This　study　systematically　investigates　the　effects　of　high-power　continuous　wave　laser　(CWL)　treatment　on　the　mechanical　behavior　and　failure　mechanisms　of　SM400A　steel,　comparing　these　outcomes　with　those　of　untreated　specimens.　The　findings　reveal　that　while　CWL　treatment　enhances　surface　hardness,　it　has　minimal　impact　on　the　strength　of　thick　structural　steel　components.　However,　excessive　laser　energy　density　leads　to　surface　defects　and　softening　of　the　microstructure,　adversely　affecting　the　material＇s　toughness.　This　results　in　a　reduction　in　elongation　at　fracture,　transitioning　the　failure　mode　from　ductile　to　brittle.　The　study　concludes　that　to　ensure　the　safe　use　of　laser-treated　structures,　the　laser　energy　density　should　be　carefully　controlled　not　to　exceed　3000　J/cm2.　©　2024　The　Authors