The effect of laser microstructuring modes on Carbon concentration and the level of residual stresses in the surface layer of carbon steel products

The purpose of the work was to study the effect of laser microstructuring on changes in carbon concentration and zonal residual macro stresses of the first kind in the laser exposure zone of carbon steel sheet samples of grades 20, 35, 45 after laser microstructuring according to various modes.
Methods. Structural carbon steels of grades 20, 35, and 45 were selected as objects of research. To study the effect of laser modification on changes in the structure and mechanical properties of machine parts using laser cutting, special samples were made in the form of square plates (35×35 mm) with a thickness of 2 mm (St20 and St45) and 4 mm (St35). After laser cutting according to the modes, one of the sides of the sample was subjected to mechanical grinding in order to remove a layer with a modified structure of the material obtained during laser cutting. Next, laser microstructuring of the sample surfaces was performed using a continuous fiber laser. X-ray diffraction studies to determine the carbon content, sign, and level of residual stresses of the first kind (macro stresses) were performed using a DRON- 4.0 X-ray diffractometer in cobalt Ka radiation in the discrete point survey mode.
Results. Using the method of X-ray diffraction phase analysis, an increase in the carbon content in the surface layer of samples after laser microstructuring of medium-carbon steels of grades 35 and 45 was revealed, significantly exceeding the values established by GOST 1050-2013. The revealed increase in carbon concentration is probably related to the realization of the Soret effect (thermodiffusion) under conditions of exposure to high temperatures. It has been established that laser microstructuring of the working surfaces of medium-carbon steels of grades 34 and 45 leads to the formation of high zonal residual compression stresses (up to -2300...-3800 MPa). The obtained result indicates the positive effect of laser treatment on the mechanical properties of the surface layer.
Conclusion. The results obtained can be used in the creation of resource-saving material processing processes.

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