost the same, while in the central and mixed zones of the weld spot, its percentage content is 51 and 41% higher in the experiments carried out with ultrasonic exposure. The analysis shows an increase in the hardness of weld spots within 5%. A conclusion is made about the advisability of developing and using a laser-acoustic processing method.