Abstract
This study aims to investigate and compare the structural, morphological, and phase transformations occurring in low-alloy steel 09G2S during laser cutting when using air and pure oxygen as assist gases. The study aims to investigate the impact of gas type on cut quality, heat-affected zone (HAZ) characteristics, oxidation, and potential defect formation. The experiments were conducted on 16 mm thick sheets using an 8 kW fibre laser under optimized conditions. Optical microscopy, scanning electron microscopy, as well as X-ray diffraction analysis were used to assess the HAZ. The results show that during air blowing, an uneven cutting surface, the formation of an oxidized layer up to 200 μm thick, and the formation of martensite in the near-surface zone are observed, due to an increased heat load and inefficient melt removal. While the use of oxygen ensures a more stable cutting process, resulting in an even and clear edge with a homogeneous microstructure in the HAZ and a reduced oxide content. Elemental analysis confirmed the low oxidation state and the absence of hydrogen in oxygen cutting, which minimizes the risk of flocken formation.